Sebastian Vizcay

Panagiotis Kourtesis

Ferran Argelaguet

Claudio Pacchierotti

Maud Marchal

Electrotactile Patterns for Single Finger Interactions in VR

Electrotactile feedback has been proven effective in improving mid-air interactions in Virtual Reality (VR) scenarios. However, the elicited sensation is often described as unnatural. We explore standard stimulation patterns or effects (FXs) found in the literature and how they can get coupled with common VR interactions. We propose 6 implementations of these patterns and, based on our expectation that some couplings work better than others, we evaluated their coherence in an experiment (N=8).

Introduction

Matching user's expectations while interacting in VR is an important factor of presence [START_REF] Skarbez | A survey of presence and related concepts[END_REF] and agency [START_REF] Jeunet | do you feel in control?": towards novel approaches to characterise, manipulate and measure the sense of agency in virtual environments[END_REF]. Tactile feedback needs to ensure a coherence between the user's interaction and the elicited sensations. While electrotactile feedback has been proven effective in rendering contact information when interacting with virtual objects [START_REF] Vizcay | Electrotactile Feedback For Enhancing Contact Information in Virtual Reality[END_REF], one of its disadvantages is that it elicits sensations that are often described as unnatural, due to the fact that it directly stimulates the skin nerves endings. Electrotactile feedback is still capable of rendering rich sensations thanks to the high density of actuators, their high wearability, and the wide number of parameters that can be customized. This paper investigates and present preliminary results of how different set of electrotactile actuation parameters can be used to render different tactile sensations and how these are perceived while performing single finger interactions in VR.

Methodology

We propose the study of three common single finger interactions: tapping an object, sliding the finger along a surface, and pressing down objects (see Fig. 1left). From the literature, we collected six common tactile effects rendered using electrotactile feedback. We use a custom electrical stimulator (see Fig 1 right) that has up to 32 channels which can be configured as cathode or anode. The stimulator produces biphasic cathodic square pulses with a pulse frequency in the range Hz and with pulse widths between [30-500] µs. Amplitude of the pulses can be set between the range of [0.1-9.0] mA. For this particular experiment, we connected a 7-channels electrode (6 cathodes and 1 anode) with the cathodes laid out in a 2×3 matrix.

We designed 6 electrotactile patterns (FXs) which can be easily distinguished. The feedback design was done for a 2×3 pads electrode (see Fig 1 right). The six patterns (or FX) are described in detail in this accompanying technical report [START_REF] Vizcay | Tactile patterns for electrotactile simulation[END_REF].

Eight subjects are asked to use their index finger, equipped as shown in Fig. 1, to interact with a virtual environment in three different ways -tapping an object, sliding the finger along a surface, and pressing down objects. We tested the performance of each of these interactions when rendered in the six different ways mentioned above, in order to understand the best way to render such interactions through electrotactile feedback. Each interaction is repeated 6 times per each pattern, leading to 108 interactions in total.

At the end of the task, participants answer a post-experience questionnaire providing us additional feedback regarding the perception of the tactile patterns during the considered interactions.

Results and discussion

The ranking and the distribution of the scores for all interactions are reported in Fig. 2.

For the tapping interaction, the best patterns are the direction, the intensity, and the binary ones. This is also corroborated with the ranking data. We emphasize here that the directional pattern behaves similarly to the intensity one, having as only difference the activation of 2 central active pads rather than only one [START_REF] Vizcay | Tactile patterns for electrotactile simulation[END_REF].

For the press interaction, we found similar results, but these are more pronounced given that the interaction span is longer. The directional and intensity patterns are still the best but this time the intensity pattern takes the first place most often in the ranking data.

Finally, for the slide interaction, we see clearly the preference for the directional pattern which is a richer pattern compared to the others, thanks to the additional interaction input data. It is interesting to notice in the ranking data that 2nd and 3rd best are the clockwise and random patterns, indicating that one of the most important factors for rendering a coherent sensation for this particular interaction is having a stimulus that changes location over time.

As next step, we will recruit more participants in order to perform a statistical analysis and verify that the differences are significant. We will also analyze the interaction data that we have collected such as time spent per interaction, object interpenetration, button compression and sliding speed to see if the tactile FXs have an incidence in the way participants interact with the virtual objects. Fig. 2. Ranking order (top) and distribution of the scores (bottom) of the tactile patterns (FXs) per each interaction: tapping an object, sliding the finger along a surface, and pressing down objects. The six considered patterns are detailed in [START_REF] Vizcay | Tactile patterns for electrotactile simulation[END_REF].

  This work was supported by the European Union's Horizon 2020 research and innovation program under grant agreement No. 856718 (TACTILITY).

Fig. 1 .

 1 Fig. 1. VR scenario with 3 interactable objects (left) and equipment used (right), with electrode layout in the inset.


Aboud Kourieh

Lise Giorgis-Allemand

Liacine Bouaoun

Marie Lefevre

Patricia Champelovier

Jacques Lambert

Bernard Laumon

Anne-Sophie Sophie Evrard
email: anne-sophie.evrard@univ-eiffel.fr

Marie Lefèvre

Incident hypertension in relation to aircraft noise exposure: results of the DEBATS longitudinal study in France

Keywords: epidemiology, longitudinal study, aircraft noise exposure, incident hypertension

des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

INTRODUCTION

According to the World Health Organization (WHO), environmental noise causes the loss of at least one million healthy life years every year in Western Europe [START_REF] Who | Burden of disease from environmental noise: Quantification of healthy life years lost in Europe[END_REF]. Epidemiological studies have previously linked long-term exposure to aircraft noise to several health risks such as sleep disturbance [START_REF] Nassur | Aircraft Noise Exposure and Subjective Sleep Quality: The Results of the DEBATS Study in France[END_REF][START_REF] Nassur | The impact of aircraft noise exposure on objective parameters of sleep quality: results of the DEBATS study in France[END_REF][START_REF] Basner | WHO Environmental Noise Guidelines for the European Region: A Systematic Review on Environmental Noise and Effects on Sleep[END_REF], noise annoyance [START_REF] Lefèvre | Understanding the relationship between air traffic noise exposure and annoyance in populations living near airports in France[END_REF][START_REF] Guski | WHO Environmental Noise Guidelines for the European Region: A Systematic Review on Environmental Noise and Annoyance[END_REF], impaired cognitive performance in children [START_REF] Clark | WHO Environmental Noise Guidelines for the European Region: A systematic review on environmental noise and cognition[END_REF] and cardiovascular morbidity [START_REF] Evrard | Does exposure to aircraft noise increase the mortality from cardiovascular disease in the population living in the vicinity of airports? Results of an ecological study in France[END_REF]9] including hypertension [10,11]. The association between noise exposure and hypertension has been explained by the physiological stress response that may be triggered by noise exposure, resulting in activation of the sympathetic and neuroendocrine systems, which in turn leads to increased levels of stress hormones [12]. This increase itself is associated with higher heart rate and blood pressure [13].

A growing number of cross-sectional studies have shown a significant association between exposure to aircraft noise and the prevalence of hypertension [10]. Nevertheless, after aggregating the results of nine cross-sectional studies (comprising 60,121 residents, including 9,487 cases), the review of Van Kempen et al derived a non-significant relative risk (RR) of 1.05 (95% confidence interval (CI): 0.95; 1.17) per 10 dB(A) increase in day-evening-night aircraft noise levels [10].

In addition, there is a lack of studies on the incidence of hypertension with only a few longitudinal studies that have addressed this issue. In a cohort of 4,854 participants from Stockholm County between 1992 and2006, Pyko et al. observed an increase in the incidence of hypertension with increasing aircraft noise levels, with a hazard ratio (HR) of 1.16 (95% CI:

1.08; 1.25) per 10 dB(A) increase in day-evening-night aircraft noise levels one year prior to the event, and of 1.16, 95% CI: 1.08; 1.24) per 10-dB(A) increase in day-evening-night timeweighted average of aircraft noise levels five years preceding the event [14]. These results are consistent with those of Dimakopoulou et al. who followed the 420 HYENA (Hypertension and Exposure to Noise near Airports) participants living near the Eleftherios Venizelos airport in Athens (Greece) [15]. This cohort study reported an increased incidence of hypertension with increased exposure to aircraft noise at night (OR= 2.63, 95% CI:1.21; 5.71 per 10 dB(A) increase) [16].

Thus, in this context of insufficient longitudinal studies investigating the incidence of hypertension, this paper aimed to study the association between exposure to aircraft noise and the incidence of hypertension over four years of follow-up (2013-2017) of the French DEBATS study.

METHODS

Study population

Participants in this study were adults over 18 years of age at the time of interview. They were recruited in 2013 near three major French airports: Paris-Charles-de-Gaulle, Lyon-Saint-Exupéry, and Toulouse-Blagnac (Figure 1) [START_REF] Evrard | Does exposure to aircraft noise increase the mortality from cardiovascular disease in the population living in the vicinity of airports? Results of an ecological study in France[END_REF]11]. Eligible participants were randomly selected on the basis of their home address after being stratified for aircraft noise contours which divided the study area into four aircraft noise level categories in terms of Lden: <50 dB(A), 50-54 dB(A), 55-59 dB(A) and >=60 dB(A). Lden is a day-evening-night noise indicator corresponding to an annual 24-hour average of sound pressure levels, with an additional weighting of 5 dB(A) for evening noise (18:00 to 22:00) and 10 dB(A) for night noise (22:00 to 6:00) to reflect people's sensitivity to noise [17].

A total of 1,244 participants were enrolled at baseline (Figure 2) and completed a questionnaire in a face-to-face interview at their home with a trained interviewer to collect demographic and socio-economic characteristics, anthropometric measurements, lifestyle factors (sports activities, tobacco and alcohol consumption), and personal medical history (cardiovascular disease, medication use, noise sensitivity and annoyance due to aircraft noise).

Two follow-ups were conducted two (T2 in 2015) and four (T4 in 2017) years after baseline (T0 in 2013). A total of 992 adults participated in the first follow-up visit (T2) and 811 in the second (T4), corresponding respectively to 80% and 65% of baseline participants (Figure 2).

At each visit, participants completed a very similar questionnaire.

Blood pressure and incident hypertension

At each visit, participant's systolic blood pressure (SBP) and diastolic blood pressure (DBP) were measured three times, while seated, by the interviewer using a validated and automated blood pressure (BP) measuring device (Omron® M6 comfort), in accordance with recommendations of the American Heart Association [18]. The first measurement was taken after a 5-minute rest at the beginning of the interview and was followed by a second measurement 1-minute later. The average of these two BP measurements was used to define SBP and DBP. A third reading was recorded approximately 1 hour later (at the end of the interview) and was used as a validity control to exclude, in a sensitivity analysis, 15 participants at T2 and 9 at T4 from the incident hypertension analysis on one hand, and 73 participants at T0, 75 at T2 and 43 at T4 from SBP and DBP analyses on the other hand, for whom this third reading was significantly different (±20 mm Hg) from the mean of the first two measurements (results not shown).

Participants were classified as hypertensive if their BP levels exceeded the WHO predefined threshold (SBP≥140 mm Hg or DBP≥90 mm Hg) [19], or if they reported a previous diagnosis of hypertension by a physician and the use of anti-hypertensive medication in the 12 months prior to the interview. The fact that these medications corresponded to antihypertensive medications was verified from the ATC codes. At each visit, participants with BP levels exceeding the WHO standards were recommended to visit their doctor for a possible diagnosis of hypertension.

Analyses for incident hypertension included only participants who were not classified as hypertensive at baseline (T0). Incident cases were defined as being classified as hypertensive for the first time during the study at T2 or at T4.

Aircraft noise exposure assessment

Exposure to outdoor aircraft noise at each participant's place of residence was assessed in 1 dB(A) (A-weighted decibel) intervals from noise maps generated by Paris airports (Paris-Charles de Gaulle, 2013-2017) and the French Civil Aviation Authority (Lyon-Saint-Exupéry 2004, Toulouse-Blagnac, 2003) using the Integrated Noise Model (INM) [20]. The assessment was carried out by linking the participants' home addresses at each follow-up to the noise contours using Geographic Information System (GIS) technique.

In addition to L den, three other noise level indicators were calculated and used in the following statistical analyses: LAeq,24h, Lday and Lnight. LAeq,24h is the A-weighted equivalent continuous noise level over a 24-hour period, Lday is the day-evening time indicator (6:00 to 22:00) and Lnight is the night time indicator (22:00 to 6:00) [17]. For participants living near Paris Charles de Gaulle airport, the modelled aircraft noise levels for the years 2014 and 2016 were used for the incident hypertension analysis, while the modelled aircraft noise levels for the years 2013, 2015 and 2017 were used in SBP and DBP analyses.

Statistical analysis

The characteristics of the participants were compared by study timepoint using the Pearson chi-squared test for categorical data, and Kruskal-Wallis test for continuous data. The correlation between noise indicators was evaluated using the Spearman rank-order correlation coefficients.

Incident hypertension

Mixed Poisson regression models using the log-link function with a random intercept at the participant level were used. Those models estimate incidence rate ratios (IRR), i.e. the exponentials of the beta coefficients, with corresponding 95 % confidence intervals (CI).

Confounders were included in the models ensuring that they preceded the onset of hypertension [21] and the visit time indicator variable included in the models had two levels (0/2). Level 0 corresponded to the participant's hypertension information collected at T2 and the main potential confounders measured at T0. Likewise, level 2 corresponded to hypertension information collected at T4 and the main potential confounders measured at T2. All multivariable Poisson regression models included the following confounders obtained from the questionnaire: gender, age (continuous), body mass index (BMI; three categories: underweight or normal/overweight/obese), sports activities (yes/no), occupational activity (yes/no) and alcohol consumption (three categories: no/light/moderate or heavy). The selection of these a priori confounding factors was mainly based on results from a previous cross-sectional study of the baseline (T0) data in the same population [11].

Smoking was initially included in the models, but it was not included in the end as it did not contribute significantly to the models and did not modify the noise effect estimates.

Participants with missing values were excluded from the visit time for which they had missing values.

Sensitivity analyses were conducted: 1) restricting analysis to participants who had resided at their inclusion address for at least 5 years prior to the baseline interview (T0) and had not moved at the time of the follow-up visit, i.e. participants were excluded from T2 and T4 if they moved between T0 and T2 and participants were excluded from T4 if they moved between T2 and T4; 2) using at all time points the main potential confounders measured at baseline (T0);

3) restricting analysis to the participants who took part in all three visits; 4) using prevalent hypertension as an outcome instead of incident hypertension, i.e. hypertensive participants at T0 were included in this analysis.

Noise annoyance and noise sensitivity could mediate or modify the association between noise exposure and hypertension [22]. Their mediating and moderating effects were investigated following Baron and Kenny's recommendations [23]. These variables were considered in two categories in the models (highly annoyed/not highly annoyed; low or medium/high, respectively).

Systolic and diastolic blood pressure

Mixed linear regression models with a random intercept for each participant were used. The first-order autoregressive covariance structure was used to account for repeated measurements on participants. Outcomes (SBP or DBP) and a priori confounders included in these models were measured during the same visit, and the visit time indicator had three levels representing the corresponding visit. The confounders were similar to those included in the incident hypertension analyses, with the addition of anti-hypertensive medication use (yes/no).

Sensitivity analyses were similar to those conducted for incident hypertension. In addition, the study population was restricted to those who did not report anti-hypertensive medication use in the same visit.

Analyses were performed using the GLIMMIX and MIXED procedures of SAS 9.4 software (SAS Institute, Cary NC). Two-sided p-values were used with a 5% statistical significance.

RESULTS

Participants' characteristics were similar over the three visits, except that anti-hypertensive medication use and the mean age of participants significantly increased with follow-up (Table 1). The mean age was 51 years at T0, 53 years at T2, and 56 years at T4 (Table1). At T0, 16% of the participants reported using anti-hypertensive medication. They were 21% at T2 and 25% at T4 (Table 1).

The distribution of participants in the four categories of Lden noise exposure did not vary over the follow-up period (Table 1). The mean aircraft noise exposure in terms of Lden was 54 dB(A) at T0, T2 and T4. The Spearman rank-order correlation coefficients between the noise indicators were significant and higher than 0.9.

The prevalence of hypertension was 34% at T0, 35 % at T2, and 38% at T4 (Table 1).

After excluding participants with hypertension (n=426) or missing hypertension status (n=14) at T0, participants lost to-follow-up (n=252, including 2 with missing hypertension status and 93 with hypertension at T0) and participants with missing hypertension status at T2 [START_REF] Evrard | Does exposure to aircraft noise increase the mortality from cardiovascular disease in the population living in the vicinity of airports? Results of an ecological study in France[END_REF], the population at risk at T2 consisted of 639 participants (n=1,244-426-14-(252-2-93)-8), 80 of whom had incident hypertension at T2. Then, after excluding these 80 participants, those lost to follow-up between T2 and T4 (n=113, including 13 with incident hypertension at T2) and those with missing hypertensive status at T2 or T4 (9), the population at risk at T4 consisted of 450 (n=639-80-(113-13)-9) participants, 47 of whom had incident hypertension at T4 (Table 1 andsupplementary Table 1).

The characteristics of participants with incident hypertension at T2 and T4 were relatively similar (supplementary Table 2).

Incident hypertension

Table 2 shows the IRRs for incident hypertension in relation to the main a priori confounding factors. The incidence of hypertension increased with age (IRR=1.03, 95% CI: 1.02; 1.05), and was higher in men than in women (IRR=1.72, 95% CI: 1.22; 2.41). The incidence of hypertension was also higher in overweight (IRR=1.86, 95% CI: 1.27; 2.74) and obese (IRR=2.36, 95% CI: 1.51; 3.68) participants than in those of normal weight or underweight. Table 3 presents adjusted IRRs of the four aircraft noise indicators on incident hypertension.

Higher incident hypertension was observed with a 10 dB(A) increase in aircraft noise levels in terms of Lden (IRR=1.36, 95% CI: 1.02; 1.82), LAeq,24h (IRR=1.43, 95% CI: 1.05; 1.96), Lday (IRR=1.41, 95% CI: 1.07; 1.85) and Lnight (IRR=1.31, 95% CI: 1.01; 1.71). Results of the sensitivity analyses were very similar compared with our main results (Table 3).

Higher incident hypertension was found for highly annoyed participants compared to those who were not but the association was not significant (IRR=1.24, 95% CI: 0.84; 1.83, M0 model, supplementary Table 3). When aircraft noise annoyance was included in the M2 model (also called main model in Table 3), the association between aircraft noise levels and incident hypertension became slightly lower and not significant (IRR=1.29, 95% CI 0.97-1.71, for a 10 dB(A)-increase in Lden) (M3 model) (supplementary Table 3).

No association was observed between noise sensitivity and incident hypertension (IRR=0.91, 95% CI: 0.70; 1.18, for high noise sensitivity versus medium or low noise sensitivity, M1 model). When noise sensitivity was included in the M2 model, the association between aircraft noise levels and incident hypertension remained similar (IRR=1.34, 95% CI 1.02-1.77, for a 10 dB(A)-increase in Lden) (M4 model) (supplementary Table 3).

The association between aircraft noise exposure and incident hypertension was very similar in highly annoyed and not highly annoyed people (M5 model). The association between aircraft noise exposure and incident hypertension was slightly but not significantly higher in people with high noise sensitivity (IRR=1.62, 95% CI 1.07-2.44, for a 10 dB(A)-increase in Lden) than in those with medium or low noise sensitivity (IRR=1.26, 95% CI 0.94-1.70, for a 10 dB(A)increase in Lden) (M6 model) (supplementary Table 4).

Systolic and diastolic blood pressure

The multivariate associations between systolic and diastolic blood pressure and main a priori confounding factors are presented in supplementary Table 5.

A statistically significant increases in both SBP and DBP with increasing aircraft noise exposure levels can be seen for all noise indicators (supplementary Table 6). A 10 dB(A) increase in the day-evening-night noise level (Lden) was associated with a 1.93 mm Hg increase in SBP (95% CI: 0.79; 3.08,) and a 1.08 mm Hg increase in DBP (95% CI: 0.27; 1.88). Similar results were observed in sensitivity analyses (supplementary Table 6).

DISCUSSION

This study examined the longitudinal associations between exposure to aircraft noise and the incidence of hypertension using information from three visits of residents living near three major French airports.

Our results indicate that a 10 dB(A) increase in Lden, Lday, LAeq,24h or Lnight was statistically significantly associated with a higher incident hypertension. These associations were confirmed by the statistically significant increase observed in both systolic and diastolic blood pressures with increasing aircraft noise levels.

These results are consistent with those obtained in the previous cross-sectional analyses of DEBATS' baseline observations. Indeed, a significant association was found between aircraft noise exposure and the risk of hypertension in men (OR=1.34, 95% CI: 1.00; 1.97 for a 10 dB(A) increase in aircraft noise exposure at night (Lnight)), but not in women (OR=0.90, 95% CI: 0.66; 1.22) or in men and women combined (OR=1.10, 95% CI: 0.90; 1.37) [11]. When the present longitudinal analysis was conducted for men and women separately, the main model did not converge. It only converged when removing the BMI variable and using the age variable not as a continuous variable but in six categories, and gave a significant association for men but not for women. This association was slightly higher for men (IRR=1.41, 95% CI: 1.02; 1.94 for a 10 dB(A) increase in Lnight) than for women (IRR=1.26, 95% CI: 0.81; 1.96 for a 10 dB(A) increase in Lnight) (supplementary Table 7). Furthermore, the stronger associations found in the longitudinal analyses, for the total population, are most likely attributable to the use of incident hypertension instead of prevalent hypertension, which led to the exclusion of participants considered as hypertensive at baseline, and the use of the repeated measures approach at T0, T2 and T4 instead of a cross-sectional analysis of baseline data at T0.

Our results are in line with several previous studies showing that exposure to aircraft noise increased the risk of hypertension [24,25,15,[26][27][28]. However, the evidence was considered to be inconclusive in a recent WHO review although the pooled estimate showed a tendency towards a positive association (RR= 1.05 per 10 dB (A) increase in Lden, 95% CI: 0.95; 1.17)

[10]. It should be emphasized that the majority of the reviewed studies were cross-sectional in design (nine studies out of ten) and most were judged to be at high risk of bias, mostly due to selection bias or determination of hypertension status through self-reporting only [10].

Our results are also somehow consistent with those obtained in the only two longitudinal studies that addressed this issue [14,16]. Although there were methodological differences between this study and the two cohort studies mentioned above (including in particular the different statistical methods used -Cox regression for Pyko et al, logistic regression for Dimakopoulou et al -as well as differences in the confounding factors), the findings of the three studies can still be considered consistent and support the hypothesis that exposure to aircraft noise was associated with an increase in the incidence of hypertension.

In contrast, the largest case-control study to date, around Frankfurt airport in Germany involving 137,577 cases and 355,591 controls, did not observe an association between aircraft noise and hypertension as recorded in health insurance claims data, with an OR of 0.99 (95% CI 0.98-1.01) per 10 dB(A) increase in aircraft noise levels in terms of LAeq,24h [29].

Nevertheless, a significant association was found in a sub-group of newly diagnosed hypertension cases with a subsequent diagnosis of hypertensive heart disease (OR=1.14, 95% CI: 1.09; 1.19). However, one of the major limitations of this study highlighted by the authors was the lack of individual data on confounding factors.

The results of the present study remained similar in all sensitivity analyses. In particular, limiting the analysis to participants who had resided at their inclusion address for at least 5 years and had not moved at the time of visit did not change the results significantly, apart from the loss of statistical significance that could be explained by the smaller sample size. This result does not suggest any habituation to noise. This is consistent with the finding of Pyko et al. that the increased risk of hypertension was similar when considering time weighted average of aircraft noise exposure one or five years prior to the event [14].

This study showed a non-significant association between aircraft noise annoyance and incident hypertension (M0 model). When aircraft noise annoyance was included as a covariate in the M2 model, including the noise indicator together with the confounders, (M3 model), the association between aircraft noise levels and incident hypertension became slightly lower and not significant. Moreover, as aircraft noise levels were significantly associated with aircraft noise annoyance in DEBATS [START_REF] Lefèvre | Understanding the relationship between air traffic noise exposure and annoyance in populations living near airports in France[END_REF], according to Baron and Kenny [23], a potential mediating role of aircraft noise annoyance in the relationship between aircraft noise levels and incident hypertension cannot be excluded. Conversely, as no association was observed between noise sensitivity and incident hypertension, noise sensitivity would not play a mediating role in this association. Finally, no significant increase in the incidence of hypertension related to aircraft noise levels was found in participants who were highly annoyed by noise compared to those who were not highly annoyed. In contrast, the association between aircraft noise exposure and incident hypertension was slightly but not significantly higher in people with high noise sensitivity than in those with medium or low noise sensitivity. These latter results suggest that unlike noise annoyance, noise sensitivity may moderate the relationship between aircraft noise levels and the incidence of hypertension. However, further investigations using specific methodology and tools related to mediation and moderation analyses are needed to better understand this role.

The main strength of the current study certainly lies in its longitudinal design, whereas most epidemiological studies on the health effects of aircraft noise are cross-sectional and only two cohort studies to date have addressed hypertension with a longitudinal design. This design made it possible to study the incidence of hypertension and to strengthen the results previously obtained from cross-sectional studies on the prevalence of hypertension. A similar questionnaire was administered at each follow-up visit to collect information on sociodemographic characteristics and lifestyle factors. In addition, standardized questions validated in other studies were used in particular to assess participants' health status, including hypertension. A validated protocol was used to measure participants' blood pressure at their home by trained interviewers [18]. Similarly to the HYENA study in particular, we used a physician's diagnosis of hypertension and the use of anti-hypertensive medication in conjunction with blood pressure measurements to define incident cases of hypertension [15].

The fact that the medications reported by the participants corresponded to antihypertensive medications was verified from the ATC codes. As the use of these medications can only be done after a medical prescription, this was a means to verify the diagnosis of hypertension.

The fact that blood pressure was measured only during visits raises the question of possible limitations in the definition of hypertension. Moreover, while there may be recall bias in the information collected on a diagnostic of hypertension and the use of anti-hypertensive medication, it is unlikely that this bias is dependent on exposure to aircraft noise. Thus, the associations observed in this study would tend to underestimate the true associations, if they exist.

Another strength of this study is the validity of the noise maps used estimate aircraft noise exposure at each participant's place of residence. Indeed, these modelled noise levels differed by only 0.5 to 1.5 dB in terms of Lden from measurements from permanent stations (Aéroports de Paris, 2007) [30] or during specific campaigns [31]. Moreover, they were also very similar to those calculated from acoustic measurements carried out during one week in the homes of a sub-sample of 112 participants in DEBATS' longitudinal study, with a mean relative difference of 5% and a 95th percentile of 11% [START_REF] Nassur | The impact of aircraft noise exposure on objective parameters of sleep quality: results of the DEBATS study in France[END_REF]. Finally, in particular, aircraft noise levels observed in our study were very consistent with those observed in the HYENA study conducted near six major European airports [32].

A main weakness of the study is that the assessment of aircraft noise exposure was based on noise maps from 2004 for Lyon-Saint-Exupéry and 2003 for Toulouse-Blagnac, while the participants were interviewed in 2013, 2015 and 2017. However, no more recent noise maps were available for these airports.

Exposure misclassification cannot be ruled out in this study. Indeed, only the exposure to aircraft noise at the participants' homes has been estimated. No information was available on their exposure outside the home, especially in the workplace. Even if exposure misclassification exists, it is probably non-differential because the exposure errors are probably not related to hypertension. It would thus have led to an underestimation of the associations observed here. On the other hand, estimating exposure to aircraft noise at night is certainly less prone to error because most people sleep at home. Here, the association between Lnight and incident hypertension remains relatively similar to that observed for Lden. In addition, it was not possible to measure exposure to environmental noise from other sources than aircraft, and no estimated noise levels for sources other than aircraft were available. However, in the questionnaire, participants were asked whether they considered that they worked in a noisy environment or whether they engaged in leisure activities that exposed them to noise. As these variables did not modify the noise effect estimates, they were not included in the final models. Moreover, it was not possible to adjust the models for road noise levels. Indeed, data were not available for residents of Toulouse-Blagnac and Lyon Saint-Exupéry airports and those for residents of Paris-Charles de Gaulle airport were of considerably poorer quality than those concerning aircraft noise levels (heterogeneity of input data and methodologies used).

Another limitation is potential for selection bias. Indeed, participation rate in the study at baseline was low, about 30% (1,244 participants for 4,202 eligible individuals) (Figure 2). Nevertheless, it did not differ much from studies on the same issue conducted in Germany, Italy or the United Kingdom [15] and, it is very similar in the four noise categories (<50, 50-54, 55-59, 60 dB(A) and above) used to stratify participants' selection. In addition, a comparison of the demographic and socio-economic characteristics of the participants and those who refused to participate in the study showed only minor differences according to the four categories of noise exposure [11]. Attrition is a major issue in longitudinal studies that could lead to biased estimates but here the rate of loss to follow-up was relatively low, with 65% of the 1,244 participants recruited that participated in the last follow-up (T4). Furthermore, the loss to follow-up did not differ significantly between highly annoyed and not highly annoyed participants, nor between participants with high noise sensitivity and those with medium or low noise sensitivity. Moreover, a homogeneous distribution of participants in the four noise categories was maintained throughout the study. It should also be noted that the results remain similar when the analyses focus on the participants who took part in all three visits (Table 3).

Figure 1 .

 1 Figure 1. DEBATS study area and DEBATS participants at baseline with and without hypertension. DEBATS, Discussion on the health effect of aircraft noise.

Figure 2 .

 2 Figure 2. Flow chart of the study participants.

Table 1 . Characteristics of the study population at each visit (T0, T2 and T4) T0

 1

		T2	T4
	(N=1244)	(N=992)	(N=811)

* Reported a diagnosis by a physician and the use of anti-hypertensive medication in the questionnaire a p-value calculated using χ2 test for categorical variables and Kruskal-Wallis test for continuous variables b 16 missing values at T0, 15 at T2 and 11 at T4

Table 2 . Adjusted estimates and 95% confidence intervals (CIs) for incident hypertension in relation to the main a priori confounding factors

 2

	Hypertension
	N= (T2: 630 a ; T4: 450)

Table 3 . Adjusted estimates of the effects of various aircraft noise indicators* on incident hypertension N of cases/N total

 3

	Noise indicator dB(A)	IRR (95% CI)	p-value

Table 2 . Characteristics of incident cases of hypertension at T2 and T4 T2

 2

		T4
	(N=80)	(N=47)

Table 4 . Adjusted estimates of the effects of various aircraft noise indicators on incident hypertension in highly annoyed/sensitive to noise participants compared to those who are not

 4 Per 10 dB(A) increase in aircraft noise exposure M5 and M6 models included age, gender, BMI, sports activities, alcohol consumption, occupational activity and visit time indicator a p-value for the interaction between noise indicator and aircraft noise annoyance b p-value for the interaction between noise indicator and noise sensitivity

	M5 model

*

Acknowledgements

The Airport Pollution Control Authority (Acnusa) requested the French Institute of Science and Technology for Transport, Development and Networks (Ifsttar) to carry out this study. The authors would like to thank them for their confidence.

The authors are grateful to all the participants in the study and their interviewers.

The authors also thank Paris Airports and the French Civil Aviation Authority for providing noise exposure maps, and are also grateful to Inès Khati for her participation in the implementation of the study.

Funding

The present study was supported by funds from the French Ministry of Health, the French Ministry of the Environment, the French Civil Aviation Authority, and the Airport Pollution Control Authority (Acnusa). The authors would like to thank them.

The funders had no role in the design of the study, in collection, analysis, and interpretation of data and in writing the manuscript.

CONCLUSION

This study is one of the very few longitudinal studies in Europe and the first in France to investigate the association between exposure to aircraft noise and the incidence of hypertension. These results strengthen those obtained by the cross-sectional analysis of the data collected at the time of inclusion in DEBATS, as well as those from previous studies conducted in other countries. Hence, the findings in this study support the hypothesis that aircraft noise exposure may be considered as a potential risk factor for hypertension. They also show a potential mediating role of noise annoyance and a moderating role of noise sensitivity in this association but these latter results deserve further investigation.

Ethics approval and consent to participate

Two national authorities in France, the French Advisory Committee for Data Processing in Health Research and the French National Commission for Data Protection and the Liberties approved the present study (DR 2012-361).

The participants signed and returned an informed consent by mail.

Competing interests

The authors declare that they have no competing interests.

Authors' Contributions

ASE and BL with JL and PC conceived and designed the study. ASE and ML conducted the study. JL interpreted the aircraft noise data and PC interpreted the annoyance data. ML was involved in data extraction. ML, AK and LGA did data preparation. AK performed the statistical analyses, supervised by ASE, LB and LGA. The analyses were interpreted by AK with LB,

LGA, ASE and BL. AK, LGA and ASE drafted the initial report. All co-authors revised the report and approved the final version. ASE is responsible for the overall content as the guarantor of this paper.


Elaheh Elyasi
email: elyasi.elaheh@gmail.com

Antoine Perrier
email: antoine.perrier@twinsight-medical.com

Mathieu Bailet
email: mathieu.bailet@twinsight-medical.com

Yohan Payan
email: yohan.payan@univ-grenoble-alpes.fr

Biomechanical Lower Limb Model to Predict Patellar Position Alteration after Medial Open Wedge High Tibial Osteotomy

Keywords: knee, patellofemoral, finite element, multibody, High tibial osteotomy

Medial open-wedge high tibial osteotomy is a surgical treatment for patients with a varus deformity and early-stage medial knee osteoarthritis. Observations suggest that this surgery can negatively affect the patellofemoral joint and change the patellofemoral kinematics. However, what causes these effects and how the correction angle can change the surgery's impact on the patellofemoral joint has not been investigated before. The objective of this study was to develop a biomechanical model that can predict the surgery's impact on the patellar position and find the correlation between the opening angles and the patellar position after the surgery. A combined finite element and multibody model of the lower limb was developed. The model's capabilities for predicting the patellofemoral kinematics were evaluated by performing a passive deep flexion simulation of the native knee and comparing the outcomes with magnetic resonance images of the study subject at various flexion angles. The model at a fixed knee flexion angle was then used to simulate the high tibial osteotomy surgery virtually. The results showed a correlation between the wedge opening angles and the patellar position in various degrees of freedom. These results indicate that larger wedge openings result in increased values of patellar distalization, lateral patellar shift, patellar rotation, and patellar internal tilt. The developed model in this study can be used in future studies to monitor the stress distribution on the patellar cartilage and connecting tissues to investigate their relationship with observations of pain and cartilage injury due to postoperative altered patellar kinematics.

INTRODUCTION

Medial open-wedge high tibial osteotomy (OWHTO) is a treatment for patients with a varus deformity who are suffering from early-stage medial knee osteoarthritis [START_REF] Agarwala | Comparison of closing-wedge and opening-wedge high tibial osteotomies for medial compartment osteoarthritis of knee in Asian population: Midterm follow-up[END_REF][START_REF] Duivenvoorden | Comparison of closing-wedge and opening-wedge high tibial osteotomy for medial compartment osteoarthritis of the knee: A randomized controlled trial with a six-year follow-up[END_REF][START_REF] Loia | High tibial osteotomy in varus knees: Indications and limits[END_REF]. OWHTO surgery involves a wedge osteotomy on the medial side of the proximal tibia starting just above the level of the tibial tubercle [START_REF] Hernigou | Proximal tibial osteotomy for osteoarthritis with varus deformity. A ten to thirteen-year follow-up study[END_REF][START_REF] Noyes | Opening wedge high tibial osteotomy: An operative technique and rehabilitation program to decrease complications and promote early union and function[END_REF]. The surgery aims to correct limb alignment and has been shown to provide satisfactory long-term outcomes [START_REF] Aglietti | High tibial valgus osteotomy for medial gonarthrosis: a 10-to 21-year study[END_REF][START_REF] Coventry | Proximal tibial osteotomy: A critical long-term study of eighty-seven cases[END_REF]. It successfully relieves the patient's pain and prevents secondary osteoarthritis leading to a total knee arthroplasty [START_REF] Sun | Comparison between Closing-Wedge and Opening-Wedge High Tibial Osteotomy in Patients with Medial Knee Osteoarthritis: A Systematic Review and Metaanalysis[END_REF].

Conversely, there are observations indicating that the patellofemoral pressure increases after OWHTO [START_REF] Javidan | The effect of medial opening wedge proximal tibial osteotomy on patellofemoral contact[END_REF][START_REF] Stoffel | Patellofemoral contact pressure following high tibial osteotomy: A cadaveric study[END_REF], and patellofemoral cartilage injuries progress in 41-45 % of patients in second-look arthroscopy [START_REF] Goshima | Patellofemoral Osteoarthritis Progression and Alignment Changes after Open-Wedge High Tibial Osteotomy Do Not Affect Clinical Outcomes at Mid-term Follow-up[END_REF][START_REF] Kim | Medial Open-Wedge High Tibial Osteotomy May Adversely Affect the Patellofemoral Joint[END_REF].

Additionally, it has been shown that performing large deformity corrections (wedge opening angles greater than 9-10°) may cause degeneration of patellofemoral cartilage [START_REF] Otakara | Large deformity correction in medial open-wedge high tibial osteotomy may cause degeneration of patellofemoral cartilage: A retrospective study[END_REF][START_REF] Tanaka | Deterioration of patellofemoral cartilage status after medial open-wedge high tibial osteotomy[END_REF]. Therefore, patellofemoral cartilage injuries seem to be correlated with the size of the opened wedge. The cause of this effect appears to be related to the impact of wedge opening on the patellofemoral kinematics.

The systematic review performed by Elyasi et al., 2021, has shown that after OWHTO, a significant decrease in the patellar height, patellar lateral tilt, and patellar shift is reported in various clinical studies (Bito et al., 2010a;J. C. H. Fan, 2012;[START_REF] Lee | Changes in patellofemoral alignment do not cause clinical impact after open-wedge high tibial osteotomy[END_REF][START_REF] Longino | Combined tibial tubercle osteotomy with medial opening wedge high tibial osteotomy minimizes changes in patellar height: A prospective cohort study with historical controls[END_REF]Park et al., 2017a;[START_REF] Song | Patellofemoral alignment and anterior knee pain after closing-and opening-wedge valgus high tibial osteotomy[END_REF]. Meanwhile, using a method based on Magnetic Resonance Imaging (MRI) to assess the three-dimensional patellofemoral kinematics has shown that the alteration of the kinematics after OWHTO cannot be assessed by means of conventional radiology (standing radiographs) and using the patellar position assessment methods designed on that basis (such as Insall-Salvati ratio and Blackburne-Peal ratio) (d'Entremont et al., 2014;[START_REF] Elyasi | A Systematic Review on Selected Complications of Open-Wedge High Tibial Osteotomy from Clinical and Biomechanical Perspectives[END_REF].

Therefore, it has not yet been possible to correlate the deterioration of patellofemoral cartilage status with the patellar position due to the limitations of the investigation methods and, more importantly, due to the fact that a quantitative relationship between the size of the opened wedge and the exact patellar position in its various degrees of freedom is missing in the literature.

Computational models of the knee joint have shown their ability to predict patellofemoral kinematics once validated against cadaveric or in vivo experiments [START_REF] Ali | Validated computational framework for evaluation of in vivo knee mechanics[END_REF][START_REF] Ali | Validation of predicted patellofemoral mechanics in a finite element model of the healthy and cruciate-deficient knee[END_REF][START_REF] Erdemir | Considerations for reporting finite element analysis studies in biomechanics[END_REF][START_REF] Müller | Prediction of patellofemoral joint kinematics and contact through co-simulation of rigid body dynamics and non-linear finite element analysis[END_REF]. Consequently, this study aimed to develop a combined Finite Element (FE) and multibody model of the lower limb capable of investigating the impact of OWHTO surgery on the patellar position. The patellar position which was described in the patellofemoral joint coordinate system, was used to investigate its correlation with the opening angle. This development was a necessary step to numerically assess the stress distribution on patellar cartilage in the future and to find its relationship with degeneration of patellofemoral cartilage after OWHTO. Prior to using the model for OWHTO, the accuracy of its predictions was evaluated by performing a passive deep flexion simulation of the native knee. The patellofemoral kinematic outcomes were compared against MRIs of the subject at various knee flexion angles.

METHODS

Subject information and image acquisition

A healthy subject (male, 40 years old, 94 kg, 1.73 m) volunteered to participate in the experimental data collection as part of a pilot study approved by an ethical committee (MammoBio MAP-VS pilot study N°ID RCB 2012-A00340-43, IRMaGe platform, Univ. Grenoble Alpes). He gave his written informed consent to the experimental procedure. Five sessions of non-weight-bearing MRI using a clinical system (Achieva 3.0T dStream Philips Healthcare) and one session of computed tomography (CT) scan were conducted to acquire the imaging data of the subject's lower limb at different knee flexion angles (Figure 1).

The CT scan was done with the subject oriented in the supine position and in a low energy procedure to limit the risks associated with exposure. The scanner collected 1266 consecutive 0.8 mm thick axial slices of the right leg. Each slice had a matrix and in-plane voxel size of 512×512 and 0.43 mm. MRI scan of the subject's right knee was taken with the subject in the supine position and a slightly flexed knee (later computed to be 25.2°) to generate a volumetric dataset for segmentation of the articular and connective tissues. The scan collected 208 sagittal slices that were 0.7 mm thick each and had a matrix size of 512×512 and an in-plane voxel size of 0.31 mm. The MRI scan of the right knee was repeated for three different flexion angles (later computed to be 55.6°, 99.6°, and 137.5°) with the aim of generating a dataset for model validation. The MRI scanner collected 320 consecutive 0.5 mm thick sagittal slices while the matrix and in-plane voxel sizes were 480×480 and 0.5 mm for each slice. During these three acquisitions, the subject was lying in the left lateral recumbent position, the ankle was in a neutral position, and the hip was not flexed to avoid any influence of poly-articular muscles that could affect the patellar position.

Finally, to generate a volumetric dataset for segmentation of the muscles in a reasonable amount of time, an MRI scan was used to capture 6.99 mm thick axial slices at pelvic, thigh, knee, and shank levels. Each slice had a matrix size of 512×512 and an in-plane voxel size of 0.97 mm.

Geometry reconstruction

Manual segmentation was performed using Amira 6.5.0. The CT scan was used to segment the full bone surfaces in the extended position. These bony surfaces were used to define the bony landmarks required for defining the joint coordinate system and registering the 3D bone shapes segmented from different MRI sets. The MRI scan of the knee at 25.2° flexion and the MRI scan of the full lower limb were segmented to reconstruct the muscles, articular tissues (femoral, patellar, and tibial cartilages), ligaments (patellar ligament and patellar retinacula), and the quadriceps tendon. The MRI scans of the knee that were taken for model validation purposes were used to segment the bones at various knee flexion angles. The segmentation of the patella at each knee flexion angle was repeated three times (twice by a clinician and once by an experienced operator) to account for the impact that segmentation errors can have on the patellofemoral kinematic data points that are used for validating the model. The patella segmented from the CT scan was rigidly registered to the segmented surfaces using Geomagic® Studio 2013 to preserve the exact geometry of the patella between different positions. For this purpose, we used a manual 3-point registration process followed by an automatic global registration, and the standard deviation between the registered surfaces was less than 0.2 mm.

Model generation

A combined FE and multibody model was generated in the Artisynth open-source modeling platform (www.artisynth.org) [START_REF] Lloyd | ArtiSynth: A Fast Interactive Biomechanical Modeling Toolkit Combining Multibody and Finite Element Simulation[END_REF]. The Quadriceps Tendon (QT), Rectus Femoris (RF), Vastus Intermedius (VI), Vastus Medialis (VM), and Vastus Lateralis (VL) muscles, the patellar and femoral cartilages were modeled as 3D FE structures. The bones were modeled as rigid bodies. The medial and lateral patellar retinacula were modeled as they can affect the patellofemoral joint kinematics and tension magnitudes in the patellar ligament [START_REF] Powers | Role of peripatellar retinaculum in transmission of forces within the extensor mechanism[END_REF]. A discrete number of strands represented the patellar ligament, medial, and lateral patellar retinacula.

Mesh generation was done in HyperMesh 2019 (Altair Engineering, Inc., USA) and produced hexahedral dominant meshes (with optimized element quality and a limited number of wedge elements) for the quadriceps muscles and the quadriceps tendon. The muscular geometries were simplified near their origin and insertion to avoid very small elements. The maximum element size was approximately 6mm in the muscle meshes, and 3mm in the QT mesh. The generated model is illustrated in Figure 2.

Material modeling

The constitutive law used to describe the muscle as a continuum material is separated into a passive and an active part. The muscles normally experience large displacements and strains with a non-linear stress/strain curve. Therefore, when the muscle is in the passive state and has no activation, its behavior can be best represented using a hyperelastic material model [START_REF] Johansson | A Finite-Element Model for the mechanical analysis of Skeletal Muscles[END_REF]. This passive part can be treated as isotropic or transversely isotropic based on the level of complexity required for the model [START_REF] Blemker | A 3D model of muscle reveals the causes of nonuniform strains in the biceps brachii[END_REF].

Given the objectives of the current study, the muscles were modeled in a passive state, and we assumed that their behavior could be modelled with a nearly incompressible isotropic neo-Hookean hyperelastic material. The parameters used for the quadriceps muscles (𝑐𝑐 1 = 11.7 𝑘𝑘𝑘𝑘𝑘𝑘 𝑘𝑘𝑎𝑎𝑎𝑎 𝐷𝐷 1 = 16.3 𝑀𝑀𝑘𝑘𝑘𝑘 -1 , respectively related to the shear modulus and the volumetric variations) were defined based on the findings of Affagard et al., who presented an in vivo method to identify the muscle behavior based on a displacement field obtained from ultrasound and digital image correlation techniques [START_REF] Affagard | Identification of hyperelastic properties of passive thigh muscle under compression with an inverse method from a displacement field measurement[END_REF]. For the QT, a linear elastic material was used with a value of 30 MPa for the Young's modulus and 0.46 for the Poisson ratio that was chosen for the model after testing multiple values estimated based on the literature [START_REF] Weiss | Computational modeling of ligament mechanics[END_REF]. For the femoral and patellar cartilages, a linear elastic material was used with a Young's modulus of 15MPa and a Poisson ratio of 0.45, similar to what was previously proposed for a study on HTO in the literature [START_REF] Martay | A preliminary modeling investigation into the safe correction zone for high tibial osteotomy[END_REF].

Each ligament was represented by a number of strands that had a non-linear stiffening spring behavior at low strains (𝜀𝜀 <0.06) and had a linear stiffness at higher strains [START_REF] Blankevoort | Ligament-bone interaction in a three-dimensional model of the knee[END_REF]. In cases where more than one strand was used to model a ligament, the stiffness was divided between the number of strands. The patellar ligament was represented with seven strands (three strands for the central region and two strands for each of the medial and lateral regions). The total stiffness was set to 278 𝑁𝑁/𝑚𝑚𝑚𝑚 for the central region and 201 𝑁𝑁/𝑚𝑚𝑚𝑚 and 173 𝑁𝑁/𝑚𝑚𝑚𝑚 for the medial and lateral regions [START_REF] Yanke | Regional mechanical properties of human patellar tendon allografts[END_REF]. Five strands represented the medial and lateral patellar retinacula with the respective total stiffness of 31 𝑁𝑁/𝑚𝑚𝑚𝑚 and 97 𝑁𝑁/𝑚𝑚𝑚𝑚 [START_REF] Laprade | Biomechanical Evaluation of the Medial Stabilizers of the Patella[END_REF][START_REF] Merican | The structural properties of the lateral retinaculum and capsular complex of the knee[END_REF]. The nominal reference strain was assumed to be 0.02 for all the bundles of the patellar ligament at full extension and 0.0 for the medial and lateral patellar retinacula. The reference length of the bundles (the length at which the springs experience the reference strain) was set to be their length at full extension in the native knee. A 0.02 pre-strain was also imposed along the axial direction of the QT FE component.

Boundary conditions

Sliding contacts were defined between all muscle parts, between the patellar cartilage and the femoral cartilage, between QT and the femoral cartilage, and between the femur and the VM and VL muscles. The nodes of the proximal end of the quadriceps muscle group were attached to the femur or the iliac bone based on the definition of their origins. The nodes of the VI muscle that were closer than one millimeter to the femur surface were attached to the femur. A distance limit was set to attach the nodes on the distal insertion of the muscles to the QT. The nodes located at the distal end of the QT were attached to the patella.

The patella was free to move in all its six degrees of freedom. Gravity was neglected, and the segments' inertial parameters were not considered since the femur and pelvic were non-dynamic.

Simulation of passive deep knee flexion

A simulation of passive deep knee flexion was designed for validation purposes. For that, the position of the tibiofemoral joint at the most flexed position was used to calculate a transformation matrix and control the knee motion. The output of the simulation was the patellofemoral joint kinematics which was then compared against the kinematic data points acquired from the subject's MRI at various knee flexion angles. A schematic view of the setup used for the simulation of passive deep knee flexion is depicted in Figure 3.

Simulation of OWHTO

Virtual OWHTO surgery

Computer models with opened wedges on the tibia were developed for the same subject at 25.2° knee flexion. An oblique cut was simulated on the tibia using a plane perpendicular to the tibial frontal plane and divided the bone into proximal and distal parts. The cut passed through the lateral and medial cortex, respectively 16 mm and 37 mm distal to the tibial plateaus, as inspired from the literature [START_REF] Akamatsu | Coronal subluxation of the proximal tibia relative to the distal femur after opening wedge high tibial osteotomy[END_REF][START_REF] Kim | Medial opening wedge high-tibial osteotomy using a kinematic navigation system versus a conventional method: A 1-year retrospective, comparative study[END_REF].

Models with various angles of wedge opening ranging from 2.5°, 5.0°, 7.5°, to 10.0° were developed using a custom-made Java code in the Artisynth platform as depicted in Figure 4. For simplification, the fibula was attached to the distal part of the tibia. Once the wedge was opened, the distal and proximal parts of the tibia were reunited. To make sure that the wedge opening does alter the limb alignment in other planes than the frontal, the posterior tibial slope (PTS) was checked to remain constant in all cases (approximately 9° that is in the normal range of PTS (10° ± 3.5°) [START_REF] Paley | Principles of Deformity Correction, Principles of Deformity Correction[END_REF]).

Figure 4, Top: the virtual wedge opening on the model through cutting the tibia into a

proximal and a distal part and rotating the distal part around the defined hinge axis. The hinge axis was defined to be perpendicular to the frontal plane and passing through the most lateral point on the OWHTO cut. Bottom: close view of the tibia after different wedge openings.

OWHTO simulation setup

To perfectly isolate the effect of the distalization of the patellar ligament insertion on the patellar position and the muscles attached to the patella, the knee flexion angle was fixed at 25.2°. The patella was free to react to the forces transmitted to it and find its new equilibrium position after wedge opening. The patellar ligament insertion on the tibia was distal to the osteotomy cut.

Therefore, wedge opening during virtual surgery affected the length and tension in the non-linear springs representing its bundles.

Measurement of the quantities of interest

The bony landmarks and the knee joint coordinate system were defined based on the ISB standard [START_REF] Grood | A joint coordinate system for the clinical description of threedimensional motions: Application to the knee[END_REF], as depicted in Figure 5. The origin was placed at the most distal point of the patella to calculate the translations. The kinematics of the patella in all its six degrees of freedom were extracted during model validation with the simulation of passive deep knee flexion. In the post OWHTO models, the impact of wedge opening angle on the patellar position was assessed by monitoring the patellar shift, proximal/distal translation, tilt, and rotation.

RESULTS

Passive deep knee flexion

A schematic of the comparison between the patellar positions predicted by simulation and taken from MRI segmentation is depicted at the maximal knee flexion position in Figure 6. The patellofemoral kinematic data points acquired from MRI segmentation at various knee flexion angles were consistent with the simulation predictions (Figure 7). However, one exception was the distal patellar translation, which was predicted higher than the MRI values at higher degrees of flexion.

Patellar position after OWHTO

The simulation results showed that the position of the patella in all the analyzed translational and rotational degrees of freedom were affected by the wedge opening angle (translation and rotation alterations respectively reached 5mm and 4°) (Figure 8). The larger wedge openings resulted in distalization of the patella, shifting the patella laterally, rotating the patella, and internal (medial) tilting. The tibiofemoral joint is fixed at 25.2° knee flexion. The horizontal axis shows the wedge opening degree while the vertical axis is the patellar translational and rotational position defined based on ISB standards [START_REF] Grood | A joint coordinate system for the clinical description of threedimensional motions: Application to the knee[END_REF].

DISCUSSION

We have introduced and validated a combined FE-multibody model suitable for simulating the behavior of the patellofemoral joint in various conditions. A key feature of the model is that it can predict the patellofemoral kinematics that result from the interaction of muscles and ligaments attached to the patella and the joint contact forces. We evaluated the model predictions with a simulation of passive deep knee flexion and showed that it produced kinematics consistent with the measures obtained from independent MRI datasets of the same subject at various knee flexion angles.

The validated model was used for predicting patellar position alteration due to different wedge opening angles during an OWHTO surgery at a certain knee flexion angle. The results of the study demonstrated that the OWHTO has a significant effect on the patellofemoral joint. This means that distalization of the patellar ligament insertion due to wedge opening can modify the balance of forces on the patella and alter its position. Our observations also showed that larger wedge openings result in increased values of patellar distalization, lateral patellar shift, patellar rotation, and patellar internal (medial) tilt.

Although our methods for evaluating the change in the height of the patella after OWHTO differ from clinical studies, the qualitative conclusions of our study were consistent with the literature (J.

C. Fan, 2012;[START_REF] Longino | Combined tibial tubercle osteotomy with medial opening wedge high tibial osteotomy minimizes changes in patellar height: A prospective cohort study with historical controls[END_REF]Park et al., 2017b). Our findings show that at 25.2° knee flexion, our subject could experience a 3.8 mm post-operative decrease in proximal translation for a 10° wedge opening on the tibia (21.5% decrease from the pre-operative value). While a direct comparison is not possible, this finding is consistent with an MRI-based study (d'Entremont et al., 2014) that found a 14.2% decrease at 30° of flexion among their subject group with various correction angles.

Regarding the alteration of patellar tilt, our results show a maximum internal (or medial) tilt of 2.3° occurring for a 10° wedge opening on the tibia. This finding is consistent with the alterations found in the literature reporting significant decreases of lateral patellar tilt between 1.8° and 2.2° (Bito et al., 2010a;[START_REF] Nha | Change in Posterior Tibial Slope After Open-Wedge and Closed-Wedge High Tibial Osteotomy[END_REF]Park et al., 2017a) or a significant increase of medial patellar tilt of 2.2° with an MRI based method (d'Entremont et al., 2014).

Concerning the patellar shift, our results are consistent with the MRI-based study of [START_REF] Entremont | Effect of opening-wedge high tibial osteotomy on the three-dimensional kinematics of the knee[END_REF] who reported a lateral shift after wedge opening. However, the magnitude of the lateral shift was larger in our case. This is while several clinical papers that used conventional radiology and its corresponding methods were not able to find significant changes in patellar shift (Bito et al., 2010b;[START_REF] Lee | Changes in patellofemoral alignment do not cause clinical impact after open-wedge high tibial osteotomy[END_REF]Park et al., 2017b). This ability of the model to correctly predict the lateral shift after wedge opening is of high importance because observations are showing that lateral patellar shift can be associated with patellofemoral pain [START_REF] Macintyre | Patellofemoral joint kinematics in individuals with and without patellofemoral pain syndrome[END_REF].

Our study has the advantage of analyzing the kinematics of the patella in various degrees of freedom while overcoming the limitations of the traditionally used investigation methods. To our knowledge, our study is the first to assess the correlation between wedge angle and patellar position quantitatively. Our analysis underlines the need for reporting the opening angle in future clinical studies rather than only reporting the post-operative standing hip-knee-ankle (HKA) or Weightbearing Axis (WBA). The correlation between wedge angle and the exact patellar position could be used in the future to explain why performing deformity corrections exceeding a certain wedge opening angle can lead to progression of patellofemoral cartilage injuries [START_REF] Otakara | Large deformity correction in medial open-wedge high tibial osteotomy may cause degeneration of patellofemoral cartilage: A retrospective study[END_REF][START_REF] Tanaka | Deterioration of patellofemoral cartilage status after medial open-wedge high tibial osteotomy[END_REF].

The validated model developed in this study could be used in the future to assess the patellar kinematics after OWHTO over the full range of motion of the knee. Additionally, the stress distribution on the articular and connecting tissues could also be monitored to investigate their relationship with pain and cartilage injury due to the post-operative altered patellar kinematics.

Meanwhile, we must acknowledge some of the inherent limitations of this study. The first limitation concerns the simplifications made in the geometry and material model of the simulated muscles. The second limitation concerns the absence of the other stabilization structures connected to the patella, the aponeurosis, the articular capsule of the knee, the skin, and other muscles of the thigh.

CONCLUSION

We have developed a validated combined FE-multibody model capable of predicting the patellofemoral kinematics. In this model, the patella was in contact with the trochlear groove and was fully free to move in response to the forces transmitted to it via the 3D FE models of the quadriceps muscle group and the ligaments. This detailed model could successfully simulate passive deep knee flexion, and its predictions in terms of patellofemoral kinematics were validated using MR images of the same subject at various knee flexion angles.

The developed model was used for studying the impact of OWHTO on the patellar position at a fixed knee flexion angle and showed that wedge opening could alter the position of the patella.

Our observations suggest that larger wedge openings result in increased values of patellar distalization, lateral patellar shift, patellar rotation, and patellar internal (medial) tilt. The contribution of our study is twofold: 1) our results show a correlation between the patellar position and the opening angle on the tibia in various degrees of freedom, and 2) we describe a numerical investigation method based on an explicative biomechanical model which could lead to a better understanding of the effects at play and, eventually, to better clinical outcomes for the patients.

Figure 1

 1 Figure 1, a) Frontal and sagittal view of the right leg CT scan, b) MRI of the lower limbs and segmented muscle and bones tissues, c) High resolution MRI of the right knee and the segmented tissues demonstrated on the bottom, d) The knee MRI at three different flexion angles and the segmented bones on the bottom

Figure 2 ,

 2 Figure 2, Generated combined FE-multibody model of the lower limb validated through a simulation of passive deep knee flexion and used for investigating the effect of OWHTO on the patellofemoral joint. The FE model of the quadriceps muscle group included 2100 elements for RF, 1326 for VI, 9290 for VL and 2308 for VM. The QT was formed by 5200 elements, the femoral cartilage had a total of 1106 elements (a single layer of elements) and the patellar cartilage included 969 elements (two layers of elements).

Figure 3 ,

 3 Figure 3, Schematic view of the passive deep knee simulation setup. The position of the combined shank and foot segment is controlled through the transformation matrix obtained from MRI at different knee flexion angles. The patella is free to move in response to forces transmitted to it through the soft tissues and contacts with the femur. The bone positions at 25.2° knee flexion (the first MRI position) are used to define the initial position of the model.

Figure 5 ,

 5 Figure 5, Description of the patellofemoral JCS: lateral translation or shift is the motion of the patella along the fixed femoral axis (red), anterior translation is along the floating axis (green) and the proximal translation is along the patellar fixed axes (blue).

Figure 6 ,

 6 Figure 6, Schematic view of the patellar position predicted by simulation in comparison with its position acquired from MRI segmentation for 137.5° knee flexion angle. The patella bones depicted in light and dark blue are segmented by the first operator. The patella depicted in green is segmented by the second operator. The patella depicted in white is predicted by simulation.

Figure 7 ,

 7 Figure 7, The patellofemoral kinematics predicted by the simulation of passive deep knee flexion are plotted in blue. The horizontal axis is the knee flexion angle. The vertical axes are the motions of the patella with respect to the femur in its six DOFs. The black and red squares represent the patella kinematics obtained from MRI segmentation respectively done by the first and second operator. The first operator has repeated the segmentation twice to also account for the interoperator errors. The vertical black lines represent the range of variation between the kinematic points obtained from different MRI segmentations.

Figure 8 ,

 8 Figure 8, Predicted patellar position in response to different wedge opening angles on the tibia.

ACKNOWLEDGMENTS

This work was funded by Fondation pour la Recherche Médicale under the project FRM DIC20161236448. The IRMaGe MRI facility was funded by the ANR-11-INSB-0006 grant. The authors wish to acknowledge the continued technical support received from John Lloyd (UBC, Vancouver) throughout this study.


Thierry Le

Thierry Le Nadan

Christian Person

Jean Philippe Coupez

A Complete Integrated TX/RX Front-End Combining 3D Topologies And Global Synthesis

A complete integrated TX/RX front-end combining 3D

topologies and global synthesis

I. INTRODUCTION

In this way, RF modules can not be 'individually considered, and global synthesis techniques must be involved. We have previously reported about such approach which is really well-suited for meeting cost,

OL -+

• Beanl-lead diodes'

Diode connecting pad

Via holes Dielectric sheet Fig. 6. Beam-lead diode mounted on the modified magic Te feeding ports -3D Pads location.

The design procedure is made harder because of the . multileveled configurations to be considered. We develop an hybrid approach, by using electromagnetic simulator (HP-MoMentum) for properly describing the diodes access regions, and "circuit" simulator (HP-MDS) for modeling the complete structure. We have implemented such module on an alumina substrate (c.r =9.5 I 635µm), with intermediary dielectric sheet (c.r =4 I 30µm), for a center RF frequency of lOGHz.

CPW to alotllno As mentioned on figure 9, we obtain quite good results

(conversion losses of about 7dB, mainly due to the diodes resistance), comparable with the ones obtained by a standard uniplanar approach.

  Cost and electrical constraints related to new telecommunications systems and proposals (MMDS, . LMDS, Wireless Local Loop, ... ) must absolutely be simultaneously considered today for designing efficient RF front-ends, with performances in accordance with on board or base station equipment. contribute to reach such challenge.

  size and electrical requirements, especially about radiating elements. As a consequence, the technology has to be improved so as to provide to the designers a great design flexibility necessarily implied with such global synthesis. We have proposed a 3D multi-technologies approach, then offering various transmission line topologies and a number of available technological combination. In this paper, we first present results about efficient • filter-antenna modules, underlying the numerous advantages related to a global synthesis under a 3D integration technique. The method is then extended to the implementation of a complete integrated dual operating mode RF front end. We discuss about the great interest of a 3D technology for improving hybrid interconnections between passive and active components. Then, we emphasize on the design task, based upon the association of electromagnetic and "circuit" simulations. The dual operating mode function (modulator/mixer module) is especially described and validate through comparisons between experiments and simulations. The complete integrated RXff X module is presented and characterized in both emitting (BPSK modulation) and receiving (homodyne mixer) modes. II. A GLOBAL SYSNTHESIS METHOD FOR IMPROVING ANTENNA PERFORMANCES The figure I describes a microstrip patch antenna reported on a foam substrate (er = 1.07/tan o = 0.001), electromagnetic' aly coupled to a back-side microstrip filter on alumina substrate. A global synthesis procedure is proposed for introducing the antenna as the last resonator of the filter [l] [2] [3].

Fig. 1 .

 1 Fig. 1. Filter-antenna module on a composite substrate This antenna is modeled as a RLC resonator, R being the equivalent radiating resistance. This way, the filter synthesis procedure can be performed at Fo, assuming the output port loaded by the equivalent R resistance of the patch. The figure 2 describes the return loss parameter measured for such antenna-filter structure. An operating bandwidth of about 20% centered at 10 GHz is reached {p < -10 dB) while the radiating performances are also notified on this wide band (fig. 2b) [4]. Notes that 3D topologies have been. used for integrating the filter, regarding the required characteristic impedance, especially for the parallel stubs of the filter (Zc # 5 Q). TFMS {Thin Film MicroStrip lines) and 3D CPW (Coplanar Waveguide) have been implemented on an alumina substrate with intermediary (er =4/ 30µm) dielectric sheets.

Fig. 2 . 3 .

 23 Fig. 2. Antenna-fi lter module -Characterization If the global synthesis technique brings interesting perspectives in terms of electrical behaviour, it also induces drastic constraints on the technology to be associated. This contributes to the 3D technological orientation

Fig. 3 .

 3 Fig. 3. Dual mode RX/TX module : schematic This device is made of the previous described antenna-filter module, cascaded with a dual mode mixer/modulator function and corresponding fi ltering sub-circuits, and a local oscillator. The critical mixer/modulator function is composed of an annular slotline Magic Te structure with schottky diodes, and required filters and transitions to external feeding access. • In TX mode, the diodes are alternatively switched Off and On depending on the incident binary signal injected through the low-pass IF-filter (Intermediate Frequency), then modifying the phase of the Local Oscillator signal (LO with a 0-180 phase shift).

Fig. 5 .

 5 Fig. 5. Description of the magic TE in Mixer operating mode

Fig. 7 .

 7 Fig. 7. Hybrid design procedure. Analysis: Procedure

Fig. s :

 s Fig. s: Photography of the complete integrated module. Previous experimental characterizations were performed for evaluating the performances of the mixer.

  Fig. 9.0.1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1 1,1 1,2 1,3 1.4 1,5 l.F. Fniquancy(GHz)

Fig

  Fig.IO Test�bench with dual operating mode modules The module I is used as a up-converter mixer -see fig. I la -or as a BPSK modulator (lMbits/s modulating signal) -cf fig. 11 b.


Julian Thevenard

Ali Louzir

Dominique Lo

Hine Tong

Corinne Nicolas

Christian Person

Jean-Philippe Coupez

Ph Coupez

3D multi-sector vivaldi antennas based on metallized plastic technology

niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Introduction

Wireless Local Area Network (WLAN) is now widely deployed in companies, public areas and home environments. This success is due to the very low cost of the equipments, the ease of installation and the low maintenance cost. However, with the multiplication of the number of access points and users, the capacity of wireless networks is becoming interference-limited rather than noise limited. The use of multi-sector antennas, comprising several narrow beams, can help to solve the interference issue while improving the wireless range or/and bit rate [START_REF] Nakane | Trial Model of Adaptive Antenna Equipped With Switched Loads on Parasitic Elements[END_REF][START_REF] Preston | Electronic beam steering using switched parasitic patch elements[END_REF][START_REF] Sibille | Beam steering circular monopole arrays for wireless applications[END_REF][START_REF] Demmerle | A Biconical Multibeam Antenna for Space-Division Multiple Access[END_REF][START_REF] Simba | Planar-type sectored antenna based on slot Yagi-Uda array[END_REF].Various multi-sectored antennas have been designed and produced in the past recent years based on an omnidirectional antenna by altering the environment [START_REF] Nakane | Trial Model of Adaptive Antenna Equipped With Switched Loads on Parasitic Elements[END_REF][START_REF] Preston | Electronic beam steering using switched parasitic patch elements[END_REF][START_REF] Sibille | Beam steering circular monopole arrays for wireless applications[END_REF] or the power supply [START_REF] Demmerle | A Biconical Multibeam Antenna for Space-Division Multiple Access[END_REF]. Another widespread technique consists in using a dedicated antenna for each sector [START_REF] Simba | Planar-type sectored antenna based on slot Yagi-Uda array[END_REF][START_REF] Maruyama | Analysis and Design of Multi-Sector Monopole Yagi-Uda Array Mounted on a Ground Plane Using Moment Method[END_REF][START_REF] Thudor | Low Cost, MultiBeam antenna for WLAN applications[END_REF], space division into multiple sectors. Most of these solutions use a planar design while a significant advantage of volume antennas is their ability to offer higher design flexibility and radiation pattern control (E and H planes). Following these considerations, a conceptually simple 3D multi-sector antenna based on an original layout of Vivaldi-type antennas and compatible with metallised plastic manufacturing technology is introduced in this paper. The solution offers a great freedom in shapes and dimensions for the Vivaldi antenna and a large choice in the number of sectors and gain of each beam. The use of metallized plastic technology, based on molding 3D complex structures enables mass production of the antenna at low cost. To prove the concept a 4-sector antenna, based on a Vestodur Poly-Butylene Terephthalate (PBT) plastic material and mounted onto a FR4 switching board, has been designed in the 4.8-6 GHz band.

Concept of the multi-sector antenna and structure description

The novel concept of the Vivaldi-based multi-sector antenna is illustrated in Figure 1. Rather than using several Vivaldi antennas arranged on a uni-planar microstrip substrate to cover the entire 360° of the azimuth plane [START_REF] Thudor | Low Cost, MultiBeam antenna for WLAN applications[END_REF], the antennas are in this case vertically placed around a common central axis. Thanks to the use of the third dimension this arrangement offers much more freedom in the optimization of the radiation pattern (E and H planes), as well as the control of the gain within each beam and the number of sectors. In order to target consumer market and to reduce the manufacturing costs the metallized molded plastic technology is preferred to design this antenna. As shown in Figure 2, the constructed device is directly mounted on a horizontal microstrip motherboard including the feeding and switching circuits. Each Vivaldi antenna is fed through a microstrip to slotline transition performed on the vertical plane. The transitions between vertical and horizontal (on the motherboard) microstrip lines are obtained by a mechanical contact between metallized plastic pins and plated through holes inside the PCB. The motherboard which can contain other parts of the circuits constitutes an integral part of the antenna system and should necessarily be taken into account during the antenna design. The motherboard features (shape, dimensions, etc.) offer additional optimization parameters of the radiation pattern and the multi-sector antenna matching.

4-sector antenna system design: simulations and results

To allow an experimental validation and to create a device suitable for mass-production at low cost, we have developed a 3D 4-sector antenna working in the [4.8-6] GHz band. The MID (Molded Interconnect Device) antenna prototype is first molded with plastic material and then metallized in chemical baths after laser activation. The plastic used is the Vestodur 2230 ( r =3.7, tan =0.0012) PBT based. The simulations of the prototype presented in Figure 2 were carried out using the Finite-Element-Method (FEM) Ansoft's HFSS © software. In order to insure 90° beamwidth for a single sector in the azimuth plane, the dimensions of the Vivaldi antennas with circular profile are chosen as: 34 mm for the length of the profile, 35 mm for the aperture, 27.5 mm for the radius and a 1.5 mm ( /40) thickness imposed by the manufacturing constraints. The beams of the multi-sector antenna are switched using a single-pole 4throw switch (the Hexawave HWS451 SP4T) set at the bottom of the 90*90 mm 2 motherboard with the feeding circuits. Figures 3 and4 show the simulated performances of this 4-sector antenna combined with the motherboard. A 50% relative bandwidth, centred at 5.4 GHz, is obtained for -10 dB return loss. Figure 4 shows a close match between each response of the 4 sectors. In the useful band, the isolation levels for consecutive antennas are under -23 dB and lower than -31 dB for symmetrically opposed antennas.

Azimuth plane

Z X Y

As regards the radiation pattern, each sector is individually triggered and generates the same radiation pattern with an angular shift of 90° (Fig. 5). The maximal gain obtained is near 6 dBi, the directivity at 7.3 dBi, and the front-to-back ratio at around 12 dB with corresponding azimuth half-power beamwidth of 95° (Fig. 6). With these performances the multi-sector antenna covers the entire azimuth direction with a crossover depth of -3 dB.

The flexibility of the antenna form permits a modification of the radiation pattern characteristic. The mean beam could be tilted upwards with a asymmetrical antenna profile and/or the growth of the motherboard physical size (Fig. 7). Likewise, Gain of the antenna can be increased and half power beamwidth reduced by lengthening the Vivaldi Antenna profile (Fig. 8).

Conclusion

A novel design and simulation results of a wide-band 3D multi-sector antenna composed of Vivaldi-type antennas have been introduced. The proof-of-concept is validated by the design of a four-sector antenna in the [4.8-6] GHz band. Each individual antenna is located at 90° from each other in a vertical arrangement and mounted on a motherboard in an appropriate manner. The multi-sector antenna is associated with an integrated 1 to 4-port switch placed on the horizontal motherboard. The antenna structure itself is based on a plastic material that enables low-cost and mass production capabilities of molded and metallized 3D designs, whereas the motherboard is made of common FR4 substrate. This novelty offers a great flexibility of radiation patterns and performances (number of sectors, shape and dimensions). Furthermore, the 3D plastic device allows an easier integration onto an existing substrate of a system by means of metallized pins and holes. The realization of the proposed antenna prototype is in progress and experimental results will be presented during the conference.

Fig. 1 :

 1 Fig. 1: 8 Vivaldi antennas placed vertically around a common central axis.

Fig. 2 :

 2 Fig. 2: Plastic antenna system assembly on the horizontal motherboard.

Fig. 4 :Fig. 3 :Fig. 6 :Fig. 5 :Fig. 7 :

 43657 Fig. 4: Isolation between different ways when one sector is active.

Fig. 8 :

 8 Fig. 8: 3D 4-sector antenna with profiles of different lengths.Length of the profile


INTEGRATION OF AN ANTENNA/FILTER DEVICE, USING A MULTI-LAYER, MULTI-TECHNOLOGY PROCESS T. Le Nadan, J. P. Coupez, S. Toutain, C. Person LEST -UMR CNRS 6616 -ENST Br -BP 832 -29285 BREST CEDEX -France tel:+ 33 2 98 00 13 19 -Fax:+ 33 2 98 00 13 43 -email: Christian.Person@enst-bretagne.fr

.ABSTRACT:

In this paper, we discuss about the synthesis and the implementation of a multi function antenna/filter device, which appears as an optimum response in relation with the system's physical and electrical evolutions. Due to the extensive development of the uniplanar technology, our investigations concern the integration of a uniplanar slotline dipole directly in a standard Tchebyscheff band-pass filter. As a result, such a combination appears like a convenient solution for improving the performances of the basic antenna. To overcome technological constraints, we show that an optimum approach consists in the use of a multi-layer, multi-technology process. Preliminary experimental results prove the validity of this approach, and allow some extensions to more complex sub-systems.

INTRODUCTION:

In the last time, a lot of RF designer works have been developed to improve the performances of telecommunication systems, especially in terms of bandwidth capacities, operating frequency range and size reduction, thereby explaining, for instance, the recent emergence of millimeter wave applications in this domain (MMDS, millimeter wave LAN, and so on).

Because of these miniaturization and electrical specifications, important problems are often encountered when designing such systems through a classical cascaded basic function approach. As an alternative, a simultaneous design procedure can be used, resulting, for example, in the direct association of filters and radiating elements as new compact multi-function devices.

In fact, this new synthesis technique also leads to a significant improvement of the performances, compared to those of the initial basic elements. In the past, H. F. Pues [1] and H. An [2] have been among the first people to investigate the bandwidth enhancement of resonant antennas using an impedance matching method, without altering the element's radiating characteristics.

However, this technique has been mainly applied to microstrip antennas.

In this paper, we demonstrate that such an approach can be extended and efficiently used to enhance the operating bandwidth of some alternative radiating elements, such as uniplanar slotline dipoles, when incorporating them directly as resonators in a band-pass filter network. As a consequence, it should also provide a significant size reduction of the resulting multi-function device. Consecutively, we emphasize on the necessity of proposing an appropriate technological process, in order to meet electrical and physical requirements imposed by such a design procedure. Some authors, such as W. Menzel [3] and Ch. Person [4] have proposed a multi-layer technology approach to increase the flexibility for circuit integration. This has been applied to basic elements (like filters), but we investigate here its application to multi-function components.

To validate this work, the implementation of an integrated slotline dipole in a band-pass filter, using a multi-layer, multi-technology process, is presented. For this antenna/filter device, the experimental results, obtained in X band, are representative of the possibilities and advantages offered by this multi-function design.

PRESENTATION OF THE ANTENNA/FILTER MULTI-FUNCTION CONCEPT.

In comparison with a standard procedure, for which the usual front end devices are separatly designed and then cascaded together for building the overall system, the approach proposed here consists in a multi-function global synthesis, which allows an optimization of the system's performances. In this study, this concept has been carried out on an antenna/filter device, with very simple modeling approach, where the selected resonant antenna is considered as a lossy lumped element resonator. It thereby corresponds to a combination of a La Ca resonant structure and a resistive element Ra, which accounts for the radiated losses. Concerning the intrinsic operating bandwidth of such an antenna, it directly depends on the selectivity of the structure (i.e.

Q factor), but it remains narr ow in any way. On the other hand, a band-pass filter is basically composed by series and parallel LC resonators. Furthermore, it is classically designed on a 50 Q input-output matching load value. In our case, to optimize the multi-function circuit design, the radiating resistance of the antenna is considered as the output load impedance of the filter structure, and the La Ca resonator as the last resonator of the lumped equivalent network of this filter. In these conditions, the reactive part of the antenna's electrical model corresponds to one of the poles of the filter, which must also satisfy, if necessary CRa * 50 Q), the impedance transformation between the Ra load and the 50 0 input impedance level. Because of the integration of several functions in a same device, the advantages induced by this approach are numerous: first, it provides a great compacity, in agreement with the• system miniaturization.

Moreover, it leads to an optimization of both the function combination and the electrical performances, especially concerning the losses and the bandwidth values. Indeed, the antenna/filter device, which basically corresponds to a multi-cell function, presents a higher bandwidth than the one of a single matched dipole for example.

SYNTHESIS SPECIFICATIONS FOR A SLOTLINE DIPOLE I TCHEBYSCHEFF FILTER EXAMPLE.

The synthesis method exposed in the previous section is applied to a CPW-fed wide slotline dipole antenna and a Tchebyscheff band-pass filter. In this case, the principal aim is to enhance the radiation bandwidth of the resulting device, with respect to a single dipole antenna.

Concerning the electrical modeling approach, such an antenna and its feeder can be regarded as a parallel type resonator, which is integrated as the third resonator of a Tchebyscheff band-pass filter (n=3, bandwidth >15%, 0. 1 dB band-pass ripple). The final topology, based on a distributed solution, including 'A-gf4 stubs and 'A../4 impedance inverters, is shown in figure 1, where Zci and Zi are respectively the characteristic impedance of the i th impedance inverter and of the i th stub.

In relation with the antenna's electrical response, mainly the selectivity factor, this approach leads to strong design constraints, especially regarding the characteristic impedance values to be synthesized. Table 1 shows a set of Zc which meets the specifications previously o�'"cribed. 42 0 35 0 6.9 0 5.5 o Table 1 : Set of characteristic impedance values for the structure design.

As shown, both high and low impedance transmission lines are needed to realize the complete structure. With regular technologies, like microstrip or CPW, this wide characteristic impedance range is a real problem, given the achievable Zc values in each of these technologies. Therefore, in this work a multi-layer multi-technology integration is proposed. By use of the third dimension, extra design . flexibility is provided, in terms of discontinuity minimization and available characteristic impedances (low Zc are achievable with TFMS lines (Thin Film MicroStrip lines), while high Zc can be realized in a coplanar topology for example). As a matter of fact, such an approach allows a lot of combinations and interconnexions between different kinds of transmission lines for the implementation of a microwave function, leading to optimal solutions with regards to size reduction and to electrical performances enhancement.

A MULTI-LAYER, MULTI-TECHNOLOGY IMPLEMENTATION OF THE SLOTLINE DIPOLE/ TCHEBYSCHEFF FILTER.

The circuit, synthesized with the impedance values given in table 1, consists of three impedance inverters, realized in a multi-layered coplanar configuration, and two double parallel shorted stubs, using a TFMS approach, while the slotline dipole and its feeder are realized in a standard uni planar technology. In such a topology, the TFMS lines make use of the coplanar ground planes for their own grounding plane. The layout and dimensions of the antenna/filter circuit are presented in figure 2. This circuit is realized on an alumina substrate (er=9.6, H=635 µm), using a thin dielectric film (er=9.5, H=30 µm).

Concerning the preliminary experimental results, figure 3 gives a comparison between Sn measurements for a single matched slotline dipole and the antenna/filter device. As illustrated, a significant increase of the bandwidth can be observed (over 15%), without disturbing the radiation characteristic of the slotline dipole. Indeed, a first transmission measurement between two such circuits shows a constant gain response, through the whole bandwidth (figure 4).

FURTHER DEVELOPMENTS: REALIZATION OF AN ARRAY/FILTER DEVICE

The synthesis method developped in the previous sections is applied to the conception of an antenna-arr ay I Tchebysche:ff filter device, using a combination of two CPW, series-fed, slotline dipoles, and a TFMS shunt resonator. The multilayered topology used for this example is slightly different from the one used to realize the antenna/filter circuit. The quarter wavelength impedance inverters are implemented as regular CPW lines, while the TFMS resonator is designed on top of a thin dielectric overlay. Distance between the two radiating devices is roughly 'A.of2. Figure 5 shows a photograph of the realized circuit. Preliminary measurements (figure 6) show a good agreement with the synthesis theory, and a large SWR bandwidth can be observed. Still, radiation pattern measurements are needed to validate such an approach.

  coplanar gound planes ----�• dielectric overlay with side metallization ----

Figure 2 :

 2 Figure 2: Layout of the multi-layer, multi-technology slotline dipole/Tchebyscheff filter

Figure 3 :

 3 Figure 3: Comparison between S11 measurements of a matched slotline dipole and the antenna/filter circuit

Figure 4 :Figure 5 ;

 45 Figure 4 : Transmission measurements between two slotline dipole/filter devices

Figure 6 ;

 6 Figure 6; Comparison between simulated and measured data

CONCLUSION :

In this paper, a multi-layer, multi-technology antenna/filter device has been proposed as a convenient answer to future system performances requirements. The design procedure, based on a very simple modeling approach for both the selected uniplanar slotline dipole and the distributed Tchebyscheff band-pass filter has been described. Technological constraints have been highlighted, and a solution using multilayered topologies has been proposed. Preliminary experimental results, i.e. a large bandwidth matching and a good radiation characteristic in the whole band of this multi-function device, illustrate the validity of our approach.

As a future extension of this work, this multi-function concept, based on a multi-layer, multi-technology process, opens a lot of new perpectives for the integration of sub-systems, such as antenna array/filter or CPW-to-slotline transition/filter/antenna structure for example.

BIBLIOGRAPHY :

[l] H.F. PUES, A. R. VAN