Assaad Yammine

Iman Khalil

Pierre Clément

SEX EDUCATION IN LEBANON AND FRANCE

Keywords: Sex education, Multiculturality, religion, conceptions, teachers

This work is a comparison between France and Lebanon. It analyzes the conceptions of Lebanese and French teachers on issues concerning human sexuality and its education. Our goal is to highlight the different conceptions of teachers in both countries and to identify the parameters to which these differences are correlated. All the multivariate analyses conducted show two very different systems of conceptions, very significantly differentiating Lebanese teachers' conceptions of French teachers ones. French teachers, unlike their Lebanese colleagues, are more conducive to early learning topics related to sexuality to students between 6 and 15 years old depending on the subject. They are more likely to accept abortion and homosexuality, to focus on safer sex as an attitude that can reduce the spread of AIDS, and to consider that the teaching of STIs is not only the issue of biology teachers. The differences between Lebanon and France are not reducible to religion: each country has its own identity rooted in its specific geographical, historical, economic and cultural context.

-Context and theoretical backgrounds

Sex education (SE) presents great interest at the international level. Research in several countries confirms that the promotion of SE does not encourage young people to have early sexual intercourse [START_REF] Blum | Risk and protective factors affecting adolescent reproductive health in developing countries: an Analysis of adolescent sexual and reproductive health literature from around the world[END_REF][START_REF] Kirby | Sexual risk and protective factors: Factors affecting teen sexual behavior, pregnancy, childbearing and sexually transmitted disease: Which are important? Which can you change[END_REF] but rather put in evidence a positive effect on the maturity in the sexual behavior of students (Singh & al, 2005) and risk taking [START_REF] Coyle | Draw the Line/Respect the Line: A randomized trial of a middle school intervention to reduce sexual risk behaviors[END_REF][START_REF] Coyle | All4You! A randomized trial of an HIV, other STDs and pregnancy prevention intervention for alternative school students[END_REF][START_REF] Kirby | The impact of the Postponing Sexual Involvement curriculum among youths in California[END_REF][START_REF] Kirby | Impact of Sex and HIV Education Programs on Sexual Behaviors of Youth in Developing and Developed Countries[END_REF]Kirby & al , , 2006Kirby & al , , 2007)). In 1994, WHO pointed out that sex education (SE) has to provide students, considering their representations and basics, with information and scientific knowledge that allow them to discover and understand the different dimensions of sexuality; WHO added that SE also seeks to stimulate students' thinking based on information provided to help them develop attitudes of individual, familial and social responsibilities. According to the recommendations of international organisms such as WHO, the educational center of research and development in Lebanon (ECRD) has attempted to introduce SE in the renovated curricula of 1998. This attempt has faced many objections from several sociopolitical and religious authorities in Lebanon, which resulted in its total suppression from the curriculum of the EB8 class (students aged 12-13) (Circular n o 35/M/99, Presidential Decree n o 2066) and partial containment of the biology curriculum for the 2nd year of secondary school (15-16 years), Literature and Humanities and the 3rd year of secondary school (16-17 years) (Ministry of Education circular n o 95/M/99, decree n o 10227/97, [START_REF] Harfouch | Elaboration des Programmes au Liban : La transposition didactique externe en oeuvre[END_REF][START_REF] Yammine | Rôle des pouvoirs sociopolitiques et religieux au Liban dans la suppression du chapitre de la reproduction humaine du manuel de biologie de la classe EB8[END_REF][START_REF] Yammine | Impact de la religion sur les conceptions des enseignants libanais à propos de l'éducation à la sexualité[END_REF]. Currently, a new attempt to reintroduce SE in the Lebanese teaching context is part of a project combining the efforts of the ECRD, the UNFPA (United Nations Population Fund) and the Lebanese Ministry of Education.

French curricula have, in turn, evolved considerably during the past 50 years in human sexuality. ES is currently ruled by laws and is defined as follows: "The sex education's primary purpose is to provide students with opportunities to learn and understand the different dimensions of the -and their-sexuality, in accordance with the consciences and the right to privacy. This education, based on humanistic values of tolerance and freedom, self and others respect, should also help students to integrate positive attitudes of individual, familial and social responsibilities." (B.O N o . 46: Circular N o . 98-234 dated November 19, 1998, Sex Education and AIDS Prevention). The introduction of SE in France was initially, and is still today, more directed to the biomedical dimension than to the promotion of health [START_REF] Bernard | L'enseignement de la reproduction humaine et de la sexualité humaine dans les programmes du secondaire, en France, de 1950 à nos jours[END_REF][START_REF] Yammine | Rôle des pouvoirs sociopolitiques et religieux au Liban dans la suppression du chapitre de la reproduction humaine du manuel de biologie de la classe EB8[END_REF][START_REF] Berger | Sex education: analysis of teachers' and future teachers' conceptions from 12 countries of Europe, Africa and Middle East[END_REF]. SE in France has not met such strong resistance as in Lebanon. Lebanese society is multiconfessional. To manage it, the Lebanese refer to the National Pact (unformulated agreement, not written, signed in 1943) to apportion the responsibilities in the government [START_REF] Al-Khoury | Discours de Groupes d'écrivains, et L'Orient, 6 Avril 1957[END_REF], "which gave birth a tradition where each community was responsible for providing education to its children as it wanted and where it wanted" [START_REF] Quobeisy | State and public education in Lebanon [L'État et l'éducation publique au Liban[END_REF]. Beyond this diversity, there may be some Lebanese homogeneity in comparison with other countries. This relative homogeneity is in fact emerged in comparing conceptions of the Lebanese teachers to those of teachers from other countries on topics such as evolution [START_REF] Clément | Les convictions créationnistes et/ou évolutionnistes d'enseignants de biologie : une étude comparative dans 19 pays[END_REF], 2009), or environment education (Khalil & al, 2007a and b). It is for these reasons that we made a comparison of Lebanese and French teachers' conceptions, using samples large enough to identify a possible diversity of opinion within each country, but also to compare the two countries together, in order to identify whether, beyond their differences, the Lebanese teachers share common characteristics that distinguish them from their French colleagues. Analyzed conceptions will take into account the teachers' knowledge, values and social practices (in relation to abortion, homosexuality...) and their pedagogical projects (what should or should not be taught and at what age).

-Research Question.

Do the Lebanese and French teachers conceptions on sexuality and SE mainly differ in terms of the nationality of these teachers (thus according to their national socio-cultural context) or are they rather based on other parameters such as their religion, the degree of belief and the religious practice, or even more on their political opinion?

-Methodology

It was developed in the context of the European research project Biohead-Citizen (Biology, Health and Environmental Education for Better Citizenship; 19 countries, including Lebanon and France). Teachers respond in writing, completely anonymously and in the presence of the researcher, to a questionnaire covering six topics, including reproduction and human sexuality and teaching (24 questions) as well as their religious, social and political opinions (17 questions ), and other personal information (Clément & Carvalho 2007). The responses were subject to several types of multivariate analyses (Munoz & Clément, 2007[START_REF] Munoz | Teachers' conceptions of nature and environment in 16 countries[END_REF].

In each country, samples are strictly comparable: 1/6 in service teachers of primary schools (InP), 1/6 pre-service teachers of primary schools (PreP), 1/6 in-service teachers of biology (InB) in secondary schools (for Students 11 to 18 Years old), 1/6 pre-service teachers of biology (PreB) in secondary schools, 1/6 in-service teachers of language / letters (InL) in secondary schools, 1/6 pre-service teachers of language / letters (PreL) in secondary schools. In total, 722 teachers and future teachers were surveyed in 5 regions of Lebanon (North, South, Mount Lebanon, Bekaa and Beirut) and 732 teachers and future teachers in two regions of France (Rhone-Alpes and Languedoc-Roussillon) (Table 1).

-Results and Discussion

We restrict ourselves to the most significant effects, without presenting here the effects less or not significant (age, gender, educational level, etc.). The PCA (Figure 1) performed using the 24 questions on the SE for 1454 teachers, shows a clear difference between French and Lebanese teachers. A between analysis, supplemented by a randomization test of Monte Carlo, shows that this difference is highly significant.

In fact, French teachers, unlike Lebanese teachers, are more conducive to early learning topics related to sexuality to students aged 6 and 15 years depending on the subject (A85 à A90 et B37 à B41). They are more likely to accept abortion (A65) and homosexuality (A41), to focus on safer sex as an attitude that can reduce the spread of AIDS (A60), and to consider that the teaching of STIs is not only the issue of biology teachers. The analysis of the issues that most differentiate the two groups shows KVP interactions: Lebanese and French Teachers opposed or not to abortion, homosexuality, are in the same time or less favorable to the introduction some scientific content (K) in the SE, based on their religious values (V) and their associated social practices (P). The histogram in Figure 2a shows that while 52% of French teachers are for equal rights for homosexual and heterosexual couples, 72.3% of Lebanese teachers refuse such equality. The histogram in Figure 2b shows that 71.2% of French teachers found that incest and sexual abuse are topics to be taught at an early age (the ages of 2 fields are added here), 60.8% of Lebanese teachers that are for late teaching of these topics (> 15 years) or never at school. The 1 454 teachers' conceptions also vary quite significantly depending on their religion, which is very different in the two countries: half of French teachers are atheists or agnostics, against 0.4% of Lebanese teachers interviewed, 65% of Lebanese teachers are Muslims (Shiites, Sunni or Druze) against 1.5% of French teachers interviewed. It is therefore not surprising that when we remove the country effect, the religion effect disappears. However, when we remove the religion effect, the country effect remains very significant, which means that Christian teachers (41.5% of the French sample, 30.1% of Lebanese teachers interviewed) have different ideas about human sexuality and its teaching (Figure 3). Finally, a co-inertia analysis between firstly a PCA on the SE variables (Figure 4a) and on the other hand a PCA on the socio-political and religious variables (Figure 4b) highlights two systems of conceptions: one characteristic of most believers and teachers practitioners, less secular (more against separation between politics and religion, hence between science and religion) are more detrimental to early education of the SE at school, less accepting of homosexuality and abortion, and they prefer stable relationships of couples to "safer sex". Most of the Lebanese teachers are in this pole. The second system of conceptions brings together teachers less religious, more secular, and more favorable to the SE in school; this pole includes the majority of the French teachers.

-Conclusions

Beyond their religious diversity, the Lebanese teachers share ideas on human sexuality and SE, which distinguish them clearly from the French teachers. Each country has its own identity rooted in its specific geographical, historical, economic and cultural context. The relative homogeneity of the Lebanese teachers who has also emerged in comparing of their conceptions to those of teachers from other countries on topics such as evolution [START_REF] Clément | Les convictions créationnistes et/ou évolutionnistes d'enseignants de biologie : une étude comparative dans 19 pays[END_REF], 2009), or environment education (Khalil & al, 2007 a and b), explains the difficulties of implementing the SE in Lebanon. The perspectives opened by these results will be discussed in more details.

-References

  Figure 1aFigure1bFigure 1-(a) Individual points in the space for the first two discriminant axes differentiating the two countries as: FR = France, LB = Lebanon. (b) PCA on the SE variables (24 variables), France + Lebanon.

Figure 2a .

 2a Figure 2a. Histogram of individual responses to question A41 (values 1, 2, 3, and 4 correspond to four levels of "Likert scale")

Figure 2b .

 2b Figure 2b. Histogram of individual responses to question B39 (values 1, 2, 3, 4 and 5 correspond to five levels of "Likert scale")

Figure 3 .

 3 Figure 3. The test of randomization (Monte Carlo)

Table 1 .

 1 Submission of samples surveyed in Lebanon and France. For the group of education (InB, InL etc.), cf. the text above. For religion, AGN = Agnostics, CHR = Christians, Muslims = MUS, ELS = most: "I do not want to answer" no answers + some, + a few other religions as AGN, CHR or MUS

			Lebanon %	France %
		Total Sample 722	100 732	100
	Teaching groups InB	153	21.2	100	13.7
		InL	111	15.4	110	15.0
		InP	246	34.1	114	15.6
		PreB	59	8.2	149	20.4
		PreL	56	7.8	101	13.8
		PreP	97	13.4	158	21.6
	Religion	AGN	3	0.4	370	50.5
		CHR	217	30.1	304	41.5
		ELS	33	4.6	47	6.5
		MUS	469	65.0	11	1.5
	Level of belief	1 (+)	700	97	131	17.9
		2	9	1.2	79	10.8
		3	4	0.6	97	13.3
		4	4	0.6	68	9.3
		5 (-)	5	0.7	357	48.8
	Level of practice 1 (+)	556	77	44	6.0
		2	76	10.5	30	4.1
		3	38	5.3	9	1.2
		4	7	1.0	67	9.2
		5 (-)	45	6.2	532	72.7


Pierre Clément
email: pierre.clement@univ-lyon1.fr

Silvia Caravita

Adriana Valente

Loredana Cerbara

Charline Laurent

TEACHERS' CONCEPTIONS CONCERNING THE ENVIRONMENT ACROSS NINE MEDITERRANEAN COUNTRIES

Keywords:

Mediterranean countries share the same climate, the same nature and the same roots of civilization. Nevertheless they differ in socio-political aspects, economical development and religions. Are the teachers' conceptions on Environment linked to some of these parameters? Our research, held in the context of the BIOHEAD-Citizen project « Biology, Health and Environmental Education for better Citizenship », analysed the answers of 4189 teachers from nine Mediterranean countries to a questionnaire dealing with some topics of Environment: utilization, protection, GMO, feelings of animals, … Multivariate analyses show great divergences among the teachers' conceptions, several inside each country and some differentiating the countries. In countries from the South of Mediterranean Sea (Morocco, Algeria, Tunisia, Lebanon), the teachers' conceptions are more anthropocentric and more pro-GMO than in European Mediterranean countries (Cyprus, Malta, Italia, France, Portugal). The anthropocentric conceptions from the South Mediterranean countries are correlated with a low economical development, but also with a high degree of believing in God and practising religion (with no difference among religions) and with some socio-political positions more "at right" and against secularism. These correlations between knowledge, values and attitudes related to Environment are to be taken into account to improve the Environmental Education in each country.

Introduction

Mediterranean countries share the same roots of civilization and their cultural histories have been enriched by a ceaseless and intense array of material and non-material exchange. A greater awareness of the interdependence of society and nature and the urgent need of improving its management should be a goal for countries with so much in common. Although they share many similar characteristics (climate, nature, but also several successions of culture), Mediterranean countries differ in many respects: geographical and political conditions, social organization, lifestyle, economic development, and religion -to quote the most outstanding examples -. Callicott, who surveyed ecological ethics from the Mediterranean basin to the Australian outback, highlighted how a community is embedded in nature according to its characteristics and that cultural behaviours include codified ways of relating to nature. However, the forces of globalization not only threaten biological diversity, but cultural diversity as well (Callicott, 1994). Therefore our investigation asks the following: • Within Mediterranean countries, what are the beliefs, values, and world views of teachers concerning their relationship with the environment? • Are their views (their conceptions on Environment) diverse, depending the country or other parameters?

This research was held in the context of the BIOHEAD-Citizen European research project « Biology, Health and Environmental Education for better Citizenship » (2004Citizenship » ( -2008)), coordinated by G. Carvalho (Portugal), P. Clément (France) and F. Bogner (Germany). Environmental Education was one of the six topics of this project, which concerned 19 countries, nine of them being located around the Mediterranean Sea: Morocco, Algeria, Tunisia, Malta, Lebanon, Cyprus, Italia, France, Portugal.

Theoretical background

A wide range of educational aims addressed current challenges concerning the environment, sustainability: for instance [START_REF] Giolitto | Eduquer à l'environnement[END_REF][START_REF] Sauvé | Pour une éducation relative à l'environnement[END_REF][START_REF] Sauvé | Coordination of the issue 46 of Aster[END_REF][START_REF] Schultz | Values as predictors of environmental attitudes: evidence for consistency across 14 countries[END_REF][START_REF] Berthou | L'éducation à l'environnement dans les manuels scolaires de sciences de la vie et de la Terre[END_REF][START_REF] Caravita | Construction and validation of textbook analysis grids for ecology and environmental education[END_REF] These authors agree that knowledge, skills, and values must be addressed together within environmental education because of their significant level of interaction within one's mental processes that shape learning. "A topic that has received increasing attention in science education is the world view theory [START_REF] Cobern | Everyday thoughts about Nature[END_REF] (….) students' beliefs in the study of science are influenced by the world views commonly held in their socio-cultural environments" [START_REF] Murphy | Changing knowledge and beliefs[END_REF]. Are there different world views around the Mediterranean Sea? We analyse the teachers' conceptions as possible interactions between their Knowledge, Values and Practices: the KVP model (Clément, 2004a[START_REF] Clément | Didactic transposition and the KVP model : conceptions as interactions between scientific knowledge, values and social practices[END_REF]. Values function as an organized system: the meaning of a particular value functions as part of the ethical field to which it belongs. The various categories of values related to Environment have been discussed in the BIOHEAD-Citizen project [START_REF] Caravita | Construction and validation of textbook analysis grids for ecology and environmental education[END_REF], especially as they pertain to different dimensions of human activity related to our relationship with the environment or ways of viewing nature. [START_REF] Forissier | Les systèmes de valeurs d'enseignants du secondaire sur la nature et sur l'environnement. Une analyse comparative en France, Allemagne et Portugal[END_REF] and [START_REF] Clément | Construction des umwelts et philosophies de la nature[END_REF] traced the roots of conceptions about nature in both spiritualism and materialism. They showed how both can result in opposing ends: radical ecologism (biocentric attitudes) on one extreme and unlimited exploitation (anthropocentric attitude) on the other. Stern and Dietz (1994) proposed that there are three distinct categories of environmental attitudes: the individual, society-at-large, and all living beings, which correspond to egoistical, social, and biocentric attitudes. More authors are speaking about anthropocentric, ecocentric and biocentric attitudes [START_REF] Theys | L'environnement à la recherché d'une definition[END_REF][START_REF] Larrère | Les philosophies de l'environnement[END_REF], with a main focalisation on the anthropocentric and ecocentric views [START_REF] Schultz | A multinational perspective on the relation between Judeo-Christian religious beliefs and attitudes of Environmental Concern[END_REF]. These two categories correspond to two poles defined by [START_REF] Wiseman | A higher-order model of ecological values and its relationship to personality[END_REF] (the model 2-MEV) when analysing students' conceptions on environment: utilisation and preservation, also found in the teachers' conceptions in the BIOHEAD-Citizen project [START_REF] Munoz | Teachers' conceptions of nature and environment in 16 countries[END_REF]. A third pole (sentimentocentric) has been defined in this project, as teachers' ideas about the capacity of animals to feel or not dolour or happiness: in France, Germany and Portugal [START_REF] Forissier | Les valeurs implicites dans l'Éducation à l'Environnement. Analyse de la formation de SVT[END_REF][START_REF] Forissier | Les systèmes de valeurs d'enseignants du secondaire sur la nature et sur l'environnement. Une analyse comparative en France, Allemagne et Portugal[END_REF], in Lebanon [START_REF] Khalil | Anthropocentrées, écolocentrées ou sentimentocentrées : Les conceptions d'enseignants et futurs enseignants libanais sur la nature et l'environnement[END_REF], in Algeria [START_REF] Khammar | Les conceptions d'enseignants algériens sur la nature et l'éducation à l'environnement[END_REF] and in Morocco [START_REF] Khzami | Les conceptions d'enseignants algériens sur la nature et l'éducation à l'environnement[END_REF]). Another pole is linked to the GMO, with animated debates generally structured by an opposition vs. acceptation of GMO (Clément et al., 2007). According to European Commission (Eurobarometer, 2008) public opinion survey, the majority of Europeans (58%) are opposed to the use of GMOs (Genetically Modified Organisms). The resistance is more important in some countries as Cyprus (82%) than in other ones as Malta (28%) or Portugal (28%). In most of the European countries, the acceptance or reject of GMO is a controversial issue, opposing divergent scientific arguments generally linked to different opinions [START_REF] Berlan | Plant breeders' rights and the patenting of life forms[END_REF][START_REF] Kempf | La guerre secrète des OGM[END_REF][START_REF] Bonneuil | Disentrenching experiment? The construction of GM-crop field trials as a social problem[END_REF]. What are the teachers' conceptions related to GMO around the Mediterranean Sea?

Methodology

The total sample (4 189 teachers) comes from nine Mediterranean countries: Morocco (330), Algeria (223), Tunisia (753), Malta (198), Lebanon (722), Cyprus (322), Italy (559), France (732) and Portugal (350).

In each country, it is a well balanced proportion of six sub-samples: • 1/3 Primary School teachers (1/6 in-service and 1/6 pre-service) • 1/3 Biology teachers in Secondary Schools (1/6 in-service and 1/6 pre-service) • 1/3 Language teachers in Secondary Schools (1/6 in-service and 1/6 pre-service) Each teacher filled out a large questionnaire (144 questions), including • 29 questions related to Environment, GMO, Environmental Education • 17 questions related to personal information (age, gender, ... but also religion, religious practice, political or social opinions, ...).

The questionnaire was built by a collective work during more than 2 years [START_REF] Clément | Biology, Health and Environmental Education for better Citizenship: teachers' conceptions and textbook analysis in 19 countries[END_REF][START_REF] Caravita | Construction and validation of textbook analysis grids for ecology and environmental education[END_REF]: • A longer pilot test using already validated questions and some new ones • Translations and validation of the translations in each country • Application of the pilot test to small samples in most of the countries • Complements by interviews • Validation of the reliability of questions (the same students one month after) • Analysis of the pilot test data, and selection of questions for the final questionnaire.

All the teachers had to individually fill out the 144 questions of the questionnaire (10 pages), with a total guarantee of anonymity. It took between 30 to 45 minutes. They did that at the end of a course for the pre-service and some in-service teachers, and in their school for the other in-service teachers. The teachers were in groups when filling out the questionnaire, in presence of the researcher who immediately gathered the filled questionnaires. The data from each country were then put in an Excel file and analysed in Lyon (France) with multivariate analyses using the free software "R" (Munoz & Clément, 2007;[START_REF] Munoz | Teachers' conceptions of nature and environment in 16 countries[END_REF]. The questions related to Environment were selected from precise hypotheses, each set of questions (tables 2, 3, 4 & 5) corresponding to a precise topic. To analyse the answers, we used the concepts defined in the table 1.

Situated conceptions

When a person is answering to only one question (one situation) related to a topic.

The convergent answers of several persons to the same question (the same situation).

Conceptions

The coherences analysed by a researcher from the answers to a set of questions related to a precise topic = individual conceptions related to this topic When the same conceptions (related to a topic) are common to several persons (a social group) = collective conceptions = collective representations (Durkheim 1898) = social representations (Moscovici 1961[START_REF] Moscovici | Psychologie sociale[END_REF])

Systems of conceptions

When a social representation is correlated with another social representation; or with political, economical, social, religious opinions or contexts (multivariate analyses: PCA, Co-Inertia, …). In the first questionnaire used for the pilot test, there was 18 questions related to the feelings of animals: 6 animals with, for each, their ability to have feelings, to be happy and to feel dolour. There was a so strong correlation between feelings, dolour and happiness that we decided to use only one of these three categories. We reduced also the number of animals because nearly 100% of the teachers had the same answer for animals as dogs or monkeys. When we know in advance the answers, it is useless to maintain the questions.

The last questions are dealing with practices related to environment, and to Environmental education. We don't list them here because they had not an important weight in the results presented below.

Results and discussion

4.1 The PCA (Principal Components Analysis) to categorize the teachers' conceptions from the 9 Mediterranean countries The first Principal Component (horizontal axis in the figure 2) is opposing teachers more agreeing with "utilization" and "pro-GMO" (at right of the horizontal axis) to teachers more disagreeing with "utilization" and "pro-GMO" (at left). It is opposing teachers from North vs. South Mediterranean Sea (graph at right in the figure 2).

The second Principal Component (vertical axis) is opposing teachers more agreeing with "preservation" and "anti-GMO" (lower part of the vertical axis) to teachers more disagreeing with "preservation" and "anti-GMO" (upper part). It is opposing teachers inside each country. This result (the two first Principal Components, related with "Utilization" and "Preservation" of the Environment) is corresponding with the results obtained by Munoz et al. (2009, Biohead-Citizen project) with teachers from 15 countries, and with the 2-MeV model of Wiseman & Bogner (2003, from students' conceptions).

The teachers' conceptions strongly differ also by their idea about the ability of some animals (snails, flies, frogs) to feel happy ("feelings": figure 2 left): teachers being for "utilization" or for "preservation" of Environment can have (or not) this "sentimentocentric" attitude. The Components 3 & 4 of the PCA have a less weight, concerning conceptions of less teachers. The component 3 is opposing "feelings + anti-preservation" to "no feelings + propreservation". The component 4 is opposing "anti-GMO" to "pro-GMO": for some teachers, the conceptions Pro-or anti-GMO are independent from the conceptions related to preservation.

The results of this PCA illustrate the complexity of the Environmental Education: there are several groups of conceptions related to Environment and GMO. Are these groups of conceptions differentiating the 9 countries? The difference between countries is very significant (p<0.001, Monte-Carlo test with 1000 iterations). This difference is mainly coming from questions A16, A18, A17, A39, A32 (figure 4). In countries of South Mediterranean Sea (Lebanon, Tunisia, Algeria, Morocco), teachers are more anthropocentric (pole "Utilization"), and more pro-GMO (question 39) than in the North (European Mediterranean countries).

Between analysis to discriminate teachers' conceptions among the 9 countries

Co-inertia analysis to correlate teachers' conceptions on Environment (28 questions)

to their opinions (socio-political, religious, economical: 17 variables) The correlation between the two PCA is very significant (Monte Carlo test: p<0,0001), dealing with only the axis 1 (55% of the total variance). The anthropocentric conceptions, which differentiate the countries (A16, A18, A39, A17: figure 4) are giving the main meaning of this axis 1, the most anthropocentric conceptions being at the left of this axis. They are correlated with several teachers' opinions: P12a, P12b, A42, A34, P10, and negatively with A51, A37):

• P12a: a choice of 5 boxes between "I believe in God" and "I don't believe in God"

• P12b: a choice of 5 boxes between "I practise religion" and "I do not practise religion" • A42. Only a strong central power can put some order in my country: 4 boxes between "I agree" and "I don't agree". • A34. The government must make laws favouring the creation of firms to stimulate our economy: 4 boxes between "I agree" and "I don't agree". • P10. Which institution you trust more? 5 boxes between "Public health services" and "Private health services". • A51. Science and religion should be separated: 4 boxes between "I agree" and "I don't agree". • A37. Religion and politics should be separated: 4 boxes between "I agree" and "I don't agree".

In the graphs e and f of the figure 5, the teachers' conceptions from South Mediterranean Sea are mainly at the left of the horizontal axis 1, while those from North Mediterranean Sea are mainly at right. The anthropocentric (and pro-GMO) conceptions of teachers in the South of the Mediterranean Sea (Lebanon, Tunisia, Algeria, Morocco) are strongly correlated with:

• their religious convictions (high degree of believing in God and in practising religion)

• their political and economical opinions (for a strong central power, help of firms, private institutions)

• and low adhesion to secularist position (separation between sciences & religion, or between politics and religion) In consequence, the teachers' conceptions related to Environment are rooted in a strong system of conceptions, including religious, socio-political and economical dimensions. There are mainly two systems of conceptions: 1-In the South of Mediterranean Sea, a more anthropocentric and pro-GMO system, linked to a high religious practice and political positions more "at right" 2 -In the North of the Mediterranean Sea, a system of conceptions opposite to the precedent ones (less anthropocentric and more anti-GMO). Nevertheless, our PCA (figures 1 and 2), and another work including only the European countries of the project BIOHEAD-Citizen [START_REF] Clément | Teachers' conceptions on Environment and GMO in twelve European countries[END_REF], show an important diversity of conceptions related to Environment (and GMO) inside the European countries.

Other results

Other between analyses from the data presented here show several effects independent to the "country effect". We have no place here to present and discuss them. We nevertheless can list them:

• Teachers with diploma of biology are less anthropocentric than their colleagues.

• More the teachers studied in University (any matter, not only biology), less their conceptions are anthropocentric. • An "ageing" effect, more complex to summarize. • A strong interaction between the "country effect" and the "religion effect" (Christian, Muslim of Agnostic / Atheist). After the suppression of the "country effect", the "religion effect" is also suppressed.

• No clear "gender effect"

General Conclusion

Teachers' conceptions are very different around the Mediterranean Sea. Some important differences were found inside each country, as shown by the PCA: thinking or not that animals as snails or flies can be happy, being or not pro-GMO, being more or less anthropocentric (pole utilization) or ecolocentric (pole preservation). Nevertheless, the main differences were found among countries, with a clear opposition North / South Mediterranean Sea, mainly for the questions dealing with anthropocentric attitudes. Most of teachers from South Mediterranean think that:

• Our planet has unlimited natural resources.

• Human beings are more important than other living beings.

• Society will continue to solve even the biggest environmental problems.

• And that GMO are good for the environment While most of teachers from North Mediterranean Sea think the contrary. These two systems of conceptions are linked with great differences among these two sets of countries:

• (1) Different levels of economical development • (2) Different degrees of believing in God and practising religion • (3) Different socio-political positions The sociological research often shows links between (1) & (2), and ( 2) & (3) We also found an absence of effect of religion (Christian or Muslim) after the suppression of the "country effect". Most of the teachers of South Mediterranean Sea, in our sample, were Muslim (only in Lebanon there was also Christian teachers: see [START_REF] Khalil | Anthropocentrées, écolocentrées ou sentimentocentrées : Les conceptions d'enseignants et futurs enseignants libanais sur la nature et l'environnement[END_REF] for a more precise analysis of teachers' conceptions on Environment in Lebanon). The anthropocentric conceptions are mainly linked to more believing in God and practising religion, and to political positions more at right. [START_REF] Schultz | A multinational perspective on the relation between Judeo-Christian religious beliefs and attitudes of Environmental Concern[END_REF] also found "a link between more literal beliefs in the Bible and higher anthropocentric environmental concerns" (>2000 students from 14 countries: Latin America, Canada, US, Spain).

Finally, even if the climate and the nature are rather similar all around the Mediterranean Sea, as well as the cultural roots of our civilisations, the teachers' conceptions on Environment appear to be very "influenced by the world views commonly held in their socio-cultural environments", as proposed by [START_REF] Cobern | Everyday thoughts about Nature[END_REF]. In this research, we identified some aspects of these socio-cultural environments (religious practice, political opinions, economical development). Any conceptual change related to environment is therefore complex. The task of education is to transform world views through the development and systematization of conceptual schemes [START_REF] Murphy | Changing knowledge and beliefs[END_REF]. It is also to better understand the values and practices interacting with the taught knowledge on Environment, to be able to promote more protection for more sustainability of our world.

Figure 1 :Figure 2 :

 12 Figure 1: the main components emerging from the PCAThe first four components have some meaning, expressing the divergences and correlations of the teachers' answers, allowing us to analyse their conceptions.

Figure 3 :

 3 Figure 3: Between analysis discriminating the 9 Mediterranean countries. (a): Only the first axis (horizontal in the other graphs) is differentiating the 9 countries. (b): This axis is mainly defined by the questions A16, A18, A17, A39, A32. (c) and (d): The teachers of Tunisia (TN), Lebanon (LB), Morocco (MA) and Algeria (DZ) more answered "I agree" to these questions. (e) The horizontal axis is the same as in PCA (figure 2) but inversed. (f) The difference between the 9 countries is very significant: Monte Carlo test from 1000 iterations.

Question A16 :Figure 4 :

 A164 Figure 4: Answers of the 4189 teachers by country, related to the four questions which differentiate the most countries from South vs. North Mediterranean Sea.

Figure 5 :

 5 Figure 5: Co-Inertia analysis from the 4189 teachers' answers to the questions related to Environment (first PCA : graphs b and e) and to the questions related to their socio-political and religious opinions (second PCA : graphs c and f). (a): Only the first component (horizontal axis in the other graph) is meaningful in this co-inertia analysis. (b): this horizontal axis is the same, but inversed, as in the PCA from environmental variables (fig.2). (c) it is the main axis 1 of the PCA from only the socio-political and religious variables. (d) The correspondence between the two PCA is very significant in this co-inertia analysis (Monte Carlo test: the observed value, just above the letter (d) is outside 1000 iterations by chance (histogram at left of this graph): p<0.001). (e) Meaning of the axis 1 from the variables Environment: see the text below. (f) Meaning of the axis 1 from the variables Socio-political and religious: see text below/

Table 1 :

 1 Definition of the concepts used to define the teachers' conceptions

	individual	collective

Table 2 -

 2 The questions related to the topic "Preservation" (ecolocentric conceptions)

	A1. We must set aside areas to protect endangered species.	I agree	I don't agree
	A5.	If an intensive chicken farm were going to be created near where you live, you would be against this because it may pollute the groundwater.	I agree	I don't agree
	A7. Humans will die out if we don't live in harmony with nature.	I agree	I don't agree
	A11. Industrial smoke from chimneys makes me angry.	I agree	I don't agree
	A22. I enjoy trips to the countryside.	I agree	I don't agree
	A28. It makes me sad to see the countryside taken over by building sites.	I agree	I don't agree
	A40. It is interesting to know what kinds of animals live in ponds or rivers.	I agree	I don't agree
	A50.	All contemporary plant species should be preserved because they may help in the discovery of new medicines.	I agree	I don't agree

Table 3 -

 3 The questions related to the topic "Utilisation" (anthropocentric conceptions)

	A4. Nature is always able to restore itself.	I agree	I don't agree
	A8. People worry too much about pollution.	I agree	I don't agree
	A16. Our planet has unlimited natural resources.	I agree	I don't agree

Table 4 -

 4 The questions related to the topic GMO (Genetically Modified Organisms)

	A12. Genetically modified plants will help to reduce famine in the world.	I agree	I don't agree
	A13. Genetically modified organisms are contrary to nature.	I agree	I don't agree
	A39.	Genetically modified plants are good for the environment because their cultivation will reduce the use of chemical pesticides (e.g. insecticides, herbicides).	I agree	I don't agree
	A47.	Genetically modified plants are harmful to the environment because they will contaminate other crop plants, menacing their survival.	I agree	I don't agree
	A49.	If a person eats genetically modified plants, his/her genes can be modified.	I agree	I don't agree

Table 5 -

 5 The questions related to feelings of animals (sentimentocentric topic)

	A10. Snails are able to feel happiness.	I agree	I don't agree
	A29. Frogs are able to feel happiness.	I agree	I don't agree
	A45. Flies are able to feel happiness.	I agree	I don't agree

Acknowledgements

This work has been supported by the European Research Project Biohead-Citizen (Specific Targeted Research n° 506015, FP6, Priority 7: "Biology, Health and Environmental Education for better Citizenship"). The authors specially thank the other colleagues who gathered data from their country: Sabah Selmaoui, Boujemaa Agoram, Salahedine Khzami (Morocco), Farida Khammar, Amaria Aouar-Métri (Algeria), Mondher Abrougui, Alaya Alaya (Tunisia), Paul Pace (Malta), Iman Khalil, Fadi Haje (Lebanon), Nicos Valanides, Olia Nisiforou (Cyprus), Jérémy Castéra, Sandie Bernard, Dominique Berger, Marie-Pierre Quessada (France), Graça Carvalho, Rosa-Branca Tracana (Portugal).


Aurélie Lecestre

Pascal Dubreuil

Sylvain Noblecourt

Josiane Tasselli

Éric Imbernon

Frédéric Morancho

Anisotropic Deep Reactive Ion Etching without Aspect Ratio Dependence Etching for silicon power devices

teaching and research institutions in France or abroad, or from public or private research centers.

Anisotropic Deep Reactive Ion Etching without Aspect Ratio Dependence Etching for silicon power devices

Aurélie LECESTRE 1,3 , Pascal DUBREUIL 1,3 , Sylvain NOBLECOURT 1,2 , Josiane TASSELLI 1,3 , Eric IMBERNON 1,3 , Frédéric MORANCHO We present the optimization of the critical etching step for the fabrication of silicon Deep Trench-SuperJunction (DT-SJ) Diodes in order to obtain breakdown voltages of 1200V. The influence of the technological parameters on electrical performances has been studied by simulations, showing the importance of trenches verticality and width [1][2]. The aim is to fabricate an array of trenches of 6 µmwidth and 110µm-depth near to junction termination trenches of 80um width. The main challenge for etching deep trenches in silicon is high anisotropy with high aspect ratio: we studied the influence of DRIE passivation time on Critical Dimension loss [3]. ARDE effect (Aspect Ratio Dependent Etching) has been reduced by using a thermal silicon oxide mask: SiO 2 thicknesses have been determined in order to obtain the same depth whatever the trench aperture.

Critical points for deep trenches etching are: High Aspect Ratio (HAR), CD losses, low roughness surface of sidewalls (scalloping), narrowing on the trench top, Aspect Ratio Dependent Etching (ARDE). First of all, an HAR around 20 has been obtained thanks to Bosch process including two cycles: an etching step with SF 6 followed by a passivation one with C 4 F 8 /O 2 . This work is carried out with Alcatel -AMS4200 ICP (Inductively Coupled Plasma) DRIE equipment. In order to reduce CD loss, we have varied the passivation time/etching time ratio from 1.3 to 3. High anisotropy and low roughness surface have been achieved for a ratio of 1.75 (3.5s/2s). In these conditions, for trenches of 6µm-wide and 110µm-depth, the width difference between the top and the bottom of trenches is around 100nm and the scalloping is around 60nm (Fig. 1-a).

The second study has been carried on the ARDE effect. The aim is to obtain the same depth for two different widths. Indeed, for 80µm-trench the etch rate is two times faster than for a 6µm one. In order to reduce this etching rate difference, an oxide mask has been added only on the biggest aperture [START_REF] Belharet | Plasma Etch and Strip in Microelectronics[END_REF].

The influence of the oxide thickness on etching depth for various trench widths is reported on Fig. 2-a, for 25min and 65min etching times. Using a 1.6µm oxide, the depth gap between 6µm and 40µm apertures is 5µm, and the depth gap between 6µm and 80µm apertures is 20µm as illustrated on Fig. 1-b for a 65min etching time.

Moreover, the oxide layer on top of trenches allows the reduction of some negative effects related to Bosch process such as roughness surface (scalloping) and narrowing of the trench top (Fig. 2-b). So, the scalloping depth is decreased until 40nm.

Fig. 1 :

 1 Fig.1: SEM images of trenches with high aspect ratio (HAR>28) for an etching time of 65min: a) with SiO 2 mask (300nm). b) with a selective SiO 2 mask (1.6µm) to reduce the ARDE.

Fig. 2 :

 2 Fig.2: a) Si trenches depth variation versus SiO 2 mask thickness for two Si etching times (25min and 65min) and several trench widths (6µm, 40µm, 80µm). b) Oxide effect on narrowing after photoresist elimination.


Enrico Dallago

Daniele Miatton

Giuseppe Venchi

Valeria Bottarel

Giovanni Frattini

Giulio Ricotti

Monica Schipani

Comparison of Two Autonomous AC-DC Converters for Piezoelectric Energy Scavenging Systems

Keywords: Piezoelectric energy harvesting, active AC-DC converter, low-power circuits, environmental vibrations

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

INTRODUCTION

Energy scavenging systems are used to harvest the normally lost environmental energy (associated to vibrations, thermal gradients, solar radiation, pressure gradients) and to convert it into electrical energy. This solution can be very attractive to supply portable or low power electronic devices where batteries are a bottleneck for the whole system (i.e. they have a finite life time and their replacement or recharge is not feasible or too expensive). An energy scavenging system, instead, is a theoretically endless energy source. For this reason they are rapidly gaining popularity in the scientific and the industrial community. Typical applications are wireless sensing (both single spot and multi-nodes systems), biomedical (patient monitoring, hearing aids, etc.), automotive (using self supplied, wireless devices can help reducing the cable length on board). The challenge is twofold: on one side the power requirements of the supplied electronics should be as low as possible, on the other, given the very low energetic content associated to environmental energy, the interface circuit has to be as effective as possible in managing the harvested power. In literature many papers can be found which describe methodologies to realize an energy-scavenger [START_REF] Roundy | Energy Scavenging for Wireless Sensor Nodes with a focus on Vibration to Electricity Conversion[END_REF], [START_REF] Peano | Design and Optimization of a MEMS Electret-Based Capacitive Energy-Scavenger[END_REF], [START_REF] Stark | Thermal Energy Harvesting with Thermo Life ®[END_REF], [START_REF] Sterken | An Electret-Based Electrostatic µ-generator[END_REF]. Each case has different requirements depending on the environmental energy source considered, the characteristics of the transducer, the typical frequency of the process. No universal solution exists: each scavenger interface electronics has to be tailored to the specific transducer and application. Many of the above mentioned works are focused on the conversion of the energy associated to mechanical vibrations since they can be easily found in many environments [START_REF] Roundy | Energy Scavenging for Wireless Sensor Nodes with a focus on Vibration to Electricity Conversion[END_REF], [START_REF] Renaud | Scavenging Energy from Human Body, Design of a Piezoelectric Transducer[END_REF]. Among the available vibration transducers this paper considers a system based on a piezoelectric transducer since it is one of the most efficient which can be used [START_REF] Roundy | Energy Scavenging for Wireless Sensor Nodes with a focus on Vibration to Electricity Conversion[END_REF]- [START_REF] Roundy | Improving Power Output for Vibration-Based Energy Scavengers[END_REF]. When exposed to vibrations coming from the real world the electrical energy at the output of this transducer is a strong and irregular function of time [START_REF] Roundy | Energy Scavenging for Wireless Sensor Nodes with a focus on Vibration to Electricity Conversion[END_REF]- [START_REF] Dallago | Self-Supplied Integrable High Efficiency AC-DC Converter for Piezoelectric Energy Scavenging Systems[END_REF], [START_REF] Han | Novel power conditioning Circuits for Piezoelectric Micro Power Generators[END_REF], hence, to realize a DC supply source, an AC-DC conversion is needed. Two active AC-DC converters based on the voltage doubler topology (see Figure 1) are presented. The reasons behind the choice of this topology are the fact that is it simple and that it is able to increase the value of the input voltage by approximately a factor two. This last aspect is quite important: as it will be shown later, the piezoelectric transducer exhibits a resonant behaviour; at resonance the output voltage for a given acceleration can be quite high, but out of the resonance the same acceleration will produce a voltage much lower. In perspective of an actual application, the harvester will be exposed to an acceleration whose spectrum is spread over a range, rather than being tuned at a particular frequency, so being able to step-up the input voltage is a desired feature. The idea of implementing an active rectifier, rather than a passive one, is basically inspired by the observation that the voltage drop across the switches of the rectifier causes power dissipation and, most of all, has to be subtracted from the output voltage, decreasing it and consequently the energy that can be stored at the output (for example across a capacitor as shown in Fig. 1). Of course the active circuitry comes at the price of using a part of the harvested energy to supply the active circuitry itself: active converters can be more efficient than passive solution [START_REF] Le | Piezoelectric Micro-Power Generation Interface Circuits[END_REF][START_REF] Dallago | Self-Supplied Integrable High Efficiency AC-DC Converter for Piezoelectric Energy Scavenging Systems[END_REF], [START_REF] Dallago | Integrable High Efficiency AC-DC converter for Piezoelectric Energy Scavenging System[END_REF], but they are more difficult to be designed because their whole power consumption has to be very low. To this purpose, and for other reasons which will be illustrated in the following, two different driving circuitries were considered to command switches S1 and S2 (Figure 2). In particular, the topology shown in Figure 2a, which will be called "hard", uses comparators (CMP1-2), while in the one of Figure 2b, which will be called "soft", the switches are driven with operational amplifiers (OP1-2). Both proposed solutions use only a fraction of the harvested energy to supply the active circuitry and make the energy scavenging system autonomous. In particular, at the output a capacitance (C S ) of 1 µF is used to store the harvested energy and no external power source is required, neither during start-up nor in normal operation 1 . Since the voltage across the storage capacitor Cs increases as the energy is harvested, a supply independent bias circuitry is used in both cases: it makes the current consumption of the active part supply independent. Both circuits were diffused as test chips exploiting a 5V CMOS STMicroelectronics technology and were extensively tested. They were compared in terms of efficiency of the converter and of the average output power, evaluated under the same input conditions while varying the load. The significance of such parameters is also discussed, and a more general figure of merit is defined with the advantage of also weighting the ability of the converter to harvest all the power available at the transducer terminals. Section II deals with the design of the two considered AC-DC driving circuitries highlighting their pro and cons, while Section III shows the experimental results compared with the simulated ones.

PIEZOELECTRIC ENERGY SCAVENGING SYSTEM

Mechanical Aspects

The considered piezoelectric transducer is a cantilever which works in 31-mode when it is excited by the mechanical vibrations, as shown in Figure 3. This means 1 The presence of the output capacitor is not only required to supply the control circuitry or to filter out the voltage ripple, but it often works as an energy tank. In fact, in most cases the supplied electronics works with a duty cycle. For example a wireless sensor that transmits one measurement every 10 seconds will be active only for a few hundreds of milliseconds, while it will switch in a low consumption or standby mode for the rest of the time. During this interval the scavenger is expected to accumulate the energy required during the burst of operation. that the cantilever is exposed to a strain in the direction of axis 1 while the resulting electrical displacement is along axis 3.

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To have a maximally efficient conversion of the mechanical vibrations into electrical energy the cantilever should be excited at its resonant frequency which can be varied adding a mass (m) on its free end [START_REF] Roundy | Energy Scavenging for Wireless Sensor Nodes with a focus on Vibration to Electricity Conversion[END_REF]. This allows to move the resonance frequency of the energy transducer around the frequency which is more likely in the application. The experimental measurements shown in Table 1 and [START_REF] Roundy | Energy Scavenging for Wireless Sensor Nodes with a focus on Vibration to Electricity Conversion[END_REF] show that the frequency range of mechanical vibrations existing into civil environments is approximately (10-380) Hz. The piezoelectric transducer can be modeled at resonance by the equivalent circuit shown in Figure 1, [1]- [START_REF] Roundy | Improving Power Output for Vibration-Based Energy Scavengers[END_REF]. Generator V PO is a sinusoidal voltage source whose frequency is equal to the transducer resonance frequency and whose amplitude is equal to the open circuit output voltage, while C P is the electrical capacitance of the piezoelectric cantilever.

The presented results are based on a piezoelectric transducer with geometrical dimensions equal to (30x15x0.2) mm 3 (LxWxH). The piezoelectric material used was a soft Lead Titanate Zirconate (PZT) and it was sputtered onto a Nichel alloy support. The piezoelectric capacitance C P was measured to be 19 nF.

Figure 4 shows the experimental set-up which was used to shake the piezoelectric transducer with a controlled acceleration. It is composed of an electrodynamic shaker (Bruel&Kjiaer 4810), which moves the piezoelectric transducer, and by a triaxial MEMS accelerometer (LIS3L02AS4 of STMicroelectronics); it was screwed to the shaker movable table so to measure the acceleration given by the shaker itself and to guarantee the repeatability of the measurements.

Figure 5 shows the experimental frequency response of the piezoelectric transducer when it was excited with a sinusoidal acceleration with a peak to peak amplitude equal to 0.8 g. It is possible to see that its resonance frequency is equal about to 130 Hz. For example, the measured resonance frequency of the cantilever is about 64 Hz if a lead mass of about 0.8 grams is added.

Design of the proposed front-end circuitries: Common Parts

During the start-up the voltage across C S is too low to supply the active devices. In this case, for both solutions, the operation of the converter is guaranteed by the body-drain diode of MOSFETs S1 and S2 which implement a standard, passive diode voltage doubler rectifier. Hence, the proposed rectifiers can be seen as a parallel of two AC-DC converters: an high efficiency active one and a lower efficiency passive one, the latter working only during start-up. As soon as the output voltage is sufficient the active one comes alive and flawlessly takes over the passive one; this switch does not need any dedicated control circuitry. Furthermore, after the active part starts working, the voltage across C S varies with time as the energy is harvested. Since this voltage is used as the supply for the active devices, it is advantageous to make their current consumption independent on the supply voltage itself. Figure 6 shows the circuital topology used to implement a supply independent bias; it is modified with respect to [START_REF] Dong | Low-Voltage, Supply Independent CMOS Bias Circuit[END_REF] by introducing a diode connected MOSFET (M4). In fact, since the system requires supply currents in the range of tens of nanoamperes, in the scheme without M4 the resistance R1 would be in the order of tens of megaohms, which is too area expensive for an integrated solution. The effect of M4 is to reduce the voltage drop across R1 lowering its value for a given current. Furthermore, a start up circuit is needed. This was obtained with dummy MOSFETs ML1 and ML2: the leakage of their body-drain diode has been exploited to inject a current into nodes A and B so to have the start-up aid. This solution allows us to avoid additional start-up circuitry, reducing total power consumption. Figure 7 shows the simulated behaviour of the two bias voltages versus the supply voltage. In particular the circuitry starts to regulate when the supply voltage is higher than about 680 mV. Above this value, the voltages V BiasP and V BiasN can be used to mirror a supply independent current. The current consumption of the whole bias circuitry is about 100nA.

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Working principle of "hard" driving and design methodology

Figure 2a shows the active topology of the ac-dc converter that uses comparators CMP1 and CMP2 to drive switches S1 and S2. The comparators sense the drain to source voltages of the two MOSFETs and properly turn them on or off [START_REF] Dallago | Integrable High Efficiency AC-DC converter for Piezoelectric Energy Scavenging System[END_REF]. This is the most straightforward way to implement an active version of the voltage doubler converter, since the switches and their driving emulate some ideal diode with a very low, almost zero, forward voltage drop, but the design of the two comparators is critical because a very accurate choice of the threshold voltages is required. In principle one could use a single threshold for each comparator equal to zero; in practice the spread due to process mismatches has to be taken into account. In fact if this voltage varies, during the diffusion process, with respect to the ideal value a negative effect, (i.e. the oscillation of the driving signal), can take place [START_REF] Dallago | Self-Supplied Integrable High Efficiency AC-DC Converter for Piezoelectric Energy Scavenging Systems[END_REF]. To reduce the probability to fall into this case the comparators has be designed with an hysteretic transfer characteristic, with an hysteresis wide enough to accommodate the expected variance of threshold. Among the two, the most critical threshold voltage, for both comparators, is the one which switches S1 or S2 off, called "Th-OFF". To prevent the above mentioned oscillations the designer has to guarantee it is positive for CMP1 and negative for CMP2; but, at the same time, to minimize the unwanted discharge of the piezoelectric or of the storage capacitance caused by a delayed switching [START_REF] Dallago | Self-Supplied Integrable High Efficiency AC-DC Converter for Piezoelectric Energy Scavenging Systems[END_REF], the "Th-OFF'' should be as small as possible. These two requirements are, of course, contrasting. Figure 8a and Figure 8b show the electrical schemes of the two designed comparators that are supply and ground compatible respectively, while Figure 8c shows a picture of the diffused circuit. The bias voltages B N and B P are provided by the supply independent bias circuitry. Referring, for example, to CMP1 (similar considerations apply to CMP2) it is possible to see that the current in M 4 depends on the output voltage of CMP1 itself. This allows to obtain the hysteretic transfer function for the comparator. In fact, when output voltage of CMP1 is low, (S1 is into its ON condition) the current in M4 is equal to the current in M5; on the contrary, when the output of CMP1 is high (S1 in OFF condition), an extra current, given by M3, flows in M4. As a consequence, the two threshold voltages are different from each other.

To obtain a positive "Th-OFF" threshold voltage, a mismatch between the aspect ratio of the MOSFET M4 and M5 was introduced. In order to assure that the two "Th-OFF" voltages have the correct sign, 300 MonteCarlo simulations have been performed. The resulting distribution diagrams of the critical "Th-OFF" threshold voltages are shown in Figure 9 for both comparators. The chosen values are +9 mV and -9 mV for CMP1 and CMP2 respectively. The static current consumption of each comparator is about 110 nA and their minimum operating supply voltage is about 650 mV.

The structures indicated with "OD" into Figure 8c are two common source configuration MOSFETs whose gate terminals are connected to the output node of CMP1 and CMP2 respectively and whose drain terminals are directly connected to two output pads. These MOSFETs were added to allow the comparator output voltages to be measured, so to verify their functionality, without adding a loading capacitance too high to their output nodes.

Working principle of "soft" driving and design methodology

Figure 2b shows the active topology of the voltage doubler converter where the driving circuitry is realized with operational amplifiers OP1 and OP2 To introduce its working principle let us consider Figure 10 which shows the case of OP1. It is possible to apply Kirchhoff Voltage Law (KVL) to the external mesh:

0 V V V OS SD IN = - + (1)
If the operational amplifier has a DC gain equal to A the voltage on the gate of S1 is:

IN G V A V ⋅ = (2)
Equations ( 1) and ( 2) can be solved as a function of V G :

) V V ( A V SD OS G - ⋅ = (3)
In the ideal case the DC gain A of the operational amplifier is infinite; as a consequence the difference in equation (3) has to vanish in order to have a finite value of the gate voltage. Thus a regulation loop modulates the gate voltage V G so to keep, for each value of the drain current, the source to drain voltage is equal to Vos. In the ideal case, when drain current is positive the regulation loop sets the working point of the MOSFET at the intersection between its characteristics and the offset voltage. When the current decreases, the loop moves the working point of the MOSFET at lower values of its source to gate voltage, until the current is equal to zero. At this point the regulation loop turns the MOSFET off: since there is no intersection between the MOSFET characteristics and the offset voltage, negative values of the current are not allowed and the regulation loop holds the transistor off. This principle intrinsically guarantees that, differently from the "hard" topology, no oscillations of the driving signal can take place. Furthermore, a negative current is impeded and the discharge of the capacitances is prevented. Symmetrical considerations apply to OP2. Differently from the "hard" approach, the value of Vos is not critical because it has simply to be far enough from zero so that the process mismatches will not change its sign. While it is true that an higher offset gives higher losses on the switch, they are still negligible for practical offset values (which can be easily designed in the tens of millivolts range).

In practice, the real operational amplifier has a finite DC gain; this means that the value of the voltage across the MOSFET is slightly different from the theoretical one. Nevertheless it can be demonstrated that, with the previously described choice of the offset, this will not affect the operation of the circuit. Figure 11a shows the designed operational amplifiers while Figure 11b contains a picture of the diffused structure. Because of the level of their input voltages, OP1 and OP2 have to be supply compatible and ground compatible respectively. The bias of the operational amplifiers is given by the supply independent bias circuitry. The operational amplifiers have been designed so that they are able to work with the minimum possible value of the voltage supply. In this way the active rectifier takes over the passive one as soon as a very low energy has been stored into capacitance C S . A 5pF capacitance has been introduced to compensate the regulation loop.

The offset voltage was obtained mismatching the aspect ratio of the input MOSFETs M A and M B : the values of the obtained offset voltages are equal to 26mV and 21mV for OP1 and OP2 respectively. Figure 12 presents the simulation results of 500 MonteCarlo iterations, showing the possible spread of these voltages. It is possible to see that this spread is sufficiently small to have the correct sign also with process mismatches.

Aspect ratio of the MOSFETs S1 and S2 has to be chosen to avoid the loop saturation. The expression of the drain current when the MOSFET is turned on is, in a first approximation, equal to:

DS th GS D V ) V V ( L W k i - = (4)
where V th is the threshold voltage of the MOSFET, W/L is its aspect ratio and k is its characteristic constant. The term into the parenthesis is the overdrive voltage: its value is modulated by the regulation loop which, for each drain current, varies the gate voltage. If the overdrive voltage is enough the source to drain voltage is equal to V OS , that is: Figure 12 MonteCarlo simulations of the offset voltages of the designed operational amplifiers.

OS th GS D V ) V V ( L W k i - = (5)
On the other hand if, for a given current, the overdrive is not enough (which means that the op-amp is saturated) the regulation loop does not work and the source to drain voltage of S1 or S2 is not equal to offset voltage.

The aspect ratio has to be designed to accommodate the maximum expected current. Tab. 2 resumes the characteristics obtained for the amplifiers: in particular the current consumption is about 200 nA for each amplifier. V dd-min is the minimum supply voltage required by the operational amplifiers to work.

EXPERIMENTAL AND SIMULATED RESULTS

Before evaluating the performances of the proposed solutions an experimental characterization of the supply independent bias circuit was realized. This was done using a stand alone version of the circuit depicted in Figure 13b: three MOSFETs Ma, Mb and Mc were added to amplify the bias current by a factor 30. This current is then converted into a voltage drop by means of an external resistance, equal to 2 MΩ. Experimental characterization was done supplying the bias circuit with a triangular waveform in the range 0-5 V. Figure 13a shows that, as soon as the supply voltage is higher than 680 mV, the circuit generates a constant voltage drop across the 2 MΩ resistance which corresponds to a constant bias current, as it was predicted by the simulations.

The performances of the proposed solutions have been evaluated at different values of the load resistance R L ; in particular, the considered figures of merit were the average power at the output of the piezoelectric transducer (P P ) and the average power delivered to R L itself (P L ). The load resistance was varied between 50 kΩ to 550 kΩ.

A passive voltage doubler, realized with BAT-86 Schottky diodes that have a threshold voltage equal to 0.2 V, was considered as a benchmark. This comparison is quite significant since the selected diodes as a forward voltage drop way lower than a standard diode and the passive solution does not have any additional consumption due to the control circuitry. Figure 14 compares the experimental results of the "hard" solution with those of the passive converter. The piezoelectric transducer was mechanically excited at 130 Hz and the acceleration was regulated so that the peak value of V PO was equal to 1.5 V. The powers drawn from the piezoelectric transducer are comparable between the two cases. On the contrary, the output power of the "hard" solution is heavily affected at low load resistance values. This is due to the fact that at values lower than 100 kΩ the energy stored into C S , and hence the voltage across it, is not enough to switch the driving circuitry on and, as a consequence, only the well-source diodes of the passive path are exploited for the conversion. Conversely, at higher load values the converter works in the active way and the output power is higher with respect to the passive solution. This confirms that the lower forward voltage drop across the switches has positive effects on the output power, consistent enough to compensate for the power consumption of the control circuitry. Furthermore, the accuracy of the design has guaranteed that, in spite of the fact S1 and S2 are switched off with a delay due to comparator threshold voltage, this does not affect the energy harvesting and makes the "hard" active converter a competitive solution with respect to the passive one. The performances of the "soft" solutions were evaluated at different values of the mechanical acceleration so to obtain different values of V PO (i.e., 1.5, 2 and 2.5 V); Figure 15 a, b show the obtained results, comparing them with the corresponding behaviour of the passive converter, as usual. It is possible to see that under any condition the "soft" converter draws a lower power from the piezoelectric transducer than the passive one. On an absolute scale this means that the combination of the piezoelectric transducer and the "soft" converter makes a less effective energy harvester.

Returning to the interpretation of the experimental results the "soft" converter is generally less capable of extracting energy from the transducer with respect to both the "hard" rectifier and the passive one. At this point one should expect that also the power delivered to the load resistance P L is lower, but the experimental results of Figure 15 show that the two rectifiers are equivalent when V PO is 1.5V, that the active rectifier performs better at lower load resistance values for V PO =2, and that finally it outperforms the diode converter on a wide load range for V PO =2.5V. This means that the "soft" converter has an efficiency higher than the passive one and its advantage increases as V PO is higher. The reason is that the power consumption of the driving circuitry weights most at lower values of P P , that is at the lower values of input voltage.

Coming to a comparison between the two proposed converters, when the threshold voltages have the correct sign, the performances of the "hard" solution (ref. Figure 14b) are better with respect to both "soft" and passive converter. Efficiency (η) of an energy conversion system is defined as the ratio between its output power with respect to its input power. This is usually used as figure of merit which allows to compare different solutions which work at the same output power; this means that the system which requires the lower input power is the better one, under the hypothesis that the input source could be able to supply an infinite input power. Comparing the experimental results obtained at V PO =1.5 V (see Figure 16) for the three different AC-DC converters it is possible to see that their η can not be used as figure of merit to evaluate the performances of the energy harvesting system. In fact, the "soft" converter shows the better performance in terms of efficiency with respect any other solution, but it is equivalent at the passive one in terms of output power. Furthermore, "hard" solution outperforms any other converter in terms of output power. This is due to the fact that the input energy source, that is the piezoelectric transducer, is not an infinite energy source and its matching with the front-end circuitry is an important aspect which makes effectiveness the energy harvesting system. Furthermore, none of the systems is controlling the output voltage, hence the output power is not fixed, but it is the natural result of the behaviour of the entire system. All these considerations give strength to the choice of focusing on a different figure of merit (FoM) to compare the converters; for example this could be the ratio of the harvested power with respect to the maximum power theoretically available from the transducer. This last quantity can be defined studying the behaviour of a piezoelectric transducer, at no load condition, when exposed to a sinusoidal acceleration at frequency f which strains the transducer as shown in Figure 17. Starting from its rest condition at t 0 , that is no strain and no electrical charges on its plates, the cantilever reaches its maximum positive bending (and strain) at t 1 . At this point the collected electrical charge is Q P and the piezoelectric output voltage is equal to V PO . If an ideal front-end circuitry could recover all of this charge, completely discharging the transducer, when the cantilever reaches its maximum negative deflection at t 3 it will collect a negative charge two times higher (-2Q P ) because the deflection is doubled; in fact, at t 2 the collected charge is already equal to -Q P . As a consequence the piezoelectric peak voltage at t 3 is equal to -2V PO and the transduced energy is:

( )

2 PO P 2 PO P t t V C 2 V 2 C 2 1 E 3 1 = - = - (6)
Now imagine that at t 3 , again ideally, capacitor C P is newly, fully discharged while, at the same time, the associated energy is stored. Since the excursion in the t 3 -t 4 interval starts with no charge on the capacitor plates, it evolves as a replica of what happened in the t 1 -t 3 interval, only the sign of the voltage is inverted. This means that the available energy at t 4 is equal to:

( )

2 PO P 2 PO P t t V C 2 V 2 C 2 1 E 4 3 = = - (7)
From this moment on the phenomenon continues to repeat itself with a periodicity equal to t 4 -t 1 . Summarizing the total energy that can be harvested during one cycle becomes:

2 PO P t t t t cycle V C 4 E E E 4 3 3 1 = + = - - (8)
Finally, the maximum power theoretically available from the transducer is:

f V C 4 P 2 PO P max = (9)
The quantity expressed by (9) will be used to weight the power actually delivered to the load by the proposed rectifiers. This approach allows to compare the various circuits, but is also allows to quantify how effective a given circuit is in harvesting the power made available by the transducer. The figure of merit, which is function of R L , can be defined as: Figure 18 shows this figure of merit for the presented AC-DC converters in case of V PO equal to 1.5V. It is possible to see that "hard" topology outperforms both "soft" and passive ones but, at the same time, none of the converters is able to harvest all the power the transducer could deliver.

CONCLUSIONS

This paper presents two actives AC-DC converters which can be used into piezoelectric energy scavenging systems. The basic circuit is the voltage doubler topology, where the switches are actively driven. The two considered driving circuitries are realized with comparators and operational amplifier respectively.

It was shown that the first configuration, called "hard" is slightly more difficult to be designed than the second one, called "soft". In particular the comparators need to have an hysteretic characteristic and if the value of the thresholds is different from the ideal one the efficiency of the converter could be significantly deteriorated. Hence a lot of effort is needed to minimize the process dependence of the thresholds. On the contrary, the "soft" configuration drives the switches with a regulation loop approach, which is far less sensitive to process uncertainties.

A test chip has been diffused in STMicroelectronics 5V CMOS technology and experimental results are presented. The tests were realized using a piezoelectric transducer working in 31-mode, excited by a electro-dynamic shaker.

The performances of the proposed active solutions were evaluated at different values of a load resistance and they were compared with the ones of a passive Schottky-based voltage doubler. The average power supplied by the piezoelectric transducer and the power delivered on a load resistance were measured. The experimental results show that, under the same mechanical excitation, the "hard" solution outperforms the other two converters in terms of power delivered to the resistive load. The "soft" solution was less effective because the delivered average power by the piezoelectric transducer was lower; this was probably due to a different matching between the piezoelectric transducer and the converter itself which is better in the "hard solution". The efficiencies of the three converters were compared at different load conditions. The "soft" solution, despite its lower effectiveness, has the higher efficiency values with respect to the other two converters: this means that the converter efficiency can not be used as the only figure of merit for an energy harvesting system, it is necessary to evaluate also the effectiveness of the converter in terms of average power harvested from the transducer and delivered to the load.

To do this a dedicated figure of merit was introduced which compares the output power with the power that the transducer can theoretically deliver rather than with the power it actually delivers.

Figure 1

 1 Figure 1 Piezoelectric energy harvesting system.

Figure 2 .

 2 Figure 2. Schematics of the proposed ESS. Voltage doubler with "hard" driving circuitry (a) and with "soft" driving circuitry (b).

Figure 3 .

 3 Figure 3. Piezoelectric energy transducer working in 31-mode.

Figure 4 .Figure 5

 45 Figure 4. Picture of the measurement set-up

Figure 6

 6 Figure 6 Schematic of the proposed supply independent bias circuitry.

Figure 7

 7 Figure 7 Simulation results of the supply independent bias circuitry, bias voltages (V BiasN and V BiasP ) versus supply voltage (in the figure supply voltage has been limited to 1V for clarity. The behaviour has been verified for supply voltages up to 5V).

Figure 8 a

 8 Figure 8 a), b) Designed circuital topologies of CMP1 and CMP2 respectively; c) picture of the diffused "hard" AC-DC converter.

Figure 9

 9 Figure 9 MonteCarlo simulations of the most critical threshold voltage of the designed comparators.

Figure 10

 10 Figure 10 Regulation loop composed by the operational amplifier OP1 and MOSFET S1.

Figure 11 a

 11 Figure 11 a) Schematic of the proposed operational amplifiers; b) picture of the diffused "soft" AC-DC converter.

Figure 13

 13 Figure 13 a) Experimental results of the supply independent bias circuitry; b) circuitry used to do the characterization.

Figure 14

 14 Figure14 a, b) Experimental results about input and output powers (P P and P L ) respectively. Comparison between active "digital" converter and passive converter, this was realized with Schottky BAT86 diodes.

Figure 15

 15 Figure 15 Measured input (P P ) and output (P L ) powers at different values of V PO , comparison between passive Schottky based converter and "analog" AC-DC converter.

Figure 16

 16 Figure 16 Efficiency of the AC-DC converters at V PO =1.5V against load resistance.

Figure 17

 17 Figure 17 Mechanical strain of piezoelectric trasnducer when it is excited by a sinusoidal mechanical acceleration.

Figure 18

 18 Figure 18 Power harvested by the AC-DC converters with respect to the maximum defined in Equation 7.

TABLE 1 -

 1 EXPERIMENTAL MEASUREMENTS OF ENVIRONMENTAL VIBRATION SOURCES.

	Environmental

Vibration Source a rms [m/s 2 ] Bandwidth [Hz]

	CD reader of a desktop PC	0,30	80
	Pocket of a walking man	2,16	2
	Man walking onto stairs	3,53	2
	Into a woman bag	6,37	10
	Vibracall of a mobile phone	3,83	90
	Car dashboard [city street @ 20km/h]	0,78	30
	Car dashboard tortuous street @ 50km/h]	0,88	20
	Car front glass [primary street @ 50 km/h]	0,98	15
	Guard rail near a busy street	0,10	50
	Bridge over a railway	0,10	100
	Bus stop near a busy street	0,19	10
	Fun	1,40	100
	Web server	0,20	12

TABLE 2 -

 2 CHARACTERISTICHS OF THE DESIGNED OPERATIONAL AMPLIFIERS

	DC-GAIN	Band-Width	Vdd-min	Voffset	Current Consumption
	[dB]	[Hz]	[mV]	[V]	[nA]
	OP1 50.37	2500	730	26e-3	200
	OP2 49.78	2610	675	21e-3	200