Electrostrictive polymers for mechanical energy harvesting

Abstract

This article reviews the developments in electrostrictive polymers for energy harvesting. Electrostrictive polymers are a variety of electroactive polymers that deform due to the electrostatic and polarization interaction between two electrodes with opposite electric charge. Electrostrictive polymers have been the subject of much interest and research over the past decade. In earlier years, much of the focus was placed on actuator configurations, and in more recent years, the focus has turned to investigating material properties that may enhance electromechanical activities. Since the last 5 years and with the development of low-power electronics, the possibility of using these materials for energy harvesting has been investigated. This review outlines the operating principle in energy scavenging mode and conversion mechanisms behind this generator technology, highlights some of its advantages over existing actuator technologies, identifies some of the challenges associated with its development, and examines the main focus of research within this field, including some of the potential applications. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012

INTRODUCTION

The performance of energy harvesters is directly linked to the efficiency of the mechanical–electrical conversion within the active materials. For piezoelectric materials, the efficiency of the conversion can be estimated with the help of the coupling coefficient. For a given vibration mode, this coefficient expresses the ratio of the converted energy to the input one. Another key point for electroactive materials concerns the easiness of their integration within the whole structure.1, 2

For energy harvesters, bulk materials are widely used in the form of ceramics or single crystals. Beyond various types of materials, lead zirconate titanate ceramics (PZT) and lead-based relaxor single crystals are of significant interest. PZT ceramics are cost effective and available in various yet limited shapes and with a wide range of properties depending on their composition. They exhibit medium coupling factors of 70% at least for the longitudinal 33 mode of vibration.3, 4

Single crystals of lead magnesium niobate-lead titanate or lead zinc niobate-lead titanate have focused a lot of attention as they exhibit coupling coefficients as high as 90%, close to the theoretical values of 100%.5, 6 Because of their high coupling coefficients, these two types of materials seem to be promising for the energy conversion; however, drawbacks such as brittleness and high density may prevent their use in some applications.

An alternative solution to the use of these bulk materials is the use of electroactive polymers (EAPs). They present the advantages of being easily processed in various and complex shapes, easily deposited on large surfaces while being cost effective and very light.7

EAPs are divided into two main groups:7

• Electronic EAPs: Dielectric EAP, electrostrictive graft elastomers, electrostrictive papers, electroviscoelastic elastomers, ferroelectric polymers, liquid crystal elastomers, and so forth.

• Ionic EAPs: Carbon nanotubes, conductive polymers, electrorheological fluids, ionic polymer gels, ionic polymer metallic composites, and so forth.

Electrostriction is generally defined as a quadratic coupling between strain (S_ij) and polarization (P_m):8, 9

• (1)

where is the elastic compliance, Q_ijkl is the polarization-related electrostriction coefficient, is the inverse of the linear dielectric permittivity, T_kl is the stress and E_m the electric field. Assuming a linear relationship between the polarization and the electric field, the strain S_ij and electric flux density D_i are expressed as independent variables of the electric field intensity E_k, E_l, and stress T_kl by the constitutive relations according to the equation set:8, 9

• (2)

where is the elastic compliance under constant electric field, M_ijkl is the electric field-related electrostriction coefficient, and is the linear dielectric permittivity.

Because of their high deformation abilities and elasticity, EAPs cover a wide range of application possibilities, as shown in Figure 1, which depicts the typical strain–stress abilities of conversion materials when compared with typical application cases. In the same manner, the operating frequency of such materials suits in a much better way with the mechanical frequency contents of typical systems (Fig. 2).

Figure 1. Comparison of stress–strain abilities of conversion materials and typical applications.

Figure 2. Comparison of frequency contents of conversion materials and typical applications.

Because of their low losses that make them a premium choice for energy-harvesting purposes, this research will be focused on electronic EAPs and more specifically on electrostrictive elastomers. The “Energy-Harvesting Techniques” section provides an overview of the different methods for harvesting energy using such materials. The “Increase of the Dielectric Constant and of the Electrostrictive Coefficient with the Help of Fillers” section lies in presenting methods for enhancing the electromechanical responses of electrostrictive polymers and thus their energy-harvesting abilities. Then, the “Practical Consideration and Figure of Merit of the Conversion” section discusses practical considerations such as materials properties, circuit topologies, and so forth. Finally, the “Application of Electrostrictive Polymer Generators” section concerns with the description of potential application.

ENERGY-HARVESTING TECHNIQUES

The aim of this section is to propose a review of the possible techniques for harvesting the energy converted by the materials. Basically, three approaches can be considered for energy scavenging from vibrations using electrostrictive polymers:

• Electrostatic cycles, inspired from purely capacitive techniques.10–14

• Electrostrictive cycles, using charge and discharge operations.9, 15–17

• Pseudo-piezoelectric cycles, consisting in applying a bias voltage on the material and working around this static regime.18–20

Electrostatic-Derived Cycles

As electrostrictive polymers feature dielectric behaviors, it is possible to consider harvesting schemes usually used in purely capacitive approaches.10–14 Typically, there are two cycles that can be envisaged for such techniques:

• Ericsson (voltage constrained) cycle, which consists in:

  • 1
    Stretching the polymer.
  • 2
    Applying the electric field.
  • 3
    Releasing the applied mechanical stress while maintaining the electric field, leading to a decrease of the electric flux density.
  • 4
    Removing the electric field.

• Stirling (charge constrained) cycle, whose principles rely on:

  • 1
    Stretching the polymer.
  • 2
    Applying the electric field.
  • 3
    Releasing the applied mechanical stress under constant electric flux density (open-circuit conditions), resulting in an increase of the electric field.
  • 4
    Removing the electric field.

The associated strain (S)–stress (T) and electric displacement (D)–electric field (E) cycles are shown in Figure 3. From this curves, it can be shown that the Stirling cycle permits converting more energy than the Ericsson approach. However, the latter allows a better control of the electric field, ensuring that the maximal admissible value is never reached. The energy balance for the considered techniques is given in Table 1, where ε refers to the permittivity, M to the electrostrictive coefficient, and T₀ and E₀ to the maximal stress and applied electric field, respectively.

Figure 3. Electrostatic energy-harvesting cycles considering Ericsson and Stirling cycles.

Table 1. Energy Balance Considering Electrostatic-Based Harvesting Techniques

Electrostrictive Cycles

However, other cycles than those already used in other energy conversion systems may be considered, taking advantage of the electrostrictive nature of the materials. Many cycles have been described in ref.16, and particularly:

• Constant electric field stretching and open-circuit release:

  • 1
    Stretching under a given electric field E₀.
  • 2
    Releasing in open circuit (constant charge).
  • 3
    Decreasing the electric flux density to the original position.

• Constant electric field stretching and release:

  • 1
    Stretching under constant electric field E₀.
  • 2
    Increasing electric field to E₁.
  • 3
    Releasing the applied stress.
  • 4
    Decreasing electric field to E₀.

• Open-circuit stretching and release:

  • 1
    Stretching in open circuit (constant electric flux density) with an initial electric field E₀.
  • 2
    Increasing electric field to E₁.
  • 3
    Releasing in open circuit (constant electric flux density).
  • 4
    Decreasing electric field to E₀.

The associated energy cycles and energy balances are given in Figure 4 and Table 2, respectively. In contrast to the previously discussed cycles (electrostatic based), the pure electrostrictive cycles require nonzero electrical initial conditions (leading to nonzero initial strain as well), therefore possibly wasting energy due to the losses in the material. It can also be noted that the constant field during stretching and releasing phases and constant electric flux during stretching and releasing phases use the same principles than the Ericsson and Stirling cycles of electrostatic devices, respectively (see previous section), except that initial electrical conditions are zeros in the latter cases.

Figure 4. Energy cycles for the electrostrictive energy-harvesting techniques (adapted from ref.16).

Table 2. Energy Balance Considering Electrostrictive Harvesting Techniques

In addition, these cycles require driving the electrical conditions of the materials for a significant time period, hence making them quite complex to implement in an autonomous, self-powered fashion. A simpler way for harvesting energy from electrostrictive polymers using diodes is proposed in refs.16 and21. This system therefore permits harvesting energy in a purely passive fashion, hence making its implementation quite easy. The principles of this device, depicted in Figure 5, consist of providing energy to the polymer when its voltage reaches V_L (it is considered that the diode threshold voltages are negligible) and harvesting when it attains V_H.

Figure 5. Passive energy-harvesting circuit.

At the beginning of a new cycle, the material voltage is V_H, and the stress is increasing, resulting in a decreasing electric field. Therefore, the two diodes are blocked, and the system is in open-circuit condition. After a critical value of the stress, the voltage V_L is reached and the left diode conducts so that the electric displacement increases with the stress, yielding a provided energy density:

• (3)

where E_H and E_L are the electric field values associated with the voltages V_H and V_L. As the stress is released, the material voltage increases and the left diode is blocked. When the voltage reaches V_H, the right diode conducts and energy is extracted, until the stress is minimum. The harvested energy density is given by:

• (4)

leading to the energy density balance:16

• (5)

which is maximal when

• (6)

yielding:

• (7)

The associated energy cycles are given in Figure 6. Despite its simplicity, such an approach requires that the voltage V_H is reached by the electrostrictive material, hence necessitating a minimal stress value to operate, whose value is given as follows:

Figure 6. Energy cycles for the passive electrostrictive energy-harvesting device (adapted from ref.16).

• (8)

If the strain is small, the value of T_min can thus be approximated by

• (9)

Pseudo-Piezoelectric Cycles

The final family for harvesting energy from electrostrictive materials consists of applying a bias electric field to the sample, as shown in Figure 7, allowing simpler operations than charge and discharge cycles (with possibly reduced losses). In this device, the constant electric field, supposed to be much larger than the electric field generated by the vibration, allows the device to operate dynamically in a similar fashion than piezoelectric materials. Starting from the linearized electrostrictive equations:

• (10)

with E_DC and E_AC the bias and generated electric fields and s the elastic compliance of the material, the dynamic behavior may be expressed as follows:

• (11)

Figure 7. Pseudo-piezoelectric energy-harvesting device.

Considering that the electric field E_AC can be neglected facing the bias electric field E_DC and as long as the stress magnitude remains small enough so that , the expressions turn to:

• (12)

which are similar to those obtained when using piezoelectric element, with an equivalent piezoelectric coefficient , which depends on the bias electric field.

The energy cycles (obtained without the previous assumptions) are depicted in the top of Figure 8 when considering that energy is harvested on a purely resistive load (R in Fig. 7), yielding a harvested energy density (considering and ):20

• (13)

where ρ denotes the load resistivity. The maximum energy density is therefore given by:20

• (14)

Figure 8. Energy cycles for the pseudo-piezoelectric energy-harvesting device (adapted from ref.22).

However, to increase the conversion efficiency, it is possible to use a nonlinear approach similar to the “synchronized switch harvesting on inductor” for piezoelectric elements,23–27 which consists of reversing the dynamic voltage each time the displacement reaches a maximum or a minimum value,22 leading to the cycles depicted in the bottom of Figure 8, and allowing a harvested energy density given by:

• (15)

with γ given as the voltage inversion factor.23

Although the losses of pseudo-piezoelectric working mode may be smaller than electrostatic-based and electrostrictive cycles as the system is working around a bias point (hence no charge losses appear), the dynamic voltage across the load remains AC, preventing the use of such a system to power up electronic components that usually require DC voltage. In ref.28, an architecture was proposed to allow a DC voltage output of electrostrictive materials used as energy harvesters in pseudo-piezoelectric mode. This technique consists of filtering the bias component using a capacitor C_d and connecting a diode rectifier associated with smoothing capacitors C_s, as depicted in Figure 9. It has to be noted that in this case, the resistance R_S is no longer used for harvesting energy, but consists of preventing a dynamic short circuit of the material. Assuming and , the harvested energy density and maximum energy density using this approach are given by:28

• (16)

• (17)

Figure 9. Pseudo-piezoelectric energy-harvesting device featuring DC output (adapted from ref.28).

As previously noted, it is also possible to use the nonlinear approach to increase the performance of the microgenerator,29 leading to harvested and maximal harvested energy densities (Fig. 10):

Figure 10. Energy cycles for the pseudo-piezoelectric DC energy-harvesting device (adapted from ref.28).

• (18)

• (19)

Discussion

The comparison of the maximal harvested energy densities for each of the exposed technique is depicted in Figure 11, using parameters of Table 3, which corresponds to typical parameter values for a poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) [P(VDF-TrFE-CFE)] terpolymer. This figure shows that the electrostatic-based approaches permit the highest harvested energies. However, as stated above, losses during charge and discharge may significantly reduce the performance of these techniques. The pseudo-piezoelectric methods, and especially those using the nonlinear switching approaches, allow an harvested energy density about 5–10 times less than the electrostatic-based techniques (Fig. 12), but permit reduced losses as the system is operating around a bias value, hence preventing losses during charge and discharge from zero initial conditions. In addition, working around a bias point permits operating at much higher frequencies than charge/discharge-based systems, as the application of high electric fields in a low-cost fashion may take time.

Figure 11. Comparison of the maximum harvested energy density for each technique (electrostrictive cycles based on constant electric field or constant electric displacement during stretching/release are not depicted as they are similar to Ericsson and Stirling cycles).

Figure 12. Comparison of the normalized harvested energy densities.

Table 3. Simulation parameters

INCREASE OF THE DIELECTRIC CONSTANT AND OF THE ELECTROSTRICTIVE COEFFICIENT WITH THE HELP OF FILLERS

The previous analyses show that, whatever the technique use for EAP-based energy-harvesting purposes, the performance of the microgenerators are obviously dependent on the material properties themselves (e.g., permittivity, electrostrictive coefficient, and elasticity).

In particular, it can be shown that better performance in energy harvesting can be obtained by increasing the dielectric constant of the electrostrictive material.18–20 To do so, one solution consists of processing polymer-based composites by filling the polymer with high K fillers or conductive fillers. Currently, a variety of methods are available to increase the dielectric permittivity of polymer materials. These may be classified into two main groups: those involving composites and those based on new synthetic polymers. The first approach concerns the dispersion of a filler into the polymer matrix. The second strategy, on the other hand, deals with the synthesis of new materials with tailored characteristics.

In the first case, the content of fillers must be high (tenth of percents) to obtain a significant increase of the composite dielectric constant. The main drawback is the large increase of the Young's modulus and consequently the loose of flexibility.

On the contrary, the use of conductive fillers leads to an increase of the dielectric constant at very low contents (some percents) especially if the size of the fillers is very small (some nm), as the required electric field is decreased to obtain the same polarization than unfilled samples. As an additional consequence, the variation of the Young's modulus is kept low. This filling must be done without reaching the percolation threshold for with the composite becomes conductive and without decreasing too much the breakdown voltage. These two parameters not only depend on the fillers morphology and size and on the polymer matrix but also on the dispersion and the self-organization of the fillers within the matrix.

Table 4 summarizes some results obtained by filling polyurethane (PU) and P(VDF-TrFE-CFE) with conductive nanofillers. In the same manner, the filling can be achieved using conductive polymers dispersed within the dielectric matrix leading to the development of all-polymer percolative systems. As an example, coated polyanilines have been dispersed in a terpolymer matrix in refs.35 and36.

Table 4. Effect of Nanofillers on Material Properties

Finally, to overcome the problem of agglomeration that can exist when fillers are dispersed within the matrix and to better control their spatial distribution, Huang and Zhang37 developed chemical bonding of the filler to the backbone of the polymer matrix.

The different methods available for enhancing the dielectric permittivity of polymers are listed in Table 5, which also gives advantages and drawbacks of each technique. Random composites represent readily applicable approaches suitable for increasing the dielectric permittivity of elastomers. In the long run, the challenge consists in synthesizing a new highly polarizable polymer. All this research is necessary to achieve new generations of electrostrictive polymers, operating at lower electric fields.

Table 5. Comparison Between the Different Methods for Enhancing the Dielectric Permittivity

PRACTICAL CONSIDERATION AND FIGURE OF MERIT OF THE CONVERSION

Many of the specific material properties affect all the bulk energy-harvester properties. In this section, the material properties are enumerated and the mechanisms through which they influence the microgenerator performance are described to summarize the previous two sections. The relationships between all introduced system parameters are charted in Figure 13.

Figure 13. Relation between electrostrictive microgenerators and properties of materials.

Maximum Electric Field

In the different configurations, the harvested energy is proportional to the square of the applied electric field. Theoretically, it is appealing to work with high electric fields to convert more energy. However, there exist maximum electric fields (E_max), which can be defined as the maximum electric field strength that the sample can withstand intrinsically without breaking down, that is, without experiencing failure of its insulating properties. The electric field at which breakdown occurs depends on the respective geometries of the polymers and the electrodes on which the electric field is applied, as well as the rate of increase of the electric field. Because materials usually contain minute defects, the practical dielectric strength will be a fraction of the intrinsic dielectric strength of an ideal, defect-free, material.

In real cases, the electric field breakdown of EAP varies from 70 to 200 MV/m. It originates from various types of phenomenon such as thermal effect, effect of internal and surface discharges, and effect of path. Moreover, in the case of real microgenerators, it is important to work under moderate electric fields to avoid problems inherent with high-voltage insulation and to limit the electric loss.

Maximum Stress and Strain

The strain and stress capacities also come into account in the development of a vibration-based microgenerator. These parameters not only determine the maximum displacements but also the maximum forces necessary to produce such elongations. For example, applications that involve human movement harvesting (Fig. 14) features low stress but high deformations. Therefore, the material must be flexible (low Young's modulus) to avoid interference with the user [thus minimizing the magnitude of forces and being transparent with a low cost of harvesting (COH)]. Moreover, it must be able to feature deformation of more than 50% while minimizing mechanical and dielectric losses to ensure high conversion efficiency. However, for applications where only low strain is available (few percents) but with high stress, it is interesting to have materials with high Young's modulus to convert more energy, because the latter is proportional to the squared stress (assuming a linear strain–stress relationship), as depicted in Figure 14.

Figure 14. Illustration of the properties of young modulus for different applications.

Frequency Bandwidth

Electrical and mechanical losses are varying with the frequency. These characteristics must be considered during the development of microgenerators to ensure an optimal extraction of the energy over a wide frequency bandwidth. Figure 15 shows the Young's modulus and mechanical losses as a function of the frequency considering a constant strain in the case of pure PU material. For frequencies below 100 Hz, the losses in the material are limited; however, the losses become higher for frequencies around 1 kHz, limiting the operation of the system for frequencies below this threshold, which correspond to the typical vibration frequency contents (Fig. 2).

Figure 15. Mechanical properties of pure PU versus frequency.

Concerning the electrical losses, it is well known that the mechanisms of polarization strongly depend on the frequency and tend to disappear when the latter is increased, as shown in Figure 16, which depicts the variation of the dielectric permittivity and losses versus frequency in the case of P(VDF-TrFE-CFE) sample. For example, Maxwell–Wagner type polarization is known to be active at the lowest frequencies, which explains why a decrease in the dielectric constant was observed when the measurement frequency was increased. The effective loss tangent shows the highest value for low frequencies due to the electric conduction.38, 39 Losses then decrease with the frequency except for the frequencies where polarization mechanisms disappear.33

Figure 16. Dielectric properties of pure P(VDF-TrFE-CFE) versus frequency.

Maximum Energy Harvesting

For every energy-harvesting technique presented in the “Energy-Harvesting Techniques” section, it can be seen that the electrostrictive coefficient M appears to be an important parameter to increase the scavenging abilities of the system. Although the “Increase of the Dielectric Constant and of the Electrostrictive Coefficient with the Help of Fillers” section provides a description of the various methods available to increase this coefficient, the goal of this part is to present a figure of merits able to realize a comparison of the different technique available for harvesting energy.

Ren et al.9 demonstrated that it is possible to harvest 22.4 mJ/cm³ using the so-called constant electric field stretching and open-circuit release methods; however, in case of pseudo-piezoelectric mode, the harvested energy is equal to 34 nJ/cm³.28 Hence, the energy-harvesting abilities using the pseudo-piezoelectric behavior seems to be lower than the electrostrictive cycle-based energy-harvesting approaches. Although this could be considered a disappointing result, one should keep in mind that these values were not obtained for the same excitation and polarization field. For a fair comparison between each technique, Lallart et al.20 proposed a figure of merit of the scavenging abilities that is able to compare the different methods used for energy harvesting. This figure of merit consists of dividing the harvested energy density by the squared mechanical and squared electrical stimuli, therefore allowing a normalization of the energy with respect to the external condition. The results obtained in ref.20 demonstrate the validity of this new figure of merit and the potential as tools in helping the development of efficient microgenerators.

Passive Material

Portable applications are powered with lower voltages compatible with battery output. Hence, to generate the high electric field (typically 5 V/μm) required for working in the pseudo-piezoelectric behavior or to realize energy cycles, a step-up voltage converter has to be a part of the generator circuit as shown in Figure 17. Current challenges in the field of energy harvesting using electrostrictive polymers concern the development of systems able to ensure the generation of high electric fields at a small energy cost. This can be realized by the hybridization of electrostrictive polymer with other electroactive materials such as piezoelectric generators able to deliver high voltage.

Figure 17. Schematic representation of autonomous electrostrictive μ-generator.

In summary, this section highlighted important material properties and their relationships to microgenerators performance. The presentation of a figure of merit able to assess the performance of electrostrictive polymers in terms of energy scavenging has also been introduced. This criterion is related to the energy density per cycle per squared strain magnitude and per squared bias or applied electric field, allowing to evaluate the energy-harvesting abilities independently from extrinsic parameters such as dimensions, excitation, or bias electric field.

APPLICATION OF ELECTROSTRICTIVE POLYMER GENERATORS

Virtually, any application where there is a need of electrical energy is a potential application for electrostrictive polymer generators. However, electrostrictive polymer power generation is much more competitive for some applications when compared with others. For example, electrostrictive polymers are well suitable for harvesting energy for human motion. Natural muscle, the driving force for human motion, is typically of low frequencies and intrinsically linear, both characteristics where electrostrictive polymers offer advantages. Many other interesting generator applications exist for electrostrictive polymers. Remote and/or wireless devices are growing in use, and these devices can ideally harvest their own energy to eliminate the need of battery replacement. Electrostrictive polymers are well suited for these applications if mechanical energy is available from oscillatory or vibratory motions such as that might occur in portable devices carried by people, animals, plane, and so forth.

CONCLUSIONS

The further development of electrostrictive polymers as a viable micro-generators technology requires much work, and to this end, numerous exciting challenges lie ahead. First, the development of improved electrostrictive polymer is essential. Continued research into the effect of the incorporation of dielectric and dielectric fillers could lead to the simultaneous enhancement of electromechanical activities and the reduction of operating voltage. Such improvements would serve to broaden application spectrum of these types of microgenerators. For example, significant reduction of operating voltage could enable applications of realistic autonomous system.

EAPs and in particular electrostrictive polymers were reviewed in this article as exciting candidate materials for the development of a new age of microgenerator material. The different principles of operation of these materials were presented. The advantages of electrostrictive polymers over conventional microgenerator technologies in a number of metrics, in addition to some of the unique characteristics, which they can offer, were discussed. Electrostrictive polymers were examined at both the material and the microgenerators configuration level. Important material parameters, both mechanical and electrical, are highlighted and various approaches to optimize these properties for the development of superior energy harvester devices were addressed. Such approaches included the incorporation of dielectric fillers and conductive fillers. In conclusion, electrostrictive polymer generators have been studied extensively under laboratory conditions where they have shown promising performance. However, in practical applications, they have not yet achieved their full potential.

Biographical Information

Dr. Mickaël Lallart graduated from the Institut National des Sciences Appliquées de Lyon (INSA Lyon), Lyon, France, in electrical engineering in 2006 and received his PhD in electronics, electrotechnics, and automatics from the same university in 2008, where he worked for the Laboratoire de Génie Électrique et Ferroélectricité (LGEF). After working as a post-doctoral fellow in the Center for Intelligent Material Systems and Structures (CIMSS) in Virginia Tech, Blacksburg, VA, USA, in 2009, Dr. Lallart has been hired as an associate professor in the LGEF. His current field of interest focuses on vibration damping, energy harvesting, and structural health monitoring using piezoelectric, pyroelectric, or electrostrictive devices, as well as autonomous, self-powered wireless systems.

Biographical Information

Pierre-Jean Cottinet graduated from the Institut National des Sciences Appliquées de Lyon (INSA Lyon), Lyon, France, in 2008. He received a PhD degree in Acoustics in 2008 from the Institut National des Sciences Appliquées de Lyon (INSA), France, for his thesis on electostrictive polymer for energy harvesting and actuation. During 2011, he was at the Florida State University as a post-doctoral and working on buckypaper in High-Performance Materials Institute (HPMI). Currently, he is an associate professor at INSA de Lyon, with research interests concerning electroactive materials (polymers, CNT, etc.) and smart structures.

Biographical Information

Daniel Guyomar received a degree in physics from the Amiens University, Amiens, France, an engineering and a doctor-engineer degree in acoustics from the Compiègne University, France, as well as a PhD degree in physics from the Paris VII University, Paris, France. In 1982–1983, he worked as a research associate in fluid dynamics at the University of Southern California, Los Angeles, CA. He was a National Research Council Awardee (1983–1984) detached at the Monterey Naval Postgraduate School, California, to develop transient wave propagation modeling. He was hired by Schlumberger in 1984 to lead several projects dealing with borehole imaging, and then moved to Thomson Submarine activities in the field of underwater acoustics. In 1992, Dr. Guyomar co-created the Techsonic Company, which is involved in research, development, and production of piezoelectric and ultrasonic devices. He is presently a full-time university professor at the Institut National des Sciences Appliquées de Lyon (INSA), Lyon, France, where he manages the Laboratoire de Génie Electrique et Ferroélectricité (LGEF). He also works as a consultant for several companies. His present research interests include the field of piezo-material characterization, piezoactuators, acoustics, power ultrasonics, vibration control, and energy harvesting.

Biographical Information

Laurent Lebrun graduated from the Ecole Nationale Supérieure d'Ingénieurs de Caen, France, in 1991. He received a PhD degree in acoustics in 1995 from the Institut National des Sciences Appliquées (INSA), de Lyon, France, for his thesis on piezoelectric motors. During 2001, he was a visiting scientist at the Materials Research Institute of the Pennsylvania State University, State College, PA, in the group of Prof. Tom Shrout. Currently, he is a professor at INSA de Lyon, with research interests concerning electroactive materials (ceramics, single crystals, and polymers) and smart structures.