In the present study, a hybrid triboelectric/piezoelectric generator was proposed to combine simultaneously the piezoelectric and triboelectric effects to improve the device's performances. When subjected to the shaker motion, the hybrid generator delivers an open circuit voltage of 318 V, a short-circuit current of 4.95 mu A and a maximum power of 349 mu W dissipated in a load resistance of 40 MS2 under the application of a force of 8.5 N at a frequency of 2 Hz after rectification by two diode bridges. A capacitor of 80 mu F capacitance was charged with the piezoelectric, triboelectric and hybrid systems with vibrating shaker. Thanks to the triboelectric-piezoelectric hybridization, the charging time is reduced by 74 % compared to the piezoelectric system alone and 39 % compared to the triboelectric system alone. Finally, a temperature sensor was powered by a 1 mF capacitor charged to 4.5 V by the hybrid tribo/piezoelectric generator.

Faced with the growing global energy demand, the search for alternative and sustainable solutions is increasing. This quest for new technologies requires an in-depth investigation of material properties, particularly the study of multiphysics couplings that are still under intense investigation. Flexoelectricity, defined as the coupling between a mechanical strain gradient and electrical polarization in dielectrics and semiconductors, is of particular interest due to its potential for mechanical-to-electrical energy conversion. To date, few studies have investigated the flexoelectric response of polymers. This article aims to address this gap by examining the influence of the PSS to PEDOT ratio in the semiconducting PEDOT:PSS blend on its dielectric and flexoelectric properties. To this end, we fabricated devices with a trilayer cantilever structure (top electrode/polymer/bottom electrode) and analyzed the impact of various PSS to PEDOT mass ratios (ranging from 2.5, 6 and 20) on the thermal, morphological, mechanical and dielectric properties of the material. Additionally, we studied the effect of incorporating a small fraction of xylitol as a secondary dopant into the PEDOT:PSS blend. This addition significantly enhanced the flexoelectric coefficient of PEDOT:PSS (1:2.5) from 1.3 to 11 mu C/m. Regarding flexoelectric energy conversion efficiency, which depends on the dielectric, mechanical and flexoelectric properties, the PEDOT:PSS (1:6) composition offered the best compromise. Finally, we examined the influence of postrinsing treatment of the polymer film with ethanol and methanol on the flexoelectric coefficient. This treatment, combined with the addition of xylitol, led to a large improvement in the flexoelectric coefficient of PEDOT:PSS (1:6) from 6.21 to 11.41 mu C/m.

Nowadays, the increasing demand for sustainable energy has brought piezoelectric materials to the forefront due to their capability to convert mechanical energy into electrical energy. In response to increasing environmental concerns, cellulose has emerged as a promising piezoelectric material, owing to its availability, biocompatibility, sustainability, biodegradability and cost-effectiveness. Despite significant research on the use of various forms of cellulose for piezoelectric energy harvesting, a systematic review focusing on the factors that can affect the piezoelectric property in cellulose remains notably absent. The main goal of this review is to fill this gap by understanding the piezoelectric behaviour of cellulose at different hierarchical levels, from macro-scale natural materials to nano-scale structures. This review presents an overview of the general aspects of the piezoelectric effect, followed by a detailed examination of the piezoelectric properties of cellulose. It further explores the piezoelectric behaviour of cellulose-based natural materials. The review then addresses the piezoelectric characteristics of nanocellulose and regenerated cellulose in turn. Furthermore, the review examines cellulose-based hybrid materials and their piezoelectric properties. In conclusion, the review highlights the current challenges and outlines promising directions for future research in this emerging area.

This paper presents a flexible piezoelectric device that has been realized by depositing lead zirconate titanate (PZT) thin films by chemical solution deposition (CSD) on a commercial aluminum foil as a substrate. The thermal treatment required for the crystallization of the PZT thin films leads to the oxidation of the substrate and a parasitic intermediate layer of alumina (Al2O3) is formed between the substrate and the first PZT layer. The comparison with and without the use of a conductive ruthenium dioxide (RuO2) interlayer, which can shunt the insulating alumina layer, showed the influence of the latter on the different characteristics of the material. The thickness of the alumina layer on the surface of the aluminum substrate after deposition of the PZT film (approximate to 39 nm) was determined by calculation and confirmed by transmission electron microscopy (TEM). Dielectric characterization of the sample without considering this layer gives the permittivity of the Al2O3/PZT bilayer and not the active material alone (PZT). A relative permittivity value of 313 is measured against 558 for the single PZT layer if the alumina layer is taken into account, which means a decrease of 44%. The piezoelectric characterization is also influenced by the alumina layer, the piezoelectric coefficient is 14 pC/N while it is 26 pC/N when this layer is taken into account. This study evidences and quantitatively evaluates the influence of the oxidation layer (Al2O3) on the dielectric and piezoelectric characteristics and mechanical energy harvesting performances.

In this work, we evaluated the flexoelectric and piezoelectric contributions to the overall macroscopic polarization in cellulose films. To this end, the flexoelectric μ31 and transverse effective piezoelectric e31,f coefficients of cellulose films were determined using cantilever beam bending. The experiments were based on theoretical developments allowing to separate the flexoelectric from the piezoelectric contribution, represented by an effective flexoelectric coefficient, μeff, depending on both e31,f and μ31. Five free-standing and stainless steel/cellulose bilayer films were prepared from cellulose showing different morphologies and surface charge degrees: two almost neutral cellulose microfibers (CMF) and three (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO)-oxidized cellulose micro- (TCMF) and nanofibers (TCNF) bearing negative charged groups on the surface. The dielectric properties of the films indicated a low dielectric constant for unmodified CMF, and a huge increase for TEMPO-oxidized samples, which were up to 9 times higher than poly(vinylidene fluoride)-based polymers. TEMPO-oxidized cellulose films exhibited the largest flexoelectric coefficients (almost 7 times higher than those of synthetic polymer dielectrics), which evidenced that the presence of polar groups and surface charge boosted both flexoelectricity and piezoelectricity in unpoled cellulose films. These findings pave the way towards sustainable cellulose-based curvature sensors with large effective flexoelectric coefficients, without the need of preliminary energy consuming poling step.

This paper presents the flexoelectric effect in semiconducting polymeric blend (poly(3,4-ethylene dioxythiophene): polystyrene sulfonate (PEDOT:PSS)) films. Flexoelectricity can be considered as an alternative transduction mechanism to the piezoelectricity to directly detect curvature. It is simply defined as the coupling between the strain gradient and polarization in solid dielectrics and semiconductors. In this study, flexoelectricity in PEDOT:PSS films works on the basis of electrical energy generation induced by dynamic bending. Of particular interest is the phenomenon of polarity change during bending, i.e., the reversal of the polarization direction. In this paper, the procedure to obtain free-standing PEDOT:PSS polymer films for mechanical/electrical bending conversion based on the flexoelectric effect is presented. Here, we report the flexoelectric characterization of 30-mu m-thick flexible films of PEDOT:PSS encapsulated between two polyethylene terephthalate (PET) sheets. This characterization reveals a much higher transverse flexoelectric coefficient than those recently reported in the literature for free-standing PEDOT:PSS films with a coefficient that reaches 76 mu C/m at 0.5 Hz. It was also demonstrated that it was possible to determine the curvature of the sample up to 62 m(-1) through signal acquisition of the current and thus the possibility of using the encapsulated PEDOT:PSS films as a large curvature sensor. Their efficiency in converting a strain gradient into electrical energy, combined with their robustness and flexibility, may open a promising route toward organic semiconductors-based curvature sensors and ambient mechanical energy harvesting devices with large effective flexoelectric coefficients.

This paper presents an ultra-flexible piezoelectric air flow energy harvester capable of powering a wireless sensor. The method to easily adapt the aero-electric generator to the wind is presented. In the wind tunnel, different configurations have been tested to determine the best one for energy harvesting at low wind speed. In particular, the galloping configuration, with the addition of a bluff body at the free end of the cantilever which allows to improve the performance of the micro-generator by coupling the vibrations induced by the vortices and the galloping phenomena. In this study, we also present a method to optimize the energy harvesting without increasing the volume of the device. The effects of mechanical and electrical coupling of several generators on the performance of energy harvesting are presented. Thus, with the electrical parallel coupling of four generators, we obtained a maximum power of 60 mu W instead of 30 mu W with two generators for a wind speed of about 6 m/s. The mechanical coupling of the micro-generators allowed the device to keep the same volume (asymptotic to 540 cm(3)), however the threshold wind speed to increase (> 6 m/s). The harvested energy was then used to operate a wireless sensor.& nbsp;(c) 2021 Elsevier Ltd. All rights reserved.

We report the use of poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) as a transducing material in the fabrication of mechanical-to-electrical conversion devices based on the flexoelectric-like response of this polymer. Devices are made in a cantilever-based three-layer stainless-steel/PEDOT:PSS/top metal electrode configuration to assess the effective transverse flexoelectric coefficient μ12′. We investigated the influence of the nature of the top electrode in the flexoelectric response comparing samples with gold and aluminum top electrodes and demonstrated the huge impact of adding a small fraction of a second dopant such as xylitol to the PEDOT:PSS polymer blend and the benefits of a post-treatment of the polymer film with ethanol and methanol on the flexoelectric coefficient. The combination of xylitol addition and the rinsing of the polymer films with ethanol and methanol, along with the use of gold as a top electrode, led to a significant improvement of μ12′ to ca. 24 μC m−1, which is in the range of those reported for high permittivity oxide materials. These findings support the use of conjugated polymers as an alternative to inorganic materials in flexoelectric-based applications, where large flexibility is required.

In the last decade, the polymeric poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) semiconductor has been widely studied for their electrical and electrochemical properties and used in various applications such as flexible and transparent electrodes, optoelectronics and thermoelectric devices. Here, we report the intrinsic electromechanical coupling in trilayered stainless steel/PEDOT:PSS/Aluminum composites. The PEDOT:PSS thin film integrated in the multi‐layer serves as the transduction material itself and yields a remarkable flexoelectric‐like response when the cantilever shaped‐ device assembly is subjected to beam bending. Two orders of magnitude larger flexoelectric coefficients (up to μ′12 = 6 μC/m) were obtained for semiconducting PEDOT:PSS thin films, in comparison with those measured for insulating polymers. Besides, it is observed that flexoelectric effect may be enhanced when the conductivity of the trilayer device increases to a certain extent, especially after a simple dilution treatment that induces partial removal of excess hydrophilic PSS. These first results may open a new avenue for simply preparing flexible and highly sensitive curvature sensors with single electroactive semiconducting polymer layer between metal electrodes.

The conversion of vibrations into electrical energy for powering low-power small electronic components has been investigated by researchers from different disciplines in the last decade. Among the possible mechanisms, piezoelectricity has received particular attention. In the field of low frequency cantilever-based vibration energy harvesters, the proof mass is essential in order to reduce the resonance frequency and increase the stress along the beam to increase the output power. In this work, a manufacturing process of a micro generator is proposed to easily modify and increase the dimensions of the cantilever, and thus tune its resonance frequency. The effect of the position of the mass on the performances of this flexible piezoelectric energy harvester is also studied. For a proof mass at 8 cm from clamping, we obtain a resonance frequency of 9.9 Hz, a maximum power of 127 mu W against a resonance frequency of 16 Hz and a maximum power of 72 mu W with a mass at 4 cm. This shows that the maximum power extracted varies in congruent to 1/f(R) for a constant acceleration of 1 g (9.81 m/s(2)), as expected theoretically. These promising results show that the prototype can be considered for a low power application as an energy harvesting-based micro-generator. (C) 2020 Elsevier B.V. All rights reserved.

Recent evolution in wireless communication and flexible electronics [1], where planar antennas are subject to external mechanical constraints such as bending requires to customize the main components such as the dielectric to make it more suitable for the upcoming trends. Developing soft dielectric brings many advantages as it significantly reduces the weight and permits to design engineered alternatives to the existing rigid antennas. For instance, it is of a great importance to develop soft dielectric substrate with low dielectric loss in order not to hinder the radiation of antenna. In this work, we present a novel soft dielectric thermoplastic elastomer based on standard polyolefins like polypropylene and polyethylene and to our knowledge, no characterization method was reported to similar blends in microwave frequencies. We propose an established methodology of dielectric characterization up to 40 GHz based on the ring resonator with grounded coplanar waveguide [2] by the GSG (Ground Signal Ground) probe that was tailored for a 200-µm thick soft dielectric thermoplastic elastomer. The rings were prepared via photolithography of the copper layer deposited by sputtering over a thermo-molded thermoplastic dielectric film. The proposed methodology first consists in extracting the dielectric permittivity and dielectric loss up to 10 kHz based on the metal insulator metal model, where measurements were carried out using impedance meter Agilent 4294A. Then the ring geometric dimensions were optimized by High frequency electromagnetic simulations. Different ring radiuses were tested to minimize the error in calculation of the dielectric properties and the results were obtained by using an Agilent E8364B Vector Network Analyzer (VNA) (bandwidth from 10 MHz to 50 GHz) and Cascade ACP40-AW-GSG probes (40 GHz bandwidth, 500 µm pitch). The whole test system was controlled using Wincal Cascade software. The measured dielectric constant and loss tangent up to 40 GHz were extracted from the resonant peaks of the S12 and were found to be r ~ 2.42 and tan ~ 0.008 at ~15 GHz respectively for a polyethylene octene copolymer (OBC) and styrene-ethylene-butadiene-styrene (SEBS) based blend (Young’s Modulus : ~5 MPa). The low dielectric loss in the X-band makes the soft dielectric blend promising for microwave devices such as antenna applications.

This paper presents a soft low dielectric loss thermoplastic blend based on polyolefins as a dielectric material for microwave applications. To determine the dielectric properties, more precisely the relative permittivity εr and tan δ, characterization techniques and the elaboration of samples were customized to the 200-μm thick dielectric film. Dielectric properties were extracted from the peaks of the transmission coefficient S 12 measured from 10 MHz to 40 GHz with probe station and coplanar waveguide ring resonator. The measured dielectric constant and loss tangent of the investigated blends were found to be around ε r ≈ 2.45 and tan δ ≈ 0.01 in X-Band. A proof of concept of a patch antenna based on the developed soft dielectric film of polypropylene (PP)-based polymer blend was also made. The measured return loss of the antenna showed great agreement with simulation results with HFSS® software and reached -30 dB at an operating frequency of 9.7 GHz. An investigation of the radiation characteristics in the far field in anechoic room was made. The gain and the efficiency of the patch microstrip antenna, which were extracted and calculated from the radiation pattern attained 4.56 dB and 47% respectively. These here reported results are promising for the development of blend compositions for high frequency applications.

All organic soft dielectrics are growing more and more interest in the electronic industry owing to their light weight, low cost and the flexibility they yield compared to the rigid devices. In the specific field of microwave communicating devices planar printed (patch) antennas on a soft dielectric substrate are sought for their conformability and advantageous compactness. In this article, two soft thermoplastic elastomer blends based on polypropylene (PP) or low-density polyethylene (LDPE) were tested. The fabrication process and the established characterization steps have been fully presented. More specifically, in order to characterize the dielectric film up to 40 GHz, the microstrip ring resonator with coplanar waveguide access has been adapted to a new configuration specimen sample. The results of the characterizations obtained showed very encouraging performances for microwave applications. Indeed, the measured dielectric constant and loss tangent up to 40 GHz were found to be and for both blends. The fabrication and the radiation characteristics of a patch antenna on a new performing PP or LDPE-based elastomer blends as the soft dielectric substrate was demonstrated and analysed. The proof of the concept of the investigated device consists of a microstrip patch antenna with an operation frequency of about 10 GHz. These dielectric features render the polyolefin based blends very promising as a soft material for microwave engineering, which is confirmed by the measured antenna properties: the gain, the directivity as well as the efficiency have been calculated from the measured radiation pattern and were recorded as 4.6 dB, 7.7 dB and 46% respectively for the r-PP based blend and 4.8 dB, 8.1 dB and 51% for the LDPE based blend.

Dans le cadre des projets N-air-J, MIGAC et Airbivore, finances respectivement par la region Pays de la Loire, le RFI WISE et le CNRS, des films piezoelectriques flexibles de zircono-titanate de plomb (PZT) ont ete developpes sur substrat flexibles au sein de l’Institut d’Electronique et de Telecommunications de Rennes (IETR). L’objectif principal de ces projets est d’etudier la possibilite de recuperer l’energie mecanique de courants d’air grâce a l’utilisation de micro-generateurs piezoelectriques flexibles. Les couches minces de PZT, lorsque elles sont electriquement polarisees, possedent en effet des proprietes piezoelectriques macroscopiques leur permettant de convertir l’energie mecanique en energie electrique, et inversement. De par le budget thermique eleve necessaire a la cristallisation du PZT (autour de 650 °C), ces couches minces sont generalement deposees sur des substrats rigides de silicium, de saphir ou encore de MgO. Dans cette presentation est decrit le procede de fabrication par Chemical Solution Deposition (CSD) de films de PZT flexibles deposes sur feuille d’aluminium en structure Metal-Isolant-Metal (MIM)1, ainsi que les caracterisations ferroelectriques et piezoelectriques des condensateurs obtenus. De par leur faible epaisseur (20 µm) et la conformabilite de l’aluminium, les films realises sont facilement decoupables et permettent d’obtenir des geometries originales. Ces films, etant realises pour des applications de recuperation d’energie, ont ete caracterises sur un banc mecanique a des frequences d’excitations forcees tres basses (dans la gamme de l’Hertz). Du fait de la forte permittivite du PZT et de sa faible epaisseur, le generateur piezoelectrique presente une forte capacite (autour de 200 nF), ce qui limite la tension de sortie du generateur a quelques centaines de millivolts. Afin d’augmenter cette tension de sortie, et par consequent la puissance du generateur, le film de PZT est transfere par voie chimique sur un film polymere de polyterephtalate d’ethylene (PET). La suppression du plan de masse, allie a une structure d’electrodes interdigitees (IDE) permet d’obtenir des tensions de sortie superieures a 30V.

Electroactive polymers (EAPs) are promising materials for actuation and energy harvesting applications. Among the EAPs, polyurethane (PU) material is of considerable interest given its high values of deformation under an electric field. The electromechanical properties were found to be dependent on the processing technique and the thickness of the film. To understand this relationship, a comprehensive study was carried out on polyether-based thermoplastic PU elastomer films elaborated by solution casting with thicknesses between 12 and 220 mu m. Microstructural, dielectric, mechanical, and electrostriction studies were conducted. Thin films present a lower strain for a given electric field compared to thick films. The films exhibit a structural gradient along the thickness direction: a fast evaporation in the upper part of the film close to the interface with air inhibits the phase separation but a more favored one in the lower part. This is consistent with the modeling based on the gradient of dielectric constant and the experimental, mechanical, and dielectric characterizations. (c) 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 46981.

Among the transduction mechanisms of interest for sensing and/or actuation applications at nano/micro scale, the piezoelectric effect has been widely exploited owing to the solid state nature of piezoelectrics, the large ability of specific classes of materials for the mechanical-to-electrical energy conversion and easy integration. However, every piezoelectric (also generally ferroelectric) presents well-known intrinsic drawbacks such as required poling step and related aging. In contrast, uniquely flexoelectric materials do not suffer from these disadvantages because flexoelectricity, a universal effect in all dielectric solids defined as the electrical polarization induced by a strain gradient, does not imply preliminary electric field-induced macroscopic polarization. Besides, strain gradient may be easily obtained by bending plate or cantilever-shaped structure and in this case it is nothing but the local curvature of the flexible system. Thus, as strain gradient (curvature) inversely scales with both elastic stiffness and thickness, this study will focus on the evaluation of the potentialities of flexoelectric effect in soft polymer films for electromechanical applications, with an emphasis on the thickness influence. In this way, analytical results combined to experimentally obtained effective flexoelectric coefficients for some typical polymer classes may provide guidelines for the development of soft and low frequency flexoelectric mechanical transducers.

In this paper, we present the fabrication of piezoelectric thin film based-vibration energy harvesters with interdigitated electrodes (IDE) on a polymer substrate. The deposition of the lead zirconate titanate thin layers onto aluminium foil and the transfer onto a polymer substrate are realized using sol-gel process and a chemical method, respectively. The characteristics were studied using a bending cantilever structure under controlled oscillations. We show that harvested energy with constant acceleration is inversely proportional to the resonant frequency tuned by adding proof mass to the cantilever. For a proof mass located at 8 cm from the clamped end, a maximum power output of 127 μW was obtained at 9.9 Hz against a resonance frequency of 16 Hz and a maximum power of 72 μW with a mass at 4 cm. These results demonstrate the high flexibility and the potentialities of the so-called hybrid polymer/oxide micro-generator for mechanical energy harvesting from wind flow or body motion.