Properties Of Piezoelectric Materials Research Articles

Effects of thickness and orientation on electromechanical properties of gallium nitride nanofilm: A multiscale insight

The coupling between size and surface effects on the mechanical and piezoelectric properties of wurtzite-type piezoelectric materials at the nanoscale is still not entirely exploited. The influence of surface orientation and thickness of wurtzite GaN nanofilms on their electromechanical properties (mechanical, piezoelectric and dielectric properties) is therefore investigated in this study by means of a multiscale analysis. The density functional theory (DFT) is utilized to study the atoms reconstruction phenomenon near surface region. Molecular dynamics (MD) simulation is employed to examine the effects of different thicknesses and surface orientations on the electromechanical properties. A continuum mechanics model incorporating the effects of both thicknesses and surface orientations is then developed and can be helpful for investigating the structure–property of GaN nanofilms. It is found through MD simulations that the elastic constant decreases in the out-of-plane direction but increases in the in-plane direction, regardless of surface orientations. This can be justified by DFT-based calculations, which show that the change of surface electron density of the nanofilm causes the reconstruction of surface atoms, leading to the extension of bond length in the out-of-plane direction and the shortening of bond length in the in-plane direction and thereby the difference between surface elasticity and bulk elasticity. The change of surface elasticity further affects the surface piezoelectric and dielectric properties. Also, the developed continuum mechanics model can reproduce the thickness- and orientation-dependent behaviors of the electromechanical parameters by fitting MD results. Finally, the developed continuum mechanics model is applied for predicting the thickness dependence of the piezopotential coefficient, showing that the piezopotential increases by 10% when the nanofilm thickness is 3 times the crystal constant.

Acoustic Biosensors and Microfluidic Devices in the Decennium: Principles and Applications.

Lab-on-a-chip (LOC) technology has gained primary attention in the past decade, where label-free biosensors and microfluidic actuation platforms are integrated to realize such LOC devices. Among the multitude of technologies that enables the successful integration of these two features, the piezoelectric acoustic wave method is best suited for handling biological samples due to biocompatibility, label-free and non-invasive properties. In this review paper, we present a study on the use of acoustic waves generated by piezoelectric materials in the area of label-free biosensors and microfluidic actuation towards the realization of LOC and POC devices. The categorization of acoustic wave technology into the bulk acoustic wave and surface acoustic wave has been considered with the inclusion of biological sample sensing and manipulation applications. This paper presents an approach with a comprehensive study on the fundamental operating principles of acoustic waves in biosensing and microfluidic actuation, acoustic wave modes suitable for sensing and actuation, piezoelectric materials used for acoustic wave generation, fabrication methods, and challenges in the use of acoustic wave modes in biosensing. Recent developments in the past decade, in various sensing potentialities of acoustic waves in a myriad of applications, including sensing of proteins, disease biomarkers, DNA, pathogenic microorganisms, acoustofluidic manipulation, and the sorting of biological samples such as cells, have been given primary focus. An insight into the future perspectives of real-time, label-free, and portable LOC devices utilizing acoustic waves is also presented. The developments in the field of thin-film piezoelectric materials, with the possibility of integrating sensing and actuation on a single platform utilizing the reversible property of smart piezoelectric materials, provide a step forward in the realization of monolithic integrated LOC and POC devices. Finally, the present paper highlights the key benefits and challenges in terms of commercialization, in the field of acoustic wave-based biosensors and actuation platforms.

Selectively doped piezoelectric ceramics with tunable piezoelectricity via suspension-enclosing projection stereolithography

The macroscopic piezoelectric properties of piezoelectric materials can be regulated via localized control of microstructures to introduce site-specific electric displacement vectors, but much of the current research is centered around design and manipulation of meso-scale architectural units that are inherently limited in achieving high functionality. In this study, we propose a stereolithography-based additive manufacturing (AM) strategy to spatially tune the properties of piezoelectric ceramics at a grain-microstructural scale through selectively incorporating dopants into the ceramic materials for tailoring the grain development. The effects of different doping parameters (including ceramic solid loading, dopant type, and dopant concentration) on the microstructures and properties of printed piezoelectric ceramics are investigated. The thermodynamics and kinetics of different doping additives in the dopant-ceramic interaction are experimentally and numerically studied to enable location-specific inhibition of microstructures. Our results indicate that a doping concentration of 2 wt% promoted the homogeneity of local grain growth, resulted in a higher compressive strength and lower porosity, and improved dielectric permittivity and piezoelectric voltage constant in printed piezoelectric ceramics. Moreover, our results suggest that thermochemically stable particles (e.g., ZrO2) with a high melting point and a low vapor pressure exhibited micro-scale diffusion behaviors, in contrast to millimeter-scale diffusion behaviors of common doping additives (e.g., ZnO), which are more suitable as a locally incorporated dopant for achieving location-specific property tuning. Test cases of selectively doped piezoelectric components in predefined patterns highlight the potential of the proposed approach in creating novel piezoelectric materials with programmable location-specific properties.

Quantitative spectral electromechanical characterization of soft piezoelectric nanocomposites

We present a modular system for the quantitative characterization of the piezoelectric coefficient of piezoelectric polymers and soft polymeric nanocomposites in the compression mode. Our approach is based on an apparatus providing spectral information on the electro-mechanical response in aselected range of frequencies of compressive loads (10–1200 Hz), with high sensitivity (down to 0.5 pC/N) and automated data acquisition modalities, enabling repeatability and reproducibility of the electro-mechanical characterization in the low-force regime (0.1 N 1.5 N). The system is modular and can be developed to cover the 2 mHz-1.2 kHz frequency range in charge mode and the 2 μHz-1200 Hz in voltage mode. We calibrated and validated the apparatus functionality using a commercial PVDF piezoelectric polymer. The suitability of the system for the quantitative measurements of the piezoelectricity of soft polymeric nanocomposites was then assessed by performing measurements of a novel piezoelectric nanocomposite material. This consisted of a polydimethylsiloxane (PDMS) matrix with embedded BaTiO3 nanoparticles, engineered with functional surface coatings to favor their homogeneous dispersion into the polymer. The proposed system demonstrated to be an effective solution for the systematic characterization of the electro-mechanical conversion properties of soft piezoelectric materials in view of soft robotics and energy harvesting applications.

Wave propagation analysis in non-local flexoelectric composite materials

The effective flexoelectric properties of heterogeneous piezoelectric materials are computed in the context of periodic homogenization, whereby a variational formulation is developed, articulated with the extended Hill macro-homogeneity condition. This framework accounts for higher gradient effects that may be induced by a strong contrast of properties of the composite constituents. The obtained homogenized properties are employed for the determination of the wave propagation attributes of piezoelectric composites. The dynamic equilibrium equations, accounting for higher gradient effects, are formulated to deal with wave propagation in flexoelectric media, considering the Classical Flexoelectric Theory (CFE) and the Non-Local Flexoelectric Theory (NLFE). The obtained dispersion relations show that flexoelectric medium are dispersive medium. Furthermore, it can be observed that the flexoelectric medium becomes more anisotropic when increasing the wavenumber unlike the piezoelectric medium. The analysis of the influence of the nonlocality reveals that the frequency of propagating waves is decreasing when increasing the non-local parameter.

Understanding the Origin of Enhanced Piezoelectric Response in PVDF Matrices with Embedded ZnO Nanoparticles, from Polarizable Molecular Dynamics Simulations.

The pervasive use of portable electronic devices, powered from rechargeable batteries, represents a significant portion of the electricity consumption in the world. A sustainable and alternative energy source for these devices would require unconventional power sources, such as harvesting kinetic/potential energy from mechanical vibrations, ultrasound waves, and biomechanical motion, to name a few. Piezoelectric materials transform mechanical deformation into electric fields or, conversely, external electric fields into mechanical motion. Therefore, accurate prediction of elastic and piezoelectric properties of materials, from the atomic structure and composition, is essential for studying and optimizing new piezogenerators. Here, we demonstrate the application of harmonic-covalent and reactive force fields (FF), Dreiding and ReaxFF, respectively, coupled to the polarizable charge equilibration (PQEq) model for predicting the elastic moduli and piezoelectric response of crystalline zinc oxide (ZnO) and polyvinylidene difluoride (PVDF). Furthermore, we parametrized the ReaxFF atomic interactions for Zn-F in order to characterize the interfacial effects in hybrid PVDF matrices with embedded ZnO nanoparticles (NPs). We capture the nonlinear piezoelectric behavior of the PVDF-ZnO system at different ZnO concentrations and the enhanced response that was recently observed experimentally, between 5 and 7 wt % ZnO concentrations. From our simulation results, we demonstrate that the origin of this enhancement is due to an increase in the total atomic stress distribution at the interface between the two materials. This result provides valuable insight into the design of new and improved piezoelectric nanogenerators and demonstrates the practical value of these first-principles based modeling methods in materials science.

Three-dimensional thermal fracture analysis of piezoelectric material by extended finite element methods

The effect of poling direction and thermal fracture analysis of penny-shaped crack (PSC) in piezoelectric material (PM) exposed to a uniform temperature and steady-state heat flow is presented using the XFEM approach. The intrinsic coupling, thermo-electro-mechanical under thermal shocks are studied and thermal stress intensity factors (TSIFs), and electrical displacement intensity factors (EDIF) are evaluated using the strain energy-based, thermal interaction integral. The discontinuous crack surfaces are treated as adiabatic and electrically impermeable. The discontinuity in both the temperature gradient and electrical field displacement over the crack surface is enriched using the Heaviside enrichment function. The fracture parameters, TSIFs, and EDIF of penny-shaped crack are a function of applied temperature fields and the thermo-electro-mechanical properties of piezoelectric material are studied. Further, the effect of poling direction, and in-plane and out-plane offset of crack position, and the inclined crack on the TSIFs and EDIF are presented. The comparison of both analytical and numerical results of the intended formulation showed excellent accuracy which has been verified on benchmark problems. The results are quite useful for the design of the sensors, transducers, and actuators in heat transfer applications.

About anomalous properties of porous piezoceramic materials with metalized or rigid surfaces of pores

The electromechanical properties of piezoelectric materials can be modified for some specific applications, e.g., hydrophone sensing applications, by incorporating a controlled porosity into them. This work investigates the effective moduli of a newly developed piezoelectric composite, fabricated using a novel approach, in which micro-and nanoparticles of specific metals or stiffer polymers were added to pore-forming agents and transported into ceramic matrices. This technique results in a porous piezocomposite with a metalized pore boundary. According to Newnham’s classification, it is a three-phase piezocomposite with connectivity 3–0–0. We considered a simple unit cell model composing of a cube of the piezoceramic material with a compound spherical pore at its center. The compound pore consists of a spherical vacuum pore and a spherical layer on its boundary. The spherical layer models the material deposited at the interface between the piezoceramic matrix and the pore. Based on the characteristics of this spherical layer, we studied porous piezocomposite with mechanically weak electrically conductive, mechanically hard dielectric, and mechanically hard electrically conductive pore surface. We assumed that this spherical layer is filled with a piezoelectric material. Very high dielectric permittivity moduli simulate the electrical conductivity, very high elastic stiffness moduli modulate the mechanical rigidity, while the piezoelectric moduli are negligible. We developed specific algorithms in ANSYS APDL to calculate the effective moduli of different composites understudy using the finite element method and the theory of effective moduli, considering the Hill–Mandel principle for energy conservation, under certain essential boundary conditions. Our simple unit cell model used for the main calculations was analogous to the model of the corresponding periodic composite. The findings of this basic model were also compared to a more complicated 3–0 random porosity composite model. We confirmed that the effective moduli versus porosity trends in both models are similar. We verified the numerical expectations by studying analytically the homogenization problem of an isotropic dielectric composite. The findings of this work confirm that the effective moduli of the developed piezocomposites significantly depend on the characteristics of material deposited between the piezoceramic and pore phases. The results of this study suggest that there may be several functional applications for these new piezocomposites.

AC Conductivity and Dielectric Properties of BiScO3–PbTiO3 Piezoelectric Ceramics

Bi-based BiMeO3 (where Me is a transition metal) has been extensively studied owing to its outstanding ferroelectric properties. The dielectric and electrical properties of piezoelectric ceramics can be enhanced by the addition of Bi-based materials such as BiAlO3, BiScO3 , and Bi(Mg, Ti)O3. Among them, BiScO3–PbTiO3 ceramics have shown excellent piezoelectric properties and temperature stability near the morphotropic phase boundary (MPB) region. Meanwhile, it is important to study the electrical properties of piezoelectric materials such as dielectric permittivity, conductivity of ferroelectric compounds, since dielectric and conductivities are related to pyroelectricity and piezoelectricity. In this study, the AC conductivity and dielectric properties of BiScO3–PbTiO3 ceramics were investigated with a wide range of frequencies and temperatures. Especially,the effect of PbTiO3 content on dielectric behavior of the BiScO3–PbTiO3 system was intensively studied by impedance spectroscopy.

Dependence of Modified Butterworth Van-Dyke Model Parameters and Magnetoimpedance on DC Magnetic Field for Magnetoelectric Composites.

This study investigates the impedance curve of magnetoelectric (ME) composites (i.e., Fe80Si9B11/Pb(Zr0.3Ti0.7)O3 laminate) and extracts the modified Butterworth–Van Dyke (MBVD) model’s parameters at various direct current (DC) bias magnetic fields Hdc. It is interesting to find that both the magnetoimpedance and MBVD model’s parameters of ME composite depend on Hdc, which is primarily attributed to the dependence of FeSiB’s and neighboring PZT’s material properties on Hdc. On one hand, the delta E effect and magnetostriction of FeSiB result in the change in PZT’s dielectric permittivity, leading to the variation in impedance with Hdc. On the other hand, the magnetostriction and mechanical energy dissipation of FeSiB as a function of Hdc result in the field dependences of the MBVD model’s parameters and mechanical quality factor. Furthermore, the influences of piezoelectric and electrode materials properties on the MBVD model’s parameters are analyzed. This study plays a guiding role for ME sensor design and its application.

Optimization of bimorph cantilever based piezoelectric energy harvester for high efficiency

Various attempts are being carried out to convert variety of ambient energies. Every conversion mechanism has its own limitations on efficiency. In this context, piezoelectric phenomenon found to be promising over electromagnetic and electrostatic considering mechanical oscillations in to useful electrical energy. In this work, we use piezoelectric effect because it has an advantage of high converting power efficiency and ease of application. Cantilever uses piezoelectric effect to harvest energy from load. Bimorph cantilever based piezoelectric energy harvester with three different materials; PZT-5A, PZT-8 and cadmium sulfide for three different proof mass patterns 3.5 µm × 2 µm, 3 µm × 2.5 µm, 2.5 µm × 3 µm in the frequency range 60 to –90 Hz and applied load of 100 N to 100 KN has been simulated using software tool COMSOL Multiphysics v 5.2. From the analyses of simulation results, PZT-5A material-based piezoelectric energy harvester with the proof mass dimension of 3.5 µm × 2 µm was found to exhibit maximum efficiency. The reasons for such high efficiency have been discussed in detail by means of physical properties of piezoelectric materials used, range of applied load and proof mass patterns.

Optimizing K0.5Na0.5NbO3 Single Crystal by Engineering Piezoelectric Anisotropy.

K0.5Na0.5NbO3 is considered as one of the most promising lead-free piezoelectric ceramics in the field of wearable electronics because of its excellent piezoelectric properties and environmental friendliness. In this work, the temperature-dependent longitudinal piezoelectric coefficient was investigated in K0.5Na0.5NbO3 single crystals via the Landau–Ginzburg–Devonshire theory. Results show that the piezoelectric anisotropy varies with the temperature and the maximum of deviates from the polar direction of the ferroelectric phase. In the tetragonal phase, parallels with cubic polarization direction near the tetragonal-cubic transition region, and then gradually switches toward the nonpolar direction with decreasing temperatures. The maximum of in the orthorhombic phase reveals a distinct varying trend in different crystal planes. As for the rhombohedral phase, slight fluctuation of the maximum of was observed and delivered a more stable temperature-dependent maximum and its corresponding angle θmax in comparison with tetragonal and orthorhombic phases. This work not only sheds some light on the temperature-dependent phase transitions, but also paves the way for the optimization of piezoelectric properties in piezoelectric materials and devices.

Ferroelectric-relaxor boundary in La-modified Pb(Mg1/3Nb2/3)O3-xPbTiO3 crossover showing enhanced dielectric and piezoelectric properties

The dielectric and piezoelectric properties of La-modified Pb(Mg1/3Nb2/3)O3-xPbTiO3 crossover ceramics were systematically studied. In this crossover region, there is a ferroelectric-relaxor boundary separating the ferroelectric and relaxor states, which is determined by the spontaneous transition from relaxor to ferroelectric state with decreasing temperature. At the ferroelectric-relaxor boundary, the maximum permittivity increases from 18,200 to 23,500, and piezoelectric coefficient (d33) increases from 300 pC/N to 450 pC/N accompanied by the electrostrain improved from 0.09% to 0.12%, as compared with adjacent ferroelectric specimen. These enhancements may originate from the low energy barrier for polarization rotation induced by the existence of spontaneous transition and the coexistence of macrodomain and polar nanodomain configuration. This work indicates that the ferroelectric-relaxor boundary in crossover region may become an effective approach to enhance the dielectric and piezoelectric properties of ferroelectric materials.

The preparation of PVDF-BTO composite film and the influence of polarization intensity on the piezoelectric properties of composite film

In this study, the PVDF-BTO composite film was prepared by the casting method. Through FTIR, SEM and other phase structure and microstructure analysis of the composite film, it was found that the introduction of BTO can promote the growth of β-PVDF. The relative content of β-PVDF in PVDF-BTO composite film reached 62.7%, indicating that BTO acts as a nucleating agent in PVDF. PVDF-BTO composite piezoelectric film is obtained after high temperature stretching and field polarization. After testing the electrical properties of the composite piezoelectric film, it is found that the piezoelectric performance of the PVDF-BTO composite film is higher than that of the pure PVDF film. It shows that the blending of BTO and PVDF to prepare the film promotes the deflection of the electrical properties of the film to the inherent electrical properties of BTO. The influence of different polarization intensities on the piezoelectric properties of composite materials was studied. The results show that the optimal polarization intensity of the PVDF-BTO composite piezoelectric film is 30 KV/mm, and the highest piezoelectric constant d33 is 13 pC/N.

Threshold voltage shift induced by intrinsic stress in gate metal of AlGaN/GaN HFET

Mechanical stress/strain is altering the charging properties of piezoelectric materials. For AlGaN and GaN heterostructures, this phenomenon has been described theoretically (Ambacher et al 2000 J. Appl. Phys. 87 334–44). Recently it was shown that a mechanically stressed SiN x passivation layer may produce local strain in the AlGaN/GaN layers underneath the gate at certain conditions. This results in a threshold voltage (V th) shift (Osipov et al 2018 IEEE Trans. Electron Devices 65 3176–84). It is therefore straightforward to also investigate the influence of an intrinsically stressed gate metal on the device characteristics. In this study, AlGaN/GaN HFETs were fabricated on nominally identical wafers with variations of intrinsic stress in the gate metallization and in the first passivation. It is verified that the built-in mechanical stress of the gate metal can shift the threshold voltage. In detail we varied the intrinsic stress of both the first passivation layer (SiN x ) and the gate metallization (Ir) by about 1 GPa. These variations result respectively in 0.65 and 0.20 V threshold voltage shift. We have additionally analyzed the thermal stability of SiN x and iridium films with respect to their mechanical properties and the resulting threshold voltage shift.

Electromechanical properties of ultra‐low porous auxetic piezocomposite: from the perspective of Poisson’s ratio

AbstractIn this study, the ultra‐low porous auxetic piezoelectric composite made of lead zirconate titanate (PZT) and hollow polyvinylidine difluoride (PVDF) is first proposed by combining “additive” and “subtractive” approaches. The electromechanical properties of the auxetic piezoelectric composite are investigated by finite element analysis. It is found that the ultra‐low porosity in the composite may lead to great extensibility along with the excellent figures of merit obtained in conventional highly porous piezoelectric ceramics. The small amount of additional PVDF can greatly tune the electromechanical properties of composite and effectively reduce the maximum stress of PZT. To elucidate the role of Poisson’s ratio on the electromechanical properties of piezoelectric materials, the relationship expressions among some electromechanical coefficients are derived. Moreover, the semi‐empirical expression of “longitudinal” compliance coefficients and a simple strategy for predicting some electromechanical coefficients are presented to instruct design and application of the ultra‐low porous auxetic piezoelectric materials.

Hybrid integral transform and p-version FEM for thermo-mechanical analysis of a functionally graded piezoelectric hollow cylinder subjected to asymmetric loads

As the first endeavor, a combination of fast Fourier transform and p-version of finite element method is proposed for electro-thermo-elastic analysis of a thick hollow cylinder under asymmetric thermal loadings. Especially in shells of revolution, the proposed FFT-pFE method is accompanied by a significant decrease in the computational costs. Due to the problem periodicity in such structures, the fast Fourier transform technique is used to discretize the governing equations into a set of harmonics in circumferential direction. Each harmonic is then partitioned using higher order finite elements. Hierarchical finite elements based on Legendre polynomial interpolation functions are utilized to discretize 2D governing equations of a functionally graded piezoelectric (FGP) cylinder. 3D governing equations of a FGP hollow cylinder are then discretized by using the higher-order Lagrangian finite elements. The effects of FFT grid-size as well as the order of the interpolation functions are investigated on convergence behavior of the proposed mixed FFT-pFE method. The piezoelectric material properties, with the exception of the Poisson’s ratio, are considered to vary along the radius of the cylinder and pursue the power function. The governing equations are derived using the principle of virtual displacements. For a 3D FGP hollow cylinder, the influence of ...

Probing the prediction of effective properties for composite materials

This article presents different micromechanical modelling techniques based on analytical and numerical approaches to determine the effective elastic and piezoelectric (piezoelastic) properties of graphene-based composite materials. Different types, orientations and shapes as well as different geometrical parameters of fiber reinforcement are considered for estimating the effective properties. The effective properties of composite are predicted with and without considering the strong covalent bond which provides interaction and in-plane stability of 2Dcrystalline graphene or strong van der Wall forces formed between graphene layers and the matrix. It is revealed that the axial, transverse and shear effective piezoelastic properties of graphene reinforced piezoelectric composite (GRPC) are significantly enriched due to the incorporation of graphene into the epoxy matrix. The importance of incorporating graphene as nanofillers/interphase into the conventional epoxy matrix to form an advanced composite and its effective properties are illustrated while these results show excellent agreement with previously reported experimental estimates. These results reveal that due to incorporation of graphene nanofillers, there is a significant enhancement in effective properties of composite. The results would also help to recognize the most important material properties with respect to different shapes and orientation of reinforcements which influences the performance of system significantly. To confirm safety, robustness and sustainability of the structure, it is the most prior requirement to determine the effective properties of composites considering different parameters for the different static and structural analyses.

Influence Function Measurement Technique Using the Direct and Indirect Piezoelectric Effect for Surface Shape Control in Adaptive Systems

Since the introduction of adaptive systems for corrective measures, static and dynamic disturbances have been reduced through the manipulation of surface shape in a well-controlled manner. One important application where adaptive systems are highly needed is in the future photo-lithography machines, particularly the wafer table where disturbances affect overlay and focus performance. To reduce overlay and focus errors, a dense array of actuators must be integrated into the wafer table to apply both in- and out-of-plane corrective deformations to the wafer surface. To realize a certain wafer shape, influence functions are linearly superimposed. Accurate models of the influence functions result in an accurate prediction of the final wafer shape. To reduce calibration errors, the influence function of every actuator needs to be determined. Here, we propose a technique to rapidly measure the influence function: the influence function measurement (IFM) technique. Using the actuate-sense property of piezoelectric materials, the influence function is determined by activating one piezo-actuator and measuring the charge induced on the neighboring piezo-actuators. The measured charges are compared to the results of finite element simulations and the absolute difference of 0.3 &#x0025; is reported for the inter-actuator charge coupling parameters. This clearly indicates the potential of the proposed technique. <i>Note to Practitioners</i>&#x2014;A critical step during the integrated-circuit lithographic fabrication process is the exposure. A particular practical challenge in this step is to correct for the mismatch between the optical image plane and the wafer surface, caused by wafer deformations. The mismatch negatively impacts the overlay and focus performance. To reduce the mismatch, actuators can be embedded into the wafer table to counteract wafer deformations, where the overall wafer surface shape is a superposition of each actuator&#x2019;s influence function. As part of the calibration for the embedded actuators, their influence functions are measured and stored. However, errors arise when influence functions are not measured for every actuator. Additionally, for different wafers, the influence functions vary hence the calibration should be done per wafer. This calibration process takes time and should not influence throughput. Our paper presents a viable approach that reduces the calibration time of active wafer tables, which is also relevant for other adaptive systems such as deformable mirrors. Since the technique requires the actuators to be mechanically coupled, it is limited to continuous surfaces. The proposed technique is numerically tested and experimentally verified to demonstrate performance.

The intrinsic piezoelectric properties of materials - a review with a focus on biological materials.

Piezoelectricity, a linear electromechanical coupling, is of great interest due to its extensive applications including energy harvesters, biomedical, sensors, and automobiles. A growing amount of research has been done to investigate the energy harvesting potential of this phenomenon. Traditional piezoelectric inorganics show high piezoelectric outputs but are often brittle, inflexible and may contain toxic compounds such as lead. On the other hand, biological piezoelectric materials are biodegradable, biocompatible, abundant, low in toxicity and are easy to fabricate. Thus, they are useful for many applications such as tissue engineering, biomedical and energy harvesting. This paper attempts to explain the basis of piezoelectricity in biological and non-biological materials and research involved in those materials as well as applications and limitations of each type of piezoelectric material.