Direct Piezoelectric Effect Research Articles

On the measurement of piezoelectric d33 coefficient of soft thin films under weak mechanical loads: A rapid and affordable method

Thanks to their intrinsic flexibility, energy efficiency and high portability, soft piezoelectric thin films represent the most effective technological approach for wearable devices to monitor health conditions. In order to improve effectiveness and applicability, more and more innovative and high-performing soft piezoelectric materials are being developed and benchmarked through their piezoelectric d33 coefficient. However, most existing methods to measure the d33 were developed for ceramic or bulk materials and cannot be applied to soft materials because high force/pressure can deform and damage the material structure. This work introduces a simple, effective, and fast method to accurately measure the d33 of soft and thin piezoelectric films by applying weak sinusoidal forces to avoid any damage to the sample, and simultaneously measuring the charges produced by the direct piezoelectric effect. The approach is versatile as it can be used for different types of materials and sizes of the active area. This method represents an effective solution to speed up the process of material optimization, paving the way for the rapid development of novel wearable piezoelectric devices.

Porous Structure Enhances the Longitudinal Piezoelectric Coefficient and Electromechanical Coupling Coefficient of Lead-Free (Ba0.85Ca0.15)(Zr0.1Ti0.9)O3.

The introduction of porosity into ferroelectric ceramics can decrease the effective permittivity, thereby enhancing the open circuit voltage and electrical energy generated by the direct piezoelectric effect. However, the decrease in the longitudinal piezoelectric coefficient (d33) with increasing porosity levels currently limiting the range of pore fractions that can be employed. By introducing aligned lamellar pores into (Ba0.85Ca0.15)(Zr0.1Ti0.9)O3, this paper demonstrates an unusual 22-41% enhancement in the d33 compared to its dense counterpart. This unique combination of high d33 and a low permittivity leads to a significantly improved voltage coefficient (g33), energy harvesting figure of merit (FoM33) and electromechanical coupling coefficient ( ). The underlying mechanism for the improved properties is demonstrated to be a synergy between the low defect concentration and high internal polarizing field within the porous lamellar structure. This work provides insights into the design of porous ferroelectrics for applications related to sensors, energy harvesters, and actuators.

Comparison between acoustic emission sensors and piezoelectric patches for damage detection in concrete beams

Acoustic emission (AE) sensing is an established technique to monitor crack nucleation and propagation in different types of structural elements and for different damage scenarios. Although effective for crack monitoring in civil infrastructure, off-the-shelf AE sensors can be expensive, discouraging their installation in large numbers for assessing the global structural performance or monitoring multiple assets in the infrastructure network. For this reason, this paper explores the use of piezoelectric patches as an alternative low-cost solution to AE sensors. These patches are considerably cheaper, do not require external power supply and can be easily attached to existing structural elements or embedded into new structures. Moreover, thanks to the direct and inverse piezoelectric effect, the same set of patches can act both as sensors and actuators, meaning that they can be used to “passively” monitor crack propagation over time, as well as to locate and characterize damage in ageing structures at a certain time by using the patches as emitters and receivers of waves. In this framework, this paper proposes a comparison between traditional AE sensors and piezoelectric patches. The comparison is performed on a set of three concrete beams subjected to four-point bending loading, each equipped with two grids of sensors, i.e. 8 AE sensors and 8 patches. The beams are tested under increasing monotonic loading, from zero-load uncracked condition up to collapse.

Challenges and opportunities in piezoelectric polymers: Effect of oriented amorphous fraction in ferroelectric semicrystalline polymers

AbstractDespite extensive research on piezoelectric polymers since the discovery of piezoelectric poly(vinylidene fluoride) (PVDF) in 1969, the fundamental physics of polymer piezoelectricity has remained elusive. Based on the classic principle of piezoelectricity, polymer piezoelectricity should originate from the polar crystalline phase. Surprisingly, the crystal contribution to the piezoelectric strain coefficient d31 is determined to be less than 10%, primarily owing to the difficulty in changing the molecular bond lengths and bond angles. Instead, >85% contribution is from Poisson's ratio, which is closely related to the oriented amorphous fraction (OAF) in uniaxially stretched films of semicrystalline ferroelectric (FE) polymers. In this perspective, the semicrystalline structure–piezoelectric property relationship is revealed using PVDF‐based FE polymers as a model system. In melt‐processed FE polymers, the OAF is often present and links the crystalline lamellae to the isotropic amorphous fraction. Molecular dynamics simulations demonstrate that the electrostrictive conformation transformation of the OAF chains induces a polarization change upon the application of either a stress (the direct piezoelectric effect) or an electric field (the converse piezoelectric effect). Meanwhile, relaxor‐like secondary crystals in OAF (SCOAF), which are favored to grow in the extended‐chain crystal (ECC) structure, can further enhance the piezoelectricity. However, the ECC structure is difficult to achieve in PVDF homopolymers without high‐pressure crystallization. We have discovered that high‐power ultrasonication can effectively induce SCOAF in PVDF homopolymers to improve its piezoelectric performance. Finally, we envision that the electrostrictive OAF mechanism should also be applicable for other FE polymers such as odd‐numbered nylons and piezoelectric biopolymers.

Composite material based on piezoelectric core-shell nanofibers for tactile recognition

In recent years, self-sensing composite materials based on the direct piezoelectric effect have attracted widespread interest as they combine the composite material's mechanical performances with the piezoelectric phase's sensing capability. In this context, piezoelectric nanofibers exhibit minimal impact on the mechanical structure of the composite – differently from bulky films or ceramic disks - and represent a promising strategy for robotic applications or wearable devices. This work aims to develop a self-sensing laminate based on piezoelectric core-shell nanofibers (PEDOT:PSS-based core and P(VDF-TrFE)-based shell). Each layer of the laminate is made of a flexible epoxy material and embeds aligned nanofibers. By orthogonally overlapping two layers, the intersection points of the matrix-like arrangement of the nanofibers generate a network of piezoelectric pixels, which are responsible for sensing. Such a self-sensing composite material exhibited a noticeable capability to recognize the exact position of a mechanical stimulus on its surface.

Dynamics of a piezoelectric vibration energy harvester with a pseudoelastic SMA spring

The development of small-scale and low power consumption devices has been motivating the design of intelligent mechanisms, exhibiting a wide power density spectrum across various external sources. Smart materials come up as an attractive alternative due to their intrinsic multi-coupling between different physical domains. In this context, piezoelectric materials allow conversion of mechanical energy of movement into electrical power through the direct piezoelectric effect. This work investigates a piezoelectric energy harvester combined with a shape memory alloy (SMA) spring to explore the combination of both the smart materials for energy harvesting. The pseudoelastic hysteretic effect of SMA is explored in order to passively change the internal system properties such as stiffness and damping during the harvesting process. Numerical analyses are performed considering the normalized power converted by the harvester, focusing on the influence of the SMA martensite phase transformation under different scenarios. The results exhibit an increment in the harvester bandwidth when compared with a traditional linear piezoelectric energy harvester.

Structure-Dependence and Mechanistic Insights into the Piezoelectric Effect in Ionic Liquids.

We reported recently that two imidazolium room-temperature ionic liquids (RTILs) exhibit the direct piezoelectric effect (J. Phys. Chem. Lett., 2023, 14, 2731-2735). We have subsequently investigated several other RTILs with pyrrolidinium and imidazolium cations and tetrafluoroborate and bis(trifluoromethylsulfonyl)imide anions in an effort to gain insight into the generality and mechanism of the effect. All the RTILs studied exhibit the direct piezoelectric effect, with a magnitude (d33) and threshold force that depend on the structures of both the cation and anion. The structure-dependence and existence of a threshold force for the piezoelectric effect are consistent with a pressure-induced liquid-to-crystalline solid phase transition in the RTILs, and this is consistent with experimental X-ray diffraction data.

Biodegradable, Bifunctional Electro-acoustic Transducers Based on Cellular Polylactic Acid Ferroelectrets for Sustainable Flexible Electronics.

Nowadays, humans rely increasingly on smart electronics to address grand challenges and to improve life conditions in the era of digitalization and big data. However, electronics often have a limited lifespan, and they may bring electronic waste problems after their service. To mitigate this problem, environmentally sustainable methods of electronic device production and disposal are highly recommended, where advanced functional materials should be redesigned with improved sensing performance over the entire operational life while also being naturally degradable at the end. Herein, a biodegradable and flexible bifunctional electroacoustic transducer was fabricated with the utilization of cellular polylactic acid (PLA) ferroelectret films, possessing a small acoustic impedance of ∼0.02 MRayl which is quite close to that of air and a high figure of merit (FOM: d33·g33) of ∼11 GPa-1. Such devices have a prominent signal-to-noise ratio (SNR) of ∼23.5 dB @1 kHz and can work either as a microphone by direct piezoelectric effect or a loudspeaker by reverse piezoelectric effect in air medium. When used as a microphone, the flexible device exhibits a prominent receiving sensitivity up to 4.2 mV/Pa (∼-47.5 dB/ref. 1 V/Pa) at 1 kHz. When served as a loudspeaker, it is capable of yielding high sound pressure levels (SPLs) ranging from 60 to 103 dB (ref. 20 μPa) in a broad frequency range of 1-80 kHz with an active area of 3.14 cm2. Additionally, the electrical response curve of the device is very flat in a wide frequency range from 300 to 3000 Hz. With the high-performance acoustic-electric conversion capacity, the PLA ferroelectret-based flexible and filmlike electroacoustic transducer was used to realize accurate speech recognition and control, providing a strong impetus for its advanced and eco-friendly applications in the era of the internet of things (IoT) and artificial intelligence.

From stress to charge: investigating the piezoelectric response of solvate ionic liquid in structural energy storage composites.

Solvate ionic liquids (SILs) are a class of ionic liquids where the liquid-state salt is chelated by a coordinating solvent, and of interest due to their advantageous properties such as low vapour pressure and superb thermal and chemical stability for energy storage applications. The electromechanical and piezoelectric effect were studied in lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) solvated by triethylene glycol dimethyl ether (triglyme, G3), forming [Li-G3]TFSI. These effects were also investigated in full solid polymer electrolyte (SPE) used in energy storage devices, consisting of [Li-G3]TFSI paired with an epoxy-based resin system. The SIL's electromechanical response was first established in isolation, as well as within the SPE. Experimental data demonstrates the effect of a major part of the SPE contributing to the electrical potential generation during application of force and subsequent pressurisation as well as depressurisation, underlined by a direct piezoelectric effect. SPE response to applied load is explored after the recent discovery of liquid-to-crystalline phase transition following pressurisation in pure ionic liquids. This finding has the potential to ameliorate the performance of energy storage composites via additional effects of charging such a device by subjecting it to stress, leading to increased efficiency. Results to date show a bulk potential difference across the SIL of up to 150 mV, while the SPE potential response is scaled down due to a significantly lower volume of SIL at the interface (∼30 mV). Nevertheless, such findings can still significantly affect the performance of carbon fibre (CF)-based structural supercapacitors and batteries that are able to store and release electrical energy whilst simultaneously contributing to load-bearing performance.

DEVELOPMENT OF AN INFORMATION-MEASURING SYSTEM FOR DIAGNOSING INSULATORS ON OVERHEAD POWER LINES

The largest percentage of emergency shutdowns falls on overhead lines (overhead lines), which are the most vulnerable objects of the electric power complex. Frequent disconnections of overhead power transmission lines (VLEP) are caused by the overlap of insulators (due to complete destruction or the presence of defects). To change the current situation, it is urgent to develop an information system for determining the location of the damaged insulator and notifying about the (possible upcoming) disconnection of the section of the overhead line. It is proposed to install a piezoelectric contact sensor based on a direct piezoelectric effect on a garland of insulators. The changing acoustic pressure of the ultrasonic wave (formed by a change in the electric field strength caused by the deterioration of the insulating properties of the insulator) will generate an alternating voltage of the same frequency on the piezoelectric element. This indicator is supposed to be used as an indicator of the condition of the predamage of the insulator and transmit information to the operational control point.

Compositional Modification of Epitaxial Pb(Zr,Ti)O3 Thin Films for High‐Performance Piezoelectric Energy Harvesters

AbstractIn this study, Piezoelectric energy harvesters (PEHs) are fabricated based on epitaxial Pb(Zr,Ti)O3 (PZT) thin films deposited by an RF magnetron sputtering with varied Zr/[Zr+Ti] ratio. For a compatibility with micro‐electromechanical systems, the epitaxial PZT thin films are deposited on Si substrates (PZT/Si). The morphotropic phase boundary (MPB) are formed in the compositional range of 0.44 ≤ Zr/[Zr+Ti] ≤ 0.51 of the epitaxial PZT/Si, which is far broader than that of the bulk PZT. Meanwhile, effective transverse piezoelectric coefficient (|e31,f|) values are evaluated by the direct and converse piezoelectric effects using the unimorph cantilever method. Among the compositions, the rhombohedral‐dominant MPB (MPB‐R) of Zr/[Zr+Ti] = 0.51 exhibits a direct |e31,f| of 10.1 C m−2 and a relative permittivity (εr) of 285, leading to the maximum figure of merit of 40 GPa in this study. On the other hand, the maximum converse |e31,f| of 14.0 C m−2 is measured from the tetragonal‐dominant MPB (MPB‐T) of Zr/[Zr+Ti] = 0.44. At a resonance frequency, the MPB‐T presents a high output power density of 301.5 µW−1/(cm2 g2) under an acceleration of 3 m−1 s−2, which is very promising for the high‐performance PEH applications.

Synergy of morphotropic phase boundary and internal bias fields to achieve high d33 and d33* simultaneously in lead-free BNT-based ceramics

It is difficult to obtain high d33 and d33* simultaneously in one piezoelectric ceramic system via a conventional method due to the conflicting structure–properties responding mechanism between the direct piezoelectric and converse piezoelectric effects. In this work, a synergistic approach of constructing morphotropic phase boundary and introducing the internal bias fields in (Bi0.5Na0.5)TiO3 ceramics is proposed through Sr2+ and Li+ doping for mitigating the conflict between d33 and d33*. By this strategy, both high d33 (197 pC/N) and d33* (1500 p.m./V) are realized in Srx(Bi1-xNa0.97-xLi0.03)0.5TiO3 when x = 0.24. The large d33 stems from rhombohedral and tetragonal (R3c and P4bm) phase coexistence. The internal bias field introduced by defect dipoles tends to counteract the effects of depolarization field, thus greatly aiding the external fields with higher actual excitation fields. The superposition of internal bias field, depolarization field and external fields yields strong asymmetry bipolar strain curves, thereby contributing to the large d33*. Thus, this work opens a new door for developing lead-free ceramics with excellent piezoelectric performance.

(Keynote) The Piezoelectric Effect and Ionic Liquids

We have studied the response of room temperature ionic liquids to surface charge and had found the establishment of a free charge density gradient, ρf , in these materials that persists for ca. 50 μm (e-1 depth). We have also applied mechanical force to room temperature ionic liquids with the resulting development of a potential across the ionic liquid when contained in a vessel. These two effects are manifestations the converse and direct piezoelectric effects, respectively. For the converse piezoelectric effect, the induced gradient is seen to be ca. 100 μC/cm3/μm and for the direct piezoelectric effect, the relationship between force applied and potential developed is ca. 16 mV/N. We will discuss the observation of the direct piezoelectric effect in the liquid phase and its possible utility.

Sensitivity analysis of electro-mechanical properties of soft and hard piezoelectrics using the complex finite element method

The sensitivity analysis of the anisotropic properties for PZT-4 and PZT-5 have been performed using the complex variable finite element method (ZFEM) on a two-dimensional geometry. A thin film model is subjected to a uniform boundary load to induce mechanical strain yielding variations in the electric potential field. The numerical results from mechanical displacements and electric potential fields are verified against the solution from a commercial software. The first order derivatives obtained from ZFEM illustrate the sensitivity of material properties as design parameters for real time tunability of additive manufacturing processes. Results show that the largest sensitivities for the direct piezoelectric effect emerge from and the elastic anisotropic coupling of normal and shear stresses through coefficient followed by the dielectric and piezoelectric constants in the poling direction.

Reconfigurable localized effects in non-Hermitian phononic plate

Skin effect is one of the intriguing phenomena exhibited by non-Hermitian wave systems. It reflects the localization of the modes at the boundaries of the structure. We demonstrated the skin effect for elastic waves propagating in a non-Hermitian phononic plate containing piezoelectric components in their unit cells. The latter behave as sensors and actuators by using the direct and inverse piezoelectric effects. The demonstration is based on the calculation of the complex non-reciprocal dispersion curves and their analysis for any direction of the wavevector in the two-dimensional space. Therefore, localization phenomena at different boundaries and corners of a finite square structure are presented. Furthermore, by applying different levels of non-Hermiticity in different parts of a square structure, it is shown that the localized features can appear at different positions and with various shapes. These localized phenomena can be reconfigured by acting on the non-Hermiticity parameters. Our results provided a feedback control strategy to introduce the non-Hermitian skin effect in two-dimensional elastic systems for potential applications, such as vibration control, energy harvesting, and sensing.

Investigation of the electric response of the piezoelectric curved beam considering the direct piezoelectric and flexoelectric effects

The performance of piezoceramic devices can be significantly affected by the size and shape of the component structures, owing to the coexistence of piezoelectricity and flexoelectricity. Here, we establish a theoretical model employing the energy variation approach and static equilibrium analysis to characterize the electrical generation mechanism of the transverse isotropic Euler curved beams by considering both piezoelectricity and flexoelectricity. Based on the energy variational approach (model I), the numerical calculation is used to estimate the impact of the shape and loading mode of the piezoelectric curved beam on the electric response. Furthermore, a comparative study using the static equilibrium analysis (model II) and numerical simulations is also conducted. The results show that when the circumferential loading is applied to the free end of the beam, the generated electric voltage of the nanobeam reaches the maximum value when the radian of nanobeam around 133.57°, and for a radial loading, the optimal radian is 0° Moreover, it is demonstrated that flexoelectricity plays a dominated role on the electricity generation as the size of the curved beam shrinks to a nanometer scale. The finding here provides alternative strategies for designing and fabricating a new generation of highly efficient piezoelectric energy harvesters.

Reprogrammable acoustic metamaterials for multiband energy harvesting

Acoustic metamaterials are artificial materials that possess the remarkable ability to control and manipulate acoustic waves, which makes them ideal for acoustic energy harvesting. However, the current limitation is that these metamaterials can only effectively harvest energy within a narrow band defined by a single defect mode. To overcome this challenge, a new type of reprogrammable acoustic metamaterial has been developed. This metamaterial incorporates local resonance and magnetic modulation of the structure to enable multiband piezoelectric energy harvesting. The design of triple-band energy localization and regulation involves the utilization of the Bloch theorem and magnetic dipole model. The Bloch theorem is utilized to investigate the propagation of waves within acoustic metamaterials. Electromechanical conversion is achieved through the direct piezoelectric effect of piezoelectric ceramic. Pressure acoustics, solid mechanics, electrostatics and electrical circuit modules are employed to simulate the coupling effects among sound, mechanical and electrostatic fields for acoustic energy harvesting. The magnetic dipole model is employed to determine the magnetic force between the carbon steel cylinders of reprogrammable acoustic metamaterials and the permanent magnet used for magnetic modulation. The structural resonance of the acoustic metamaterials is in charge of band I from 35 Hz to 60 Hz. The local resonance is in charge of band II from 1650 Hz to 2050 Hz. The synergy between the structural resonance and local resonance contributes to band III from 4800 Hz to 5700 Hz with dominance of the structural resonance. The harvested powers of the acoustic metamaterials are 0.10 mW, 0.23 mW and 0.13 mW for different bands. By utilizing reprogrammable magnetic modulation on the structural resonances, the harvested powers for band I and band III experience remarkable enhancements of 655% and 214%, respectively. This breakthrough has the potential to revolutionize the field of acoustic energy harvesting, enabling the harvesting of energy across a wider range of frequencies. We anticipate that the implementation of the multiband acoustic metamaterial energy harvesting wall will expedite the growth of advanced technologies pertaining to acoustic energy localization and self-powered sensing.

Scanning Tunneling Microscopy as a Method for Analyzing the Correlation of Local Resistive and Ferroelectric Properties in Memristive Compositions

The creation of multilayer resistive memory devices based on nanolayer memristive compositions with thin ferroelectric (FE) films, in which resistance switching is caused by a combination of effects related to the influence of interface regions, polarization states, charge transport mechanisms, and microscopic features of nanostructures, requires the development of new experimental approaches to the study of local electrophysical properties. One of the most common ways to investigate local electrophysical properties is the use of various atomic force microscopy (AFM) techniques, including the Kelvin probe microscopy, tunneling AFM, and piezoresponse AFM. The main reason for switching from AFM to scanning tunneling microscopy techniques when studying the local resistive properties of memristive compositions with FE films is the need to stabilize the probe-sample contact. The main obstacle to the effective use of AFM techniques to study the local ferroelectric properties in nanolayer memristive compositions with thin FE films is the occurrence of a strain gradient during scanning, which leads to the contribution of the flexoelectric effect and direct piezoelectric effect in the measurement results. In this work, we have developed a method of investigating the local FEproperties using scanning tunneling microscopy (STM) and spectroscopy (STS) techniques under ultra-high vacuum conditions. The essence of the proposed approach is to identify the contribution of polarization charges, as well as the features of their screening on the free surface of the FE film, to the results of STS measurements at different polarization orientations in the FE film. In combination with STM measurements of local morphological features, the analysis of experimental results makes it possible to identify the state of FE polarization, determine the contribution of the surface screening of polarization charges to the manifestation of memristive effects, and investigate the correlation between the local resistive and FE properties in nanolayer memristive compositions with thin FE films.

A robust-based configuration design method of piezoelectric materials for mechanical load identification considering structural vibration suppression

Piezoelectric materials have received considerable attention to structural vibration suppression and health monitoring by virtue of their transform ability between electric energy and mechanical energy. This study investigates a novel robust-based configuration design method for piezoelectric materials under the assumption of identical configurations for actuator and sensor layers. Firstly, underlying the inverse piezoelectric effects, a load-independent layout design framework of piezoelectric actuators is developed in the context of topology optimization, in which the desired structural vibration suppression can be achieved and the robustness of system performance index representing actuating energies may be guaranteed once uncertainties are involved. Then, based on the direct piezoelectric effects, some piezoelectric sensors are effectively selected from the optimized distributed piezoelectric elements for mechanical load identification considering inevitable signal noises and material dispersion To improve the accuracy of identified results, an adaptive load identification method and an independence-driven sensor selection strategy are conducted. To strengthen the robustness of identified results, an uncertain-oriented load identification method and variance-driven sensor selection strategy are completed. Moreover, interval quantification and propagation methods are adopted to deal with multi-source uncertainties. Eventually, two numerical examples are discussed to demonstrate the validity and feasibility of the developed approach.

Whirl-flutter control through direct piezoelectric effect

The aeroelastic instability known as whirl-flutter must be considered during the design of a propeller-driven aircraft. Usually, aircraft with single or multiple rotors may suffer with such phenomenon, especially when large rotor diameter is applied, such as vertical take-off and landing aircrafts (VTOL) with or without tilt rotors. Depending on the cruise speed, the whirl-flutter influences the project of rotors, wings and pylons. With the advent of modern air mobility, a better understanding of such phenomenon, as well as the development of vibrational control techniques to increase the stability margins becomes important. Although smart materials, such as piezoceramics, are commonly applied to control aeroelastic phenomena, the application to whirl-flutter control remains uninvestigated. Thus, the present research proposes passive control technique based on the direct piezoelectric effect, in a unimorph and bimorph harvester configurations, observing its effect on the aeroelastic system’s behavior. As main result of the piezoelectric material presence, an increased the flutter speed is observed, improving the system’s stability. Additionally, the bimorph configuration is more efficient to postpone the critical speed.