Piezoelectric Composite Structures Research Articles

Quasi-closed diaphragm based piezoelectric micromachined ultrasonic transducer with reduced Q and stress sensitivity for in-air rangefinding

To improve the performance of the Piezoelectric Micromachined Ultrasonic Transducer (PMUT) based rangefinder and decrease its stress sensitivity, a novel design with quasi-closed structure is proposed. It adopts a circular piezoelectric composite diaphragm structure with clamped boundary, in which all the deposited stack layers in its central region are intentionally removed and additional cross-slits are created into the remaining silicon device layer. Due to the reduced mass and the enhanced thermal-viscous damping at slits, a 35.2 % decrease in quality factor Q has been achieved in the proposed PMUT when compared with the conventional design, resulting in a distinctly reduced blind area from 231.3 mm to 170.7 mm. At the same time, the proposed quasi-closed PMUT facilitates the release of accumulated stress in the device structure during fabrication and operation. As a result, an approximate 50 % reduction in frequency deviation between different as-fabricated PMUTs across the same wafer has been successfully obtained. Moreover, due to the increased linear operation range, the developed bare PMUT chip demonstrates a maximum detection distance of 3 m at the operation frequency of 71.5 kHz under 40 Vpp driving voltage. Given the advantages of lower Q, insensitivity to stress, good fabrication consistency and large linear operation range, the proposed quasi-closed PMUT design can well address the requirements on small blind area and large detection range for distance sensing applications.

Three-dimensional vibration analysis of multilayered composite and functionally graded piezoelectric plates and shells

In the present paper, a coupled 3D exact electro-elastic shell model for Functionally Graded (FG) and composite piezoelectric structures is proposed. Primary variables of the electro-elastic model are the electric potential and the three displacement components. The model allows to evaluate the piezoelectric effect in terms of frequencies and vibration modes. Both closed and open circuit configurations are analyzed and compared. The 3D equilibrium equations and the 3D divergence electric displacement equation for spherical shells give the set of partial differential equations for the electro-elastic problem. The proposed model for spherical shells automatically degenerates into simpler models for plates and cylindrical shells via properly considerations on radii of curvature along in-plane directions. The orthogonal mixed curvilinear coordinates α, β and z are employed. The partial differential governing equations have constant coefficients considering fictitious layers and they are solved using the Navier harmonic form and the exponential matrix method. These features lead to an exact solution for simply-supported boundary conditions. Free vibration analyses are conducted and circular frequencies for the first three thickness vibration modes are computed. After a global assessment phase to verify the correctness of the developed model, new benchmarks are proposed: different thickness ratios and material configurations are investigated. The present work can be intended as a reference general solution for those scientists interested in the study of piezoelectric structures via 2D analytical and numerical formulations.

Love-type waves generated by an impulsive source in a conductive polymer-coated piezoelectric composite structure

Love-type waves generated by an impulsive source in a conductive polymer-coated piezoelectric composite structure

A piezoelectric wave energy harvester equipped with a sequential-drive rotating mechanism and rotary piezoelectric harvesting component

This study developed a sequential rotary-driven piezoelectric wave energy harvester (SRD-PWEH), comprising a cylindrical buoy, sequential-drive rotating mechanism based on a pair of one-way bearings, and rotary piezoelectric harvesting component. The harvesting component was based on a circumferentially arranged piezoelectric composite cantilever beam array. The one-way bearings converted the repetitive rotary motion of an input shaft into a unidirectional rotational motion without reverse rotation to drive the rotary piezoelectric harvesting component. Considering that the rotary-driven process is kind of noncontact-driven, it can effectively reduce the risk of damage to the piezoelectric composite cantilever beam structure. The SRD-PWEH was tested in a wave flume under two wave amplitudes and five wave periods. Results showed that the experimental condition of the wave amplitude and period of 75 mm and 0.9 s, respectively, achieved the highest electrical power. The root-mean-square voltage and maximum average power with the fault diagnosis rate filter circuit were 2.46 V and 0.49 mW, respectively.

1-3-Type piezoelectric composites with three-layer cascade structure

This paper proposes a 1-3-type piezoelectric composite structure based on a three-layer cascade structure, utilizing flexible silicone rubber to promote the thickness vibration mode of piezoelectric ceramics. The sandwiched ceramic layer is adopted to improve the mechanical stability. Based on the uniform field theory, we build a theoretical model for the cascade composite and analyze how the thickness of the sandwiched layer and the volume fraction of the ceramic component affect the performance parameters, including the thickness electromechanical coupling coefficient, the density, the sound velocity and the characteristic impedance. Finite element analysis is employed to evaluate the material and validate the theoretical model. The three-layer cascade piezoelectric composites are fabricated using the “dice-and-fill” technique. The tested results demonstrate that the cascade piezoelectric composite exhibits a concentrated thickness vibration mode, and its thickness electromechanical coupling coefficient is up to 0.71, which is 15.5% higher than that of traditional 1–3 piezoelectric composites. It has great potential in developing promising ultrasonic transducers with high transmitting-receiving response.

On Bending of Piezoelectrically Layered Perforated Nanobeams Embedded in an Elastic Foundation with Flexoelectricity

Analysis of the electromechanical-size-dependent bending of piezoelectric composite structural components with flexoelectricity has been considered by many researchers because of the developments of nanotechnology and the applicability of piezoelectric composite nanobeam structures in Micro/Nano-Electro-Mechanical Systems (MEMS/NEMS). Therefore, the work investigates the size-dependent electromechanical bending of piezoelectrically layered perforated nanobeams resting on elastic foundations including the flexoelectric effect. Within the framework of the modified nonlocal strain gradient elasticity theory, both the microstructure and nonlocality effects are captured. The governing equilibrium equations including piezoelectric and flexoelectric effects are derived using Hamilton’s principle. Closed forms for the non-classical electromechanical bending profiles are derived. The accuracy of the proposed methodology is verified by comparing the obtained results with the available corresponding results in the literature within a 0.3% maximum deviation. Parametric studies are conducted to explore effects of perforation parameters, elastic foundation parameters, geometric dimensions, nonclassical parameters, flexoelectric parameters, as well as the piezoelectric parameters on the bending behavior of piezoelectrically layered perforated nanobeams. The obtained results demonstrate that incorporation of the nondimensional elastic foundation parameters, Kp = 2 and Kw = 20, results in a reduction in the relative percentage reduction in the maximum nondimensional mechanical transverse deflection due to increasing the perforation filling ratio from 0.2 to 1 from 199.86% to 91.83% for a point load and 89.39% for a uniformly distributed load. On the other hand, with Kp = 5 and Kw = 50, the relative percentage difference of the electromechanical bending deflection due to increasing the piezoelectric coefficient, e311, reaches about 8.7% for a point load and 8.5% for a uniformly distributed load at a beam aspect ratio of 50. Thus, the electromechanical as well as mechanical behaviors could be improved by controlling these parameters. The proposed methodology and the obtained results are supportive in many industrial and engineering applications, i.e., MEMS/NEMS.

Higher-order asymptotic homogenization for piezoelectric composites

In this work, we developed a higher-order asymptotic homogenization method (AHM) for efficient multiscale analysis of piezoelectric composite structures. Instead of solving the composite structural problems directly with all heterogeneities considered, AHM first solves the microscale problem at each order of expansion to obtain the corresponding microfluctuation functions and effective properties; the latter is then passed to the macroscale to solve coupling governing differential equations, with the macroscale physical quantities passed back to the microscale and combined with microfluctuation functions to recover the local response. Governing differential equations are formulated and solved in Cartesian coordinates, which is much beneficial for understanding the multiscale-multiphysics behavior of flat piezocomposite structures such as Micro Fiber Composite transducers. Two numerical examples are solved using AHM, i.e., a 1D piezocomposite rod and a 2D piezocomposite plate, and the results are compared with direct numerical solution (DNS) to validate the accuracy and efficiency of the proposed method. The developed multiscale analysis algorithm largely saves the computational cost compared with DNS when a large number of inclusions are included in piezocomposites, thus making it an efficient tool for solving multiphysics composite structural problems with piezoelectricity.

Study of 1-3 piezoelectric composites based on phononic crystals theory

To further improve the working performance of 1-3 piezoelectric composites, in this paper, they are regarded as two-dimensional phononic crystals, the band structures, transmission characteristics and vibration modes are firstly calculated by the finite element method, and the suppression of lateral vibration by 1-3 piezoelectric composite structure is investigated based on band gap theory to obtain a purer thickness vibration. Secondly, the influence of the lattice system on the band gap as well as the overall working performance of piezoelectric composites is analyzed, finite element models of square and hexagonal lattice piezoelectric composites are established, and their operating parameters such as transmitting voltage response level and total radiated power are calculated by simulation. This study shows that the working frequency of 1-3 piezoelectric composites can be set in the band gap of phononic crystals to obtain better lateral vibration suppression; compared with square lattice, 1-3 piezoelectric composites with piezoelectric phase hexagonal lattice arrangement can obtain larger working bandwidth and higher total radiated power in the thickness mode, the overall working performance is better. This study is a guideline for the design and application of piezoelectric components in the fields of acoustics and medicine.

Nondestructive Wafer Level MEMS Piezoelectric Device Thickness Detection.

This paper introduces a novel nondestructive wafer scale thin film thickness measurement method by detecting the reflected picosecond ultrasonic wave transmitting between different interfacial layers. Unlike other traditional approaches used for thickness inspection, this method is highly efficient in wafer scale, and even works for opaque material. As a demonstration, we took scandium doped aluminum nitride (AlScN) thin film and related piezoelectric stacking layers (e.g. Molybedenum/AlScN/Molybdenum) as the case study to explain the advantages of this approach. In our experiments, a laser with a wavelength of 515 nm was used to first measure the thickness of (1) a single Molybdenum (Mo) electrode layer in the range of 100-300 nm, and (2) a single AlScN piezoelectric layer in the range of 600-1000 nm. Then, (3) the combined stacking layers were measured. Finally, (4) the thickness of a standard piezoelectric composite structure (Mo/AlScN/Mo) was characterized based on the conclusions and derivation extracted from the aforementioned sets of experiments. This type of standard piezoelectric composite has been widely adopted in a variety of Micro-electromechanical systems (MEMS) devices such as the Piezoelectric Micromachined Ultrasonic Transducer (PMUT), the Film Bulk Acoustic Resonator (FBAR), the Surface Acoustic Wave (SAW) and more. A comparison between measurement data from both in-line and off-line (using Scanning Electron Microscope) methods was conducted. The result from such in situ 8-inch wafer scale measurements was in a good agreement with the SEM data.

Transference of SH waves in a piezoelectric fiber-reinforced composite layered structure employing perfectly matched layer and infinite element techniques coupled with finite elements

Most commercially used piezoelectric materials suffer from certain drawbacks like low piezoelectric output, brittle nature, etc. Thus, they cannot be utilized to their fullest extent in dynamic applications involving actuators, transducers, Surface Acoustic Wave (SAW) devices, and Love wave sensors, among others. The present work focuses on the transference attributes of anti-plane SH wave in a layered structure composed of a piezoelectric fiber-reinforced composite (PFRC) layer lying over a piezoelectric half-space. The PFRC composed of PZT-5A-epoxy is micro-mechanically modeled using Strength of Materials and Rule of Mixtures, and some of its electro-mechanical advantages over monolithic PZT-5A are discussed. The dispersion relation is obtained by analytical means, as well as two numerical techniques, viz., Semi-Analytical Finite Element - Perfectly Matched Layer (SAFE-PML) technique and Semi Analytical Infinite Element (SAIFE) technique with (1/r) type decay. The Rayleigh–Ritz method and Gauss 3-point quadrature formula are employed to derive the dispersion relation numerically. The effects of the existing parameters, viz. fiber volume fraction, PML length, PML function, etc., on the dispersion curves are graphically demonstrated and discussed. The present work is validated by matching the obtained results with the ones found in the extant literature.

Electromechanical study of graphene reinforced lead-free functionally graded tile for vibration energy harvesting

This study focuses on the electromechanical analysis of functionally graded graphene reinforced piezoelectric composite (FG-GRPC) structures in order to identify circuit metrics such as voltage and power. The graphene platelets (GPLs) scatter evenly and parallelly in each graphene platelets reinforced piezoelectric composite (GRPC) tile. The effective modulus of elasticity for the GRPC tile is calculated by the Halpin-Tsai (HT) parallel model. The rule of the mixture (ROM) is employed to estimate the effective mass density, poisson’s ratio, and piezoelectric properties of GRPC structure. A simple power law distribution is responsible for the spatial disparity in composition over the thickness to generate FG-GRPC structural tiles. The first-order shear deformation theory and Hamilton’s principle are used to derive the governing finite element equations for the FG-GRPC plates. The impact of external resistance, frequency, volume fraction, piezoelectric characteristics, and geometry of the tile on the circuit metrics of FG-GRPC structures are thoroughly examined. Our results reveal that the circuit metrics of FG-GRPC plates are significantly enhanced due to consideration of material grading exponent and a small quantity of GPLs. This article will provide the necessary physical insights for modeling the electromechanical coupling in multipurpose piezoelectric materials, devices, and large-scale systems, allowing them to be used in industrial applications such as pressure sensors, miniature ultrasonic motors, fuel injectors, active controllers, and robotic systems.

Modeling and simulation of thin-walled piezoelectric energy harvesters immersed in flow using monolithic fluid–structure interaction

A monolithic numerical scheme for fluid–structure interaction with special interest in thin-walled piezoelectric energy harvesters driven by fluid is proposed. Employing a beam/shell model for the thin-walled structure in this particular application creates a FSI problem in which an ( n − 1 ) -dimensional structure is embedded in an n -dimensional fluid flow. This choice induces a strongly discontinuous pressure field along the moving fluid–solid interface. We overcome this challenge within a continuous finite element framework by a splitting-fluid-domain approach. The governing equations of the multiphysics problem are solved in a simultaneous fashion in order to reliably capture the main dynamic characteristics of the strongly-coupled system that involves a large deformation piezoelectric composite structure, an integrated electric circuit and an incompressible viscous fluid. The monolithic solution scheme is based on the weighted residuals method, with the boundary-fitted finite element method used for the discretization in space, and the generalized- α method for discretization in time. The proposed framework is evaluated against reference data of two popular FSI benchmark problems. Two additional numerical examples of flow-driven thin-walled piezoelectric energy harvesters demonstrate the feasibility of the framework to predict controlled cyclic response and limit-cycle oscillations and thus the power output in typical operational states of this class of energy harvesting devices. • A fully monolithic model tailored to flow-driven thin-walled piezoelectric energy harvesters (PEHs). • A novel method to tackle the strongly discontinuous pressure field of the fluid field. • The computational framework is validated against classical FSI benchmark problems. • The importance of optimized PEH electrode coverage is revealed by two new benchmarks. • Reference implementation using the open-source finite element framework FEniCS.

A power-intensive piezoelectric energy harvester with efficient load utilization for road energy collection: Design, testing, and application

Piezoelectric energy harvesters (PEHs) convert mechanical energy into electrical energy providing a new method for road infrastructure energy self-consistency. However, the structural design process of the existing PEH is not clear, some PEH structures have deficiencies, and the secondary construction when PEH is combined with pavements is cumbersome. Given this, considering engineering applications and energy output, the design of a new PEH is expounded from five perspectives. A harvester package structure that utilizes 100% of the vehicle load is proposed. The output characteristics of the PEH are tested, and the effects of the load characteristics and arrangement of the piezoelectric ceramic array inside the harvester on the piezoelectric output are studied. By abandoning the conventional “cold combination” method, the piezoelectric pavement is formed by the “hot combination” method. The feasibility of integral molding PEHs and pavement structures is explored. The piezoelectric response and long-term service performance of the harvester under indirect stress in a pavement structure are tested using accelerated-loading tests. The PEH test results show that the load level and speed significantly affect the piezoelectric output of the harvester. Irrespective of the connection state between piezoelectric ceramics, the array arrangement affects the piezoelectric output. The negative effect of the tandem is more obvious. The power density of the PEH under an excitation of 0.7 MPa–20 Hz reaches 0.0926 mW/cm3, which is 23.96–138.05% higher than that of the same type of excellent PEH. The piezoelectric pavement loading results show that the piezoelectric response of the harvester indirectly stressed on the pavement depends on the tire load. It is worth noting that vehicle speed can increase the output power of the harvester but not necessarily its energy output. After 500,000 cycles of loading, the open-circuit voltage of the harvester is reduced by only 2.6%, and the rut depth of the pavement structure is 2.1 mm. The harvesters in piezoelectric pavements are in normal service, and the integrated molding method is a convenient construction method. Finally, the potential normalization factors affecting the energy output of the harvester are discussed, and a method to improve the performance of the piezoelectric pavement composite structure is presented. This study provides a reference for the structural design of PEHs and their road applications.

Controllable electromechanical stability of a torsional micromirror actuator with piezoelectric composite structure under capillary force

Various types of micro/nano functional devices are being widely designed as optical switches, micro scanners, micromirrors and other core optical devices. The continuing miniaturization of the functional devices makes the size dependence of electromechanical property significant in micro/nano scale due to the sharp increase of surface interactions such as capillary force from liquid bridge, van der Waals and Casimir forces from quantum fluctuations. The surface interactions can cause the pull-in instability, adhesion between parts, and even failure of device. This work provides an active control method to avoid the pull-in instability of an electrostatically driven circular micromirror by applying voltage on a torsional piezoelectric composite structure. The influences of the three types are compared of dispersion forces on the electromechanical stability of the micromirror actuator. A comprehensive electromechanical model of a torsional piezoelectric beam was established to numerically investigate the electromechanical coupling of the micromirror. The results show that the influence of capillary force on the stability of the micromirror is as significant as van der Waals force and Casimir force. By introducing piezoelectric nanoplates into the laminated torsional structure, the micromirror stability can be controlled based on the piezoelectric effect of the torsional piezoelectric composite structure. This work can contribute to the structural optimization design and manufacture of micromirror systems. Cited as: Liu, M., Chen, Y., Cheng, W., Chen, S., Yu, T., Yang, W. Controllable electromechanical stability of a torsional micromirror actuator with piezoelectric composite structure under capillary force. Capillarity, 2022, 5(3): 51-64. https://doi.org/10.46690/capi.2022.03.02

Analysis of Love waves propagation in a functionally graded porous piezoelectric composite structure

Propagation of Love waves in a composite structure, containing a functionally graded porous piezoelectric material layer over a dielectric elastic half space, is studied. The material properties gradually vary with the layer thickness. Constitutive equations for a functionally graded porous piezoelectric material layer are laid down and then their analytical solutions are derived by using the Wentzel-Kramers-Brillouin method. Variations in the mechanical properties and electrical properties are considered and dispersion equations are derived for both electrically short and open boundaries. The effects of porosity and grade coefficients on the phase velocity of the Love waves and on electro-mechanical coupling are discussed. Numerical computation of the phase velocity and electromechanical coupling factor is done for different levels of thickness of the layer and results, obtained, are validated by deriving earlier results as a special case of this study. This study finds application in making high-performance surface acoustic wave devices.

Tunable acoustic metasurface based on tunable piezoelectric composite structure.

Due to the potential engineering needs, the passive tunable metasurfaces with a high performance equivalent to the active phased array is worthy of research. Here, a passive ultrathin metasurface unit composed of a piezoelectric composite structure (PCS) connected to an external capacitor, which can modulate the phase of the transmitted acoustic waves at a deep subwavelength scale only by controlling the external capacitor but without changing the structure, is proposed. Then, a tunable acoustic metasurface composed of 20 identical PCSs is introduced to realize three acoustic functions, beam steering, beam focusing, and tweezer-like beam generating, just by changing the external capacitors. The phase-control abilities of the PCS unit and three functions of the designed metasurface are proved both numerically and experimentally. This study provides the possibility to design ultrathin tunable acoustic metasurfaces with the ability of precise control and passive materials.

Broadband tunable acoustic metasurface based on piezoelectric composite structure with two resonant modes

In this letter, we propose a deep-wavelength tunable acoustic metasurface composed of a fixed piezoelectric composite structure with a broad operating frequency range. The metasurface unit has two tunable resonant frequencies determined by specific external inductors and can continuously modulate the phase of the transmitted wave. The influence of the inductors on resonant frequencies are studied by simulation and experiment. Moreover, the functions of acoustic beam steering and focusing by the designed metasurface at three arbitrarily chosen frequencies are verified in simulation. This work may have good potential in the design of acoustic metasurfaces with broadband operating frequencies.

Investigation of Electromechanical Properties on 3-D Printed Piezoelectric Composite Scaffold Structures.

Piezoelectric composites with 3-3 connectivity gathered attraction due to their potential application as an acoustic transducer in medical imaging, non-destructive testing, etc. In this contribution, piezoelectric composites were fabricated with a material extrusion-based additive manufacturing process (MEX), also well-known under the names fused deposition modeling (FDM), fused filament fabrication (FFF) or fused deposition ceramics (FDC). Thermoplastic filaments were used to achieve open and offset printed piezoelectric scaffold structures. Both scaffold structures were printed, debinded and sintered successfully using commercial PZT and BaTiO3 powder. For the first time, it could be demonstrated, that using the MEX processing method, closed pore ferroelectric structure can be achieved without pore-former additive. After ceramic processing, the PZT scaffold structures were impregnated with epoxy resin to convert them into composites with 3-3 connectivity. A series of composites with varying ceramic content were achieved by changing the infill parameter during the 3D printing process systematically, and their electromechanical properties were investigated using the electromechanical aix PES device. Also, the Figure of merit (FOM) of these composites was calculated to assess the potential of this material as a candidate for transducer applications. A maximum for the FOM at 25 vol.% of PZT could be observed in this study.

Multi-material topology optimization of piezoelectric composite structures for energy harvesting

Energy harvesting is an essential technology for enabling low-power, maintenance-free electronic devices, and thus has attracted much attention in recent years. In this paper, we propose a multi-material topology optimization approach for the design of energy harvesting piezoelectric composite structures. The energy conversion efficiency of piezoelectric composite structure is maximized by optimally distributing elastic, piezoelectric and void materials. To this end, a multi-material interpolation model is particularly established. In order to improve gradient-based mathematical programming algorithms, analytical sensitivities of topological design variables are derived using the adjoint method. An additional constraint on structural compliance is considered in design to maintain the load-carrying capability and improve the convergence. A variety of numerical experiments are performed to test our approach on a benchmark composite beam with piezoelectric layers. The proposed approach has been shown effective in increasing the energy conversion efficiency by the simultaneous distribution of the piezoelectric and non-piezoelectric materials. The performance calibration of the optimized design and the reconstructed topologies based on computer-aided design demonstrate the effectiveness of the proposed method under both static and harmonic load conditions.

Investigation on a Linear Piezoelectric Actuator Based on Stick-Slip/Scan Excitation

To perform a high resolution and long stroke application in optical precision instruments, a linear piezoelectric actuator operated in stick-slip/scan modes for driving a linear motion table is presented. The proposed piezoelectric actuator is a piezoelectric composite structure, which includes a metal elastomer, a piezoelectric stack, and a frictional ball. The purpose of this paper is to describe the operation principle, design, and the running test and resolution test of the linear motion table driven by the proposed piezoelectric actuator. The notable feature is the flexible hinges of the actuator, including composite hinge, pre-pressure adjustment flexible hinge, and transmission flexible hinge, which are designed for decoupling the motion in the action direction of the piezoelectric stack and the direction in which the pre-pressure is applied. A prototype has been fabricated and two operation modes of the piezoelectric actuator, stick-slip and scan mode, were utilized to test the driving characteristics of the linear motion table. Experimental results show that the finest step resolutions in stick-slip mode and scan mode achieved 12 nm and 4 nm, respectively.