Electromechanical Coupling Effect Research Articles

Surface effects in Mode III fracture of flexoelectric bodies

Flexoelectric materials exhibit mechano-electro coupling between the strain gradients and electric polarization (direct flexoelectricity) and/or between electric field gradients and elastic strains (converse flexoelectricity). As the design of flexoelectric structures is required more and more at decreasing length scales, surface effects become more significant, often resulting in considerable size effects which affect overall deformation of the structure. This further complicates fracture mechanisms in flexoelectric materials particularly at micro- and nano-sized structures. In this paper, we incorporate surface effects with the direct flexoelectricity, to study the electro-mechanical coupling effects of a Mode III crack at the nanoscale structures. We derive the corresponding governing equations together with the associated boundary conditions. Using Williams’ eigenfunction expansion and the J-integral’s path independence, we have obtained the asymptotic field to analyze the singularity indices at the Mode III crack tip in flexoelectric materials. With the use of Fourier transforms, the corresponding mixed boundary value problem is reduced to a hypersingular integro-differential equation in which surface effects are incorporated explicitly. The resulting hypersingular integral equation is solved numerically using Chebyshev polynomials. The influence of both surface and flexoelectric effects on the displacement field, polarization field, strain gradient field along with the actual physical stress field are revealed and displayed graphically.

Nonlinear phase velocities in tri-directional functionally graded nanoplates coupled with NEMS patch using multi-physics simulation

The nonlinear phase velocities analysis of tri-directional functionally graded (FG) nanoplates is crucial for optimizing their performance as nano-electro-mechanical systems (NEMS). By understanding the nonlinear phase velocities of various wave modes within the nanoplate, engineers can accurately predict and enhance the efficiency of NEMS. This analysis allows for the precise tuning of the piezoelectric patches to capture vibrational energy more effectively, ensuring maximum energy conversion efficiency. Moreover, it helps in identifying the optimal placement and orientation of the piezoelectric patches, minimizing energy loss and enhancing the reliability and durability of the NEMS. Ultimately, this leads to more efficient utilization of ambient vibrations in airplanes, providing a sustainable power source for various onboard sensors and monitoring systems, contributing to reduced reliance on external power sources, and improved overall energy management. For this issue, for the first time, nonlinear phase velocity in the tri-directional functionally graded nanoplate coupled with a piezoelectric patch via COMSOL multi-physics simulation, physics-informed deep neural networks (PIDNNs), and mathematics simulation are presented. In the mathematics simulation domain, nonlocal strain gradient theory for modeling both the hardening and softening behavior of the current nanoplate is presented. The electromechanical coupling effect and the abrupt change in material properties at the interfaces will have a major influence on the mechanical performance of tri-directional functionally graded (TD-FG) nanoplate coupled with a piezoelectric patch if transverse shear deformations cannot be well modeled. Thereby, in the current simulation, a quasi-3D refined theory with 10 variables is presented. Also, for coupling the composite structure with the piezoelectric patch, compatibility conditions are considered. An analytical solution procedure is presented for solving the nonlinear partial differential equations of the current electrical system.

Multiple electromechanical coupling in wrinkled monolayer MoS2

Abstract The electromechanical coupling of two-dimensional (2D) transition metal dichalcogenides (TMDs) is crucial for the design of highly efficient optoelectronic devices. However, achieving multiple electromechanical coupling effects in one 2D material remain a major challenge. Here, we investigate the coexistence of energy funneling, piezoelectricity, and flexoelectricity in wrinkled monolayer TMDs through the atomic-bond-relaxation approach. We find that the periodic undulation strain induced by wrinkles can lead to multiple electromechanical coupling properties. The synergistic interaction of energy funneling, piezoelectric, and flexoelectric effects can result in spatially orthogonal charge separation and transport, as well as the suppression of recombination during charge separation and transport processes. Our study provides a new route for the design of 2D material based optoelectronic devices.

Tunable flexural waves by piezoelectric metasurface with shunt circuits

Elastic metasurfaces have been rapidly developed for effective modulation of elastic wave propagation. Among them, utilizing the electromechanical coupling effect of piezoelectric materials provides a promising way to design tunable and multifunctional elastic metasurfaces, but piezoelectric metasurfaces still face big challenges in theoretical guidance and experiments. In this paper, a tunable piezoelectric metasurface is proposed for achieving modulation of flexural wave in broad working frequency range. Based on the developed electromechanical coupling model, the piezoelectric patch with shunt resistor–inductor circuit is analyzed, and the functional unit of metasurface with only two piezoelectric patches is designed for modulating the flexural wave in thin plate. By using Antoniou’s circuit and considering the effect of impedance in circuit, the arbitral phase shift of functional unit is experimentally achieved by adjustable shunt circuits to verify the turnability in a full 2π range. Further, the piezoelectric metasurface by assembling functional units can realize multiple functions, like tunable anomalous refraction and wave focusing, by adjusting shunt circuits.

Flexural wave compression behaviors of programmable graded piezoelectric meta-beams

Active electromechanical metamaterials have drawn significant attention due to their remarkable tunability and adaptability in vibration and wave control. Exploiting the electromechanical coupling effect via controlled biased fields enables precise manipulation of the structural vibrations and wave transmissions. In this research, we have developed a programmable graded piezoelectric meta-beam that successfully imitates the wave compression behavior of an acoustic black hole without modifying the structural geometries. The effective parameters of the meta-beam are reshaped into a gradient distribution by tuning the electrical impedances of the digital shunting circuits. With such graded effective parameters, it becomes feasible to tailor the local wavenumber distribution of the meta-beam and hence achieve the desired wave compression. Numerical results validated our proposed paradigm of the programmable black hole in both straight and curved beams. In contrast to the straight beam, curvature of the curved beam reduces the tunable range of the local wavenumber. A comprehensive parametric study was conducted to investigate the influences of the gradient profile, electric damping, and curvature on the wave control function. For a given desired frequency, programmable control of wave compression location and amplified output of electrical signals are achieved.

Mechanically induced built-in electric field in BCTZ nanostructures for piezocatalysis: Experiments and modeling

Ba(Ti0.80Zr0.20)O3–0.5(Ba0.7Ca0.3)TiO3 (BCTZ) piezoelectric nanofibers (NFs) and nanoparticles (NPs) were fabricated using electrospinning and sol-gel methods, respectively. The impact of BCTZ nanostructure on piezocatalysis was investigated, revealing that both poled NFs and NPs exhibit a piezocatalytic degradation rate of 2.8 × 10–2 min-1, which is significantly higher than their unpoled counterparts at 2.3 × 10–2 min-1 and 1.9 × 10–2 min-1, respectively. The enhanced piezocatalytic degradation rates of the poled BCTZ nanostructures are attributed to their superior piezoelectricity, resulting in larger built-in electric fields under external strain. Moreover, BCTZ NFs provide numerous active piezocatalytic reaction sites confined to the one-dimensional (1D) fibrous boundaries. Simulation results indicate that BCTZ NFs exhibit greater displacement and higher piezoresponse compared to nanoparticles, due to the electromechanical coupling effect facilitated by the 1D nanostructure. This study provides an efficient pathway to understanding the coupling mechanism between the poled built-in electric field and piezotronics.

Coupling of Piezo/Flexoelectricity and Its Effect on the Band Structure of Wrinkled ZnO Monolayers

AbstractWrinkles are used in manufacturing stretchable electronics, soft materials, smart displays, and microstructures. The emerging 2D materials enable the investigation of the intertwined piezoelectric and flexoelectric coupling effect in wrinkled structures and their energy, sensing, and other applications. However, current studies of the electromechanical coupling effect often consider it one effect or even overlook one of the two effects. This oversimplification leads to inaccuracies in the analysis. Here, a theoretical model is proposed to separate the piezoelectric and flexoelectric coefficients by fitting polarization formulas with discrete polarization values calculated using density functional theory. Wrinkled ZnO monolayers are built to mimic the realistic situation, where six nonzero coefficients are successfully isolated, revealing that the coupling of piezo/flexoelectricity and the contribution of piezoelectric and flexoelectric polarizations to the total polarization vary in different directions. Combined with the dipole moment analysis, the relationship between the polarization, piezoelectric coefficient, flexoelectric coefficient, and wrinkle amplitude is established. This study demonstrates that increasing the wrinkle amplitude significantly decreases the energy gap of 560 meV. The separation and quantification of piezoelectric and flexoelectric effects advance the understanding of wrinkles' mechanical and electromechanical properties and lay the foundation for their future applications.

Finite element analysis of the electro-mechanical coupling effects in piezoelectric laminated structures

This study utilized the COMSOL Multiphysics software to conduct finite element analysis on the piezoelectric coupling effect of the composite layer structure. The article begins by introducing the basic principles and history of the piezoelectric effect, emphasizing the importance and widespread application of piezoelectric materials in the field of smart materials. Subsequently, it defines in detail the models of bimorph piezoelectric beams and multilayer composite piezoelectric plates, and conducts potential verification. The bimorph piezoelectric beam model uses PVDF material, and the potential distribution is monitored by boundary probes, confirming the influence of the quantity and distribution of sensor electrodes on voltage distribution. The multilayer composite piezoelectric plate model combines a Si non-piezoelectric semiconductor layer with a PZT-4 piezoelectric material layer, demonstrating the in-plane distribution of potential under lateral mechanical loads. This study not only verifies the reliability of COMSOL software in piezoelectric coupling analysis but also provides an in-depth understanding of the behavior and performance of piezoelectric materials in complex environments.

Modelling of electromechanical coupling dynamics for high-speed EHT system used in HEV and characteristics analysis

As the development of hybrid electric vehicle (HEV) to high-speed, heavy-load, the electromechanical coupling vibration becomes the bottleneck in high-speed electromechanical hybrid transmission (EHT) system. To explore the dynamics characteristics and optimization direction for high-speed EHT system, an electromechanical coupling dynamics model under multi-source excitations is established with lumped-distributed parameter method and verified with experiment data. The dynamics model shows higher accuracy in both time and frequency domain analysis. On this basis, firstly, the comparison between lumped-shaft and distributed-shaft model is studied under time and frequency domain. Comparing with the lumped-shaft model, the distributed-shaft model shows higher accuracy, and can better reflect the coupling vibration of multi-stage planetary gears (PGs). Secondly, the inherent vibration model is derived, and the effect of electromechanical coupling and high-speed working conditions on inherent vibration characteristics are studied. Thirdly, a new method called ‘machine-electricity-magnet coupling interface’ is proposed to reveal the coupling vibration phenomenon. In addition, the signal of stator current and electromagnetic torque includes the frequency of PGs, which is a basis on the fault diagnosis and state monitor of EHT system. Last but not the least, the vibration acceleration of EHT system is analysed under variable speed and load working conditions. Rotation speed and gear meshing force is found as the main influencing factor of series EHT system, and the specific optimization direction is also given.

A centipede-inspired bonded-type ultrasonic actuator with high thrust force density driven by dual-torsional-vibration-induced flexural traveling waves

This paper presents an ultrasonic actuator with high thrust force density driven by dual-torsional-vibration-induced flexural traveling waves. Here, the PZT plates are bonded onto a duralumin vibrating body in a block shape to accomplish a compact configuration and they operate in the 2nd torsional vibrations, whose strong electromechanical coupling effect facilitates the enhancement of the driving force. Interestingly, the operating principle somewhat imitates the movement pattern of the centipede’s feet. To test the validity, first, by using a Mason-equivalent-circuit-based dynamic model, several key dimensions were tuned to increase the driving-force-to-weight ratio. Meanwhile, the driving feet’s configurations are adjusted based on a kinetic model to make the elliptical motion shape close to a circle. Then, an actuator prototype with the size of 48 × 47 × 6 mm3 and the weight of 29 g was fabricated and the moving/loading/positioning performance was evaluated. When the actuator adopts a continuous operation, its maximal sliding speed reached 630 mm/s at the frequency of 24.95 kHz. Moreover, it yielded the maximal thrust force and the maximal output power of 4.38 N and 527.8 mW, corresponding to the thrust force density and the power density of 151.2 N/kg and 18.2 W/kg, respectively. In a stepping operation, the minimal step displacement was 0.91 μm. These results demonstrate that the dual-torsional-vibrations-induced traveling wave allows the actuator to produce the high thrust force density and provides a new actuating principle to design powerful ultrasonic actuators.

A general solution for electromechanical analysis of electroelastic composite plates with arbitrary holes

Stroh formalism provides an elegant method of solution for two-dimensional anisotropic elasticity problems through the generalized eigen relation associated with the dual coordinate system that gives the material eigen values and eigen vectors, and also the fundamental elasticity matrix and its associated Barnett-Lothe tensors. The extended Stroh-like formalism of Hwu and Hsieh has expanded the scope of basic Stroh formalism by addressing the electro-mechanical coupling effects in electro elastic plates. This paper presents an inclusive solution that addresses the two-dimensional problems in infinite electro-elastic, anisotropic, and isotropic plates with an arbitrary hole under remote arbitrary coupled electro-mechanical loading. This is achieved by adopting the Stroh formalism and its subsequent versions to consider the anisotropic and electro-elastic plates, and further, by incorporating the arbitrary biaxial loading condition into the boundary conditions, and the generalized mapping function into the basic formulation to accommodate all types of in plane loading and a variety of hole shapes respectively. Various equations of the solution are derived explicitly for easy understanding and computer implementation. The stress function is derived explicitly to satisfy the condition of traction free hole with remote electro-mechanical loading under generalized plane stress-open circuit condition. The stresses and electric displacements around the hole boundary are obtained by taking the derivative of the stress function with respect to unit normal along the hole boundary. The solution presented can be degenerated to the anisotropic or isotropic case by choosing the corresponding material properties, or appropriate values of complex parameters respectively. This general solution has exactly reproduced the results of other solutions in the literature for piezoelectric plates given by different methods. New results of stresses and electric displacements are obtained for various arbitrary holes in [PZT5H/45/-45/PZT5H]s graphite/epoxy plate and PZT 4 plates. Results for holes in piezoelectric laminates and PZT 4 piezo layer are also presented by FEM.

Enhanced flexoelectricity of liquid with hydrated ions

Flexoelectricity, denoted as an electromechanical coupling effect from strain gradient introduced polarization, is prevalent in dielectric materials. However, its application in low-viscosity liquids has been limited by the scale of the flexoelectric coefficient. This study explores the flexoelectric coefficient of various hydrated ion solutions through a series of experiments. Additionally, the interplay between ion adsorption and the flexoelectric effect is investigated by using interfacial voltage detection. By introducing hydrated structures into liquids, a significant enlargement of the flexoelectric coefficient up to 2.3 × 10−9 C m−1 is obtained in Fe2(SO4)3 solution by four times than DI water. These findings highlight the remarkable electromechanical properties of liquid materials with hydrated ions and suggest promising avenues for the application of liquid dielectrics in hydrovoltaic technology, ionotronic devices, and energy harvesters.

Efficient large-deformation shell elements for the simulation of electromechanical coupling effects in incompressible dielectric elastomers

So-called electro-active polymers are not only capable of undergoing very large deformations, but they also exhibit different electromechanical coupling effects due to their dielectric or electrostrictive characteristics. In the present paper the sub-class of dielectric elastomers is studied; in particular, we focus on thin dielectric elastomer shells, which undergo large deformations under an applied electric field. We develop a framework for the modeling and subsequent efficient simulation of thin structures made from incompressible dielectric elastomers. A thermodynamically consistent phenomenological continuum model based on the free energy density is adapted imposing the kinematic assumptions of Kirchhoff-Love shells in combination with including the thickness deformation and the electric field as independent unknown fields. To make the formulation accessible to finite element simulations, existing non-linear elastic shell mixed finite elements are extended to the present hyperelastic electromechanically coupled formulation for dielectric elastomer shells. Computational results of the shell theory are compared to three-dimensional results validating the proposed modeling and numerical simulation methodology, and showing high accuracy already for coarse finite element discretizations of the shell.

A mechanical manipulated electromechanical coupling design with stretchable electret film: mechanical sensing, energy harvesting, and actuation

Electrical and mechanical energy converts around the nature, and electromechanical coupling effect is applied in various conditions such as mechanical sensing, electrical actuation, and self-powering. During the energy type conversion, electromechanical parameters are among the key issues, such as enlarging the sensitivity and range of mechanical sensing, and energy harvesting efficiency. In this work, a mechanical manipulated approach with stretchable electret is proposed to continuously manipulate the electromechanical parameters. An electromechanical coupling demonstration with pre-stretched electret films and non-contact electrodes are applied, verifying high and regulable electromechanical coupling parameters, and it is advantaged from large deformable and overload permissible capability. This mechanical manipulation approach proposes a new possibility on simplifying the structural and mechanical design of various electromechanical devices, and further enhancing the general applicability with certain geometry and material with ultra-high and tunable electromechanical coupling parameters.

Mechanical clamping by inverse piezoelectric effect to improve the electromechanical coupling effect of a 1-3 PZT/P(VDF-TrFE) composite sheet

Mechanical clamping by inverse piezoelectric effect to improve the electromechanical coupling effect of a 1-3 PZT/P(VDF-TrFE) composite sheet

Energy-based modeling of rate-independent hysteresis and viscoelastic effects in dielectric elastomer actuators

Dielectric elastomer (DE) transducers are known to exhibit a rate-dependent hysteresis in their force-displacement response, which is commonly attributed to the viscoelastic behavior of elastomer materials and compliant electrodes. In the case of DE materials characterized by low mechanical losses, such as silicone, the mechanical hysteresis often turns out to be practically rate-independent in the low frequency range (sub-Hz), whereas rate-dependent hysteretic effects only become relevant at higher deformation rates. Most of the existing literature focuses on describing DE hysteretic losses using viscoelasticity theory. This approach results in relatively simple dynamic models, which are not capable of describing rate-independent hysteretic behaviors. In this work, we propose a control-oriented modeling framework for both rate-dependent and rate-dependent hysteresis occurring in uniaxially loaded DE actuators. To this end, classic thermodinamically-consistent modeling approaches for DEs are combined with a new energy-based Maxwell-Lion formalization of the hysteretic losses. The resulting dynamic model comprises a set of nonlinear ordinary differential equations, and is capable of simultaneously describe geometric dependencies, large deformation nonlinearities, electro-mechanical coupling, and rate-independent and rate-dependent hysteretic effects. To deal with the large number of involved parameters, a novel systematic identification algorithm based on quadratic programming is also proposed. After presenting the theory, the model is validated based on experiments conducted on a silicone-based rolled DE actuator. Its superiority compared to classic DE viscoelastic models is quantitatively assessed.

Performance analysis of electrical signal output of multi-state flexoelectric structures with parameter uncertainties through quasi-Monte Carlo method

Flexoelectric effect is a more universal electromechanical coupling effect than piezoelectric effect. Flexoelectric beams as the main structural component of flexoelectric power signal output have broad application prospects in the next generation of micro–nano electromechanical systems. However, the electrical signal output of flexoelectric structures in macro-scale is far less than the output of the piezoelectric signal. Therefore, it is urgent to explore the influence of the parameter uncertainties on the electrical signal output of the flexoelectric structures, in order to improve the electrical signal output of flexoelectric materials with excellent design performance. Based on the quasi-static theory, the output voltage model and the output charge model of flexoelectric structures as well as the effective piezoelectric coefficient model are constructed. Then the influences of the flexoelectric parameters on the output voltage and the output charge are researched as well as the influence of the effective piezoelectric coefficient. Finally, the influences of uncertain parameters under different electrical states (e.g. the electrical open circuit and short circuit states) on the output performance of flexoelectric signal are studied by the quasi-Monte Carlo method, in order to further provide a reference for the reliability analysis and optimization design of the flexoelectric structures.

Optimizing dispensing performance of needle-type piezoelectric jet dispensers: a novel drive waveform approach

The dispensing performance of needle-type piezoelectric jet dispenser constitutes a crucial factor that ensures the quality of additive manufacturing processes. In this paper, a novel approach is proposed to enhance the dispensing performance of needle-type piezoelectric jetting dispensers by introducing a more adaptable driving waveform based on Bézier curves. Initially, the approach considers the electromechanical coupling effect of the needle-type piezoelectric dispenser and constructs a high-precision fluid–solid coupling model of the dispensing process. Subsequently, a multi-physics field joint simulation platform combining Matlab and Fluent is established to systematically analyze control strategies in real service conditions. Next, a new driving waveform based on Bézier curves is introduced, and the control parameters are optimized using a genetic algorithm to address issues such as air bubbles in the droplets and instability of the dispensing process. The optimized waveform based on the Bézier curve reduces the volume of air suction during the dispensing process by over 20% compared to the traditional waveform and eliminates the uncontrolled vibration state of the needle in the fluid, ensuring the stability of the entire fluid refill process. Finally, the optimized control strategy is verified through experiments and compared with traditional methods. The experiment demonstrates its advantages in addressing issues with no air bubbles in the droplets and consistency of the droplets. This study provides valuable insights into optimizing the dispensing performance of needle-type piezoelectric jetting dispensers regarding control strategy.

Electromechanical coupling dynamics of dual-motor electric drive system of hybrid electric vehicles

In this study, to investigate the electromechanically coupled dynamics of a dual-motor electric drive system (DEDS) of hybrid electric vehicles under typical conditions. Considering the time-varying stiffness of gears, a dynamic model of the gear system and permanent magnet synchronous motor (PMSM) was developed, and a comprehensive electromechanical coupling dynamics model of DEDS applicable to coupling dynamics analysis was obtained. Based on this model, the impacts of the transmission error and electromechanical coupling effect on the dynamics of DEDS under steady-state and acceleration conditions were simulated and analyzed. This study demonstrates the significant impact of transmission errors on the dynamic load of high-speed gear pairs and the speed synchronization characteristics of the system. The study also reveals that the electromechanical coupling effect exacerbated the fluctuation of the gear dynamic load. During the speed change process, the electromechanical coupling effect did not introduce new resonance points. However, transmission errors tend to induce low-frequency resonance of the gear dynamic load and speed synchronization error (SSE). In addition, when the system is operated near the resonant speed, a large torsional vibration dominated by the resonant excitation frequency is generated, distinguished using the current signal to assess the resonance risk. The research results are important for the integrated design and condition monitoring of DEDS and offer valuable insights for enhancing the operational efficiency and reliability of the system.

Nonlinear dynamic morphing of conical bistable dielectric elastomer actuator

The bistable dielectric elastomer actuator (BDEA) possesses two stable positions which offers notable advantages of stable-state self-maintenance, fast response, and threshold snap-through characteristic in comparison with conventional dielectric elastomers. However, the strong nonlinearity induced by the coupling among materials, structure, and electrostatic fields greatly affect the dynamic response and gives rise to stability issues. Hence, a novel BDEA is proposed by introducing DEA film centrally connected with one mass block and linear spring, and the bistability can be adjusted by applying external voltage. A nonlinear dynamical model considering the electro-mechanical coupling effects is established using the Euler-Lagrange method, with which the snap-through procedure is theoretically analyzed and validated through the analytic method and finite element method. The influences of the electric actuation and structural parameters on the number of stable states and natural frequency are analyzed. Additionally, the supercritical pitchfork bifurcation and saddle-node bifurcation are investigated through dynamic analysis under forced vibration. Furthermore, the ranges of electrical actuation parameters can be determined for preventing the bifurcation phenomena under parametric excitations. Moreover, an active morphing strategy for achieving nonlinear dynamic morphing between steady states of BDEA using drive voltage is obtained, thereby enhancing the versatility of conical BDEA.