Search Results (67)

This study analytically investigates shear horizontal (SH) wave propagation in a layered structure consisting of a piezoflexoelectric (PFE) layer bonded to an elastic substrate, considering an imperfect interface. A frequency equation is derived by applying appropriate boundary and interfacial conditions, capturing the effects of flexoelectric coupling, interface imperfections, the layer thickness, and the material properties. The resulting dispersion relation reveals that both interface imperfections and the flexoelectric strength significantly alter the phase velocity of SH waves. Numerical simulations show that increasing flexoelectric coefficients or interface imperfections lead to notable changes in dispersion behavior. Comparative analyses under electrically open (EO)- and electrically short (ES)-circuited boundary conditions demonstrate their impacts on wave propagation. These findings offer new insights into the design and analysis of piezoflexoelectric devices with realistic interface conditions. Full article

In recent years, the flexoelectric effect has demonstrated significant potential for applications in sensing, actuation, energy acquisition and other related fields. As the primary structure of flexural output, the flexoelectric beam structure also exhibits substantial potential for development and application. However, flexoelectric output is unable to function effectively at the macroscale, and the impact of the uncertainty of the parameters of flexoelectric material on the flexural output remains unclear. To address the issue of parameter uncertainty, this paper employs the analysis method based on variance-driven coupled with moment-free measure to study the impact caused by structural parameters on the uncertainty of the output voltage of the flexural electron beam in the case of an open circuit, the influence on the output charge uncertainty under short-circuit conditions, and the influence on the effective piezoelectric coefficient uncertainty. This study of parameter uncertainty offers a valuable reference for the reliability assessment and structural optimization design of flexural electric beam and provides theoretical support for the macroscale application of the flexoelectric effect. Full article

Flexoelectricity arises in materials under strain gradients, which can be particularly significant for situations in which the existence of other electromechanical properties is absent or generating large flexoelectric properties is achievable. This effect has also been observed in some biological materials, whose understanding can hugely help to further enhance our understanding of vital biological processes like mechanotransduction, as well as the development of applications in regenerative medicine and drug delivery. While the field of flexoelectricity as a relevant topic in biological materials is relatively new and still developing, the current study aims to review available results on flexoelectric effects in biological materials such as cells and cell membranes, hearing mechanisms, and bone, and their potential applications in biomedical research. Therefore, we first provide a brief background on two main electromechanical couplings (piezoelectricity and flexoelectricity) and further, how flexoelectricity has been experimentally and theoretically identified. We then review flexoelectricity in different biological materials as the main aim of the current study. Within that, we provide additional emphasis on the influence of this effect on bone and bone remodeling. In particular, the study outlines current limitations and provides potential directions for future work, emphasizing the crucial role in the development of next-generation electromechanical devices and optimizing their function in the area of biomedical research. Full article

This paper presents a numerical homogenization method for estimating the effective converse flexoelectric coefficients. A 2D model made of two-phase composite is developed at the microscale in consideration of a representative volume element that includes a continuous flexoelectric fiber embedded in a pure elastic matrix. In the implementation, the constitutive equations are derived from the electromechanical enthalpy accounting for higher-order coupling terms. Electric boundary conditions associated with an inhomogeneous electric field are imposed, allowing the approximation of the generated mechanical strains and stresses. Accordingly, the numerical simulations yield the overall equivalent converse flexoelectricity tensor for the longitudinal, transversal, and shear couplings. The results showed that the composite undergoes an obvious straining, which creates actuation due to the converse effect. The components of the homogenized longitudinal and transverse coefficients were found to be dependent on the volume fraction and elastic properties of the constituents. Full article

Piezoelectric material structures with an excellent mechatronic coupling property effectively promote self-power energy harvesting in micro-/nano-electro-mechanical systems (MEMS/NEMS). Therein, the characteristics of the microscale and multi-physical aspects effect significant influence on performance, such as attaining a fast response and high power density. It is difficult to use the classical mechanical and heat conduction models to effectively explain and analyze microscale physical field coupling behaviors. The purpose of this study is to develop the piezoelectric thermoelastic theoretical model, firstly considering the non-uniform physical field. The generalized equations governing thermo-electro-elastic vibration energy harvesting in a microbeam model were obtained based on Hamilton’s principle and the generalized thermoelastic theory was developed by considering thermopolarization and thermal hysteresis behavior. After that, the explicit expressions for voltage and output power were derived using the assumed-modes method; meanwhile, effects such as the piezo-flexoelectric aspect, size dependence, etc. are discussed in detail. It was found that thermal and microscale effects significantly promote the voltage and output power. The research is also helpful for the design and optimization of self-powered and high-performance micro/nano devices and systems. Full article

Controlling the balance between piezoelectric and flexoelectric effects is crucial for tailoring the electromechanical responses of a material. In twisted graphene, it is found that the electromechanical response near the domain walls (DWs) is dominated by either the flexoelectric effect as in twisted bilayer graphene (tBLG) or the piezoelectric effect as in twisted monolayer–bilayer graphene (tMBG). The codominance of both effects in a single system is rare. Here, utilizing lateral piezoresponse force microscopy (LPFM), we show that piezoelectric and flexoelectric effects can coexist and are equally important in twisted double bilayer graphene (tDBG), termed as the piezo-flexoelectric effect. Unlike tBLG and tMBG, distinctive two-step LPFM spatial profiles are captured across the moiré DWs of tDBG. By decomposing the LPFM signal into axisymmetric and antisymmetric components, we find that the angular dependence of both components satisfies sinusoidal relations. Quantitatively, the in-plane piezoelectric coefficient of DWs in tDBG is determined to be 0.15 pm/V by dual AC resonance tracking (DART) LPFM measurement. The conclusion is further supported by continuum mechanics simulations. Our results demonstrate that the stacking configuration serves as a powerful tuning knob for modulating the electromechanical responses of twisted van der Waals materials. Full article

The functionally graded (FG) flexoelectric material is a potential material to determine the structural morphing of aircrafts. This work proposes the penalty 20-node element based on the consistent couple stress theory for analyzing the FG flexoelectric plate and shell structures with complex geometric shapes and loading conditions. Several numerical examples are examined and prove that the new element can predict the size-dependent behaviors of FG flexoelectric plate and shell structures effectively, showing good convergence and robustness. Moreover, the numerical results reveal that FG flexoelectric material exhibits better bending performance and higher flexoelectric effect compared to homogeneous materials. Moreover, the increase in the material length scale parameter leads to a gradual increase in the natural frequencies of the out-of-plane modes of FG flexoelectric plate/shell, while the natural frequencies of the in-plane modes change minimally, resulting in the occurrence of mode-switching phenomena. Full article

In the present review, the merits and demerits of machine learning (ML) in materials science are discussed, compared with first principles calculations (PDE (partial differential equations) model) and physical or phenomenological ODE (ordinary differential equations) model calculations. ML is basically a fitting procedure of pre-existing (experimental) data as a function of various factors called descriptors. If excellent descriptors can be selected and the training data contain negligible error, the predictive power of a ML model is relatively high. However, it is currently very difficult for a ML model to predict experimental results beyond the parameter space of the training experimental data. For example, it is pointed out that all-dislocation-ceramics, which could be a new type of solid electrolyte filled with appropriate dislocations for high ionic conductivity without dendrite formation, could not be predicted by ML. The merits and demerits of first principles calculations and physical or phenomenological ODE model calculations are also discussed with some examples of the flexoelectric effect, dielectric constant, and ionic conductivity in solid electrolytes. Full article

In this work, we explored the potential of the ferroelectric gate of (Pb_0.92La_0.08)(Zr_0.30Ti_0.70)O₃ (PLZT(8/30/70)) for flexible graphene field effect transistor (GFET) devices. Based on the deep understanding of the V_Dirac of PLZT(8/30/70) gate GFET, which determines the application of the flexible GFET devices, the polarization mechanisms of PLZT(8/30/70) under bending deformation were analyzed. It was found that both flexoelectric polarization and piezoelectric polarization exist under bending deformation, and their polarization direction is opposite under the same bending deformation. Thus, a relatively stable of V_Dirac is obtained due to the combination of these two effects. In contrast to the relatively good linear movement of V_Dirac under bending deformation of relaxor ferroelectric (Pb_0.92La_0.08)(Zr_0.52Ti_0.48)O₃ (PLZT(8/52/48)) gated GFET, these stable properties of the PLZT(8/30/70) gate GFETs make them have great potential for applications in flexible devices. Full article

In this study, for the first time, free and forced vibrational responses of a unimorph nanobeam consisting of a functionally graded base, along with a dielectric layer of both piezoelectricity and flexoelectricity, is investigated based on paradox-free local/nonlocal elasticity. The formulation and boundary conditions are attained by utilizing the energy method Hamilton’s principle. In order to set a comparison, the formulation of a model in the framework of differential nonlocal is first presented. An effective implementation of the generalized differential quadrature method (GDQM) is then utilized to solve higher-order partial differential equations. This method can be utilized to solve the complex equations whose analytic results are quite difficult to obtain. Lastly, the impact of various parameters is studied to characterize the vibrational behavior of the system. Additionally, the major impact of flexoelectricity compared to piezoelectricity on a small scale is exhibited. The results show that small-scale flexoelectricity, rather than piezoelectricity, is dominant in electromechanical coupling. One of the results that can be mentioned is that the beams with higher nonlocality have the higher voltage and displacement under the same excitation amplitude. The findings can be helpful for further theoretical as well as experimental studies in which dielectric material is used in smart structures. Full article

Flexoelectric liquid crystalline membranes immersed in asymmetric viscoelastic media is a material system model with physiological applications such as outer hair cells (OHCs), where membrane oscillations generate bulk flow. Motivated by this physiological process, here we extend our previous work by characterizing the force transmission output of our model in addition to viscoelastic fluid flow, since solid–fluid interactions are an essential feature of confined physiological flow and flow in immersed elastic structures. In this work, the rigidity of the confinement results in a passive force reception, while more complete solid–fluid interactions will be considered in the future. A significant contribution of this work is a new asymmetry linear viscoelastic electro-rheological model and the obtained implicit relation between force transmission and flow generation and how this relation is modulated by electric field frequency and the material properties of the device. Maximal force and flow are found at resonant frequencies of asymmetry viscoelastic bulk phases, flexoelectric and dispersion mechanisms through the elastic and Womersley numbers. Full article

Lipid bilayers are supramolecular structures responsible for a range of processes, such as transmembrane transport of ions and solutes, and sorting and replication of genetic materials, to name just a few. Some of these processes are transient and currently, cannot be visualized in real space and time. Here, we developed an approach using 1D, 2D, and 3D Van Hove correlation functions to image collective headgroup dipole motions in zwitterionic phospholipid bilayers. We show that both 2D and 3D spatiotemporal images of headgroup dipoles are consistent with commonly understood dynamic features of fluids. However, analysis of the 1D Van Hove function reveals lateral transient and re-emergent collective dynamics of the headgroup dipoles—occurring at picosecond time scales—that transmit and dissipate heat at longer times, due to relaxation processes. At the same time, the headgroup dipoles also generate membrane surface undulations due a collective tilting of the headgroup dipoles. A continuous intensity band of headgroup dipole spatiotemporal correlations—at nanometer length and nanosecond time scales—indicates that dipoles undergo stretching and squeezing elastic deformations. Importantly, the above mentioned intrinsic headgroup dipole motions can be externally stimulated at GHz-frequency scale, enhancing their flexoelectric and piezoelectric capabilities (i.e., increased conversion efficiency of mechanical energy into electric energy). In conclusion, we discuss how lipid membranes can provide molecular-level insights about biological learning and memory, and as platforms for the development of the next generation of neuromorphic computers. Full article

The flexoelectric effect, which is sensitive to size, refers to the phenomenon of coupling between the strain gradient and electrical polarization and involves higher-order derivatives of physical quantities such as displacement, and the analytical process is complicated and difficult. Therefore, in this paper, a mixed finite element method is developed considering the effects of size effect and flexoelectric effect on the electromechanical coupling behavior of microscale flexoelectric materials. Based on the theoretical model of enthalpy density and the modified couple stress theory, the theoretical model and finite element model of microscale flexoelectric effect are established, and the Lagrange multiplier is used to coordinate the higher-order derivative relationship between the displacement field and its gradient, and the C¹ continuous quadrilateral 8-node (displacement and potential) and 4-node (displacement gradient and Lagrange multipliers) flexoelectric mixed element. By comparing the numerical calculation results and analytical solutions of the electrical output characteristics of the microscale BST/PDMS laminated cantilever structure, it is proved that the mixed finite element method designed in this paper is an effective tool for studying the electromechanical coupling behavior of flexoelectric materials. Full article

The flexoelectric effect, which exists in all dielectrics, is an electromechanical effect that arises due to the coupling of strain gradients (or electric field gradients) with electric polarization (or mechanical stress). Numerous experimental studies have demonstrated that ferroelectric materials possess a larger flexoelectric coefficient than other dielectric materials; thus, the flexoelectric response becomes significant. In this review, we will first summarize the measurement methods and magnitudes of the flexoelectric coefficients of ferroelectric materials. Theoretical studies of the flexoelectric coefficients of ferroelectric materials will be addressed in this review. The scaling effect, where the flexoelectric effect dramatically increases when reducing the material dimension, will also be discussed. Because of their large electromechanical response and scaling effect, ferroelectric materials offer vast potential for the application of the flexoelectric effect in various physical phenomena, including sensors, actuators, and transducers. Finally, this review will briefly discuss some perspectives on the flexoelectric effect and address some pressing questions that need to be considered to further develop this phenomenon. Full article

Flexoelectric polarization, which is caused by symmetry breaking in a distortion of material, was investigated in liquid crystalline elastomers composed of wedge-shaped mesogens prepared by cross-linking under horseshoe-shaped deformation. X-ray diffractometry suggested that splay distortion along the depth direction was induced in the pseudo-isotropic phase. While almost no electric charge was observed in the smectic A phase, an electric charge caused by polarization due to the flexoelectric effect appeared and reached −1367 pC/mm² in the pseudo-isotropic phase. We tentatively conclude that the macroscopic polarization due to the flexoelectric effect emerged and was fixed in the liquid crystalline elastomers by cross-linking under horseshoe-shaped deformation. Full article