A review on piezoelectric transformer structural modeling is presented. The operating principle and the basic behavior of piezoelectric transformers as governed by the linear theory of piezoelectricity are shown by a simple, theoretical analysis on a Rosen transformer based on extensional modes of a nonhomogeneous ceramic rod. Various transformers are classified according to their structural shapes, operating modes, and voltage transforming capability. Theoretical and numerical modeling results from the theory of piezoelectricity are reviewed. More advances modeling on thermal and nonlinear effects also are discussed. The article contains 167 references.

A Cu₄I₄–MOF-based mixed matrix membrane which can be a highly sensitive and selective naked-eye sensor for gaseous HCl is reported.

We analyze coupled flexural vibration of two elastically and electrically connected piezoelectric beams near resonance for converting mechanical vibration energy to electrical energy. Each beam is a so-called piezoelectric bimorph with two layers of piezoelectrics. The 1D equations for bending of piezoelectric beams are used for a theoretical analysis. An exact analytical solution to the beam equations is obtained. Numerical results based on the solution show that the two resonances of individual beams can be tuned as close as desired by design when they are connected to yield a wide-band electrical output. Therefore, the structure can be used as a wide-band piezoelectric power harvester.

We study extensional vibrations of a ZnO piezoelectric semiconductor fiber driven by a time-harmonic end force. A theoretical analysis is performed using a one-dimensional model based on the phenomenological theory of piezoelectric semiconductors consisting of the equations of piezoelectricity coupled to the continuity equation of electrons. A series of resonance frequencies are identified. It is found that these frequencies are lower than those of the corresponding piezoelectric dielectric fiber because the mobile charges in the semiconductor screen the effective polarization charges and thus weaken the piezoelectric stiffening effect. Various electromechanical fields at resonances are calculated and examined. Numerical results show that the effective surface polarization charge plays a more dominant role than the effective body polarization charge. The mobile charges can screen the body polarization charges greatly, but not the surface polarization charges.

We study the extension of a composite fiber of piezoelectric dielectrics and nonpiezoelectric semiconductors. A theoretical analysis is performed using a one-dimensional model. It is shown that mechanical loads cause redistribution of mobile charges in such a composite fiber. Thus, the composite fiber exhibits piezotronic couplings like a homogeneous piezoelectric semiconducting fiber. The couplings are a product property of the composite, enabling the design of piezotronics devices beyond materials with direct piezotronics couplings. The basic behavior of the composite fiber and the effects of various parameters on piezotronic couplings are calculated and examined. It is observed that piezotronic couplings in these fibers are sensitive to material and geometric parameters and can be optimized through design.

We present a theoretical study on the equilibrium state of a PN junction, which is created by two piezoelectric semiconductor half spaces doped oppositely, based on the equations of linear piezoelectricity and the conservation of charge for holes and electrons. The nonlinearity associated with the drift currents of electrons and holes, which appears as products of the unknown carrier concentrations and the unknown electric field, is linearized for small carrier concentration perturbations. An analytical solution is rigorously derived, which is able to show the shaping of the PN junction near the interface. The electromechanical fields and concentrations of electrons and holes near the interface of the PN junction, and the forward-bias current-voltage characteristics of the PN junction under different applied stresses, are calculated and discussed. The effects of a few physical parameters on the properties of the PN junction are investigated as well.