It is shown that, for a plane bulk acoustic wave propagating in arbitrary piezoelectric media, the densities of mechanoelectrical and electromechanical energies are always equal in absolute value and have opposite signs. However, in general, the mechanoelectrical and electromechanical power flows of such a wave calculated by the traditional expression for the Poynting vector do not compensate each other, although the total density of these energies is always equal to zero. A discovered discrepancy based on the dissymmetry of piezoelectric constants with respect to the electrical and mechanical indexes may cause difficulties for calculation of important parameters for practical applications such as energy transport velocity of acoustic waves in piezoelectric materials.

The energy density and power flow of acoustic waves propagating in piezoelectric materials

This paper investigates the effect of acoustic wave propagation direction along the a-direction (〈11−20〉) and m-direction (〈1−100〉) on the frequency responses of c-plane AlN based surface acoustic wave (SAW) devices systematically. The experimental results indicate that the resonant frequency (), quality factor (Q), electromechanical coupling coefficient (), insertion loss and out-of-band rejection can be improved for the a-direction compared with the m-direction of an AlN based SAW resonator on sapphire. The Q is 1347 for a one-port SAW resonator along the a-direction, and the minimum insertion loss is 8.71 dB for a two-port SAW resonator along the a-direction. The insertion loss is 3.23 dB lower for the a-direction compared to the m-direction of the AlN film, which may be attributed to the larger acoustic power flow density. The is 45% higher for the a-direction compared to the m-direction of the AlN film, which may be attributed to the larger elastic constant. In addition, our finite element model simulation results reveal the C 11 and C 44 for the m-direction are 345 GPa and 102 GPa, while C 11 and C 44 for the a-direction is increased to 429 GPa and 128 GPa, respectively. Our work demonstrates that the a-direction is better than the m-direction of the AlN film for high performance SAW device applications.

https://iopscience.iop.org/article/10.1088/1361-6463/ab0bf6/pdf

Enhanced performance of AlN SAW devices with wave propagation along the 〈11-20〉 direction on c-plane sapphire substrate

This paper is devoted to detailed theoretical investigation of energy density and power flow of homogeneous (bulk) and inhomogeneous (surface and plate) plane acoustic waves in piezoelectric materials and structures. The analysis of these waves in different materials of various crystallographic orientations allowed us to establish some energy regularities. These regularities are the same for instantaneous energy characteristics of homogeneous waves and for time-average energy characteristics on unit of aperture of inhomogeneous waves if the electrical energy and power flow in vacuum are taken into account. It has been shown that, for strong piezoactive waves, the electric energy density may exceed the mechanical energy density more than three times

The peculiarities of energy characteristics of acoustic waves in piezoelectric materials and structures

A numerical method for the analysis of thickness modes in piezoelectric plates with full account of the electromechanical coupling is presented. Numerical data for the main electroacoustical characteristics of some highly efficient piezoelectric crystals are given. Some inconsistencies with the available theoretical models are discussed.

A numerical data analysis of thickness modes in arbitrary coupling piezoelectric plates

Surface Acoustic Wave Energy in Piezoelectric Material

Acoustic power flow in a LiNbO3 single crystal was calculated to find the optimal crystal cutting orientation and the wave propagation direction for the efficient excitation of acoustic waves in the crystal. By solving the stiffened Christoffel equations and calculating the acoustic Poynting vectors with piezoelectric effect included, maximum longitudinal acoustic power flow in a 30° Z‐rotated, Y‐cut LiNbO3 crystal was found.

F. C. Fu

Papers

Optimal crystal cuts and propagation directions for excitation of acoustic waves in LiNbO3