Solid-liquid coupled vibration characteristics of piezoelectric hydroacoustic devices

This study investigated the vibration characteristics of piezoelectric bimorphs with regard to the solid-liquid coupling effect in piezoelectric-acoustical devices. Experimental measurements and finite element numerical calculations were used to determine the resonant frequencies and mode shapes of piezoelectric bimorphs, which could be used to promote the flow of air, water, and glycerin. Two piezoelectric devices were designed to verify the solid-liquid coupled vibrations of the piezoelectric bimorphs: (1) Type A with bimorph located above the surface of the fluid and (2) Type B with bimorph located within the fluid. The first type has a piezoelectric bimorph bonded to PDMS polymer, such that resonant vibrations produce changes in the volume of the chamber, which increases the flow of fluid. Another is a biomimetic design, in which a piezoelectric bimorph embedded in the chamber imitated the tail of a fish in order to promote the flow of liquid. Three experimental techniques were used to determine the solid-liquid coupled vibration characteristics. Electric speckle pattern interferometry (ESPI) was used to measure the resonant frequencies and mode shapes associated with the vibration of piezoelectric bimorphs interacting with fluids. Second, a laser Doppler vibrometer (LDV) was used to obtain the frequency spectrum of vibrating displacement using dynamic signal swept-sine analysis. The third experiment involved analyzing impedance in the piezoelectric bimorphs in order to identify the resonant frequencies and anti-resonant frequencies of the piezoelectric material under the influence of a fluid. Finite element method (FEM) was used for the analysis of vibration characteristics associated with the interaction between the fluids and piezoelectric-solid elements paired with (1) acoustic elements only or (2) acoustic elements and solid elements with viscoelastic properties. The numerical calculations of solid-acoustical coupled vibration are in good agreement with solid-liquid coupled experimentally results. The FEM solid elements with viscoelastic properties can be applied to predict the dynamic behaviors for lower frequency of the solid-acoustical coupled vibration. This study proposes an efficient methodology of the development of piezoelectric hydroacoustic devices by FEM, which has been verified by experimental measurements in this paper.