Fluid damping models are developed for resonant (standing wave) flexural plate wave (FPW) devices, which are rectangular plates or diaphragms with structural layers, a piezoelectric layer, and interdigitated conducting combs for driving and sensing. This configuration is often used in micromechanical chemical, biological, or nonvolatile residue sensors. Where much of the previous work on fluid effects in FPW devices focused on delay lines, this effort investigates resonant devices both analytically and experimentally. The fluid model is based on closed-form solution of a wide beam vibrating into a semi-infinite fluid volume and is mated directly into the beam equation. While the fluid's pressure versus wave motion solution has been reported previously, the application to the resonant FPW is mathematically rigorous and leads to a greater understanding of the FPW damping regimes. Frequency responses of FPW devices constructed from silicon with deposited piezoelectric aluminum nitride and operating in water and alcohol compared well with analytic results with some discrepancies noted.

Fluid damping in resonant flexural plate wave device

This paper presents an approximate analysis for predicting the generation of elastic waves in multi-layered piezoelectric materials, when these waves are generated using interdigital transducers (IDTs). Each IDT finger is assumed to act as a source of plane (partial) waves propagating in all directions, and the condition for efficient wave generation is taken to be when the waves from adjacent pairs add in phase. The width of the IDT fingers is not explicitly taken into account and neither are the finite dimensions of the IDT. The conditions for surface or guided wave propagation between IDT transmit and receive pairs are then determined by satisfying the boundary conditions on the surfaces and at the interfaces of the substrate, using the partial waves already determined. The outer surfaces of the substrate may be either metallized or free. The model thus predicts discrete frequencies of operation of IDT devices, corresponding to the generation of surface or guided waves. No `width' is attached to these frequencies, because of the neglect of IDT finger width and of overall IDT dimensions. Wave profiles within the piezoelectric substrate are calculated by summation of the partial waves, to depict the depth-dependence of the mechanical displacement, electric potential and energy flow. This information is used to distinguish surface waves from guided waves and to show the depth of penetration of the surface waves. The paper is essentially divided into three parts. The model formulation is presented, computational methods and associated difficulties are discussed, and sample model predictions for Rayleigh and SH wave devices in ST cut quartz are compared with experiment, showing good agreement.

An approximate analysis of waves in layered piezoelectric plates from an interdigital source transducer

In this research we report theoretical model and experimental measurements for the leaky Lamb wave propagation behaviors in a X-cut lithium niobate immersed in a conductive fluid. Starting with wave equations, a partial wave analysis procedure is taken for the modeling of plane wave reflection coefficient, which characterizes the dispersion relation of piezoelectric plate immersed in a dielectric fluid. Fluid conductivity is modeled by modeling the fluid as lossy dielectric media. Bulk wave ultrasonic transducers with V-shape arrangement are used in this particular experiment, running in pitch-catch manor. Close comparison with fairly well agreement between theory and measurements is obtained.

https://ieeexplore.ieee.org/iel5/6171/16493/00762177.pdf

Guided waves propagating in a piezoelectric plate immersed in a conductive fluid

This study employs a theoretical modeling and an experimental measurement for investigating the dispersion behavior of guided waves propagating in a bi-layer system consisting of a piezoelectric plate and a dielectric fluid layer. The theoretical model is based on a recursive asymptotic stiffness matrix method (RASM) with the fluid layer modeled as an equivalent elastic body. A laser ultrasound technique is used to measure the dispersion relations of the bi-layer system. Behaviors of mode couplings between guided modes propagating in the piezoelectric plate and those in fluid layer are characterized in the modeling and measurements. Dispersion behaviors of guided modes propagating in the bi-layer system are discussed for varying fluid thicknesses. For all of the investigated cases, the theoretical modeled dispersion spectra agree well with the measurements.

Guided waves propagating in a bi-layer system consisting of a piezoelectric plate and a dielectric fluid layer

Double-layer PVDF transducer and V(z) measurement system for measuring leaky Lamb waves in a piezoelectric plate

Detailed ultrasonic reflection measurements in piezoelectric LiNbO3 are reported which are compared to the results of the theoretical analysis of the previous paper, part I. Differences in mode coupling and behavior are illustrated in several calculated examples. The calculated numerical results are demonstrated in a full image format. It is shown how dielectric fluid loading influences the reflection behavior and how strong piezoelectric coupling can lead to unexpected dispersion in the fundamental symmetric mode. The data confirms in each case the predictions of an exact partial‐wave analysis of the problem, including the dielectric influence of the fluid. These phenomena play a role in the design and performance of piezoelectric sensing devices.

D. E. Chimenti

Papers

Guided plate waves in piezoelectrics immersed in a dielectric fluid. II. Experiments