Abstract
The propagation of the fundamental symmetric Lamb mode S0 along wz-BN/AlN thin composite plates suitable for telecommunication and sensing applications is studied. The investigation of the acoustic field profile across the plate thickness revealed the presence of modes having longitudinal polarization, the Anisimkin Jr. plate modes (AMs), travelling at a phase velocity close to that of the wz-BN longitudinal bulk acoustic wave propagating in the same direction. The study of the S0 mode phase velocity and coupling coefficient (K2) dispersion curves, for different electrical boundary conditions, has shown that eight different coupling configurations are allowable that exhibit a K2 as high as about 4% and very high phase velocity (up to about 16,700 m/s). The effect of the thickness and material type of the metal floating electrode on the K2 dispersion curves has also been investigated, specifically addressing the design of an enhanced coupling device. The gravimetric sensitivity of the BN/AlN-based acoustic waveguides was then calculated for both the AMs and elliptically polarized S0 modes; the AM-based sensor velocity and attenuation shifts due to the viscosity of a surrounding liquid was theoretically predicted. The performed investigation suggests that wz-BN/AlN is a very promising substrate material suitable for developing GHz band devices with enhanced electroacoustic coupling efficiency and suitable for application in telecommunications and sensing fields.
Highlights
Electroacoustic devices based on the propagation of surface and bulk acoustic waves (SAW and BAW) are known for their wide range of applications in chemical, biological and physical sensing fields
The present paper investigates the acoustic wave propagation along wz-Boron nitride (BN)/AlN thin composite plates that are suitable for the development of high-frequency electroacoustic devices for telecommunications and sensing applications [10]
We report on the observation of very high velocity guided modes along thin BN/AlN composite plates, which exist when the plate thickness is about an order of magnitude smaller than the wavelength, while maintaining the electromechanical coupling coefficient of the piezoelectric AlN
Summary
Electroacoustic devices based on the propagation of surface and bulk acoustic waves (SAW and BAW) are known for their wide range of applications in chemical, biological and physical sensing fields. The fundamental symmetric Lamb mode, S0, as well as the higher order symmetrical and antisymmetrical modes are elliptically polarized and have a velocity higher than that of the surrounding liquid medium, and they are not suitable for sensing applications in liquids, except for some special cases These cases include the linearly-polarized modes, such as the longitudinally-polarized Anisimkin Jr. modes (AMs), with a dominant longitudinal displacement component U1 with a constant amplitude along the whole depth of the plate, the shear components, U2 and U3, being at least 10-times less than U1 at any plate depth. The present paper investigates the acoustic wave propagation along wz-BN/AlN thin composite plates that are suitable for the development of high-frequency electroacoustic devices for telecommunications and sensing applications [10]
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