Theoretical and Experimental Studies on Sensitivity and Bandwidth of Thickness-Mode Driving Hydrophone Utilizing A 2-2 Piezoelectric Single Crystal Composite

Abstract

Piezoelectric composites, which consist of a piezoelectric material and a polymer, have been extensively studied for the applications of underwater sonar sensors and medical diagnostic ultrasonic transducers. Acoustic sensors utilizing piezoelectric composites can have a high sensitivity and wide bandwidth because of their high piezoelectric coefficient and low acoustic impedance compared to single-phase piezoelectric materials. In this study, a thickness-mode driving hydrophone utilizing a 2-2 piezoelectric single crystal composite was examined. From the theoretical and numerical analysis, material properties that determine the bandwidth and sensitivity of the thickness-mode piezoelectric plate were derived, and the voltage sensitivity of piezoelectric plates with various configurations was compared. It was shown that the 2-2 composite with [011] poled single crystals and epoxy polymers can provide high sensitivity and wide bandwidth when used for hydrophones with a thickness resonance mode. The hydrophone element was designed and fabricated to have a thickness mode at a frequency around 220 kHz by attaching a composite plate of quarter-wavelength thickness to a hard baffle. The fabricated hydrophone demonstrated an open circuit voltage sensitivity of more than −180 dB re 1 V/μPa at the resonance frequency and a −3 dB bandwidth of more than 55 kHz. The theoretical and experimental studies show that the 2-2 single crystal composite can have a high sensitivity and wide bandwidth compared to other configurations of piezoelectric elements when they are used for thickness-mode hydrophones.

Two orientation effects and large anisotropy of parameters in piezo-active 2–1–2 composites based on [0 1 1]-poled crystals

“…The second ferroelectric component of the 2-1-2 composite can be described as a system of parallel long ceramic rods with remanent polarisation P (2) r || OX 3 . These rods in the shape of an elliptic cylinder are arranged periodically in a large polymer matrix (see inset 2 in figure 1), and therefore layer II can be described as a piezo-active 1-3 composite due to the continuous distribution of each rod along the OX 3 axis.…”

“…In accordance with the 2-1-2 connectivity notation, the SC, ceramic and polymer components of the composite shown in figure 1 are continuously distributed along two, one and two coordinate axes, respectively. The parallel orientation of the polarisation vectors P (1) s ∥P (2) r ∥ OX 3 and interfaces x 1 = const (where 'const' means constant) (see figure 1) favours an effective poling of the composite sample as a whole.…”

“…Advanced composites based on ferroelectric domainengineered single crystals (SCs) with important physical properties are of significant interest not only in an academic sense but also in a variety of transducer applications. Numerous two-component piezo-active SC-based composites, which were manufactured and studied recently, are characterised by either 2-2 [1][2][3] or 1-3 [4][5][6][7][8][9][10][11] connectivity written in terms of [12]. The connectivity indices such as 2-2 or 1-3 indicate [12,13] the number of axes of a rectangular coordinate system along which the first and second components of the composite are continuously distributed, respectively.…”

“…These 2-2 and 1-3 composites based on domain-engineered SCs exhibit a high piezoelectric performance that leads to large electromechanical coupling factors (ECFs) and figures of merit (FOMs). The aforementioned and other parameters enable one to use 2-2 composites, for instance, in hydrophone [2] and acoustic transducer [3] applications. The 1-3 composites studied recently are effective in various transducer [6,7,10,11] and energy-harvesting [9] applications, as elements of medical [4] and bio-electronic [9] devices.…”

“…As distinct from the piezo-active composites studied in [15][16][17][18][19][20][21], a 2-2 composite based on a domain-engineered SC poled along a specific crystallographic direction [22] is an active element of a thickness-mode driving hydrophone, and the performance of this SC-based composite was studied within the framework of theoretical and numerical methods. An important result of [2] is that the 2-2 SC/polymer composite provides a higher sensitivity and wider bandwidth in the case of the SC component poled along the [0 1 1] direction.…”