On the SH0 directivity of an array with flexible PZT transducers for beam steering control

Abstract Shear horizontal (SH) guided waves find numerous applications for continuous health monitoring in plate-like structures in contact with a liquid due to limited acoustic energy leaking. This research focuses on the fundamental SH0 mode for its practical advantages over the higher SH and Lamb wave modes. The acoustic transducers considered in this research are rectangular flexible PZT transducers that can be attached permanently to the plate even when there is slight waviness or surface curvature. A single transducer with these characteristics can produce a very complex acoustic field topology. To control directivity and beam focusing, the use of an array of flexible transducers is studied. The directivity was estimated using a proposed semi-analytical method, combining an exact formal solution and numerical source stress distributions obtained using the finite element method. The estimated directivity was validated with experimental tests and applied to detect a through-hole discontinuity in a thin aluminum plate. Results show that the directivity of the main lobe from the 2-MFC array exhibits a spatial filtering effect with angular and amplitude variations, improving focusing and enhancing sensitivity and resolution to discontinuities compared to a single transducer. Finally, the potential application of a linear array formed by 2-MFC subarrays to beam steering using beamforming theory is numerically investigated.