Pb(In_1/2Nb_1/2)O₃–Pb(Mg_1/3Nb_2/3)O₃–PbTiO₃ piezoelectric single-crystal rectangular beams: Mode-coupling effect and its application to ultrasonic array transducers

Pb(In_1/2Nb_1/2)O₃–Pb(Mg_1/3Nb_2/3)O₃–PbTiO₃ (PIN–PMN–PT) piezoelectric single-crystal rectangular beams with the PIN:PMN:PT ratio of 0.33:0.35:0.32 are prepared, and their mode-coupling effect is investigated both theoretically and experimentally for ultrasonic array transducer applications. The PIN–PMN–PT rectangular beams become a tall-narrow beam and a short-wide plate, and so exhibiting an uncoupled height-extensional (beam) mode and an uncoupled thickness-extensional (plate) mode, at a width-to-height ratio G (= L/H) of <0.7 and >6.0, respectively. With G varying in the range of 1.6 to 3.1, the beam mode not only couples strongly with the width (lateral) mode, but also coexists obviously with the plate mode, giving high electromechanical coupling coefficients k’₃₃ and k_t of ~0.75 and ~0.50, respectively. With the guide of the mode-coupling results, a multifrequency ultrasonic array transducer having three distinct operational frequencies of 1.52, 2.60, and 6.01 MHz, corresponding to the coupled/coexistent beam mode, lateral mode, and plate mode, respectively, is developed using a mode-coupled rectangular beam of G = 1.6. Two different single-frequency ultrasonic array transducers, fabricated using two different uncoupled rectangular beams, one operating in uncoupled beam mode with G = 0.6 at 2.24 MHz and one working in uncoupled plate mode with G = 10.0 at 5.75 MHz, are also developed for comparison.