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Based on the Fresnel half-wave band interference, a micromachined self-focusing piezoelectric composite ultrasound transducer was proposed in this paper. The theoretical analysis was deduced based on the concept of constructive interference of acoustic waves and electromechanical response of piezoelectric composites. The calculated and simulation results showed that it combined the advantages of composite transducer and plate self-focusing transducer, and can achieve high electromechanical coupling coefficient, low acoustic impedance, high intensity, short focal length and micro size. Because it was based on the micro-electromechanical systems, the fabrication process was accurate and controllable, which made it have good potential for interventional ultrasound imaging, cellular microstructure imaging, skin cancer detection and industrial nondestructive testing applications.

Usually focused transducers have acoustical lens or large concave surface in order to generate focused high intensity ultrasound beam. Therefore these traditional focusing transducers are commonly large in size and long in focal length, which are not suitable for interventional ultrasound imaging or therapy. For solving this problem, in this paper, a micro machined self-focusing piezoelectric composite ultrasonic transducer was designed and evaluated. The theoretical analysis was deduced based on the electromechanical response of piezoelectric composites and theory of Fresnel half-wave bandinterference. This self-focusing transducer has many advantages, including micro size, short focal length, low acoustic impedance, high electromechanical coupling coefficient. Besides these, because it was based on micro-electromechanical systems, the fabrication process precision is high and reliable. These results hold good potential for interventional ultrasound therapy or imaging applications.