Development of Self-Focusing Piezoelectric Composite Ultrasound Transducer Using Laser Engraving Technology

Based on the Fresnel half-wave band interference and laser engraving, a high-frequency self-focusing piezoelectric composite ultrasound transducer (FPCUT) is presented in this article. The theoretical analysis was performed based on the concept of constructive interference of acoustic waves and the electromechanical response of piezoelectric composites. The calculated and simulation results showed that the FPCUT combined the advantages of the composite transducer and the plate self-focusing transducer and can achieve high electromechanical coupling coefficient (>0.66), low acoustic impedance (~15 MRayl), high intensity, and short focal length. Furthermore, a 30-MHz self-focusing piezoelectric composite transducer prototype was fabricated and tested. It is composed of 11 lead zirconate titanates (PZTs) and ten epoxy annuluses. A UV engraving laser with a linewidth of 10 μm was used in each of the PZTs to form the annuluses, and the kerf among the annuluses was filled with epoxy. The measured center frequency, bandwidth, and focal length were 27 MHz, 50.37%, and 3.7 mm, respectively. A vertical wire phantom was imaged using a fabricated transducer and a contrast flat transducer; the images showed significant improvement in the lateral resolution over a range of 9 mm. Because this self-focusing piezoelectric composite transducer was based on the precise laser engraving systems, the fabrication process was accurate and controllable, which enabled it to have good potential for medical imaging and industrial nondestructive testing applications.