Design of 20 MHz wideband piezoelectric transducers for close proximity imaging

Quarter wave matching of ultrasonic transducers with two layers (glass and parylene) were studied with computer simulation. These layers are located between the piezoelectric transducer and the acoustic load. The purpose is to achieve a short impulse response and high efficiency broadband transfer in a practical manner for high frequency transducers. The acoustic impedances of these layers were chosen based on transmission line theory. A method to measure acoustic properties of the matching layers and a method to choose the material are discussed. The advantages in using a quarter wavelength of glass and parylene as the matching layers are given. The 6 dB fractional bandwidth of the simulated transmission-reception transfer was found to be 0.75, which is a factor of at least 6 improvement over a nonmatched transducer.