P5K-4 High-Overtone Self-Focusing Acoustic Transducer for High Frequency Ultrasonic Imaging

This paper reports the use of high-overtone self- focusing acoustic transducers for high frequency ultrasonic imaging application. For an acoustic transducers working for ultrasonic imaging, the resolution is primarily determined by the acoustic wavelength, which is normally proportional to the piezoelectric substrate thickness. Using a harmonic frequency of a bulk PZT with a novel Fresnel lens based on air-reflectors for a focused acoustic beam, we reduce the wavelength and obtain strong signals at the center frequencies of the 3rd (60 MHz) and 5th (100 MHz) harmonics for ultrasonic imaging. The bandwidth at -6 dB was over 20 %, even without a front matching layer.