Katsuhiro Wakabayashi

Fabrication of Ultrasonic Transducers with KNbO3 Piezoelectric Single Crystal for Detecting Harmonic Signals

An ultrasonic transducer with a circular aperture has been designed and fabricated for the development of a harmonic imaging system with high sensitivity. The transducer consists of two piezoelectric elements; one is made from Pb(Zr, Ti)O3 (PZT) ceramics for transmitting a finite-amplitude ultrasonic pulse, and the other is made from a KNbO3 (KN) piezoelectric single crystal for receiving second harmonic signals generated in a nonlinear medium. They are arranged coaxially. Using this transducer, acoustic characteristics were measured and the observation of sponge phantom images was performed. Compared with other transducers with PZT and PbTiO3 (PT) ceramics, we have confirmed that higher sensitivity and stronger correlation between the sensitivity and figure-of-merit can be obtained. Additionally, the third harmonic detection has been demonstrated.

Improvement of Spatial Resolution for Third Harmonic Detection using a Separately Arranged Transmitting/Receiving Ultrasonic Transducer

The aim of the present study is to demonstrate, experimentally, the feasibility of third-harmonic imaging with high quality. In order for the third-harmonic detection to be effective, a new ultrasonic transducer system for high spatial resolution, which consists of a separately arranged transmitting/receiving ultrasonic transducer (SATRUT) and a simple filter with a capacitor and a inductor, has been proposed. The observation of pulse echo spectra from a ball target, back-scattered images of it, and B-mode images of a sponge phantom have confirmed the improvement of the spatial resolution in the images visually which is testified quantitatively using an auto-correlation method.