Underwater Ultrasonic Wave Transducer Using Chirped Interdigital Electrodes and Application to Acoustic Images

Abstract

A new acoustic transducer with electronic focusing and scanning capabilities is presented. An interdigital transducer radiates acoustic waves in oblique directons with respect to the substrate surface when it is placed in water. A linear chirped interdigital transducer for the acoustic beam scanning was constructed on piezoelectric substrate. The chirped interdigital transducers consist of interdigital electrodes whose period and width are linearly changed. Moreover, the electrode is divided into several sections, each of which is placed to form a one dimensional Fresnel phase plate. In this structure, the focused acoustic beam scanning was achieved by changing the applied frequency. Experimental verification has been carried out using a chirped Fresnel phase plate type interdigital transducer which covers the frequency from 20 to 50MHz. A scan length of 9mm for a focused acoustic beam about 0.3mm in width has been obtained.