Lateral Resolution of a Broad-Band Dual-Element Ultrasonic Transducer

Abstract

In the pulsed ultrasonic Doppler blood flowmeter, two types of resolution are of importance; these are the range resolution and the lateral resolution. A random signal correlation type of a pulsed ultrasonic system has been developed recently. In this system broad-band noise is used as the transmitted signal. Since the range resolution and the bandwidth of the transmitted signal are inversely related to each other, an improvement in range resolution is thus achieved. The lateral resolution of the system depends upon the dimensions of the ultrasonic transducer face. This may be improved by focusing the ultrasonic beam with lenses. However, this technique increases the complexity of the system and is associated with the risk of generating acoustic intensities harmful to living tissues. To obviate these difficulties, a broad-band dual-element ultrasonic transducer was developed. This paper describes the dual-element transducer and presents experimental results comparing the lateral resolution of the dual-element transducer with the existing single-element transducer. A tenfold improvement in the lateral resolution in the nearfield was achieved, while a fivefold improvement was achieved in the farfield.