Image Scanner Using Diode Switching

Abstract

A system is described for ultrasonic viewing of objects by flooding them with coherent CW ultrasound, focusing the scattered or reflected energy through a single sonic lens, and projecting this onto a rotating sonic mirror, which sweeps a sonic image across a linear transducer placed at the appropriate focal distance. The transducer is a single narrow crystal bearing on its rear face a vertical row of 64 small, closely-spaced electrodes, which are sampled in sequence for the piezoelectric voltage they are detecting. Conventional electronic circuitry is described for converting the electrode voltages into a video signal by way of diode switching. Horizontal spot motion on an oscilloscope is controlled by voltage derived from the scanning mirror position and vertical spot position relates to the particular electrode being sampled. A sonic mirror sweeping the image across the crystal in 15 sec and an electrode sampling rate of 20 000 samplings/sec is able to give 4000 picture elements or a picture of 64 lines where the horizontal and vertical resolutions are about equal. Mechanical and circuit diagrams of the system are shown and static video signals of two simple image conditions are illustrated. Critical comparisons are made between this and other systems for ultrasonic viewing, possible advantages and disadvantages of this system are mentioned, and practical and theoretical design problems are discussed.