Ultrasonic Image Converter

(also, electronic acoustical converter), a device for converting acoustic signals into electric signals.

An ultrasonic image converter is an electron-beam device with a screen that consists of a perforated metal disk, the holes of which are sealed with fine wires that are enclosed in glass so as to be insulated from the disk. The polished, inner side of the disk is coated with a dielectric that has a high secondary-emission ratio. On the other side of the disk, the wires are electrically connected to elements of an array made of a piezoelectric material.

When an acoustic wave acts on the array elements, electric potentials are transmitted along the wires to the inner side of the disk, and the charge pattern on the dielectric then corresponds to the amplitude distribution of the sound pressure in the plane of the array. An electron beam that systematically scans each portion of the screen (as in a television camera tube) “reads” the electron image of the acoustic field and converts it into a train of electric signals.

In addition to their use as high-speed electronic commutators, ultrasonic image converters are employed in ultrasonic flaw detectors, underwater acousto-optical imaging equipment, and medical diagnostic instruments.