Electronic Imaging of Ultrasonic Fields

Abstract

An ultrasonic image-converter system is described which provides two-dimensional visual images of incident-sound fields. The system is based on an electronically operated image-converter tube, similar to a television-camera tube, except that the photosensitive surface is replaced by a slab of piezoelectric x-cut quartz. The spatial distribution of sound pressure produces a similar distribution of piezoelectric potential at the ungrounded quartz surface which is scanned by a 500-v electron beam. The output of the converter, dependent upon secondary emission from the quartz, is used to generate a cathode-ray tube display of the sound field. Constructional details of the continuously pumped converter tube are described, including electrode configurations, crystal bonding, and vacuum techniques. With the water-immersed converter face irradiated by a pulsed 7-Mc/sec collimated sound beam directed normally to the face, a 12-mm-diam metallic wire intercepting the sound beam is easily discernable on the cathode-ray tube display. Laminar-type defects measuring 0.75 mm diam and 0.01 mm thick, simulated in a steel plate and oriented normal to the sound beam, are resolved by suitable electronic processing of the converter output pulses. Applications to flaw detection and medical diagnostics are discussed.

Acoustical Holography

“…Television methods for detecting ultrasound images have been described by several investigators (4,5,9,21,26,(74)(75)(76)(77). Television camera tube systems have been shown to provide a linear response e 1) over a wide range of ultrasonic intensities (3 x 10-9 to 3 X 10-3 W/cm 2 ), and a threshold sensitivity e) as low as 2 x 10-11 W /cm 2 has been discussed.…”