GB1408683A - Device for converting an acoustic pattern into a visual image - Google Patents

Abstract

1408683 Acoustic-to-visual image converters BENDIX-CORP 22 Nov 1973 [12 Dec 1972] 54209/73 Heading H4D [Also in Division H1] An acoustic-to-visual image converter includes a piezo-electric transducer for acoustic intensity-to-electric charge pattern conversion, a photo-cathode associated with the transducer, a monochromatic radiation source irradiating the photo-cathode and having a wavelength to bias the photo-cathode electrons at an energy level such that the electron current they provide is modulated by the electric charge pattern and has at any point a time-averaged value which depends on the acoustic intensity there, and means for converting the electron current to a visual image. In the Fig. 1 embodiment a quartz plate 1 receives an acoustic image and generates a charge pattern which modulates an electron current distribution produced by illuminating photo-cathode 3 (which may be, e.g., caesium iodide, caesium telluride, bi-alkali, tri-alkali, S-1, S-20, or S-25). The illuminating wavelength (200-800 nm) is chosen such that it corresponds to a non-linear part of the sensitivity versus wavelength graph (Fig. 2) for the photocathode material, whereby at any point on the photo-cathode the mean electron current I<SP>1</SP> depends on the local acoustic intensity. The modulated current is fed via a channel-plate electron multiplier 7 to a phosphor screen 9 on a fibre-optic substrate to form the visual image. Voltages at the photo-cathode, channel-plate input, channel-plate output and phosphor screen are typically 0, 300, 1300, 6300 v. respectively. The channel-plate is omitted in a second embodiment. The image converter may be packaged in an evacuated envelope.