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Abstract

An embodiment of the electrostatic image sensor comprises essentially two electrodes, one layer of photoconductive material and one dielectric layer comprising an electret designed to polarize the photoconductive layer without requiring a voltage source during the recording of an image. During a recording stage, a change-over switch short-circuits the electrodes. Photocarriers are released by the X-rays that have crossed an object to be radiographed. The said photocarriers move in the electrical field created by the electret and tend to cancel the electrical field at the interface between the two layers. During a reading stage, the change-over switch connects the electrodes to the inputs of a current amplifer while a light beam scans the layer of photoconductive material. The photocarriers move and completely cancel the electrical field at every point of the interface between the two layers. The current detected by the amplifier makes it possible to display an image on a cathode ray tube. During an initialization stage, the layer of photoconductive material is brought to the neutral state by means of a direct voltage generator connected to the electrodes by the change-over switch.

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First Claim