| 摘要 |
There is disclosed herein an ultrasonic system for detecting internal discontinuities in a body. The system includes: an ultrasonic transducer for directing sonic energy toward a body; a liquid crystal, acousto-optical detector cell for detecting ultrasonic energy passing through said body; an optical system for illuminating said liquid crystal cell; and a liquid medium for coupling the transducer body and cell. The acousto-optical cell includes a pair of substantially rigid covers, a liquid crystal material positioned between said covers and a peripheral spacer and sealing member surrounding said liquid crystal and sealingly engaging said covers. Each of the covers is substantially acoustically transparent and at least one of said covers is optically transparent. The optically transparent cover is a laminate having at least three layers, with each of said layers of said laminate having a thickness much much less than 1/4 of the wave length of the ultrasonic energy propagating through said layer. The other cover has at least one layer and the thickness of that layer is much much less than 1/4 of the wave length of the ultrasonic energy propagating therethrough. In this construction, it is essential that the acoustical impedence of the cell approximates the acoustical impedence of the coupling medium so as to minimize signal loss and image degradation. Furthermore, the liquid crystal material is usually of the nematic type and is homeotropically aligned.
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