| 摘要 |
An ultrasonic imaging system for use in non-destructively testing objects, includes a source (10) of ultrasonic energy, a liquid crystal detector cell (16) and an optical viewing system (20, 22, 24). The cell includes a pair of acoustically transmissive covers (32, 34) which encase a nematic liquid crystal material (30). The material exhibits an acoustic-optic effect, and in particular, exhibits birefringence in response to ultrasonic energy. The cell construction, geometry, and material are acoustically matched to the frequencies of the isonifying ultrasonic transducer so as to optimize the performance of the cell. The covers are substantially acoustically transparent to ultrasonic energy incident on the cover at both normal and oblique attitudes. The acoustic impedance of the covers match as closely as possible to that of the coupling medium. The average alignment of the liquid crystal molecules, as indicated by the director, is selectively aligned to be oblique to the ultrasonic beam and by reason thereof the cell exhibits high sensitivity and high image resolution in the "non-streaming" region. Electric field enhancement may be used to cooperate in aligning the liquid crystal molecules and to enhance the resolution and sensitivity of the image. |
