Nondestructive tests liquid crystals

Fergason, J.L. Liquid crystals in nondestructive testing. Appl. Optics 7, 1729—1737 (1968)... 

Liquid crystals (LCs) are widely used In Informationprocessing devices, for optical visualization of physical Influences (heat, IR, high-frequency radiation, pressure, etc.), for nondestructive testing, and for thermography. 

In future, we may face certain nontraditional applications of liquid crystals, such as large area optically variable windows, nondestructive testing of solid surfaces, etc. We will briefly consider the main trends in the application of liquid crystals, and only reviews and the most important papers will be included in the References. 

Compared with scanning electron microscopy, which is conventionally referred to as nondestructive testing, the method of liquid crystal defectoscopy needs no sophisticated and expensive equipment. At the same time it is simple and fast, and requires no irradiation by an electronic beam which might lead to a charge accumulation and an increase in a leakage current in the devices being tested. 

The application of liquid crystals to thermography is widespread, and covers areas as diverse as infant bath and feed temperature indicators, medical screening and diagnostics, nondestructive testing, thermometers for fish tanks and refrigerators, battery testing, jewellery, advertising, aerodynamics research and art. Some specific applica-... 

Most applications rely on the steady state method as it is cheaper and less complex than transient measurements. A bibliography of nondestructive testing using thermo-chromic liquid crystals was published in 1972 [176], and more recently by Hallcrest [5], so only a few examples are described here. Indeed, in most cases the approach is the same, and only the test object differs. 

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