Transducer for multicolor distinction with ECB mode liquid crystal cell

A small transducer for distinguishing color with high spectral selectivity is proposed. It consists of an Si p-n junction photodiode and a filter consisting of an electrically controlled birefringence (ECB) mode liquid-crystal cell mounted on the photodiode. Since the spectral transmittance of the filter can be electronically tuned by regulating the applied voltage across the liquid-crystal cell, a filter having continuously different spectral response with time can be realized. The filter can accurately distinguish colors by observing the photodiode output at increasing or decreasing voltage across the liquid-crystal cell. Eight kinds of colored paper are discerned by the transducer