Berns'alternative system, which he calls multispectral imaging, currently involves taking 30 photographs of a painting through a special liquid crystal filter that is repeatedly adjusted to allow different frequencies of light through.
12.
The most common use of crystal filters are at frequencies of 9 MHz or 10.7 MHz to provide selectivity in communications receivers, or at higher frequencies as a roofing filter in receivers using up-conversion.
13.
Cady held more than 50 patents, and was the inventor of the crystal-controlled oscillator, the highly selective narrow-band crystal filter, one of the principal theorists of the ferroelectricity in crystals, and a historian of the science of piezoelectric crystals.
