Abstract
A BRIEF outline of the history of the crystal filter has been publishad by J. E. Bsnson (A.W.A. Tech, Rev., 5, 191; 1941). The earliest application of piezo-electric crystals to frequency - selective circuits appears to have been made in 1920 by W. G. Cady, whose patent describes the behaviour of piezoelectric elements near resonance and their consequent use in the selection and measurement of high frequencies. L. Ezpenschied (Jan. 3, 1927) described the quartz-crystal band-pass filter having recurrent sections. This was followed by W. A. Marrison's patent (June 7, 1927) for a balanced crystal-gate filter designed for sharp response at a single frequency. In the same year, C. W. Hansell developed a similar bridge-balanced system, in which the parallel capacity of the crystal was balanced out of an equal capacity supplied from the input circuit in opposite phase to the crystal. Single-frequency rejection filters of the T -section type having a piezo-electric element in the shunt arm were described at about the same time by I. F. Byrnes. J. Robinson's stenode radiostat using a balanced crystal-filter circuit appeared in 1929.
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Piezo-Electro Crystal Filters. Nature 149, 20 (1942). https://doi.org/10.1038/149020a0
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DOI: https://doi.org/10.1038/149020a0