a complete frequency-selective filter constructed on a single piezoelectric crystal plate. A piezoelectric crystal is one in which a physical deformation or movement takes place when a voltage is applied to its surfaces. A series of six properly spaced platings (electrodes) on a single quartz crystal plate, for example, functions like a six-section filter. Thus a complete filter section can be contained on a single crystal plate without the use of coils. See also band-pass filter.