PIEZOELECTRIC PHASE LOCKED LOOP CIRCUIT

摘要

PIEZOELECTRIC PHASE LOCKED LOOP CIRCUIT A structural member having a piezoelectric transmitter film and a piezoelectric receiver film adhered thereto. The transmitter film produces a vibration upon activation by a voltage controlled oscillator which forms part of a phase-lock loop circuit. The vibrations of the rigid member generate electric signals on a second receiver film, which feed into a phase comparator. The other input of the phase comparator is the voltage controlled oscillator. The phase comparator will output a dc signal proportional to the difference in phase between the two signals. When the structural member becomes damped the phase comparator will go into saturation, thereby producing a voltage which can activate an alarm signal or other device.