초록 ▼

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 structural member generate

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 structural member generate electric signals on the receiver film, which feed into a phase comparator. The other input of the phase comparator is the output signal of 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.

대표청구항 ▼

A piezoelectric phase-lock loop circuit comprising: (a) a structural member having a piezoelectric transmitter film and a piezoelectric receiver film adhered thereto, said transmitter film producing electro-mechanical vibrations in said structural member upon activation by an alternating current inp

A piezoelectric phase-lock loop circuit comprising: (a) a structural member having a piezoelectric transmitter film and a piezoelectric receiver film adhered thereto, said transmitter film producing electro-mechanical vibrations in said structural member upon activation by an alternating current input signal, said receiver film producing alternating output signals in response to vibration of said structural member; (b) voltage controlled oscillator means for generating said alternating input signal; (c) phase comparator means for comparing the phase angle of the signal produced by said receiver film with the phase angle of said alternating input signal and for outputting a signal corresponding to the differential in phase angle; (d) low pass filter means connected to the output of said phase comparator means for inputting a dc error signal corresponding to said phase differential to said voltage controlled oscillator means, said dc error signal forcing the frequency of said voltage controlled oscillator means to track said output signal whereby a predetermined phase relationship is maintained between said output and input signals.