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...http://www.google.com.au/patents/US4841256?utm_source=gb-gplus-sharePatent US4841256 - Piezoelectric phase locked loop circuit
