Electronic Warning System Based on Surface Acoustic Wave Vibration Sensors

In the paper feasibility analysis of the surface acoustic wave based electronic warning system was presented. As a transducer in the system the surface acoustic wave delay line was proposed. It is fabricated in standard single mask process as a pair of interdigital transducers placed on the top of piezoelectric crystal substrate. Transducer is a plate with rectangular cross-section and it converts all environmental vibration to electric signal. From electronic point of view it was considered as a two-port network. Necessary condition for proper sensor operation is that the input signal frequency from external generator should be close to central frequency of delay line. Principle of operation of the sensor is that the measured phase shift of high frequency signal has frequency equal resonant frequency of vibrating plate and its amplitude is proportional to vibration amplitude of transducer. The environmental vibrations are defined by amplitude of the output signal and the threat location is pointed by resonant frequency of excited transducer. The described above principles of sensor operation allow us designing electronic warning system consisting of many sensors with different resonant frequencies of transducers. Output signals from precisely located sensors contain all necessary information about the whole warning system. This information is easy to transmit and detect by simple electronic circuits based on phase detector and proper data acquisition system, for which necessary conditions are presented.