A Compact and Highly Sensitive Voice-Eavesdropping Microresonator

Abstract

A compact cantilever-based voice-eavesdropping microresonator is proposed. The dynamic vibration of the cantilever-microresonator system induced by an applied acoustic pressure is converted into a modulation of the cavity resonances. Then, the resonance-shift-induced optical transmission change is utilized to detect the applied acoustic signals. The enhancement of both the vibration and optical response makes the proposed system highly sensitive and have better performance than many other optical acoustic sensors. The noise equivalent pressure of the proposed system at 900 Hz is 52 μPa/Hz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/2</sup> . The system has a favorable broad frequency response range covering 0∼6 kHz. Experimental results prove that the system can acquire and reconstruct a voice signal 7 m away with high sensitivity and reliability, which can meet a variety of needs, such as indoor eavesdropping. Furthermore, the system is easy to fabricate, has low power consumption and is fairly tunable in terms of the frequency response range and sensitivity. This microcavity-based novel acoustic sensor is promising for opening up new possibilities in intrusion detection, voice eavesdropping and many other vibro-acoustic analysis applications.