Micro-tip Cantilever as Low Frequency Microphone

We propose a very compact diaphragm free optical microphone consisting a tapered micro-tip in cantilever configuration for detection of low frequency acoustic signals. The change in the light coupling between the micro-tip and the source fiber caused by the acoustic pressure is utilized to detect the external acoustic signal. The sensitivity and working range of the sensor depend on three key factors, the length of the micro-tip cantilever, the distance between the micro-tip and SMF, and the offset between the micro-tip central axis and SMF central axis. Hence, by changing any of these parameters, the performance of the sensor can be easily tuned. Experimental results show that for a cantilever length of 15 mm, the probe has a maximum acoustic sensitivity of 10.63 mV/Pa or −159.5 dB re 1 V/μPa, noise-limited minimum detectable pressure of 19.1 mPa/√Hz and the linear frequency range is 0–400 Hz. The SMF only structure along with photodetector-based interrogation makes this acoustic sensor economical.