Polymer Film Integrated Optical Fiber-Cantilever-Based Highly Sensitive Low-Frequency Acoustic Sensor

A polyvinylidene fluoride (PVDF) film-assisted optical fiber cantilever-based acoustic sensor with high sensitivity is presented for low-frequency applications. The sensing cantilever is fabricated by developing a PVDF film on a bare optical fiber. The light is coupled from an input fiber to the output cantilever fiber using the butt-coupling method. The end tip of the input fiber is mounted on a fixed holder, while the output fiber-PVDF cantilever is free to vibrate. The acoustic pressure vibrates the fiber-PVDF cantilever, which causes the change in transmitted power. The sensor’s output is measured in terms of variation in the output light intensity. An advanced double cantilever method is also demonstrated to improve the sensor’s sensitivity, which delivers two natural frequencies with high signal amplitude. The sensitivity of the PVDF-assisted fiber cantilever is observed as 958 mV/Pa or −0.37 dB re 1 V/Pa, which is significantly better than the bare optical fiber cantilever having a sensitivity of 5 mV/Pa or −46 dB re 1 V/Pa at the resonance frequency. The dynamic range of the sensor is 100–4000 Hz with a minimum detectable pressure (MDP) of 0.21 mPa/
$\sqrt {\text {Hz}}$
measured at the resonant frequency. The sensor exhibits a maximum signal-to-noise ratio (SNR) of 70 dB at the resonance frequency. Numerical analysis and simulations are also performed to substantiate the experimental demonstrations. The proposed sensing system is developed using a conventional drop-casting method. Consequently, the sensor is recognized as advantageous over the previous reports in terms of sensitivity, MDP, SNR, and fabrication feasibility.