Intensity demodulation-based acoustic sensor using dual fiber Bragg gratings and a titanium film

We report on recent experimental results obtained with fiber Bragg grating (FBG) microphone for acoustic measurement. The sensing element is formed by longitudinally sticking ends of two FBGs onto a titanium film, and then being packaged in an aluminum cylinder. Due to wavelength shift of the FBGs induced by the external acoustic disturbance, the corresponding periodic fluctuation in power can be observed on the optical oscilloscope. Theoretical analysis verifies that the optical power variation, result of the titanium film vibration caused by the acoustic disturbance, possesses a linear relationship with the sound pressure in a specific range. A relatively flat frequency response in the range from 100 Hz to 1 kHz with the average signal-to-noise ratio (SNR) above 22 dB is experimentally demonstrated. The maximum sound pressure sensitivity of the proposed sensor is found to be 90 μW/Pa within a sound pressure range 100.3–118.5 dB. The sensing system presents good stability and reliability, and has the advantage of direct self-demodulation.