Specialty Fiber Grating-Based Acoustic Sensing
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Aiming at the high sensitivity, high precision, small size, and low cost acoustic detection requirements, a novel fiber sensor for curvature and acoustic wave measurement based on a thin core ultra-long period fiber grating (TC-ULPFG) has been proposed in this chapter. By tracking the power variation of different resonant wavelength caused by TC-ULPFG, high curvature sensitivity of 97.77 dB/m−1 is achieved, to best of our knowledge, which is highest than other structures at the same measurement range. Thus, the desired curvature property of the TC-ULPFG is used for acoustic measurement. The polyethylene terephthalate (PET) film is selected as a transducer, on which TC-ULPFG is tightly pasted. The acoustic pressure sensitivity of 1.89 V/Pa is two orders higher than other structures based on the diaphragm transducer, and the noise-limited minimum detectable pressure is 1.94 mPa/Hz1/2 at 200 Hz. In addition, the frequency fluctuations are nearly ±0.4 dB from 70 to 200 Hz and ±0.2 dB from 1 to 3 kHz, respectively. Therefore, the proposed optical fiber acoustic sensor (OFAS) has a flat frequency response in relatively lower frequency. The TC-ULPFG shows many advantages including high sensitivities of curvature, high acoustic pressure sensitivity, easy fabrication, simple structure, and low cost.
KeywordsThin core ultra-long period fiber grating (TC-ULPFG) Optical fiber acoustic sensor (OFSA) Flat frequency response
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