Fiber-Based Infrasound Sensing

With the maturity of optical fiber sensing technology, its related applications have penetrated into various fields. Fiber-based acoustic sensors (FAS) are one of the most important research fields in fiber optic sensors. So far, it has been widely applied in natural disaster warning, medical diagnosis, geological exploration, and even battlefields. In recent years, natural disasters such as earthquakes have occurred frequently, and modern naval warfare technology has developed rapidly. Due to the special demand on acoustic detection in these fields, FAS have developed in the direction of high precision, low frequency, low cost, and miniaturization. Aiming at the low frequency or infrasound detection requirements for special applications and taking the advantages of fiber interferometric sensing structure, this chapter proposes a composite diaphragm-type fiber (external Fabry–Perot interferometer) EFPI infrasound sensor. The circular composite film is formed by combining a polymer film and an aluminum foil; then, an EFPI interferometer structure is formed between the composite film and the end face of the fiber FC joint. By theoretically simulating and optimizing the materials, sizes, and structures of the transducer, the relevant parameters are selected according to the detecting requirements. Then, the fiber EFPI infrasound sensor is well fabricated and packaged. In the simulated infrasound field environment, a comparison test was performed with a standard B&K infrasound sensor. The experimental results show an acoustic sensitivity of up to −138.3 dB re 1 V/μPa (~121 mV/Pa) in the infrasound frequency range of 1–20 Hz, which is higher than the commercial acoustic sensor used for comparison.