Air-coupled fiber Fabry-Perot ultrasonic sensor formed by diaphragm for seismic physical model imaging

We presented a miniature fiber ultrasonic sensor based on the principle of Fabry-Perot(F-P) interferometer, which comprises a single-mode fiber(SMF) spliced with a hollow core fiber (HCF), whose end face is adhered with UV glue(NOA68). The interface of NOA68 diaphragm-air as one of the two interfaces of F-P cavity is sensitive to ultrasonic wave due to its low Young's modulus. Thus, it has the ability to detect weak ultrasonic wave reflected from seismic physical model (SPM) in air. Furthermore, the compact sensor has a characteristics to identify orientation of ultrasonic source because of its perfectly symmetrical structure and is capable of detecting wide ultrasonic frequency range from 300 KHz to 5 MHz. The spectral band-side filter technique is used for the interrogation of ultrasonic signal. As expected, using the designed sensing probe, we can reconstruct the SPM in 2D and 3D by the time-of-flight approach.