Broadband elastic wave detection based on dual FBGs capable of automatically matching the spectra

Abstract

Fiber Bragg grating (FBG)-based sensors can be used to detect middle/high frequency elastic waves via intensity demodulation. Temperature change or structural deformation at the location where the sensing FBG is adhered to may shift the FBG spectrum and mismatch the interrogator filter and sensing FBG spectra, leading to sensing failure. This paper proposes a broadband elastic wave measurement system with a trackable work point based on dual FBGs together with a piezoelectric transducer (PZT), wherein one FBG is pasted on the PZT as a filter and tracker. By applying AC + DC excitation to the PZT and sweeping the DC bias, the two FBGs’ spectra are autonomously matched by searching the max amplitude of the receiving AC signals to maintain high sensitivity. It is experimentally demonstrated that the proposed system can detect up to 500 kHz broadband elastic waves. The proposed system is replicated to produce four sets that are successfully used to detect and locate the impact on an aluminum plate.