3D imaging of mural model in air using sensitivity-improved ultrasonic sensor based on fiber-optic Fabry-Perot interferometer

Abstract A sensitivity-improved ultrasonic fiber optic sensor is proposed and demonstrated for ultrasound wave (UW) imaging of mural models. The sensor contains a Fabry-Perot (F-P) cavity at one end of a single-mode fiber (SMF) and a gold-coated ceramic ferrule. Because the gold film is 120 nm thick, the sensor has extremely high ultrasonic sensitivity. Compared to similar sensors in the literature, by changing its package structure, removing the acoustic lens and using a thinner film in the interference cavity, the signal-to-noise ratio (SNR) of the proposed sensor can reach 68.18 dB. Using the sideband filtering method, the echo wave signal can be extracted, the cross sectional image of hollows in the mural model can be obtained by 1D scanning, and 3D images can be reconstructed by 2D scanning. We calculated the thicknesses of the three hollows in the ground layer to be 0.1986 cm, 0.6752 cm, and 0.3873 cm, and the thickest part of the efflorescence area to be 2.857 cm. The ultrasonic sensor helps archaeological conservators to detect information on size of defects in the mural ground layer.