Abstract
In order to effectively enhance the sensitivity and response range of optical fiber Fabry–Pérot (FP) ultrasonic sensors, this article proposes an implementation method of an optical fiber FP ultrasonic sensor with a controllable cavity length and variable diaphragm. On the basis of optimizing the viscosity coefficient of the polydimethylsiloxane (PDMS) material, a PDMS diaphragm with the thickness ranging from 20 to 60 µm is fabricated on the end face of a Φ200/128 µm hollow glass tube using a multiple transfer method. Then, a piece of Φ125 µm single-mode optical fiber is threaded into the hollow glass tube from the other end and encapsulated to form an optical fiber FP ultrasonic sensor based on a PDMS diaphragm. The intensity of the corresponding ultrasound signal and its spectral characteristics can be inverse-analyzed by detecting the FP interference spectra formed on the fiber end and the PDMS diaphragm surface under the action of dynamic ultrasound signals. The experimental results show that the highest ultrasonic detection frequency response of the proposed PDMS diaphragm optical fiber FP ultrasonic sensor can reach 430 kHz and the signal-to-noise ratio can reach up to 70 dB. The above-mentioned results indicate that the optical fiber FP ultrasonic sensor with a PDMS diaphragm proposed in this article has obvious advantages in terms of sensitivity and response range.
Highlights
INTRODUCTIONSince the optical fiber ultrasonic sensor was first proposed and implemented by the U.S Naval Laboratory in the 1970s, it has been widely studied due to its characteristics, such as high sensitivity, compact size, light weight, anti-electromagnetic interference, corrosion resistance, and long-range detection. the fiber ultrasonic detection technology poses fantastic application prospects in a variety of areas, such as structural health monitoring, biomedicine, and ultrasonic imaging. Generally, fiber Bragg gratings, Mach–Zehnder interferometers, Michelson interferometers, Sagnac interferometers, and Fabry–Pérot (FP) interferometers can be used as optical fiber ultrasonic sensors; a fiber Bragg grating requires extremely expensive inscription instruments and technology, and the structure of the Mach–Zehnder interferometer, Michelson interferometer, and Sagnac interferometer lacks compactness needs to be simplified. motivated by the FP interferometer, the demands of microminiaturization with low cost and good measurement performance for optical fiber acoustic detection can be met
In order to test the characteristics of the optical fiber FP ultrasonic sensor, two detection systems are constructed in this paper, namely, the dynamic ultrasonic detection system and the pulsed laser-induced ultrasonic detection system
The above-mentioned experiments show that there is a strong signal response in the range of about 40–90 kHz, and a good response can be detected for the ultrasonic signal generated by the laser source, which proves that the PDMS diaphragm optical fiber FP ultrasonic sensor fabricated in this article has superior ultrasonic detection characteristics with a wide frequency response range and high signal-to-noise ratio
Summary
Since the optical fiber ultrasonic sensor was first proposed and implemented by the U.S Naval Laboratory in the 1970s, it has been widely studied due to its characteristics, such as high sensitivity, compact size, light weight, anti-electromagnetic interference, corrosion resistance, and long-range detection. the fiber ultrasonic detection technology poses fantastic application prospects in a variety of areas, such as structural health monitoring, biomedicine, and ultrasonic imaging. Generally, fiber Bragg gratings, Mach–Zehnder interferometers, Michelson interferometers, Sagnac interferometers, and Fabry–Pérot (FP) interferometers can be used as optical fiber ultrasonic sensors; a fiber Bragg grating requires extremely expensive inscription instruments and technology, and the structure of the Mach–Zehnder interferometer, Michelson interferometer, and Sagnac interferometer lacks compactness needs to be simplified. motivated by the FP interferometer, the demands of microminiaturization with low cost and good measurement performance for optical fiber acoustic detection can be met. The authors of Ref. 19 proposed a fiber coupled FP interferometer with an open micro-cavity based on a cantilever beam to detect ultrasonic pressure, with an SNR of up to 58.7 dB It required high cost femtosecond laser technology to fabricate the sensor. A gold diaphragm-based FP interferometer ultrasonic sensor was proposed and experimentally demonstrated by Zhang et al, where acoustic signals from 20 to 150 kHz can be detected well with the SNR up to 48 dB.. There are many works that extensively investigated the fabrication and application of the fiber ultrasonic sensor, the issues of high sensitivity and a wide spectral response range still need to be comprehensively observed. A PDMS diaphragm structure-based fiber ultrasonic sensor with high sensitivity and a wide spectrum response range is examined by utilizing the multiple transfer method.
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