Research On Underwater Sensing Technology Based On Polished Fiber Bragg Grating

As an effective carrier for information transmission,ultrasound is widely used in underwater long-distance information transmission.The traditional hydroacoustic sensor can realise the detection and identification of the position information of the underwater target by converting the collected ultrasound.The traditional piezoelectric ceramic ultrasonic sensor has low detection efficiency and high detection cost.In view of this,the study of an ultrasonic sensor with high sensitivity and stability can provide new solutions for the problems encountered by China’s ultrasonic detection technology and application systems in the fields of national defense,military and civil industry,especially in the field of marine ultrasonic detection.Based on the side polished fiber Bragg grating(SPFBG)technology,this topic has developed an underwater ultrasonic detection sensor.The main research is as follows:First of all,the basic theory of ultrasound and the sensing mechanism of fiber grating are introduced,and the feasibility of SPFBG detection of ultrasound is demonstrated.The influence of ultrasound on SPFBG is studied,and the differences between horizontal and vertical reception modes of SPFBG are explored.Secondly,the simulation software is used to establish a one-sided and two-sided grinding optical model,and explore the relationship between the side grinding depth and the characteristics of the fiber Bragg grating.Using a wheeled optical fiber Bragg grinder to process the fiber grating,the D-type and Fan-type SPFBG were prepared,and the flat characteristics of the fiber grating grinding area were verified.Thirdly,the experimental scheme and equipment composition of the underwater ultrasonic detection and sensing system are designed,and the ultrasonic signal detuning scheme is optimised.A water temperature sensing system was built to study the water temperature sensitivity characteristics of SPFBG inorder to eliminate the influence of water temperature on the sensor results.Finally,an underwater ultrasonic detection and sensing experimental system is built.The performance of the sensor unit is validated by comparing the prepared SPFBG with the simulated findings.The original FBG and SPFBG are compared and tested by ultrasonic sensing characteristics from frequency response,amplitude response,detection direction and other indicators.In summary,the underwater ultrasonic sensing system designed in this paper can realise the detection ultrasonic signals and rebuild the original ultrasonic signal.The experimental results show that the underwater ultrasonic detection performance of SPFBG is significantly better than that of the original FBG.It offers theoretical backing and an experimental foundation for the creation of an underwater ultrasonic detector.