Research On Frequency Response Characteristics And Application Of Fiber Bragg Grating Sensor To Ultrasonic Signal

With the uncleared mechanical mechanism related to the ultrasonic vibration source,conventional methods of measuring ultrasonic signals using resonant electrical sensors represented by Piezoelectric ceramic transducer(PZT)have the limitation in the frequency of the signals.Restricted by the resonant frequency of the ceramics,PZT can only respond well to ultrasonic signals near the resonant frequency,but for the ultrasonic signals far from resonant frequency,the response is not good enough.One potential way to break these limitations is to apply Fiber Bragg grating(FBG)sensors instead of PZT for ultrasonic nondestructive detection.Therefore,it is necessary to make further research on the frequency response characteristics of fiber grating sensors.The detail contents are as follows:1.A standard ultrasonic signal generation platform is built,which can generate ultrasonic longitudinal waves in the frequency range of 100 k Hz～1.5MHz.Firstly,use commercially available software ANSYS to analyze the mode and harmonic response of the vibrating platform model,and obtain its displacement response under different frequency excitation signals,which is used to analyze the influence of the reflected waves from the edge of the aluminum alloy plate on the receiving ultrasonic signals.Next,through measuring the effects of different methods to suppress the reflected waves,we demonstrated the best way is wrapping sound-absorbing materials around the aluminum alloy plate.2.An ultrasonic fiber grating sensing system was built.Besides,in terms of the problems that the system is susceptible to the noise interference and low measurement sensitive,balanced photoelectric detection technology is introduced to solve these issues.On this basis,using the Phase-shifted Fiber Bragg Grating(PS-FBG)and FBG sensor,we experimental investigate the frequency response of the ultrasonic signal in the range of 100 k Hz～1.5MHz,respectively.The experimental results show that under the excitation of the burst signal,the frequency response sensitivity of the PS-FBG sensor to the ultrasonic signal in the range of 100 k Hz～1.5MHz is 37.7 ± 3.49 d B.Therefore,we demonstrate that the ultrasonic signal has the characteristic of broad spectrum response.3.The fiber grating sensor is applied to the two-point damage location identification,and we use different algorithms to test the validity and reliability of the measurement results from the fiber grating sensor.In view of less damage data amount leading to serious overfitting of the convolutional neural network model,a small sample training method based on transfer learning is introduced,and fine tuned based on the pre-training model.The accuracy of this model to identify the location of damage is 98.2%,which is 15.3% higher than the one-dimensional convolutional neural network model.