Research On High Resolution Fiber Laser Acoustic Emission Detection And Multiplexing Technique

Acoustic emission?AE?sensors are needed to monitor Faults such as wear or fracture of acoustic emission occurred during working process of mechanical equipment in railway transportation,petrochemical industry,aerospace and many other fields.Compared with traditional electric AE sensors,optical fiber AE sensors have the advantages of wide bandwidth,no electromagnetic interference,high sensitivity,small size,no need to contact with the object under test,and long distance between electronic equipment and sensor.The AE sensor system based on distributed feedback?DFB?fiber laser proposed in this paper not only has the above advantages,but also has the advantages of simple structure,high strain resolution,wide dynamic range,wide detection frequency range and strong multiplexing ability.The main research work and achievements in this paper are as follows:?1?Summarize the research status of optical fiber acoustic emission detection technique at home and abroad.Then introduce the basic detection principle of acoustic emission signal,the working principle of DFB fiber laser and the sensing principle of DFB fiber laser under the action of acoustic emission signal.The response of DFB fiber laser under the action of longitudinal wave?transient sine wave?is emphatically analyzed.It is demonstrated that DFB fiber laser can detect acoustic emission signal.?2?A single-channel fiber laser acoustic emission detection system,an optical frequency comb?OFC?system and a multi-channel fiber laser acoustic emission detection system are designed and implemented.The three demodulation systems are tested and the strain resolution is calculated.Then the acoustic emission detection sensitivity of DFB fiber laser is calibrated for the single channel fiber laser acoustic emission detection system.?3?A single DFB optical fiber laser sensor and several DFB optical fiber laser sensors are constructed on the steel plate.Acoustic emission signals are collected by PZT acoustic emission experiment and low-speed impact detection experiment.Then the time domain spectrum and frequency spectrum of frequency of the beat signals of the two acoustic emission signals are analyzed.Thus verify the single-channel and multi-channel fiber laser acoustic emission detection system can accurately detect acoustic emission signals.?4?Finally introduce the principle of the Hilbert-Huang transform?HHT?method to improve the frequency resolution.and the method is used to improve the frequency resolution of single-channel and multi-channel fiber laser acoustic emission detection systems.The strain resolution of the demodulation system can be up to 10^-4 level to complete the detection of AE signal,so it is hopeful to have a good application.