Application Of Optical Fiber Acoustic Emission Sensor Array In Impact Monitoring

With the advancement of science and technology,the number of equipment such as industrial instruments,large bridges,and aerospace vehicles has become increasingly large.Because of their special working environment,these devices are often subject to accidental impacts from the natural environment or man-made,such as earthquakes,floods,and storms.If these devices are not repaired in time after being impacted by the outside world,the internal material parameters of the devices will occur.Changes,such as material stiffness,strength,toughness,etc.,no matter the degree is serious or not,because these devices have been exposed to high pressure or high temperature for a long time,there is great stress inside the device itself,and small internal defects may become subsequent occurrences.The cause of greater damage.When the device is impacted,the internal structure generates an acoustic emission signal.The detection and calculation of the acoustic emission signal can obtain information such as the location of the impact point or the internal structure of the device.Therefore,a method that can detect the impact signal from the outside is proposed.The sensor system is very necessary.As a kind of optical device with wide application and excellent performance,fiber optic sensor is used for its many characteristics such as anti-electromagnetic interference,high temperature resistance,long transmission distance,light volume and reusability.It is widely researched and applied in the field of structural health detection.Based on the above problems,a ring acoustic emission sensing system based on a fiber Fabry-Perot filter is designed.This system uses a semiconductor optical amplifier as the system light source and multiple fiber Bragg gratings(FBG)as sensing elements,the center wavelength shift of the grating caused by the external acoustic emission signal is converted into an intensity change signal by the fiber Fabry-Perot filter to realize the acoustic emission demodulation,and an acoustic emission source location algorithm is proposed to calculate the plane impact point coordinates.The specific contents of the research are as follows:(1)The working principle of the proposed optical fiber sensing system is described.A single FBG sensor is used and the ultrasonic transducer is used as the acoustic emission source to perform a standard sine wave signal demodulation experiment.The results show that the system Acoustic emission signal demodulation up to 450 k Hz can be achieved with good results;the ultrasonic vibrator experiment on the aluminum plate compared with the piezoelectric sensor proves that the FBG sensor has directional sensitivity to the acoustic emission source;the upper lead experiment on the aluminum plate is carried out to verify the optical fiber the sensing system's ability to detect complex sound signals.(2)The fiber optic sensing system is expanded,and the sound emission multiplex demodulation is performed using the FBG sensor of different central wavelengths,and three FBG sensors form a positive triangle array for impact detection on the aluminum plate,and use a piezoelectric sensor to compare the experiment.The results indicate that the proposed fiber sensing system has multiplexed emission demodulation capabilities and is ideal.(3)A wavelet transform-based acoustic emission source location calculation method is proposed,and the Lamb wave dispersion equation is solved numerically to draw the Lamb wave group velocity curve on the aluminum plate.(4)The proposed positioning method is used to calculate the impact acoustic emission results of the optical fiber sensor system and the piezoelectric sensor on the aluminum plate,and compare them with the actual position.The positioning method and the proposed optical fiber acoustic emission sensor the system has a good effect on the localization of the impact sound emission source.(5)Based on the comparison of the experimental results of the piezoelectric sensor and the optical fiber sensor,the pros and cons of the two sensing systems are analyzed and compared.