High Frequency Dynamic Strain Sensor System Based On Array Waveguide Grating

The frequent occurrence of catastrophic events such as earthquakes,hurricanes and floods will seriously affect the health of structures and induce potential life-threatening situations.The influence of these external forces is not easy to predict at the beginning of design.For this reason,the technology called structural health monitoring(SHM)has emerged in recent years,which has opened up a new research field for different branches of engineering discipline.The main purpose of SHM is to detect the performance degradation of structure or material in the service life of structure.SHM systems contain a large number of node arrays that continuously monitor the quantities of interest by means of proper transducers,thus tracking the health of the particular structure.SHM system can evaluate the structure and the change of its geometric properties.Therefore,the need to identify structural damage and monitor its evolution promotes the development of SHM technology.In this paper,SHM technology based on Fiber Bragg grating(FBG)sensor is reviewed.The inherent characteristics of FBG make it one of the most promising technologies in SHM.FBG sensors take advantage of the characteristics of optical fiber,such as low transmission loss,anti-electromagnetic interference,electrical isolation,light weight and so on.These features make them very suitable for harsh environments.In addition,the inherent advantages of FBG such as high signal-to-noise ratio,compactness,high linearity,high sensitivity and anti-interference should be considered.Anti-hashing environment,low noise(generated by information coding in wavelength domain),and the possibility of multiplexing a large number of FGB based sensors in the same optical fiber reduce the need of multiple and heavy wiring used in traditional sensing.FBG sensors are easily affected by the external environment,which will affect the fiber Bragg response through the expansion or contraction of grating elements and the strain optical effect.Therefore,domestic and foreign scholars have conducted in-depth research on fiber grating demodulation technology,and proposed a variety of sensor demodulation schemes,but these schemes are not satisfactory in terms of demodulation speed,sensitivity and so on.Therefore,in order to solve the above problems,this paper mainly does the following work based on FBG sensing demodulation technology:(1)The research status of FBG sensor at home and abroad is briefly described and compared.The sensing characteristics and sensing principle of FBG are studied theoretically.The advantages and disadvantages of several common FBG demodulation techniques are compared and analyzed.Based on this,the research content of this subject is obtained,and the application prospect of AWG as wavelength demodulation element of FBG in WDM system is deeply analyzed,as well as the structure of AWG and the working principle of multiplexing/ demultiplexing.A FBG sensing system based on ASE broadband light source demodulation technology is proposed.Because ASE broadband light source has high output power,high temperature stability and good output spectral flatness,it can ensure that the power of narrow-band light signal reflected from FBG sensor is strong enough and stable output.The experimental results show that the FBG sensing system based on ASE broadband light source demodulation can be applied to monitor the vibration signal generated by piezoelectric transducer,and the time-domain response is good when the frequency response range is between 1k Hz and 20 k Hz.(2)Aiming at the problem of low response frequency and small range of FBG sensing system based on ASE broadband light source demodulation technology,a fiber ring laser dynamic strain sensing system based on an arrayed waveguide grating module is proposed.The sensing system is composed of a fiber ring laser cavity,a sensing part and the demodulation part.The fiber ring laser based on erbium-doped fiber amplifier(EDFA)and fiber Bragg grating(FBG)are used as the wavelength selection element of the fiber ring laser to detect the external dynamic strain signals,and an arrayed waveguide grating is used as the intensity demodulator outside the fiber ring laser cavity.Erbium-doped fiber amplifier(EDFA)has the advantages of polarization independent high gain,no fresnel reflection and limited quantum noise.It is used not only as light source of the fiber ring laser,but also as the gain medium.Firstly,the frequency response range of the vibration signal generated by the piezoelectric transducer is studied,that is,12 k Hz to 40 k Hz.In order to demonstrate the influence of different vibration devices on the demodulation results,we put the FBG sensor in the ultrasonic cleaning machine with the working frequency of 33 k Hz.The experimental results show that the sensing system successfully realizes the ultrasonic detection in water.Then we stick the FBG on the aluminum plate with the optical glue,and drive the FBG sensor with external impact.The sensing system detects the response frequencies of 50 k Hz.Finally,it is proved that the sensing system can realize the synchronous detection of dual channel FBG sensor.(3)Taking advantage of the fiber ring laser cavity,a more optimized system is proposed,which is a semiconductor ring laser dynamic strain sensing system based on arrayed waveguide grating demodulation.In this system,semiconductor optical amplifier(SOA)is superior to erbium-doped fiber amplifier(EDFA)because of its significant non-uniform broadening.Compared with the fiber ring laser dynamic strain sensing system based on an arrayed waveguide grating module,the frequency response range of the sensing system using piezoelectric transducer is 48 k Hz to 120 k Hz.And the underwater ultrasonic detection is successfully realized.Then we stick the FBG on the aluminum plate with the optical glue,and drive the FBG sensor with external impact and 50 W ultrasonic transducer respectively.The sensing system detects the response frequencies of 60 k Hz and40 k Hz respectively.Finally,it is proved that the sensing system can realize the synchronous detection of dual channel FBG sensor.