Study On Low Frequency Vibration Characteristics Of Excessively Tilted Fiber Bragg Grating Integrated With Graphene

With the development and continuous progress in science and technology,in China,more and more engineering buildings are under construction,such as bridges,high-speed rail,buildings,drilling and the like,and so on.Timely and accurate detection and investigation of a variety of low frequency,high frequency vibration are particularly important.Since its introduction,FBG has been widely used in practical engineering due to its small size,strong anti-interference ability,high sensitivity and strong reusability.At present,exploring different structures,properties of FBG vibration sensor system,improving the sensitivity,stability and reducing the cost,are still engineering research hotspot in this field.Comparing with conventional FBG,ExTFG is a new type of multifunctional special fiber grating in the detection of low-frequency vibration signal,but the relevant study are relatively few.Graphene is a type of two-dimensional material with good optical,electrical and mechanical properties,providing a new direction for the study of low frequency vibration sensing.Sensing studies of combining graphene with ExTFG is very important in low frequency vibration sensing and nanomaterials.Based on the above research background,in this paper,the principle of ExTFG and graphene is deduced and analyzed,and the experimental system of axial strain,bending strain and vibration sensing are designed,optimization of graphene ExTFG low frequency vibration transducer is conducted,and the axial,bending and vibration of low frequency before and after graphene coating on ExTFG are studied.The main contents are as below:?1?Based on ExTFG coupled mode theory,analysis of ExTFG axial strain,bending strain and low frequency vibration sensing theory,it is proposed to use ExTFG 3dB point of the resonant peak to detect the vibration signal.Then we analyze the influence of graphene film on the transmission of light field and Young's modulus of ExTFG,thus establishing the theoretical basis for experimentation.?2?Designing the axial strain,bending strain,low frequency vibration sensing experimental system based on ExTFG,and then conducting related experiments.Experimental results show that,when the axial strain and bending strain of ExTFG occur,the resonant wavelength will?blue shift?,axial strain of TE mode and TM mode sensitivity are-2.8pm/??and-1.8pm/??,respectively,and bending strain of TE and TM mode sensitivity is 0.026dB/cm^-1 and 0.012dB/cm^-1,respectively.In the vibration signal detection,the vibration acceleration sensitivity of the 3dB point of the TE and TM mode of the Ex-TFG are S_TE=113.54 mv/g and S_TM=100.93 mv/g,respectively,more than twice those of 100%point of the resonance peak,and the signal-to-noise ratio?SNR?of the former is also¹0dB higher than that of the latter.?3?Graphene ExTFG low frequency vibration sensor is prepared by CVD copper substrate single-layer graphene,and graphene transferred to the sensor surface is characterized.The axial strain,bending strain and low-frequency vibration sensing experiments are carried out to obtain the spectral characteristics and sensing characteristics of graphene ExTFG,which show that resonance wavelength red shift,peak intensity attenuate,change of axial strain sensitivity is small,the bending strain sensitivity,the vibration acceleration sensitivity and the signal-to-noise ratio will obviously decrease.Although graphene coating of ExTFG will reduce the sensitivity,it greatly enhances the Young's modulus and stiffness of the sensor,and can effectively protect the sensor in practical engineering applications.