Study Of Optical Fiber Coherence Imaging Detection For The Damage State Of Painted Fresco

China is famous for splendid culture and history.The ancients left a large number of precious murals and cultural relics.These cultural relics reflect the development of science and technology as well as the cultural characteristics of different ethnic groups in different periods,regions,and ethnic groups.However,with the passage of time,changes of the natural environment and man-made damage may cause many typical diseases to the murals,such as hollowing out,raising nails,crisp alkali,and smoking,among which hollowing and armoring are the commonest and most harmful.these diseases will cause the permanent damage to the murals,if they can not be effectively and timely treated.Before handling and protection,the complete understanding of the degree and situation of damage in the damaged mural is necessary.Therefore,the non-destructive testing method is indispensable.Most of the available detection methods can not meet the requirements,such as the visual inspection method containing too many subjective factors;near-infrared hyper spectral technology can only detect the surface of lesion region;although,knocking,infrared thermal imaging technology and ground penetrating radar method,etc.can be used for detection with the accuracy of detection which can not reach the standard.Optical coherence tomography is a three-dimensional imaging technology originating from the 1990 s.It was first used for medical ophthalmic diagnosis.The depth of its image in the air can reach 2mm,and the imaging resolution is the micron range.It is very suitable for detecting the diseases of murals,such as ultrasound tomography technology is can get the defect inside the measured object by detecting the ultrasonic echo.By this method,the imaging depth can reach more than ten centimeters,and the resolution reaches the millimeter level making it very suitable for the detection of empty drum.Based on the mural disease detection,fresco armor and hollowing phenomenon were detected by the optical coherence tomography technology and the ultrasonic tomography technology respectively.(1)The imaging of the mural phenomenon of murals can be realized by the technique of optical coherence tomography.Besides,the noise in the image is analyzed and removed by the wavelet threshold denoising method.(2)The working principle and characteristics of the interferometric fiber-optic ultrasonic sensor are introduced firstly,and the F-P interferometric fiber-optic ultrasonic sensor is applied in the experiment.Theoretical analysis and experimental results show that since the acoustic detection sensitivity of the FP type optical fiber ultrasonic sensor is inversely proportional to the modal modulus of the FP cavity fabrication material,the NOA 68 UV adhesive with low Young's modulus is used to fabricate the FP optical fiber sensor,which can detect ultrasonic in the air.Under the action of 300 k Hzultrasonic,the sensitivity of the detection by the sensor is 48.13 d B.In the air,the imaging of seismic physical model and mural hollow drum simulation structure can be realized by the sensor made in this work.