Research On Acoustic Testing Based On Optical Principle

With the progress of the development of technology and industry,material in many industriesdemand become higher and higher. Wehas paid attention on the health of the material in the long-termprocess of serving.Therefore,the damage detection techniques used for materials of structural healthmonitoring have a great significance.Acoustic detection technology with large area,high speed and good detection accuracy, is one ofthe important methods for damage detection, which has been widely used indamage detection ofmaterials. The performance of the transducer used atthe acoustic detection is not high enough, whichaffects the detection precision.In order to make up for the shortcomings, we can use the opticalmeasurement method with high spatial resolution, the good detectability and accessibility. The opticaldetection with acoustic nondestructive testing method of fusion is becoming more and more attention.Based on the optical fiber detection system as an example, this paper analyze the principle ofintensity, phase and wavelength modulated optical method. Andwe analyze the principle ofthree kindsofoptical method access of acoustic wave in the thin plate. Then design and build three kinds ofacoustic detection systemsincludedoptical fiber,the acoustic excitation module, optical fiber sensingmodule, signal acquisition and demodulation module, computer analysis module.We have conductsome experiments with the designed system. The acoustic detection system of intensity modulatedfiber hashigh response sensitivity, high signal-to-noise ratio and strong anti-interference ability, buthas a small amplitude signal. However,acoustic detection system ofphase modulated fiber has fastresponse, high accuracy andlarge signal amplitude which realize the non-contact scanning detection,but lack of anti phase interference ability.We used the addwindow sine signalto study the effect ofmaterials, parameters and excitation frequency on signal at the two system.For the fiber Bragg gratingof the wavelength modulation fiber-optic acoustic detection system, at firstwe used static loading onthe experiment, in order to get fiber Bragg grating location and material damage characteristics. Thentobtain the sound signal with the frequency of30kHz in the high-frequency signal sensing experimentby fiber Bragg gratings.The results show that the system is suitable for high frequency, which showsthat acoustic detection technology combine with the optical method has the advantages of highsensitivity, high accuracy, and applicability.