Measurement Research By Ultrasonic Speckle Correlation Method Under The Special Conditions

When coherent waves incident on the rough interface or spread in theInhomogeneous medium, there will be a speckle field with Randomly DistributedAmplitude and Phase in the space because of the interference between the refractionwaves and the back-scattered waves. The properties and variation of ultrasound specklealso contains the deformation information of objects scattering interface and structural.Ultrasonic Speckle Correlation not only can be applied to the static measurement of theIn-plane and out-of-plane displacement, but also the dynamic response measurement ofunderwater vibration modes. This is a new measurement method combined withUltrasonic, electronic, mechanics, information and other disciplines.Firstly, the ultrasonic speckle correlation method is used to measure the in-plane andout-of-plane displacement of the inner surface of an object in water in this paper, thenThe influence of the roughness and strain of the outer surface of the specimen upon theinner surface displacement measurement is examined. The results show that theroughness of the outer surface has little effect on the measurement.But when strain onthe outer surface is produced, the correlation between the speckle fields on the innersurface before and after strain on the outer surface decreases with the increase of thestrain. This de-correlation phenomenon will result in the error increases of the innersurface displacement measurement. Secondly, when traditional ultrasonic specklecorrelation method is applied to the displacement measurement, the correlationcoefficient is a multiple peak function, which causes a great measurement error. To avoidthis kind of errors, the ultrasonic speckle multiple spectrum correlation method isproposed in this paper. This method not only avoids the misjudgment of correlationcoefficient main peak effectively, but also improve the displacement measurementaccuracy. Finally, ultrasonic speckle measurement technology is applied to measurenon-contactly the frequency, amplitude and phase of testing points on a vibratingcantilever beam underwater. This new technique offers effective methods to analyze thevibration mode of structures underwater.