Quantitative Imaging Method Of Ultrasonic Frequency-domain Inverse Scattering Model Based On Reflectivity Of Damage Surface

Ultrasound phased array utilizes the damage scattering signals acquired by sensor arrays with complementary spatial information,which greatly improves the detection ability and imaging effect of micro-damage.Total Focusing Method(TFM)has been widely used because of its high resolution and high signal-to-noise ratio.However,the traditional TFM algorithm only considers the ultrasonic propagation time in the imaging process,ignoring the interaction between incident wave and damage,so it is fail to enhance the imaging quality without using the physical parameters of materials.Therefore,the whole process of ultrasonic excitation,interaction between incident wave field and damage and receiving ultrasonic signal by sensor are analyzed in this paper.A quantitative imaging method of frequency-domain inverse scattering model based on reflectivity of damage surface is established to achieve high-precision quantitative imaging of damage.The main research work is as follows:The propagation characteristics of ultrasonic bulk wave and guided wave in isotropic media and the guided wave structure with specific frequency-thickness product are analyzed theoretically.Based on the whole propagation process of the ultrasonic arriving at the damage and returning to the array during the detection process,the relationship between the scattering sound field and the incident sound field is analyzed,and the ultrasonic damage scattering model is constructed.Then,according to the characteristics of the reflectivity of the damage surface,the frequency-domain damage inverse scattering model is obtained by IFFT,and the accurate quantitative imaging with the reflectivity of the damaged surface is realized.In order to verify the effectiveness of the proposed inverse scattering model imaging method,numerical models of ultrasonic propagation in two-dimensional andthree-dimensional damaged structures are established,and the detection of circular holes and cracks is studied by numerical simulation.Three damage imaging methods,time-domain TFM algorithm,frequency-domain TFM algorithm and inverse scattering model,are compared.The results show that three imaging methods can locate the damage,but the frequency-domain TFM algorithm has higher resolution and signal-to-noise ratio than the time-domain TFM algorithm,and the inverse scattering model imaging method is better than the frequency-domain TFM algorithm in imaging accuracy and signal-to-noise ratio.When detecting the damages in the plate,the time-domain TFM algorithm can not locate the damage and characterize the size of the damage due to the dispersion effect of the guided wave,while the frequency-domain TFM algorithm and the inverse scattering model imaging method can effectively use the dispersion relation to enhance the imaging quality and accurately determine the damage by delaying and superimposing the received signals of each frequency component in the frequency domain.Moreover,the inverse scattering model imaging method has higher imaging sensitivity and signal-to-noise ratio.Therefore,the inverse scattering model imaging method is suitable for both body wave detection and guided wave detection,and achieves high-precision quantitative imaging of the damage.The ultrasonic damage inverse scattering model based on the interaction between ultrasound and damage is used to realize the precise quantitative imaging of the damage with the index of reflectivity of damage surface.It provides a new method for the precise quantitative imaging of micro-damage and a reference for the research of micro-damage detection in composite materials.