Research And Verification Of Air Coupled Ultrasound Imaging Method Based On Virtual Aperture

Air ultrasound imaging is widely used in fields such as structural damage and defect detection due to its non-contact and high-precision advantages.Generally,uniform and dense ultrasound arrays are used to image objects,which poses challenges such as high accuracy,low cost,and long-distance.In order to solve this contradiction,this article uses sparse ultrasound arrays to replace dense arrays with a few elements for imaging,and designs corresponding sparse ultrasound imaging methods based on the principle of phase center similarity,solving the problem of long-distance imaging of ultrasound arrays in air media.Experimental verification shows that the proposed method and the developed system achieve high accuracy,low cost,and long-distance simultaneously,The main specific content is as follows:Firstly,based on the basic principles of phased array ultrasound imaging and synthetic aperture ultrasound imaging,a systematic study and summary of the relationship between the number of periods,number of elements,array size,center wavelength of the array element excitation signal and the lateral and longitudinal resolution of ultrasound imaging were conducted.Field II sound field simulation was used to verify the array and unit parameters of the ultrasound phased array,which was used for the array design of sparse array based imaging systems The meshing of imaging space and the removal of artifacts provide a reliable theoretical basis.Then,by studying the principle of phase center approximation,a design method for virtual aperture ultrasound arrays based on sparse arrays was proposed.After optimizing the transmitting and receiving array elements based on the principle of minimum redundancy and no grating lobes in the imaging area using the principle of phase center approximation,a design was achieved with 480 × A two-dimensional sparse surface array of 300 mm ^ 2 has achieved twice the array expansion.Next,based on the Back Projection(BP)imaging algorithm and the array configuration of the sparse array,a BP imaging algorithm based on the sparse array is proposed.The algorithm is implemented on FPGA and can image a water cup at a distance of 2 meters,presenting complete information of the cup contour.However,there are issues such as uneven pixel distribution and local size imbalance.Finally,this article selects the imaging intensity threshold and channel number threshold to distinguish imaging artifacts,and smoothly replaces the artifacts based on the amplitude intensity of the surrounding pixels to perform secondary reconstruction of the image.After removing the artifacts,the reconstructed image quality has been significantly improved,and problems such as uneven pixel distribution and imbalanced local size ratio have been solved.The final image resolution can reach 440 × 320,with an image signal-to-noise ratio of 3.07 d B and a spatial resolution of 13.9mm.