The Key Technology In Acoustic Lens Imaging

The thesis discussed the acoustic lens imaging technology. Four main contents wereincluded in the thesis: improving the model of sound field generated by acoustic lens;analyzing and designing acoustic lens system; testing in a tank; compressive sening theorythan can be applied in acoustic lens imaging technology.The hybrid geometric/wave acoustic model was introduced in detail, and that theadvantages and disadvantages were analyzed. The improved hybrid geometric/wave acousticmodels were proposed. Detailed structure and implementation steps of improved model weregiven. Experimental results were compared to simulation. Therefrom, the improved modelhad more accuracy than the original hybrid model.The performance of an acoustic lens system was analyzed using the improved hybridmodel, such as focal region and parameter’s influnce on beampatterns of acoustic lens. Theparameters of lens system were geometry、material、tempreture、frequency and so on. Basedon the simulation results, four acoustic lens systems were designed: single-element acousticlens system; two-element acoustic lens system; two-demension acoustic lens; compoundacoustic lens system. The simulation and picture of the designed acoustic lens system weregiven.The tank tests were operated for the designed acoustic lens system. The test were dividedinto two parts. One was the beamforming test of the acoustic lens system, the other wasbeamforming and imaging test of the prototype. The former concluded testing the focalposition, drawing the beampatterns, measuring the field of view and practical range. Thecomparison between the simulation and test results verified the good accuracy of theimproved hybrid model in modeling the sound field. The latter concluded testing thebeamwidth of the prototype in the horizontal axis, testing the fied-of-view in the horizontaland vertical axis, testing the pratical range and range resolution and imaging the objects withshape of circle and cross. The images formed by the prototype had clearcutness and rapidupdate rate. Therefor, acoustic lens system were available in underwater acoustic imaging.Compressed sensing theory had potential application in acoustic lens image technology.Three aspects of compressed sensing theory: sparse representation, acquring measured dataand reconstruction of signal were introduced in detail.Orthogonal matching pursuit series theory was researched implemented. A gradual regularized adaptive matching pursuit was presented. Simulation results proved that theproposed algorithm improved peak signal noise ratio、relative error、matching and runtimeof reconstructed image. Block compressed sensing theory was the other research focus.According to the characteristics of underwater acoustic image, a new adaptive blockcompressed sensing reconstructing scheme was proposed. The improving algorithmeliminated blocking effect between neighboring subblocks in target area. The quality ofreconstructed image was increased which was convenient for feature extraction and targetidentification.