Numerical Simulation And Experimental Research On The Planar Gradient Acoustic Lens

In this paper, the design principle of planar gradient acoustic lens is presented on the basis of Homogenization Theory and Multiple Scattering Theory. The numerical calculation model is developed in the light of COMSOL MULTIPHYSICS finite element simulation software. Based on the model, the focusing bandwidth, the influence of geometric parameters and different types of defects are analyzed and focusing mechanism is discussed. Acoustic lens with four rows of cylinders is fabricated to launch the focusing experiments. In experiments, with linear array scanning method, the acoustic field in the axial, horizontal direction and leveled plane is measured.Simulation results show that the acoustic lens has a good focusing effect and could focus sound in a broadband frequency. For sonic lens having four rows of cylinders, the largest gain is 4.6 dB and focusing frequency varies from 2000 Hz to 7000 Hz. Increasing the caliber of lens, the focusing length becomes larger while the focusing gain remains almost the same. Increasing the thickness of lens, the focusing passband becomes wider, successively larger peak number increases and the maximum gain achieved turns bigger. Reducing the dimension of the lattice makes the focus passband wider, at the same time, the frequency response characteristic curves more smooth. For acoustic lens with four rows of cylinders, the axial line defect makes the frequency response curves move to high frequency slightly, with gain remaining almost the same and focal length become bigger; Second row line defect makes the focusing effect similar to two rows of cylinders acoustic lens, however the frequency response characteristic curve moves largely to low frequency, and the gain and the focal length are smaller; 9 symmetric point defect in the transmitted face makes the focusing effect similar to three rows of cylinders acoustic lens, while the frequency response characteristic curve becomes more smooth. Finally, the focusing results of acoustic lens have a direct relationship with the energy localization among cylinders.Experimental results show that, under different frequencies, the gain which changes with axial distance demonstrates the good focusing effect acoustic lens, the gain that varies with transverse distance proves the broadband characteristics sonic lens, and the plane focusing acoustic field further verifies the acoustic lens' excellent focusing effect.