Accurate calculations of travel times and raypaths of reflection waves are important for reflection travel time tomography.The multistage shortest path method(MSPM)and multistage fast marching method(MFMM)have been wi...Accurate calculations of travel times and raypaths of reflection waves are important for reflection travel time tomography.The multistage shortest path method(MSPM)and multistage fast marching method(MFMM)have been widely used in reflection wave raytracing,and both of them are characterized by high efficiency and ac-curacy.However,the MSPM does not strictly follow Snell's law at the interface because it treats the interface point as a sub-source,resulting in a decrease in accuracy.The MFMM achieves high accuracy by solving the Eikonal equation in local triangular mesh.However,the implementation process is complex.Here we propose a new method which uses linear interpolation to compute the incident travel time of interface points and then using Snell's law to compute the reflection travel time of grid points just above the interface.Our new method is much simpler than the MFMM;furthermore,numerical simulations show that the accuracy of the MFMM and our new method are basically the same,thus the reflection tomography algorithms which use our new method are easier to implement without decreasing accuracy.Besides,our new method can be extended easily to other grid-based raytracing methods.展开更多
In this paper a flat structurally tunable acoustic metasurface is constructed based on the helical unit cell. The length of the acoustic channel can be tuned by the screw-in depth of the helix. Accordingly, the wave p...In this paper a flat structurally tunable acoustic metasurface is constructed based on the helical unit cell. The length of the acoustic channel can be tuned by the screw-in depth of the helix. Accordingly, the wave phase for the transmitted acoustic wave can be tuned and the wavefront can be manipulated. Then multifunctions such as anomalous refraction, point focusing, beam focusing and self-bending can be realized and switched just by screwing in or out the helixes. At the same time, the broadband operating frequency is also realized. The experiments for anomalous refraction and point focusing are also performed, and the results show that the designed metasurface is effective. The present studies have important applications in dynamic manipulation of acoustic waves by metasurfaces.展开更多
基金This research is jointly sponsored by National Natural Science Foundation of China(Grant No.U1901602)Shenzhen Key Laboratory of Deep Offshore Oil and Gas Exploration Technology(Grant No.ZDSYS20190902093007855)+1 种基金Shenzhen Science and Technology Program(KQTD20170810111725321)This study is also sponsored by the China Earthquake Science Experiment Project of China Earthquake Administration(Grant No.2018CSES0101).
文摘Accurate calculations of travel times and raypaths of reflection waves are important for reflection travel time tomography.The multistage shortest path method(MSPM)and multistage fast marching method(MFMM)have been widely used in reflection wave raytracing,and both of them are characterized by high efficiency and ac-curacy.However,the MSPM does not strictly follow Snell's law at the interface because it treats the interface point as a sub-source,resulting in a decrease in accuracy.The MFMM achieves high accuracy by solving the Eikonal equation in local triangular mesh.However,the implementation process is complex.Here we propose a new method which uses linear interpolation to compute the incident travel time of interface points and then using Snell's law to compute the reflection travel time of grid points just above the interface.Our new method is much simpler than the MFMM;furthermore,numerical simulations show that the accuracy of the MFMM and our new method are basically the same,thus the reflection tomography algorithms which use our new method are easier to implement without decreasing accuracy.Besides,our new method can be extended easily to other grid-based raytracing methods.
基金the National Natural Science Foundation of China(Grant Nos.11872101,and 11991031)the Joint Sino-German Research Project(Grant No.GZ 1355)the support of the National Natural Science Foundation of China(Grant No.11902171).
文摘In this paper a flat structurally tunable acoustic metasurface is constructed based on the helical unit cell. The length of the acoustic channel can be tuned by the screw-in depth of the helix. Accordingly, the wave phase for the transmitted acoustic wave can be tuned and the wavefront can be manipulated. Then multifunctions such as anomalous refraction, point focusing, beam focusing and self-bending can be realized and switched just by screwing in or out the helixes. At the same time, the broadband operating frequency is also realized. The experiments for anomalous refraction and point focusing are also performed, and the results show that the designed metasurface is effective. The present studies have important applications in dynamic manipulation of acoustic waves by metasurfaces.
