Highly Efficient Generation of Angular Momentum with Cylindrical Bianisotropic Metasurfaces

Abstract

Recent advances in metasurfaces have shown the importance of controlling the bianisotropic response of the constituent meta-atoms for maximum efficiency wavefront transformation. Under the paradigm of a bianisotropic metasurface, full control of the local scattering properties is allowed opening new design avenues for creating reciprocal metasurfaces. Despite recent advances in the perfect transformation of both electromagnetic and acoustic plane waves, the importance of bianisotropic metasurfaces for transforming cylindrical waves is still unexplored. Motivated by the possibility of arbitrarily controlling the angular momentum of cylindrical waves, we develop a design methodology for a bianisotropic cylindrical metasurface that enables perfect transformation of cylindrical waves. This formalism is applied to the acoustic scenario and the first experimental demonstration of perfect angular momentum transformation is shown.

Sound vortex diffraction via topological charge in phase gradient metagratings

“…In addition, when incident SV and scattered SV have a larger wave vector, similar to diffraction properties of planar acoustic metasurfaces ( 43 , 44 ), undesirable/parasitic diffraction orders can appear, which might lead to a low conversion efficiency. The design strategies that incorporate bianisotropy ( 27 , 45 ) could be potentially used to overcome this problem. In short, the proposed diffraction law of SVs provides a clear blueprint for manipulating SVs with azimuthal phase gradient and also enables a deep understanding of the fundamental diffraction behavior in PGM-based systems and the intrinsic link between diffraction phenomena in 2D free space and 3D cylindrical waveguides.…”

Enhanced Low‐Frequency Monopole and Dipole Acoustic Antennas Based on a Subwavelength Bianisotropic Structure

“…The Willis coupling in BMs enriches the scattered fields and provides more possibilities for acoustic wave manipulations. So far, the acoustic BMs have been employed to realize various fascinating phenomena, such as acoustic unidirectional zero reflection, broadband sound barriers, and scattering‐free wave manipulation . However, the structure design based on acoustic BMs has not been applied in acoustic antennas.…”

“…So far, the acoustic BMs have been employed to realize various fascinating phenomena, such as acoustic unidirectional zero reflection, broadband sound barriers, and scattering-free wave manipulation. [18][19][20][21] However, the structure design based on acoustic BMs has not been applied in acoustic antennas. In this work, we would like to unite acoustic Willis coupling and acoustic resonances in BHMR to realize both enhanced monopole and dipole antennas.…”

“…The field coupling in the acoustic BM is referred as Willis coupling that includes the strain‐velocity coupling in elasticity or the pressure‐velocity coupling in acoustics . The Willis coupling offers a new freedom for acoustic wave manipulation and has produced many fascinating applications . For example, Koo et al designed an acoustic BM to realize the pressure‐velocity impedance conversion for independent control of the reflection and transmission angles .…”

“…Acoustic BMs were also employed as effective sound barriers to prevent sound diffractions in low‐frequency noise control . Li et al further used gradient acoustic BMs to realize scattering‐free wavefront manipulation and high‐efficient angular momentum transformation …”