Focusing and directional beaming effects of airborne sound through a planar lens with zigzag slits

Abstract

Based on the Huygens-Fresnel principle we design a planar lens to efficiently realize the interconversion of the point-like source and Gaussian beam in the air ambience. The lens is constructed by a planar plate drilled elaborately with a nonuniform array of zigzag slits, where the slit exits act as subwavelength-sized secondary sources carrying desired sound responses. The experiments operated at audible regime agree well with the theoretical predictions. This compact device could be useful in daily life applications, such as for medical and detection purposes.

Apparent Negative Reflection with the Gradient Acoustic Metasurface by Integrating Supercell Periodicity into the Generalized Law of Reflection

“…Similar to their electromagnetic counterparts, acoustic metasurfaces have become attractive for they are able to engineer the phase profiles of the impinging waves by the artificial designed structures with subwavelength thickness instead of the space consuming solutions offered by the traditional diffractive acoustic devices. Numerous types of acoustic meta-atoms have been proposed to construct the functional acoustic metasurfaces, such as tapered labyrinthine structure14, coiling-up slit structure1516, zigzag channel17, Helmholtz resonator array18, split sphere19 and membrane based structure20. Based on these acoustic meta-atoms, a great number of acoustic wavefront manipulation devices have been constructed and operated successfully, for example, the acoustic focusing lens2122, acoustic vortex beam generator23, acoustic Airy beam generator2425, acoustic carpet cloaking2627 and so on.…”

High transmission acoustic focusing by impedance-matched acoustic meta-surfaces

“…Much effort has been devoted to reducing the impact of mismatched impedance. 6,8,9,11,15,20,[22][23][24][25][26][27][28][29] One way to do so is to utilize Fabry-Perot (FP) resonances, 6,8,15,20,22,29 which can increase the transmission energy because of the destructive interference between the multiple reflections of acoustic waves on the input and output surfaces of the acoustic lens. Because the resonant frequency of FP resonances is sensitive to the effective thickness of the acoustic lens, it may not be able to perfectly eliminate the reflection in real applications.…”

“…Acoustic meta-surfaces are planarized metamaterials that consist of carefully designed sub-wavelength building blocks. They have exceptional functionality in controlling acoustic waves, including perfect absorption, 14 collimation, 15,16 extraordinary transmission, 17 reflection, 18 wavefront steering, 19 unidirectional transmission, 20 and negative refraction. 21 In the study of acoustic lenses, especially in the transmitted domain, impedance is an important issue because mismatched impedance of an acoustic lens to the environment is detrimental to the performance of the acoustic lens.…”

Realization of compact tractor beams using acoustic delay-lines

“…Each unit cell introduces a specific phase delay. Our approach parallels developments in 2D planar metamaterials [20][21][22][23][24][25] where a layer of sub-wavelength unitcells is used to shape and steer incident fields. In our sonic devices, the phase-shifting unit cells are not limited to the size of the wavelength and the emitters are designed as part of the structure.…”