Experimental Realization of Full Control of Reflected Waves with Subwavelength Acoustic Metasurfaces

Abstract

Metasurfaces with subwavelength thicknesses have exhibited unconventional phenomena in ways that could not be mimicked by traditional materials. Here we report on the analytical design and experimental realizations of acoustic metasurfaces with hitherto inaccessible functionality of manipulating the reflected waves arbitrarily. By suitably designing the phase-shift profile with a 2π span induced by labyrinthine units, the metasurface can reflect acoustic waves in an unusual yet controllable manner. Anomalous reflection and ultrathin planar lenses are both demonstrated with carefully designed metasurfaces. Remarkably, the free manipulation of phase shifts offers great flexibility in the design of nonparaxial acoustic self-accelerating beams with arbitrary trajectories. With extraordinary wave-steering ability, the metasurface should open exciting possibilities for designing compact acoustic components with versatile potential and may find a variety of applications ranging from ultrasound imaging to caustic engineering where designing the shape of a focused trajectory of sound is required.

Ultrathin Acoustic Metasurface-Based Schroeder Diffuser

“…In addition, SDs usually do not complement the visual appearance of a space because of their large size and irregular surface. Although active methods may offer a solution to this limitation [15], they are much more expensive and complicated and therefore less practical compared to their passive counterpart.In this paper, we revisit the SD and redesign it using the concept of an acoustic metasurface [16][17][18][19][20][21][22][23][24][25]. Despite the considerable efforts dedicated to the research on acoustic metamaterials and acoustic metasurfaces , they are *…”

Broadband reflected wavefronts manipulation using structured phase gradient metasurfaces

“…Besides, some researchers have demonstrated that the structure of coiling-up space or subwavelength corrugated surface can be used to design AMS with the phase change covering 0∼2π range. [12][13][14][15][16][17][18][19][20][21][22] And then some novel phenomena are demonstrated, such as the anomalous reflection and refraction, [12][13][14][15][16][17][18] and the planar acoustic axicon and lens. [19][20][21][22] Ding et al 23,24 have proposed that the split hollow sphere and double-split hollow sphere, as acoustic resonator, can be also used to construct AMS.…”

Omnidirectional ventilated acoustic barrier

“…Here these parameters are chosen as Fig. 2(a), the coiled structure has a transmission peak and phase abruption at the frequency of 5600Hz where the Fabry-Perot resonance occurs [14,15]. On the other hand, the hollow pipe unit always allows a unity transmission as long as this unit has a subwavelength size.…”

“…Although the advance of metamaterials [10][11][12][13][14][15][16][17][18][19][20][21] has overcome the problem of limited acoustical properties available in nature and enabled substantial reduction in both the thickness and mass density of sound-proof structures such as by using membrane-type metamaterials [3][4][5][6], there is still a fundamental limit that the inserted natural or artificial materials necessarily lead to discontinuity of the surrounding air, making them not practical in environments in need of ventilation. Despite the recent emergence of open structures for sound insulation, they need to decorate the inner boundaries of a waveguide with 3 metasurfaces [14][15][16][19][20][21] for generating anomalous reflection and therefore have to be bulky-sized, angular-dependent and inapplicable to free space [7]. To date, mechanism for effectively blocking omnidirectional low frequency sound while keeping high-efficiency ventilation property is still to be explored as a result of its significance to the design and application of sound insulators.…”