Diffraction angle of sound4/11/2024 ![]() ![]() It is noted a group of phase delay φ 1 ranging from 0 to 2π can be obtained by altering d 1, and φ 1 is independent with frequency. Thus, by setting proper parameters of the SRW (e.g., W, H, S), the metagrating can achieve broadband anomalous diffraction 26, and then can be used to work as a beam splitter. To sum up, the metagrating can concentrate the transmitted waves in the 1st orders under a wide work frequency range. For example, when W = 0.8 mm, S = 0.3 mm, H = 0.43 mm, the 0th-order suppressing effect was limited to the wavelength range of 1.5 mm ~1.6 mm. Moreover, when using two SRWs, the frequency band is found to be narrowed by scanning three parameters ( W, S, H). ![]() Then the area of SRW is about three times as much as when using three SRWs. In order to obtain the same phenomenon with the same frequency band as above, the parameterized scanning calculated by COMSOL shows that H should be 0.35 mm. ( 3), which is as long as one wavelength. If one SRW is used to replace the fence, the width of waveguide should be 1.5 mm according to the condition of Eq. Simpler structures, i.e., one or two SRWs can also be used to achieve the 0th-order suppressing effect, but have the following disadvantages. Consequently, the 0th order diffraction is suppressed while acoustic waves are mostly distributed in the 1st orders. When plane waves are normally incident onto the grating, the angles of diffracted waves satisfy the grating equation of \(\sin \,)=\pi \). Figure 1(a) shows the schematic diagram of a regular phase grating. ![]() The diffraction intensity characteristics of gratingįirst, we start from the transmitted intensity through the phase grating. We further determine the multifunction of the metagrating in wave steering, such as achievement of acoustic Gaussian and Bessel beams. It is found that the metagrating can convert the normally incident waves into two symmetrical directions in a wide frequency band and provide a phase delay independently with frequency. The metagrating is composed of periodic structured elements consisted by subwavelength rectangular waveguides (SRWs) to achieve the steering of acoustic waves. In this paper, we demonstrate a broadband acoustic metagrating by reconfiguring the typical diffraction effects. Based on the grating equation, the frequency-dependent specialty can be easily eliminated in the metagratings. In fact, a new broadband optical metagrating has been proposed to achieve anomalous wave steering by engineering diffraction optical gratings 22. Recently, as an emerging kind of metasurface, the artificial metagratings have received much attentions due to their more combination functions and more advantage performance over ordinary phase gratings, such as the enhanced acoustic transmission through a rigid plate 19, directional beam forming 20, and asymmetric acoustic transmission 21. Thus, the phase aberrations make the metasurface only work in a narrow frequency band. This phase profile is usually derived from the generalized laws of diffraction 18, leading to the inherent dependence on the working frequency. For example, in order to control wave trace, the metasurface must provide corresponding phase profile in different positions. However, most of the reported metasurface have certain limiting factors, i.e., the narrow work frequency band. By properly designing the positions of periodic elements, metasurface can achieve multifunctional steering of acoustic waves, i.e., acoustic focusing 1, 2, 3, 4, 5, 6, acoustic carpet cloaking 7, 8, 9, asymmetric acoustic transmission 10, 11, acoustic trapping 12, 13, acoustic holography 13, 14, 15, sound vortices 16 and Mie resonance 17. ![]() When acoustic waves reach and react with metasurface, phase and amplitude should be modulated, and then the trace of incident waves can be manipulated artificially. Acoustic metasurface is composed of periodic subwavelength elements which can exhibit untraditional manipulation of local and far-field sound pressure distributions. ![]()
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