Acoustic guiding and subwavelength imaging with sharp bending by sonic crystal

Abstract

A sharp bending scheme for the self-collimation of acoustic waves is proposed by simply truncating the sonic crystals. An all-angle and wide-band 90˚-bending wave guide is demonstrated with nearly perfect transmissions for Gaussian beams at a wide range of incident angles. A 90˚-bended imaging for a point source with a subwavelength resolution of 0 0.37λ is also realized by the proposed structure. These results will find applicability in the manipulation of acoustic waves by sonic crystals. In the case of wave guiding, self-collimation allows varying over a wide range of incident angles and still maintaining a narrow range of propagations along with a low-loss transmission. This type of waveguide does not depend on physical channels to confine waves, thus it gains many advantages over conventional line-defect based wave guides, for which introducing of physical boundaries in SCs or PCs leads to extra coupling loss and Fresnel reflection loss [3,5]. Moreover, profited from a long flat equifrequency contour (EFC), evanescent modes of a source placed at the input port of such waveguides can also be canalized to the output port [8,9], thus self-collimation waveguides possess a promising prospect in subwavelength applications. However, such wave guide is suffered from the intrinsic inability of self-collimation to efficiently bend

Effective impedance boundary optimization and its contribution to dipole radiation and radiation pattern control

“…Recent progress in the research area of photonic and phononic crystals and metamaterials provides a new approach to realize radiation pattern control and modulation. Early studies focused on spatial dispersion affected by spatial periodicity to modulate radiation patterns-that is, utilizing crystal anisotropy to counteract the spreading of the wave [5][6][7] -and band-edge states are the most important factors for realizing it [8][9][10] . Recently, based on the forminvariant form of Maxwell's equations under certain coordinate transformations, transformation optics for controlling the electromagnetic fields has proved to be an effective approach for manipulating ray traces 11,12 .…”

Acoustic waveguiding by pliable conduits with axial cross sections as linear waveguides in two-dimensional sonic crystals

“…[11][12][13][14][15][16] Another means of wave canalization by PhCs/SCs is self-collimation, [17][18][19] where self-collimated waves can be deflected normally at diagonal cuts of PhCs. 20 Besides, graded PhCs can be utilized for beam steering over curved paths, either by gradually rotating anisotropic basis elements 21 or by defining a gradient in scatterer sizes. 22 The above methods facilitate transmitting and steering acoustic waves along fixed paths by employing periodic scatterers on pre-defined positions.…”

Flexibly guiding of acoustic waves by one-dimensional sonic crystal with omnidirectional bandgap

“…Broadband and low-loss guiding can be achieved and the designing degree of freedom in such SCWs can be further improved by grafting some additional structures such as stubs or cavities to the sidewall of the waveguide. Another method to realize SCWs is to adopt self-collimating of 2D SCs, [8][9][10][11] in which guiding of acoustic waves relies on a well designed spatially-dependent dispersion but not the existence of a bandgap. Extensions like bending or splitting for such self-collimating waveguides can be achieved by introducing extra structures into SCs.…”