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Manipulating acoustic wavefront by inhomogeneous impedance and steerable extraordinary reflection.

Zhao J, Li B, Chen Z, Qiu CW - Sci Rep (2013)

Bottom Line: We unveil the connection between the acoustic impedance along a flat surface and the reflected acoustic wavefront, in order to empower a wide wariety of novel applications in acoustic community.Our designed flat surface can generate double reflections: the ordinary reflection and the extraordinary one whose wavefront is manipulated by the proposed impedance-governed generalized Snell's law of reflection (IGSL).The realization of the complex discontinuity of the impedance surface has been proposed using Helmholtz resonators.

View Article: PubMed Central - PubMed

Affiliation: 1] Department of Electrical and Computer Engineering, National University of Singapore, Singapore 117576, Republic of Singapore [2] Department of Physics and Centre for Computational Science and Engineering, National University of Singapore, Singapore 117546, Republic of Singapore and.

ABSTRACT
We unveil the connection between the acoustic impedance along a flat surface and the reflected acoustic wavefront, in order to empower a wide wariety of novel applications in acoustic community. Our designed flat surface can generate double reflections: the ordinary reflection and the extraordinary one whose wavefront is manipulated by the proposed impedance-governed generalized Snell's law of reflection (IGSL). IGSL is based on Green's function and integral equation, instead of Fermat's principle for optical wavefront manipulation. Remarkably, via the adjustment of the designed specific acoustic impedance, extraordinary reflection can be steered for unprecedented acoustic wavefront while that ordinary reflection can be surprisingly switched on or off. The realization of the complex discontinuity of the impedance surface has been proposed using Helmholtz resonators.

No MeSH data available.


Conversion from PAWs to SAWs via SAI interface.The PAW with unit amplitude and ω = 15 Krad/s is normally incident in water. Only reflected acoustic pressure is plotted. (a) The SAI of Eq.(7) is set to be ψ(y) = −11 y for y < 0 and ψ(y) = 11 y for y > 0. SAWs are bifurcated at the origin and confined near the surface. (b) The reflected sound pressure level of (a). (c) The reflected sound pressure level when a homogeneous SAI is adopted instead.
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f4: Conversion from PAWs to SAWs via SAI interface.The PAW with unit amplitude and ω = 15 Krad/s is normally incident in water. Only reflected acoustic pressure is plotted. (a) The SAI of Eq.(7) is set to be ψ(y) = −11 y for y < 0 and ψ(y) = 11 y for y > 0. SAWs are bifurcated at the origin and confined near the surface. (b) The reflected sound pressure level of (a). (c) The reflected sound pressure level when a homogeneous SAI is adopted instead.

Mentions: Beyond the acoustic-field metamorphosis, we further establish a kind of acoustic cognitive deception about a SAI surface converting propagating acoustic waves (PAW) to surface acoustic waves (SAW) in Fig. 4, by means of IGSL. The extreme angle 0° in Eq.(6) demands ψ(y) = ± 10 y. Therefore, we set the SAI of Eq. (7) slightly over that extreme, e.g., ψ(y) = −11 y for y < 0 and ψ(y) = 11 y for y > 0 are set along the flat interface symmetrically with respect to the z. In Fig. 4(a), the bidirectional surface acoustic waves are attributed to the coupling effect governed by the diffracted evanescent pre which propagates along the metasurface16. Owing to the inhomogeneous SAI interface, the ideally perfect conversion comes true in acoustics except for a little diffraction. Physically, the SAI along the flat surface provides an extra momentum to compensate the momentum mismatch between propagating waves and surface waves in acoustics, resulting in the high efficiency conversion. In contrast, if one uses a constant SAI Eq.(7) with ψ(y) = 11 along the flat surface (the homogenous SAI does not generate pre; only pro occurs), the reflected sound pressure level in Fig. 4(c) is almost uniformly spread over the space.


Manipulating acoustic wavefront by inhomogeneous impedance and steerable extraordinary reflection.

Zhao J, Li B, Chen Z, Qiu CW - Sci Rep (2013)

Conversion from PAWs to SAWs via SAI interface.The PAW with unit amplitude and ω = 15 Krad/s is normally incident in water. Only reflected acoustic pressure is plotted. (a) The SAI of Eq.(7) is set to be ψ(y) = −11 y for y < 0 and ψ(y) = 11 y for y > 0. SAWs are bifurcated at the origin and confined near the surface. (b) The reflected sound pressure level of (a). (c) The reflected sound pressure level when a homogeneous SAI is adopted instead.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3756330&req=5

f4: Conversion from PAWs to SAWs via SAI interface.The PAW with unit amplitude and ω = 15 Krad/s is normally incident in water. Only reflected acoustic pressure is plotted. (a) The SAI of Eq.(7) is set to be ψ(y) = −11 y for y < 0 and ψ(y) = 11 y for y > 0. SAWs are bifurcated at the origin and confined near the surface. (b) The reflected sound pressure level of (a). (c) The reflected sound pressure level when a homogeneous SAI is adopted instead.
Mentions: Beyond the acoustic-field metamorphosis, we further establish a kind of acoustic cognitive deception about a SAI surface converting propagating acoustic waves (PAW) to surface acoustic waves (SAW) in Fig. 4, by means of IGSL. The extreme angle 0° in Eq.(6) demands ψ(y) = ± 10 y. Therefore, we set the SAI of Eq. (7) slightly over that extreme, e.g., ψ(y) = −11 y for y < 0 and ψ(y) = 11 y for y > 0 are set along the flat interface symmetrically with respect to the z. In Fig. 4(a), the bidirectional surface acoustic waves are attributed to the coupling effect governed by the diffracted evanescent pre which propagates along the metasurface16. Owing to the inhomogeneous SAI interface, the ideally perfect conversion comes true in acoustics except for a little diffraction. Physically, the SAI along the flat surface provides an extra momentum to compensate the momentum mismatch between propagating waves and surface waves in acoustics, resulting in the high efficiency conversion. In contrast, if one uses a constant SAI Eq.(7) with ψ(y) = 11 along the flat surface (the homogenous SAI does not generate pre; only pro occurs), the reflected sound pressure level in Fig. 4(c) is almost uniformly spread over the space.

Bottom Line: We unveil the connection between the acoustic impedance along a flat surface and the reflected acoustic wavefront, in order to empower a wide wariety of novel applications in acoustic community.Our designed flat surface can generate double reflections: the ordinary reflection and the extraordinary one whose wavefront is manipulated by the proposed impedance-governed generalized Snell's law of reflection (IGSL).The realization of the complex discontinuity of the impedance surface has been proposed using Helmholtz resonators.

View Article: PubMed Central - PubMed

Affiliation: 1] Department of Electrical and Computer Engineering, National University of Singapore, Singapore 117576, Republic of Singapore [2] Department of Physics and Centre for Computational Science and Engineering, National University of Singapore, Singapore 117546, Republic of Singapore and.

ABSTRACT
We unveil the connection between the acoustic impedance along a flat surface and the reflected acoustic wavefront, in order to empower a wide wariety of novel applications in acoustic community. Our designed flat surface can generate double reflections: the ordinary reflection and the extraordinary one whose wavefront is manipulated by the proposed impedance-governed generalized Snell's law of reflection (IGSL). IGSL is based on Green's function and integral equation, instead of Fermat's principle for optical wavefront manipulation. Remarkably, via the adjustment of the designed specific acoustic impedance, extraordinary reflection can be steered for unprecedented acoustic wavefront while that ordinary reflection can be surprisingly switched on or off. The realization of the complex discontinuity of the impedance surface has been proposed using Helmholtz resonators.

No MeSH data available.