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Ultrathin acoustic cloaking by a conformal hybrid metasurface.

ABSTRACT: Ultrathin acoustic cloaking of obstacles with arbitrary shape is achieved by a conformal hybrid metasurface, which is composed of an outer layer of phase-control metasurface (PCM) and an inner layer of near-zero-index metasurface (NZIM). Here, the PCM and NZIM are discretized into two types of labyrinth elements. The NZIM is functionally equivalent to an equiphase area and can guide the waves around the obstacle, while the PCM can perpendicularly transfer the incident waves to the NZIM and then control the emergent waves from NZIM to propagate along the original incident direction. The efficient cloaking by hybrid metasurface tightly covered on the edges of the square and circular obstacles is demonstrated, with a total thickness only 0.62 times of operating wavelength.

SUBMITTER: Wang Y

PROVIDER: S-EPMC6722134 | biostudies-literature | 2019 Sep

REPOSITORIES: biostudies-literature

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Ultrathin acoustic cloaking by a conformal hybrid metasurface.

Wang Yihe Y Cheng Ying Y Liu Xiaojun X

Scientific reports 20190903 1

Ultrathin acoustic cloaking of obstacles with arbitrary shape is achieved by a conformal hybrid metasurface, which is composed of an outer layer of phase-control metasurface (PCM) and an inner layer of near-zero-index metasurface (NZIM). Here, the PCM and NZIM are discretized into two types of labyrinth elements. The NZIM is functionally equivalent to an equiphase area and can guide the waves around the obstacle, while the PCM can perpendicularly transfer the incident waves to the NZIM and then ...[more]

PMID: 31481745

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Project description:The geometry of the characteristic element forming the artificial structure of an electromagnetic metamaterial defines the way the metamaterial will interact with electromagnetic waves, and accordingly, how it will transmit, reflect, and absorb electromagnetic energy. Metamaterials have been discovered that can manipulate electromagnetic waves to create perfect absorption of incident electromagnetic energy using relatively simple elemental geometries. But the phenomenon is confined to very narrow frequency bandwidths owing to the mono-resonance characteristics of simple cellular structures. Complex cellular geometries based on the combination of many different fundamental building blocks may be able to constructively couple many more resonances and broaden the perfect absorption bandwidth. We describe here a metasurface based upon geometric inversion of a set of conformal mapping contours. The resulting geometry forms a nearly continuous series of perfect absorption resonances within an ultrathin (λ/165) metasurface to develop broadband absorption in a frequency range of interest for downhole chemical spectroscopy. The metasurface is derived from a geometric inversion of the Rhodonea, or more commonly called four-leaf roses, conformal mapping contours and was found to exhibit a near zero index metamaterial (NZIM) behavior. An uncooled microbolometer design is described that uses the metasurface geometry on a single VO2 thermometric substrate leading to an infrared detector with predicted maximum absorption of 99.94% at 4.3 μm and an absorption bandwidth of 170% FWHM on 15.8 μm center wavelength, coincident with important chemical spectra of downhole hydrocarbons. The infrared detector design has a predicted maximum detectivity D* = 1.5 × 109 cm[Formula: see text]/W and noise equivalent difference temperature NEDT of 70 mK at a frame rate of 60 Hz. These levels of detector performance conventionally would be achievable only with cryogenically cooled technologies and could represent a significant step in the effort towards deploying an in situ infrared chemical spectroscopy sensor into downhole logging applications.

Project description:Zero-refractive-index (ZRI) phononic crystals (PhCs), in which acoustic waves can be transmitted without phase variations, have considerable potential for engineering wavefronts and thus are applicable to invisibility cloaking. However, the creation of the transmissive cloaking achieved by ZRI-PhCs is challenging under an oblique incidence, which substantially hinders their practical applications. Here, we experimentally demonstrate acoustic transmissive cloaking with the adjustable capacity to the incident direction. Acoustic transmissive cloaking of arbitrarily shaped obstacles can be obtained through a hybrid acoustic structure consisting of one outer layer of a programmable phase-engineered metasurface (PPEM) and one inner layer of a double zero-refractive-index (DZRI)-PhC. The DZRI-PhC is functionally the same as an equiphase area and can guide acoustic waves around the obstacle, a process known as acoustic tunneling. The PPEM perpendicularly transfers the incident acoustic waves to the DZRI-PhC and allows the emergent waves from the DZRI-PhC to transmit along the original incident direction. The DZRI-PhC is made of an array of iron squares in the air. The reciprocal of the effective bulk modulus and the effective mass density is approximately zero at a frequency of 3015 Hz (0.5187 v 0 /a) originating from the zeroth-order Fabry-Pérot (FP) resonance that possesses infinite phase velocities. Each meta-atom of the outer metasurface consists of a line channel and four shunted Helmholtz resonators, which have effective masses that are engineered by a mechanics system. The amplitude and phase of the sound waves propagating through each meta-atom can be controlled continuously and dynamically, enabling the metasurface to obtain versatile wavefront manipulation functions. Acoustic cloaking is visually demonstrated by experimentally scanning the acoustic field over the hybrid structure at a frequency of 3000 Hz (0.5160 v 0 /a). Our work may provide applications with great potential, including underwater ultrasound, airborne sound, acoustic communication, imaging, etc.

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Ultrathin acoustic cloaking by a conformal hybrid metasurface.

Publications

Ultrathin acoustic cloaking by a conformal hybrid metasurface.

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