An invisible acoustic sensor based on parity-time symmetry

Fleury, Romain; Sounas, Dimitrios L.; Alù, Andrea

doi:10.1038/ncomms6905

Cited by 679 publications

(444 citation statements)

References 43 publications

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“…However, this technique is only valid for a single physical fi eld, e.g., an invisible electromagnetic sensor or an invisible acoustic detector. [2][3][4] Consequently, a single-functional sensor is invisible to an acoustic monitoring receiver, but it can be easily detected using a remote thermal imager. Is it possible to create a sensor that is invisible in multiple physical fi elds while maintaining the same sensing functionality?…”

Section: Doi: 101002/adma201502513mentioning

confidence: 99%

“…This is a more advanced technique because previous "cloaking a sensor" techniques were only valid in a single physical fi eld. [1][2][3][4] To this day, no theoretical or experimental works have been proposed that cloak or camoufl age a sensor in a multiphysical environment. We believe this is a step toward cloaking a sensor in a realistic environment, without it being detected by different types of remote observers.…”

Section: Doi: 101002/adma201502513mentioning

confidence: 99%

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Invisible Sensors: Simultaneous Sensing and Camouflaging in Multiphysical Fields

et al. 2015

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maintaining its receiving ability. However, this technique is only valid for a single physical fi eld, e.g., an invisible electromagnetic sensor or an invisible acoustic detector. [2][3][4] Consequently, a single-functional sensor is invisible to an acoustic monitoring receiver, but it can be easily detected using a remote thermal imager. Is it possible to create a sensor that is invisible in multiple physical fi elds while maintaining the same sensing functionality? This is very challenging, if not impossible, to achieve, even using the concept of metamaterials, which are man-made composites that control waves and energy fl ux in unprecedented ways, resulting in exotic behaviors that are absent in nature. For example, electromagnetic metamaterials were proposed to manipulate electromagnetic waves and produce an invisibility cloak. [5][6][7] This pioneering idea motivated a number of significant applications, such as the wave concentrator and rotator. [8][9][10] Other than the electromagnetic waves, metamaterials have been created to manipulate other waves such as acoustic waves, [11][12][13] elastic waves, [ 14,15 ] magnetostatic fi elds, [ 16 ] and static forces.[ 17 ]More recently, metamaterials were presented that control the DC current [18][19][20][21][22][23][24][25][26] and the heat fl ux. [27][28][29][30][31][32][33][34][35][36][37] However, these devices were designed to cloak an object in a single physical fi eld.Advanced and multifunctional metamaterials are highly desirable for most practical applications. More recently, some attempts to cloak an object in multiple physical fi elds have been made, in particular, the bifunctional thermalelectric invisibility cloak [ 38 ] and independent manipulation [ 39 ] were proposed. Later, the fi rst experiment was carried out to simultaneously cloak an air cavity in the electric and thermal fi elds. [ 40 ] This sample was fabricated through a sophisticated man-made metamaterial structure with many holes drilled in a silicon plate that were, then, fi lled with poly(dimethylsiloxane) (PDMS). In our work, we found that natural materials with simple structure can also simultaneously manipulate multiphysical fi elds. We fabricated a device that acted as a "mask" for both thermal and electric fi elds and behaved as a multifunctional invisible sensor.To date, the theory of "cloaking a sensor" is only valid for a single physical fi eld. [ 1 ] In this study, we present the fi rst invisible sensor theory for static multiphysical-fi eld. This multiphysical invisible sensor has three features that distinguish it from conventional DC and thermal metamaterial devices, especially different from the bifunctional cloak for an air cavity. [ 40 ] First, we allow the sensor to "see through and behind" the cloaked region in multiphysical fi elds. As a result, the sensor is invisible and receives proportional incoming signals at the same time, and it is able to "open its eyes" behind the cloak to receive information from the outside multiphysical When a sensor is used to probe a ph...

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Section: Doi: 101002/adma201502513mentioning

confidence: 99%

Section: Doi: 101002/adma201502513mentioning

confidence: 99%

Invisible Sensors: Simultaneous Sensing and Camouflaging in Multiphysical Fields

et al. 2015

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“…Based on unidirectional invisibility in acoustics, a noninvasive, shadow-free, fully invisible acoustic sensor with PT symmetry was recently demonstrated [140]. Unidirectional invisibility at EPs in optics may also have remarkable implications for noninvasive sensing.…”

Section: Discussionmentioning

confidence: 99%

Unidirectional reflectionless light propagation at exceptional points

et al. 2017

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Abstract:In this paper, we provide a comprehensive review of unidirectional reflectionless light propagation in photonic devices at exceptional points (EPs). EPs, which are branch point singularities of the spectrum, associated with the coalescence of both eigenvalues and corresponding eigenstates, lead to interesting phenomena, such as level repulsion and crossing, bifurcation, chaos, and phase transitions in open quantum systems described by non-Hermitian Hamiltonians. Recently, it was shown that judiciously designed photonic synthetic matters could mimic the complex non-Hermitian Hamiltonians in quantum mechanics and realize unidirectional reflection at optical EPs. Unidirectional reflectionlessness is of great interest for optical invisibility. Achieving unidirectional reflectionless light propagation could also be potentially important for developing optical devices, such as optical network analyzers. Here, we discuss unidirectional reflectionlessness at EPs in both parity-time (PT)-symmetric and non-PT-symmetric optical systems. We also provide an outlook on possible future directions in this field.

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“…This largely originates from the work of Bender [9,10], who showed that operators with real spectra are not necessarily Hermitian. PT-symmetric potentials have since been translated into optics and acoustics where it has been realised that such potentials can be perfectly transparent for waves incident from one side [11][12][13][14][15][16], 2 an effect that has been confirmed in recent experiments [16][17][18][19].…”

Section: Introductionmentioning

confidence: 98%

Spatiotemporal deformations of reflectionless potentials

Horsley

Longhi

2017

Phys. Rev. A

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Reflectionless potentials for classical or matter waves represent an important class of scatteringless systems encountered in different areas of physics. Here we mathematically demonstrate that there is a family of non-Hermitian potentials that-in contrast to their Hermitian counterpartsremain reflectionless even when deformed in space or time. These are the profiles that satisfy the spatial Kramers-Kronig relations. We start by considering scattering of matter waves for the Schrödinger equation with an external field, where a moving potential is observed in the KramersHenneberger reference frame. We then generalise this result to the case of electromagnetic waves, by considering a slab of reflectionless material that is both scaled and has its centre displaced as an arbitrary function of position. We analytically and numerically demonstrate that the backscattering from these profiles remains zero, even for extreme deformations. Our results indicate the supremacy of non-Hermitian Kramers-Kronig potentials over reflectionless Hermitian potentials in keeping their reflectionless property under deformation, and could find applications to e.g. reflectionless optical coatings of highly deformed surfaces based on perfect absorption.

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An invisible acoustic sensor based on parity-time symmetry

Cited by 679 publications

References 43 publications

Invisible Sensors: Simultaneous Sensing and Camouflaging in Multiphysical Fields

Invisible Sensors: Simultaneous Sensing and Camouflaging in Multiphysical Fields

Unidirectional reflectionless light propagation at exceptional points

Spatiotemporal deformations of reflectionless potentials

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