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We identify a new kind of physically realizable exceptional point (EP) corresponding to degenerate coherent perfect absorption, in which two purely incoming solutions of the wave operator for electromagnetic or acoustic waves coalesce to a single state. Such non-Hermitian degeneracies can occur at a real-valued frequency without any associated noise or nonlinearity, in contrast to EPs in lasers. The absorption line shape for the eigenchannel near the EP is quartic in frequency around its maximum in any dimension. In general, for the parameters at which an operator EP occurs, the associated scattering matrix does not have an EP. However, in one dimension, when the S matrix does have a perfectly absorbing EP, it takes on a universal one-parameter form with degenerate values for all scattering coefficients. For absorbing disk resonators, these EPs give rise to chiral absorption: perfect absorption for only one sense of rotation of the input wave.
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Control of the Scattering Properties of Complex Systems by Means of Tunable Metasurfaces
We demonstrate the ability to control the scattering properties of a two-dimensional wave-chaotic microwave billiard through the use of tunable metasurfaces located on the interior walls of the billiard. The complex reflection coefficient of the metasurfaces can be varied by applying a DC voltage bias to varactor diodes on the mushroom-shaped resonant patches, and this proves to be very effective at perturbing the eigenmodes of the cavity. Placing multiple metasurfaces inside the cavity allows us to engineer desired scattering conditions, such as coherent perfect absorption, by actively manipulating the poles and zeros of the scattering matrix through the application of multiple voltage biases. We demonstrate the ability to create on-demand coherent perfect absorption conditions at a specific frequency, and document the near-null of output power as a function of four independent parameters tuned through the coherent perfect absorption point. A remarkably low output-to-input power ratio P_{out}/P_{in} = 3:71 x 10^{-8} is achieved near the coherent perfect absorption point at 8.54 GHz.
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- Award ID(s):
- 2148318
- PAR ID:
- 10492133
- Editor(s):
- Sirko, Leszek
- Publisher / Repository:
- Polish Academy of Sciences
- Date Published:
- Journal Name:
- Acta Physica Polonica A
- Volume:
- 144
- Issue:
- 6
- ISSN:
- 1898-794X
- Page Range / eLocation ID:
- 421 to 428
- Subject(s) / Keyword(s):
- Coherent Perfect Absorption, tunable metasurfaces, scattering zeros and poles
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.12693/APhysPolA.144.421
