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Register a new userWideband THz Low-Scattering Surface Based on Combination of Diffusion and Absorption
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In this paper, a wideband and low-scattering metasurface in terahertz (THz) is introduced. The proposed coding metasurface is composed of four different graphene square patches in one layer, which has a distinct bias voltage. By optimizing the chemical potential of each patch, the reflection phase and amplitude of a designed element can be controlled in a real-time manner. The chemical potential optimizing approach is a promising method to develop metasurfaces, which can tune the reflection phase, magnitude, or polarization dynamically at different frequencies spectrum. Indeed, by adjusting the metasurface reflection profile, the suggested device can manipulate the reflected wave. Also, this metasurface can reduce reflection energy in the wide-band spectrum. The programmable surface disperses reflected power in various directions in a first frequency band and converts incident electromagnetic waves into heat at second frequency band. The obtained results demonstrate that more than 10 dB reflection reduction can be realized over 1.02 to 2.82 THz under both TE and TM polarized wave incidences. Due to the conformal properties of the graphene monolayer, the stealth feature of the metasurface is well preserved while wrapping around a metallic curved object. This optimization method has an excellent aptitude for phase, magnitude, and polarization control in various beamforming applications at the THz spectrum for high-resolution imaging and stealth technology.
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We propose wideband bandpass filters based on multipole resonances of spoof localized surface plasmons (SLSPs). The resonance characteristics and geometric tunability of SLSPs are investigated under microstrip excitations. Strong coupling with interlayer microstrip lines is proposed to join discrete multipole resonances into a continuous and flat passband. The SLSP filters exhibit wide passbands in compact sizes and well-balanced shapes, while holding satisfactory spurious rejection bands, group delays, and geometric tunability. This work exposes the SLSPs application potential in filters as novel resonators.
The accurate calculation of laser energy absorption during femto- or picosecond laser pulse experiments is very important for the description of the formation of periodic surface structures. On a rough material surface, a crack or a step edge, ultrashort laser pulses can excite surface plasmon polaritons (SPP), i.e. surface plasmons coupled to a laser-electromagnetic wave. The interference of such plasmon wave and the incoming pulse leads to a periodic modulation of the deposited laser energy on the surface of the sample. In the present work, within the frames of a Two Temperature Model we propose the analytical form of the source term, which takes into account SPP excited at a step edge of a dielectric-metal interface upon irradiation of an ultrashort laser pulse at normal incidence. The influence of the laser pulse parameters on energy absorption is quantified for the example of gold. This result can be used for nanophotonic applications and for the theoretical investigation of the evolution of electronic and lattice temperatures and, therefore, of the formation of surfaces with predestined properties under controlled conditions.
We propose a design of a THz-frequency signal generator based on a layered structure consisting of a current-driven platinum (Pt) layer and a layer of an antiferromagnet (AFM) with easy-plane anisotropy, where the magnetization vectors of the AFM sublattices are canted inside the easy plane by the Dzyaloshinskii-Moriya interaction (DMI). The DC electric current flowing in the Pt layer creates, due to the spin-Hall effect, a perpendicular spin current that, being injected in the AFM layer, tilts the DMI-canted AFM sublattices out of the easy plane, thus exposing them to the action of a strong internal exchange magnetic field of the AFM. The sublattice magnetizations, along with the small net magnetization vector $textbf{m}_{rm DMI}$ of the canted AFM, start to rotate about the hard anisotropy axis of the AFM with the THz frequency proportional to the injected spin current and the AFM exchange field. The rotation of the small net magnetization $textbf{m}_{rm DMI}$ results in the THz-frequency dipolar radiation that can be directly received by an adjacent (e.g. dielectric) resonator. We demonstrate theoretically that the radiation frequencies in the range $f=0.05-2$~THz are possible at the experimentally reachable magnitudes of the driving current density, and evaluate the power of the signal radiated into different types of resonators, showing that this power increases with the increase of frequency $f$, and that it could exceed 1~$mu$W at $f sim 0.5$~THz for a typical dielectric resonator of the electric permittivity $varepsilon sim 10$ and quality factor $Q sim 750$.
Microelectromechanical system (MEMS) focal plane array (FPA) with optical readout offers exciting opportunities for real-time terahertz (THz) imaging. However, conventional FPA suffers from a low THz absorption ratio, which further decreases the performance of THz imaging. Here, we present a simple and scalable approach for the realization of THz focal plane metamaterial array with a relatively high absorption ratio. The key idea is to combine the advantages of substrate-free structures with metamaterial. A 100 x100 THz FPA with a 150 x 150 {mu}m pixel is designed, fabricated, and characterized. The dependence of the THz absorption ratio on the thickness of SiNx dielectric substrate film is investigated. The fabricated FPA exhibits a 90.6% resonant absorption at 1.36 THz, agreeing considerably with the theoretical simulation results. Our results imply that such a substrate-free THz focal plane metamaterial array enables the realization of THz imaging.
We report a procedure to design 2-dimensional acoustic structures with prescribed scattering properties. The structures are designed from targeted properties in the reciprocal space so that their structure factors, i.e., their scattering patterns under the Born approximation, exactly follow the desired scattering properties for a set of wavelengths. The structures are made of a distribution of rigid circular cross-sectional cylinders embedded in air. We demonstrate the efficiency of the procedure by designing 2-dimensional stealth acoustic materials with broadband backscattering suppression independent of the angle of incidence and equiluminous acoustic materials exhibiting broadband scattering of equal intensity also independent of the angle of incidence. The scattering intensities are described in terms of both single and multiple scattering formalisms, showing excellent agreement with each other, thus validating the scattering properties of each material.
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