Abstract-Tricontrollable pixelated metasurface for absorbing terahertz radiation

Pankaj Kumar, Akhlesh Lakhtakia, and Pradip K. Jain

https://www.osapublishing.org/ao/abstract.cfm?uri=ao-58-35-9614

The incorporation of materials with controllable electromagnetic constitutive parameters allows the conceptualization and realization of controllable metasurfaces. With the aim of formulating and investigating a tricontrollable metasurface for efficiently absorbing terahertz radiation, we adopted a pixel-based approach in which the meta-atoms are biperiodic assemblies of discrete pixels. We patched some pixels with indium antimonide (InSb) and some with graphene, leaving the others unpatched. The bottom of each meta-atom was taken to comprise a metal-backed substrate of silicon nitride. The InSb-patched pixels facilitate the thermal and magnetic control modalities, whereas the graphene-patched pixels facilitate the electrical control modality. With proper configuration of patched and unpatched pixels, and with proper selection of the patching material for each patched pixel, the absorptance spectra of the pixelated metasurface were found to contain peak-shaped features with maximum absorptance exceeding 0.95, full-width-at-half-maximum bandwidth of less than 0.7 THz, and maximum-absorptance frequency lying between 2 THz and 4 THz. The location of the maximum-absorptance frequency can be thermally, magnetically, and electrically controllable. The lack of rotational invariance of the optimal meta-atom adds mechanical rotation as the fourth control modality.

© 2019 Optical Society of America

Abstract-Thermally sensitive scattering of terahertz waves by coated cylinders for tunable invisibility and masking

Andriy E. Serebryannikov, Kamil B. Alici, Ekmel Ozbay, and Akhlesh Lakhtakia

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-26-1-1

Temperature-sensitive scattering of terahertz (THz) waves by infinitely long, cylindrical core-shell structures was theoretically studied. Each structure is a dielectric cylinder coated with an InSb shell illuminated by either a transverse-electric (TE) or a transverse-magnetic (TM) plane wave. InSb is a thermally tunable semiconductor showing a transition from dielectric to plasmonic state at THz frequencies. Accordingly, the total scattering efficiency (TSE) can be thermally tuned for both polarization states of the incident plane wave. The spectral locations of the maxima and minima of the TSE of an InSb-coated cylinder can be exploited for cloaking the core. At least three scenarios lead to the strong suppression of scattering by a single core-shell structure in different spectral regimes when the temperature is fixed. The excitation of localized surface-plasmon resonances is the feature being common for two of them, while the effect of volumetric resonance dominates in the third scenario. Regimes that are either highly or weakly sensitive to the core material were identified. Weak sensitivity enables masking, i.e., the core material cannot be identified by a far-zone observer. The TSE minima are usually significantly sensitive to the polarization state, but ones with weak sensitivity to the polarization state also exist.

© 2018 Optical Society of America

Abstract-Bicontrollable Terahertz Metasurface with Subwavelength Scattering Elements of Two Different Materials

Francesco Chiadini, Akhlesh Lakhtakia

https://arxiv.org/abs/1711.06343

Transmission of a normally incident plane wave through a metasurface with bicontrollable subwavelength scattering elements was simulated using a commercial software. Some pixels comprising the $H-shaped scattering elements were made of a magnetostatically controllable material whereas the remaining pixels were made of a thermally controllable material, the metasurface designed to operate in the terahertz spectral regime. The co-polarized transmission coefficients were found to exhibit stopbands that shift when either a magnetostatic field is applied or the temperature is increased or both. Depending on spectral location of the stopband, either the magnetostatic field gives coarse control and temperature gives fine control or vice versa. The level of magnetostatic control depends on the magnetostatic-field configuration.

Abstract-Single and cascaded, magnetically controllable metasurfaces as terahertz filters

Andriy E. Serebryannikov, Akhlesh Lakhtakia, and Ekmel Ozbay
https://www.osapublishing.org/josab/abstract.cfm?uri=josab-33-5-834

Transmission of a normally incident, linearly polarized, plane wave through either a single electrically thin metasurface comprising H-shaped subwavelength resonating elements made of magnetostatically controllable InAs or a cascade of several such metasurfaces was simulated in the terahertz regime. Stop bands that are either weakly or strongly controllable can be exhibited by a single metasurface by proper choice of the orientation of the magnetostatic field, and a ∼19% downshift of stop bands in the 0.1–5.5 THz spectral regime is possible on increasing the magnetostatic field strength from 0 to 1 T. Better controllability and wider bandwidths are possible by increasing the number of metasurfaces in a cascade, although increase of the total losses can lead to some restrictions. ON/OFF switching regimes, realizable either by applying/removing the magnetostatic field or just by changing its orientation, exist.

© 2016 Optical Society of America

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