Digital metasurface for selective information distribution in the spatial domain in the THz region.

This paper presents a new, to the best of our knowledge, technique to control the flow of electron packets employing a switchable digital metasurface in the terahertz region. The proposed structure can act as a device that converts an electromagnetic (EM) wave into electron packets that can be represented in the form of digital bit sequences at the output. The top layer of the structure controls the intensity of the electron packets while the bottom layer involves the spatial distribution of the information with the help of electrical switching. The electrical switching is achieved with the application of suitable biasing across a vanadium dioxide (VO2) patch. This approach to the distribution of information helps feed the circuitry of an electronic system as per the requirement using electrical tuning, which is not possible in a conventional antenna system.

Design and mathematical analysis of a metasurface-based THz bandpass filter with an equivalent circuit model.

This paper presents successive studies of single-, double-, and triple-layered metasurface-based bandpass filters along with their equivalent circuit modeling and mathematical analyses. A triple-layered bandpass filter operating in the THz region is reported exhibiting flattop passband response while maintaining transmission of more than 95% over the entire passband starting from the design of a single-layered bandpass filter configuration. A stepwise mathematical analysis is carried out for the single-layered structure and compared with the simulation data, where the two results have been found in good agreement. Thereafter, the study is extended for double- and triple-layer bandpass filters. The triple-layered structure offers a very steep transition between passband and stopband with noise-free background, and thereby offers a potential candidate for 6G communication.

Graphene-based dual functional metadevice in the THz gap.

This paper presents a graphene-metal dual functional metadevice to provide two separate applications simultaneously, viz., absorption and cross-polarization conversion (CPC) of the electromagnetic (EM) wave without any structural deformations in the terahertz (THz) gap under two different biasing conditions. The meta-atom of the device bears stacked layers of metallic elliptical-shaped split rings, a thin zinc oxide (ZnO) layer, a slotted graphene layer printed over another ZnO layer backed by a continuous gold plate. It provides more than 70% absorptivity over a bandwidth of 3.40 THz (4.25 THz and 7.65 THz), with 90% absorptivity peak at 6.84 THz when the externally applied static electric field (ξ) on the patterned graphene surface is 8.52 V/nm. The change of the ξ to a value of 0.44 V/nm enables the device to produce a CPC ratio (CPCR) above 90% over a bandwidth of almost 3.87 THz (2.22 THz and 6.09 THz), with near unity polarization conversion ratio peaks occurring at 2.38 THz, 3.80 THz, and 5.82 THz. Both findings have been validated using an exhaustive equivalent circuit analysis. The design possesses ultrathin properties (λ0/12.49), along with compactness (λ0/5), which has been improved significantly compared to their microwave counterparts. The proposed metadevice finds useful applications in THz sensing, stealth technology, THz communication, detection, polarization manipulation of EM waves, etc.

Magnetically tunable metasurface comprising InAs and InSb pixels for absorbing terahertz radiation.

A magnetically tunable metasurface comprising meta-atoms with InSb-patched, InAs-patched, and unpatched pixels was simulated using commercial software to maximize the absorption of normally incident radiation in the terahertz spectral regime, with the patches decorating the illuminated face of a gold-backed polyimide substrate. Maximum absorptance of 0.99 and minimum absorptance of 0.95 can be obtained in 0.14-0.23-THz-wide bands in the 2-4-THz spectral regime, with an average tuning rate of 0.3THzT-1 and 0.24-THz dynamic range when the controlling magnetostatic field is aligned parallel to the incident electric field. The use of both InSb and InAs patches is much superior to the use of patches of only one of those materials. The design can be adapted for neighboring spectral regimes by exploiting the scale invariance of the Maxwell equations.

Graphene oxide-ferrite hybrid framework as enhanced broadband absorption in gigahertz frequencies.

The present investigation is focused on the in-situ synthesis of Graphene oxide (GO)-ferrite nanoparticle hybrid framework by gel-combustion method followed by fabrication of homogeneous, structurally stable thin (~100-120 µm) hybrid-polyurethane coating on a metallic aluminum substrate and its application on the properties of broadband absorption over the microwave frequency region. Microstructure studies of hybrid materials illustrated that small sized ferrite nanoparticles (~17 nm) are grafted on and through the graphene layers, which forms a homogeneous coating thereby. The hybrid-nanocomposite coating demonstrated superior broadband absorption properties with absorptivity higher than 90% throughout a bandwidth of ~6 GHz, and moreover, it was found that with increased loading of GO in the nanocomposite, the bandwidth range of absorption frequency increases with enhanced absorptivity. The real part and imaginary part of the surface impedance values of the coating was obtained as 377 Ω and 0 Ω, respectively, which imply that the free-space impedance of the hybrid-nanocomposite coating is matching correctly. The nanocomposite coating showed ultra-high absorptivity over the frequency band of 8-12 GHz, which has numerous practical applications as radar absorbing materials (RAM), stealth technology, electromagnetic shielding, and radiated electromagnetic interference (EMI) management in onboard spacecraft and many more.

Graphene-based metasurface for a tunable broadband terahertz cross-polarization converter over a wide angle of incidence.

In this paper, using a graphene-based metasurface, we demonstrate a unique design to develop a highly efficient, broadband, mid-infrared cross-polarization converter. The proposed graphene-based metasurface structure comprises periodical ϕ-shaped graphene on the top surface of a noble-metal-backed dielectric silicon dioxide (SiO2). The reported structure converts the incident linearly polarized wave into cross-polarized components with a peak polarization conversion ratio of more than 0.9 over a large band. Furthermore, the metasurface structure exhibits the full width at half-maximum bandwidth of 41.98% with respect to its center frequency of 5.98 THz. The physical insights behind electromagnetic polarization conversion are supported by field distributions and retrieved electromagnetic parameters. The structure works as a broadband cross-polarization converter up to 40° incident angle for both TE and TM polarizations. In addition, the structure is found to be as thin as ∼λ/6 with respect to lowermost frequency of the polarization conversion. The period of the unit cell is ∼λ/24 to support the fact that the structure can be treated as a metasurface.