Polarization controllable THz stereometamaterial absorber

In this paper, a rectangular metallic ring FSS (Frequency Selective Surfaces) with parallel metallic strips for multi band applications are characterized by the WCIP (Wave Concept Iterative Procedure) method. The proposed FSS structures are made of metallic elements that are simultaneously independent in the spatial domain and uncoupled in the spectral domain. Thus the FSS multiband behavior can be achieved only by a building process based on independent metallic elements in both domains. The resonant characteristics of the proposed FSS are determined. The structure shows three resonant frequencies when the incident wave is x-polarized and three resonant frequencies when the source is polarized in the orthogonal direction. A variation in the length of the strips and the rectangular ring allows a fine tuning in the FSS resonant frequencies to give raise to tuned bandwidths. The suppression of a resonant frequency can be insured either by the elimination of the responsible metallic strip or by the insertion of a PIN diode switch. Three FSS structures are manufactured and characterized. The FSS bandwidth can be enhanced in both perpendicular FSS exciting source directions by only varying the strips lengths and the ring dimensions to the corresponding resonant frequencies. A good agreement is obtained when the WCIP results are compared with the simulations of COMSOL Multiphysics software and experiment.

In this paper, a dual-band Frequency Selective Surface (FSS) absorber is presented for Wireless Local Area Network (WLAN) security. The FSS absorber is designed for two frequencies of interest, i.e., 2.45 GHz (lower band) and 5.25 GHz (upper band), respectively. FSS design consists of two layers; first layer consists of conducting square-loop elements while second layer consists of resistive square-loop elements, placed in-front of a conducting FSS layer. The proposed FSS design provides good frequency stability for oblique incidences for perpendicular (TE) and parallel (TM) polarizations. It provides better absorption rate for 2.45 GHz and 5.25 GHz frequency bands and allow the transmission of other microwave frequencies. Also, the proposed FSS design reduces multipath fading of additional WLAN signals which occurred due to the placement of conducting FSS layer. Presented results demonstrate that the proposed FSS design has a stable frequency response for the desired frequency bands for TE and TM polarizations with good absorption rate when the incident wave angle varied from 0<SUP>0</SUP> to 45<SUP>0</SUP>.

Metamaterial terahertz absorbers composed of a frequency selective layer followed by a spacer and a metallic backplane have recently attracted great attention as a device to detect terahertz radiation. In this work, we present a quasistatic dynamic circuit model that can decently describe operational principle of metamaterial terahertz absorbers based on interference theory of reflected waves. The model comprises two series LC resonance components, one for resonance in frequency selective surface (FSS) and another for resonance inside the spacer. Absorption frequency is dominantly determined by the LC of FSS while the spacer LC changes slightly the magnitude and frequency of absorption. This model fits perfectly for both simulated and experimental data. By using this model, we study our designed absorber and we analyze the effect of changing in spacer thickness and metal conductivity on absorption spectrum.

Metamaterials (MMs) are periodic and/or non-periodic subwavelength structures with a unique response to electromagnetic (EM) waves compared to conventional materials. MMs possess negative permittivity and/or permeability; the combination of both negative is not found in conventional materials. The shape, dimensions, and materials used in the MM determine its ultimate working frequency and response. Owing to their peculiar properties, MMs have found new-age applications such as cloaking, perfect absorber, hyperlenses, modulators, holography, etc. Graphene is a remarkable material with distinctive properties, including excellent thermal and electrical conductivity, very high mechanical strength, along with having a zero bandgap. Further, one of the most important properties of graphene, which has enabled it to be widely used as/along with MMs, is its tunable response to EM waves via a change in conductivity when its chemical potential is varied by applying a bias or doping. Frequency selective surfaces (FSSs), or flat MMs, and MMs utilizing graphene, find applications for defense and security systems in infrared, terahertz, and microwave frequency range. The broad areas of application include stealth, communications, and imaging. Stealth applications aim to prevent radar detection by absorbing or dissipating the incoming EM waves using graphene MMs or FSSs [which act as radar absorbing surfaces (RASs)]. Another important stealth application, although a futuristic one, is cloaking. Fast, secure, and high volume data transfer is critical for any security system, and graphene MMs can improve upon the existing technologies, particularly in the terahertz frequency range. Graphene MMs can be used to develop lenses, mirrors, hyperlenses, modulators, etc., for infrared (thermal) and terahertz imaging systems. In the current chapter, the basic properties of graphene, the working of FSSs and RASs, and applications of graphene-based MMs in defense and security systems are discussed.

Perfect metamaterial absorber (PMA) is an attractive optical wavelength absorber with potential solar energy and photovoltaic applications. Perfect metamaterials used as solar cells can improve efficiency by amplifying incident solar waves on the PMA. This study aims to assess a wide-band octagonal PMA for a visible wavelength spectrum. The proposed PMA consists of three layers: nickel, silicon dioxide, and nickel. Based on the simulations, polarisation-insensitive absorption transverse electric (TE) and transverse magnetic (TM) modes were achieved due to symmetry. The proposed PMA structure was subjected to computational simulation using a FIT-based CST simulator. The design structure was again confirmed using FEM-based HFSS to maintain pattern integrity and absorption analysis. The absorption rates of the absorber were estimated at 99.987% and 99.997% for 549.20 THz and 653.2 THz, respectively. The results indicated that the PMA could achieve high absorption peaks in TE and TM modes despite being insensitive to polarisation and the incident angle. Electric field and magnetic field analyses were performed to understand the absorption of the PMA for solar energy harvesting. In conclusion, the PMA possesses outstanding visible frequency absorption, making it a promising option.

This paper deals with a novel Frequency Selective Surface (FSS) Electromagnetic shield that operates in the low 5G vertical applications. This FSS is designed for the purpose of serving as an electromagnetic shield to eliminate EMI. The FSS designed operates at a frequency of 5GHz with a bandwidth of 1.45GHz providing a shielding of more than 40dB. The proposed FSS uses a polyester sheet as substrate and uses silver for the metallization of the FSS. Since the proposed FSS is symmetric, it behaves similarly when a Transverse Electric (TE) or a Transverse Magnetic (TM) wave is incident. The structure was designed and simulated using CST software. The results show that this FSS blocks electromagnetic radiation at lower frequencies as intended.

The plasmonic metamaterial perfect absorber (MPA) is a recently developed branch of metamaterial which exhibits nearly unity absorption within certain frequency range.[1-6] The optically thin MPA possesses characteristic features of angular-independence, high Q-factor and strong field localization that have inspired a wide range of applications including electromagnetic wave absorption,[3, 7, 8] spatial[6] and spectral[5] modulation of light,[9] selective thermal emission,[9] thermal detecting[10] and refractive index sensing for gas[11] and liquid[12, 13] targets. In this work, we demonstrate a MPA working at terahertz (THz) regime and characterize it using an ultrafast THz time-domain spectroscopy (THz-TDS). Our study reveal an ultra-thin Fabry-Perot cavity mechanism compared to the impedance matching mechanism widely adopted in previous study [1-6]. Our results also shows higher-order resonances when the cavities length increases. These higher order modes exhibits much larger Q-factor that can benefit potential sensing and imaging applications. [1] C. M. Watts, X. L. Liu, and W. J. Padilla, "Metamaterial Electromagnetic Wave Absorbers," Advanced Materials, vol. 24, pp. 98-120, Jun 19 2012. [2] M. Hedayati, F. Faupel, and M. Elbahri, "Review of Plasmonic Nanocomposite Metamaterial Absorber," Materials, vol. 7, pp. 1221-1248, 2014. [3] N. I. Landy, S. Sajuyigbe, J. J. Mock, D. R. Smith, and W. J. Padilla, "Perfect metamaterial absorber," Physical Review Letters, vol. 100, p. 207402, May 23 2008. [4] H. R. Seren, G. R. Keiser, L. Cao, J. Zhang, A. C. Strikwerda, K. Fan, et al., "Optically Modulated Multiband Terahertz Perfect Absorber," Advanced Optical Materials, vol. 2, pp. 1221-1226, 2014. [5] D. Shrekenhamer, J. Montoya, S. Krishna, and W. J. Padilla, "Four-Color Metamaterial Absorber THz Spatial Light Modulator," Advanced Optical Materials, vol. 1, pp. 905-909, 2013. [6] S. Savo, D. Shrekenhamer, and W. J. Padilla, "Liquid Crystal Metamaterial Absorber Spatial Light Modulator for THz Applications," Advanced Optical Materials, vol. 2, pp. 275-279, 2014. [7] H. Tao, N. I. Landy, C. M. Bingham, X. Zhang, R. D. Averitt, and W. J. Padilla, "A metamaterial absorber for the terahertz regime: Design, fabrication and characterization," Optics Express, vol. 16, pp. 7181-7188, May 12 2008. [8] J. Hao, J. Wang, X. Liu, W. J. Padilla, L. Zhou, and M. Qiu, "High performance optical absorber based on a plasmonic metamaterial," Applied Physics Letters, vol. 96, p. 251104, 2010. [9] X. Liu, T. Tyler, T. Starr, A. F. Starr, N. M. Jokerst, and W. J. Padilla, "Taming the Blackbody with Infrared Metamaterials as Selective Thermal Emitters," Physical Review Letters, vol. 107, p. 045901, 07/18/ 2011. [10] T. Maier and H. Brückl, "Wavelength-tunable microbolometers with metamaterial absorbers," Optics Letters, vol. 34, pp. 3012-3014, 2009/10/01 2009. [11] A. Tittl, P. Mai, R. Taubert, D. Dregely, N. Liu, and H. Giessen, "Palladium-Based Plasmonic Perfect Absorber in the Visible Wavelength Range and Its Application to Hydrogen Sensing," Nano Letters, vol. 11, pp. 4366-4369, 2011/10/12 2011. [12] N. Liu, M. Mesch, T. Weiss, M. Hentschel, and H. Giessen, "Infrared Perfect Absorber and Its Application As Plasmonic Sensor," Nano Letters, vol. 10, pp. 2342-2348, Jul 2010. [13] G. H. Li, X. S. Chen, O. P. Li, C. X. Shao, Y. Jiang, L. J. Huang, et al., "A novel plasmonic resonance sensor based on an infrared perfect absorber," Journal of Physics D-Applied Physics, vol. 45, p. 205102, May 23 2012.

Performance analysis of frequency selective reflectors based on rectangular loop pair for wideband applications

Uniformity improvement of microwave heating with switchable frequency selective surface

This paper describes a millimeter-wave thin lens that exhibits different beam-shaping characteristics depending on the polarization of the incident waves. The proposed unit cell topologies, which use multiple rectangular patches and rectangular-slotted grids, enable thinner (= 0.05λ 0 ) and smaller (= 0.168λ 0 ) features than in previous polarization-dependent lenses. An appropriate set of the proposed unit cells is shown to cover a tunable phase range of 180° with respect to one polarized wave but have an almost-zero tunable range of phase shifts with respect to another polarized wave. Thus, using this unit cell set for x-polarized incident waves, the proposed lens operates as a convex lens, whereas for y-polarized incident waves, the lens operates as a frequency selective surface. This confirms that gain variations of 13 dB or more can be differentiated according to the polarization of the incident waves on the lens, supporting polarization-dependent beam-shaping capability as a function of the polarization of incident waves.

in this paper, a novel Frequency Selective Surface (FSS) with polarization staggered bands is proposed. The beams in orthogonal polarization of different frequency bands are divided into a group and transmitted the FSS. The rest are divided into another group and are reflected by the FSS. The FSS with polarization staggered bands is good at separation the bands with narrow transition zone, which realizes transmission and reflection of the incident waves in four different physical mechanisms. What is more, a new frequency separation scheme in quasi-optical feed system is discussed. The FSS with polarization staggered bands, which separate two bands near 90GHz and 108GHz, is fabricated and tested. The reflection coefficient of TM polarization is about 1dB, and the transmission and reflection coefficients in the other band or polarization are less than 0.6dB.

In order to get the low transmission rate in both mid infrared atmospheric window and far infrared atmospheric window, an infrared frequency selective surface composed of two layers based on hexagonal ring structure was designed. Simulation analysis using CST electromagnetic software shown that the frequency selective surface had two stopbands in both 3μm~5μm and 8μm~15μm regions, of which the average transmittance is lower than 2.5%. Therefore, this frequency selective surface realized two stopbands in infrared wavebands; This paper analyzed the filtering mechanism of the frequency selective surface based on the effective medium theory. In the end, this paper researched the effect of electromagnetic wave polarization mode, incident angle and dielectric layer thickness on the transmission properties of the frequency selective surface. The results revealed that the transmission of frequency selective surface is insensitive to polarization mode and incident angle, while the dielectric layer thickness is an important factor to the transmittance of frequency selective surface.

A subwavelength metamaterial perfect absorber (MPA) in optical communication band was proposed and tested using the finite-difference time-domain method. The absorber is periodic and comprises a top layer of diamond silicon surrounded by L-shaped silicon and a gold layer on the substrate. It can achieve dual-band perfect absorption, and one of the peaks is in the optical communication band. By changing the gap (g) between two adjacent pieces of L-shaped silicon, and the thickness (h) of the silicon layer, the resonance wavelength of absorption peak can be tuned. When the incident electromagnetic wave entered the absorber, the metamaterial absorber could almost completely consume the incident electromagnetic waves, thereby achieving more than 99% perfect absorption. The absorption peak reaches 99.986% at 1310 nm and 99.421% at 1550 nm. Moreover, the MPA exposed to different ambient refraction indexes can be applied as plasma sensors, and can achieve multi-channel absorption with high figure of merit (FOM*) value and refractive index (RI) sensitivity. The FOM* values at 1310 nm and 1550 nm are 6615 and 168, respectively, and both resonance peaks have highly RI sensitivity. The results confirm that the MPA is a dual-band, polarization-independent, wide-angle absorber and insensitive to incident angle. Thence it can be applied in the fields of optical communication, used as a light-wave filter and plasma sensor, and so on.

In general metamaterial perfect absorber, the single meta-pattern makes the single absorption band. Therefore, the multi-absorption bands need the corresponding kinds of meta-patterns. Here, we introduce the triple-band metamaterial perfect absorber utilizing only single kind of pattern. We also demonstrate the absorption mechanism of the triple perfect absorption. The first and the second absorption bands were induced by the fundamental magnetic resonance of the major and the minor axes, respectively, of cut-wire bar. The third peak was caused by the third-harmonic magnetic resonance of the major axis. Additionally, the unexpected third band was formed, which was the overlapping of the third absorption peak with another absorption peak, which was made by pairs of antiparallel currents parallel or antiparallel to the incident electromagnetic wave.

This paper proposes a reconfigurable frequency selective surface (FSS) operating in the X band composed of triangular elements periodically placed on a single FR-4 dielectric layer. The reconfiguration of the proposed FSS allows a quasi-linear variation of the rejecting resonant frequency as function of the incident wave angle. The variation of the incident wave angle is provided by rotation of the FSS structure from 0° to 40°, for the TE mode, and can be used in cognitive radio technology through a micro-controlled interface.