Metallic Ground Research Articles

Electric polarization and magnetization in metals

A feature of the “modern theory” is that electric polarization is not well-defined in a metallic ground state. A different approach invokes the general existence of a complete set of exponentially localized Wannier functions, with respect to which general definitions of microscopic electronic polarization and magnetization fields, and free charge and current densities are always admitted. These definitions assume no particular initial electronic state of the crystal, and the set of microscopic fields satisfy the usual relations of classical electrodynamics. Notably, when applied to a trivial insulator initially occupying its T=0T=0 ground state, the expressions for the unperturbed polarization and orbital magnetization, and for the orbital magnetoelectric polarizability tensor obtained from these different approaches can agree. However, the “modern theory of magnetization” has been extended via thermodynamic arguments to include metals and Chern insulators. We here compare with that generalization and find disagreement; the manner in which the expressions differ elucidates the distinct philosophies of these approaches. Our approach leads to the usual electrical conductivity tensor in the long-wavelength limit; in the absence of any scattering mechanisms, the dc divergence of that tensor is due to the free current density and the finite-frequency generalization of the anomalous Hall contribution arises from a combination of bound and free current densities. As well, in the limit that the electronic ground state is that of a trivial insulator, our expressions reduce to those expected for the unperturbed polarization and magnetization, and the electric susceptibility.

Broadband phase-modulated metasurface based on vanadium dioxide patches in microwave band

Phase-modulated metasurfaces (PMMs) have attracted considerable attention because of their widespread application in many fields. However, the most existing PMMs are only available in a relatively narrow band. In this paper, we propose a design of a broadband PMM based on vanadium dioxide (VO2) patches. The unit cell of the proposed PMM is composed of a surface layer supported by a 0.5 mm F4B with a dielectric constant of εr = 2.65, and a dielectric layer with a metal ground on its back. The surface layer consists of two opposite T-shaped metal patches connected by a VO2 patch. The VO2 patch can be used as an active element due to the insulator-to-metal transition of VO2. The process of phase transition is achieved by direct heating with a heating plate, without additional feeders affecting the performance of the PMM. The designed PMM can achieve a broadband phase difference within 180° ± 37° from 6.94 to 20.84 GHz, with a fractional bandwidth of 100%. Both full wave simulation and measurement results show that the proposed metasurface presents a good phase reconstruction performance over a wideband frequency range.

A ±45°-Polarized Antenna System With Four Isolated Channels for In-Band Full-Duplex (IBFD)

An in-band full-duplex (IBFD) antenna system having four ports with good self-interference cancellation (SIC) is presented in this article. Two of the four ports provide +45°-polarized radiation and the other two generate − 45°-polarized radiation. Every port of the proposed antenna is well isolated from the other three ports, enabling simultaneous transmitting (TX) and receiving (RX) with both two polarizations. To achieve this goal, three different types of couplings need to be addressed simultaneously. In this work, a novel isolation feed network is proposed, which is the first of its kind that can achieve three targets at the same time, i.e., feeding the antenna differentially, forming the original horizontal and vertical polarizations into ± 45° polarizations, and canceling out the reflected and coupled signals between the TX and RX ports. Then, a double-antenna IBFD system with four isolated channels is attained by combining the proposed feed network, defected ground structure (DGS), cross-shaped walls, and metal baffles, which effectively mitigated all the three types of couplings at the same time. The double-antenna system has high isolations of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$&gt;$ </tex-math></inline-formula> 39 dB between any two of the four ports from 3.3 to 3.9 GHz. The four radiation patterns obtained by exciting the four ports are very similar to each other and are stable with frequency, which makes it an excellent candidate for 5G sub-6 GHz IBFD applications.

A Compact Dual-Polarized Patch Antenna With L-Shaped Short Pins

A compact dual-polarized patch antenna with L-shaped short pins is proposed. The proposed antenna is configured with two substrates of 1.524 and 1.5 mm thickness, stacked by two prepregs of 2 × 95 µm thickness. The top layer is a rectangle patch with a T-shaped slot, two T-shaped branches, and two L-shaped short pins, which are shorted to the bottom layer of the metallic ground with the same size pins, and is fed by two vertical coaxial probes. In total, two L-shaped short pins achieve high isolation between the two ports by introducing three rectangular slots etched on the ground, two L-shaped strips in the middle layer connected with the short pins, and two T-shaped branches. Moreover, a wider bandwidth is realized by two L-shaped strips. A prototype of 0.16 λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> × 0.16 λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> × 0.04 λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> has been fabricated, where λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> is the free-space wavelength at the center frequency. The measured isolation of better than 35 dB is obtained over the operating bandwidth of 3.46–3.58 GHz. The experimental results agree well with the simulation results, making it a competitive candidate for 5G applications in the indoor and terminal scene.

Strongly enhanced infrared absorption of HfSe2 monolayer by lanthanide doping: A first-principles study

Two-dimensional HfSe2 monolayer has great application potentials for photocatalysis and semiconductor devices. Using density functional theory calculations, we investigated the influence of lanthanide (LN) doping on the electronic, magnetic and optical properties of HfSe2 monolayer in this work. Compared to pristine HfSe2, which is non-magnetic with an indirect band gap, the LN-doped HfSe2 monolayers exhibit significantly altered ground states due to the introduction of defect states. Five of the considered dopants (La, Nd, Eu, Tm, and Lu) can lead to the formation of metallic ground states while the monolayer remained as semiconductor when doped with Ce and Pr. Spin polarized calculations indicate that the ground state of the Nd, Eu, Tm, and Pr doped monolayers has nonzero magnetic moment which was attributed to the unpaired f-electrons. More importantly, calculation results show that the absorption abilities of the LN doped HfSe2 monolayers with the metallic ground states are strongly enhanced in the infrared region, which suggested potential applications of such systems in solar energy harvesting. These results not only demonstrated the possibility of modulating the electronic, magnetic and optical properties of the HfSe2 monolayers via LN doping but also indicated the application potential of such systems for spintronics, nanoelectronics, and optoelectronics.

Feasibility study on a plasma based reflective surface for SatCom systems

Gaseous Plasma Antennas (GPAs) exploit an ionized gas to transmit and receive electromagnetic waves. GPAs offer several advantages over metal antennas since, while in use, they are electronically reconfigurable in terms of radiation pattern and operation frequency. When not used, the plasma can be turned “off”, and the GPA reverts to a dielectric tube with a very low radar cross-section. This makes GPAs suitable to be stacked into arrays, providing they can reduce co-site interference. Thus, GPAs are very appealing for Satellite Communications (SatCom). The antenna pointing and tracking obtained by steering the beam electronically, rather than using mechanically moving parts, can enable several space missions. A plasma-based reflective surface has been recently proposed in this framework to maximize reconfigurability. Such a device consists of many plasma discharges placed on top of a metallic ground plane, and the reflection of radio signals can be controlled by electronically varying the plasma properties (e.g., density). This work presents the first step toward practically implementing a plasma-based reflective surface in the X-band capable of electrically, rather than mechanically, tuning its beam steering and focusing capabilities. The study here presented combines numerical and experimental approaches. First, a target plasma discharge has been characterized experimentally to provide the plasma parameters needed to estimate the electromagnetic (EM) response using numerical simulations. Then, the numerical simulations were performed to preliminary design a plasma-based reflective surface. At first, a simplified single-element plasma cylinder was analysed. Then, the glass envelope needed to contain the plasma was added to the column, and its impact on the performance was evaluated. Finally, a finite surface of ten plasma cylinders (including glass vessels) has been considered. The preliminary results prove the capability to obtain beam-steering by tuning the plasma density within the discharges.

A design of dual band wearable MIMO antenna using Organza fabric for medical applications

A novel wearable dual-band MIMO antenna featuring good conformal characteristics under bending conditions is presented. The dielectric part of the antenna is built on a flexible substrate using layered lightweight plain weave fabric Organza with a relative permittivity of 1.63 to achieve a low-light and flabby textile. A defected ground structure (DGS) is employed for improving diverse parameters such as narrow bandwidth and resonant adjusting. The DGS part of the antenna is a resonant slot in the ground layer, placed directly under the patches. The electromagnetic energy is transmitted to the radiating slots using a recessed microstrip line feed along with semi co-planar waveguide (CPW) structure with defective ground metal in the bottom layer. It is worthwhile to point out that using the highly flexible Organza fabric with the ability to change the substrate thickness provided acceptable antenna characteristics under the bending condition in different directions. To validate the design, a prototype antenna is fabricated and experimentally investigated. The effect of substrate thickness on antenna performance is investigated by changing the number of Organza layers in both simulation and experiments. A good agreement is attained between the simulation results and the measurement results. The antenna properties such as scattering parameters, radiation patterns, and SAR values are investigated under bending conditions. Results show that the maximum measured gain is 7.8 dB at 2.4 GHz and 7.3 dB at 5 GHz. The simulated specific absorption rate (SAR) values are less than 0.336 W/Kg and 0.468 W/Kg at 2.4 GHz and 5 GHz for 1 g human body tissue, respectively. The SAR values for the bent antenna are less than 0.302 W/Kg and 0.458 W/Kg at 2.4 GHz and 5 GHz for 1 g human body tissue, respectively.

Design and analysis of high-sensitivity tunable graphene sensors for cancer detection.

A new metamaterial refractive index sensor based on the impedance matching idea is suggested to provide an ultra-narrowband absorption response at terahertz frequencies. In order to accomplish this, the graphene layer has been modeled as circuit components using the recently developed transmission line method and the recently proposed circuit model of Periodic Arrays of Graphene Disks. The given research gives a flowchart and equations for designing a sensor, greatly simplifying the sensor design approach. This study only explores Periodic Arrays of Graphene Disks but we think the offered technique is extensible to any available graphene forms that past designers supplied with a circuit model. We compare and contrast the full-wave simulation results with the suggested circuit model. The metallic ground prohibited the transmission of the episode wave, and all occurrence electromagnetic waves are restricted in the basic design between the graphene disk. As a consequence, a perfect narrowband absorption peak is obtained. Disk absorption spectra have been discovered for a variety of refractive lists. The findings of the circuit model and full-wave simulations appear to be balanced. This RI sensor is suitable for biomedical sensing because of the combination of its features. The proposed sensor's performance as a cancer early detection sensor was evaluated among biomedical sensors, and the findings indicated that the proposed sensor is an excellent candidate for this application.

Design of compact dual‐band shared‐aperture antenna system based on frequency selective surface

AbstractA miniaturized dual‐band dual‐polarization base station antenna array operating at 2.4–2.8 and 4.6–5.0 GHz is proposed in this paper. The upper‐band unit is embedded in the lower‐band unit to miniature the array size. The size of the proposed shared‐aperture antenna element is 0.28 × 0.28 . To ensure the normal radiation of dual‐band under the small frequency ratio, a meander slot frequency selective surface structure is introduced, which is electromagnetically transparent to the lower‐band unit and function as metal ground for the upper‐band unit to ensure the normal radiation of the upper and lower‐band units, respectively. Simulation and measured results show that the antenna array meets the following design specifications: dual‐band operating (voltage standing wave ratio [VSWR] &lt; 2), mutual coupling less than −20 dB basically, satisfactory gain and radiation characteristics.

Uniformly Improved Cross-Polar Discrimination in a Dielectric Resonator Antenna by Conduction-Current Control

This work, for the first time, investigates the comprehensive sources of cross-polarized (XP) radiation from a dielectric resonator antenna (DRA). The study uses a recently developed theory on DRA radiation and models the XP sources with the help of well-known definition by Ludwig. This eventually focuses on the conduction-current distribution on the metallic ground. The interpretation leads to a concept of synthesizing effective conduction current in order to satisfy the required condition of low XP fields. A representative prototype of a cylindrical DRA on engineered ground plane has been realized to operate in C-band. It exhibits nearly 12% matching bandwidth with more than 25 dB co-to-cross polar discrimination over both orthogonal (H-) and diagonal (D-) planes. Relative improvement in XP level promised by the measured data is <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim $ </tex-math></inline-formula> 15 dB in D- and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim $ </tex-math></inline-formula> 10 dB in H-planes. This proof of concept may now be extended to other DRA geometries and for practical applications in the near future.

Millimeter-Wave Patch Antennas With Ultralow Profile of 20 μm on Flexible Substrate

In applications of flexible communication electronics, the requirement for ultralow profile of antenna is gradually approaching a limit. In order to achieve a higher flexibility, it is necessitated to limit the vertical distance to 10 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> scale between the integrated antennas and the electrode ground (GND). Such a small Section height results in a severely reduced radiation efficiency and a narrowed bandwidth. In this article, the enhancement of radiation efficiency and bandwidth of a millimeter-wave (mmWave) patch antenna with 20 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> profile height are studied. On the metal GND, by properly opening two (or one) resonant slots with a width of 100 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> , strong resonance coupling between the patch antenna and the slots can be induced, leading to a greatly enhanced radiation efficiency. Meanwhile, the spectra width of TM10 mode of the patch antenna can also be effectively broadened by the mode coupling, giving rise to a greatly improved radiation bandwidth. The physical mechanism and the sensitive factors to maximize bandwidth, antenna gain, and front-to-back ratio are discussed.

A Millimeter-Wave Spoof-Surface-Plasmon-Polaritons-Fed Dual-Polarized Microstrip Patch Antenna Array

A novel millimeter-wave spoof surface plasmon polaritons (SSPPs)-fed dual-polarized microstrip patch antenna array is proposed in this article. A dual-polarized single-layered square patch antenna fed by SSPPs is investigated first acting as the radiators. A method of directly connecting two orthogonal SSPPs with two edges of the square patch is introduced to excite the TM10 and TM01 modes and to achieve promising performance simultaneously. The fabricated antenna element has a measured overlapped impedance bandwidth of 13.7%, an isolation of more than 15 dB between the two inputs, a gain of up to about 6 dBi, and stable dual-polarized radiation patterns. With the use of two SSPPs branches printed on different sides of the substrate, a compact SSPPs power divider with adjustable power dividing ratio is then investigated for realizing the series SSPPs feed network, whose design considerations are discussed in detail. By combining the feed network with the patch elements, a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1\times $ </tex-math></inline-formula> 4 SSPPs-fed dual-polarized microstrip patch antenna array is fulfilled. The fabricated prototype confirms a bandwidth of 15% and dual-polarized broadside radiations. Benefitted from the simple single-layered geometry without the metallic ground plane over the major region of array geometry and the dual-polarized unidirectional radiation, the presented designs are valuable to emerging millimeter-wave applications.

A new approach to design multi section wideband transmissive absorber using thin resistive sheets and dielectric slabs

A new design and analytical procedure are presented that greatly enhance the absorption bandwidth and absorptivity level with few dielectric layers without using the metallic ground plane. The performance of the proposed structure is beyond what is possible with Salisbury screen or Jaumann absorber. The performance improvement is obtained using the resistive sheets coated on the surface of each lossless dielectric slab. Reflected waves inside each dielectric layer are eliminated and input reflection coefficient can easily be written with the aid of binomial expansion without any approximation. So we can apply Binomial design and considerable improvement at the absorption level and bandwidth is realized by the selection of the resistive sheets with the critical resistivity values. Alternatively, we observed that transmission is independent from frequency and layer number and it can be controlled only by the initial and final layer’s dielectric constants. Two cases are analyzed as air to air and air to dielectric. Absorptivity, transmittivity and reflectivity variations are presented versus frequency in 0–20 GHz band, in both cases. It is shown that choosing three layers backed with a final layer (εrb=20) structure in air to air case gives absorptivity greater than 90% in 5.45–14.55 GHz band where fractional bandwidth is 91% at 10 GHz design frequency. The design is performed at normal incidence and also wide angular stability at a reasonable level is presented. CST Microwave Studio and AWR simulation programs are also used to prove the correctness of the proposed method.

Coherent heavy charge carriers in an organic conductor near the bandwidth-controlled Mott transition

The physics of the Mott metal-insulator transition (MIT) has attracted huge interest in the last decades. However, despite broad efforts, some key theoretical predictions are still lacking experimental confirmation. In particular, it is not clear whether the large coherent Fermi surface survives in immediate proximity to the bandwidth-controlled first-order MIT. A quantitative experimental verification of the predicted behavior of the quasiparticle effective mass, renormalized by many-body interactions, is also missing. Here we address these issues by employing organic $\kappa$-type salts as exemplary quasi-two-dimensional bandwidth-controlled Mott insulators and gaining direct access to their charge carrier properties via magnetic quantum oscillations. We trace the evolution of the effective cyclotron mass as the conduction bandwidth is tuned very close to the MIT by means of precisely controlled external pressure. We find that the sensitivity of the mass renormalization to tiny changes of the bandwidth is significantly stronger than theoretically predicted and is even further enhanced upon entering the transition region where the metallic and insulating phases coexist. On the other hand, even at its very edge of stability the metallic ground state preserves a large coherent Fermi surface with no significant enhancement of scattering.

A Novel Low-Cost Compact High-Performance Flower-Shaped Radiator Design for Modern Smartphone Applications

This manuscript examines the design principle and real-world validation of a new miniaturized high-performance flower-shaped radiator (FSR). The antenna prototype consists of an ultracompact square metallic patch of 0.116λ0 × 0.116λ0 (λ0 is the free space wavelength at 3.67 GHz), a rectangular microstrip feed network, and a partial metal ground plane. A novel, effective, and efficient approach based on open circuit loaded stubs is employed to achieve the antenna's optimal performance features. Rectangular, triangular, and circular disc stubs were added to the simple structure of the square radiator, and hence, the FSR configuration was formed. The proposed antenna was imprinted on a low-cost F4B laminate with low profile thickness of 0.018λ0, relative permittivity εr = 2.55, and dielectric loss tangent δ = 0.0018. The designed radiator has an overall small size of 0.256λ0 × 0.354λ0. The parameter study of multiple variables and their influence on the performance results has been extensively studied. Moreover, the impact of different substrate materials, impedance bandwidths, resonance tuning, and impedance matching has also been analyzed. The proposed antenna model has been designed, simulated, and fabricated. The designed antenna exhibits a wide bandwidth of 5.33 GHz ranging from 3.67 to 9.0 GHz at 10 dB return loss, which resulted in an 83.6% fractional impedance bandwidth; a maximum gain of 7.3 dBi at 8.625 GHz; optimal radiation efficiency of 89% at 4.5 GHz; strong intensity current flow across the radiator; and stable monopole-like far-field radiation patterns. Finally, a comparison between the scientific results and newly published research has been provided. The antenna's high-performance simulated and measured results are in a good agreement; hence, they make the proposed antenna an excellent choice for modern smartphones' connectivity with the sub-6 GHz frequency spectrum of modern fifth-generation (5G) mobile communication application.

Highly Sensitive Biosensor Based on Metamaterial Absorber With an All-Metal Structure

In this article, an all-metal metamaterial absorber as a sensitive biosensor is proposed in the terahertz regime for biomolecular detection, such as protein, bacillus bacteria, and cancer cells. Here, the highly sensitive characteristic of the proposed absorber is implemented by the enhanced electromagnetic loss of symmetry-broken metal structures, where two discontinuous hollow rectangular metal arms are arranged orthogonally above the metal ground plane in geometry. Finite integral theory (FIT)-based software is utilized for modeling and full-wave numerical simulation. The results show that a near-perfect absorption of 100% at 1.99 THz is achieved with a quality factor value of 87, which could be an excellent performance in the terahertz regime below 2 THz. The electric and magnetic field distribution analysis is performed to reveal the mechanism, which is the significant confinement of electromagnetic field in the specially designed metal structure. The sensing performance of a refractive index is also investigated, and the resonance frequency and peak absorption of the spectra will get shift due to the variation of biological samples. The maximum sensitivity and figure of merit reach 540 GHz/RIU and 23.5 RIU−1, respectively. In addition, the effect of polarization angles and performance under different incident angles is also discussed. The presented biosensor with high sensitivity and feasible fabrication is a good candidate for biomedical detection in the terahertz regime.

An Ultra-Thin, Triple-Band, Incident Angle-Insensitive Perfect Metamaterial Absorber.

We created an ultra-thin, triple-band incident angle-insensitive perfect metamaterial absorber (MMA) with a metallic patch and a continuous metal ground isolated by a central dielectric substrate. The top metallic patch, placed across the edges of the 0.58 mm thickness Rogers RO4003C (lossy) substrate, forms the bulk of the projected absorber's ultra-thin layer. Nonetheless, absorption is exceedingly strong, covering C-band, X-band and K-band and reaching levels of 97.8%, 99.9%, and 99.9%, respectively, under normal and even oblique (0° to 45°) incident conditions. In chosen ranges of frequency of 6.24, 10.608, and 18.624 GHz for both TM and TE mode, the displayed Q-factors were 62.4, 17.68, and 26.61, respectively. We correspondingly calculated the RAB (relative absorption bandwidth) to evaluate absorption performance. An equivalent circuit proved its performance capabilities, indicating that it would produce a high-quality MMA from ADS software. Furthermore, the absorber's performance has been verified in free space on a sample being tested using a different array of unit cells. Moreover, the proposed structures with HFSS simulators to display the MMA's absolute absorption at each absorption peak are somewhat inconsistent with the results of the CST simulator. Because of its superior performance, the ultra-thin absorber is suited for a wide range of applications, including satellite applications such as radar systems, stealth technology, imaging, and electromagnetic interference reduction.

Effect for the electronic configurations of LuVO4 induced by D4h crystal-field-splitting discovered in the systematic DFT investigation on photocatalysis capacities of vanadates

Vanadates are always a family of promising photocatalytic materials for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). To date, there is lack of systematic research and comprehensive comparison for different vanadates, especially rare-earth vanadates with outstanding optical properties, resulting in ambiguous priority for performance development of different materials. Therefore, crystal structures, optical properties, electronic structures and photocatalysis capacities of twenty-one different vanadates were investigated in details and systematically. AgVO3-C2/m is found to be the most favored in visible-light absorption, while SrVO3-Pm3¯m, LaVO3-Pnma, LaVO3-P21/n, CrVO4-Cmcm and FeVO4-P1¯ are predicted to be competitive in photo-electric conversion. Besides the essential capabilities for driving OER and HER are revealed in the examination of electronic structures, a novel phenomenon is discovered that valence band is mostly contributed by O 2p and Lu 4f states in the band structure of LuVO4-I41/amd, which has been discussed in the framework of crystal field theory, considering Jahn-Teller effects. And it can be described as tetragonal (D4h) symmetry-induced splitting Lu 4f orbitals into five orbitals of closely spaced energies. The incomplete occupation of Lu 4 fz3 orbital induces the metallic ground state and provides the opportunity to adopt donor electrons, driving the HER circle. Furthermore, effect on the electron configurations of V3+t2g2e2 for LaVO3 and V4+t2g1 for SrVO3 induced by Oh and D2h crystal-field-splitting, and the d-d electron transition between orbitals are proposed to provide a novel and essential research route about the photocatalysis capacities of other vanadates.

FSS Sandwiched Dual-Frequency Reflectarray for Mobile Communication Applications

Sandwiched frequency selective surface (FSS) is proposed as an additional reflection surface for a dual-frequency reflectarray system. The range of reflection phase for a reflectarray depends on the substrate thickness sensitively. Usually, a tradeoff between the smooth linear level and the wide reflection phase range is needed, especially for a dual-frequency system. By inserting an FSS between the ground plane and the reflecting element layer, a selective plane for the dual-frequency band is provided. For the higher frequency band, the FSS layer is a reflection plane. For the lower frequency band, it is transparent and the reflection plane is changed into the metal ground plane. A dual-band reflectarray with a scattering angle of 30 degrees is simulated and measured to validate this concept.

Dual-band terahertz absorber based on square ring metamaterial structure.

In this paper, a dual-band terahertz absorber based on metamaterial structure is designed, fabricated, and measured. The metal periodic array is located on the upper surface of a silicon wafer with a metal ground plane, while the metamaterial structure is created utilizing a square metal ring with four T-shaped metal strips loaded inside of the ring. Two absorption peaks are realized at 0.715 and 1.013 THz with high Q-factors of 152.1 and 98.3, respectively, under normal TE and TM polarized incidence. A prototype of the proposed metamaterial absorber is fabricated by electron beam lithography (EBL) and electron beam evaporation (EBE) technology. Furthermore, a terahertz time-domain spectroscopy (TDS) measurement system is employed to test the absorber sample, with good measurement results obtained. This work provides a new option for the design of multi-band terahertz metamaterial absorbers.