In the proposed paper, a novel design and realization of a wide-band, oblique angle-insensitive metamaterial absorbers are presented. The absorber is designed to work over a wide range of frequencies, making it suitable for Ku-band applications. To get wide band absorption, a novel SM-shaped design with a square-tooth circular ring resonator structure is designed efficiently. The unit cell structure is designed with a dielectric substrate (FR4) with a thickness of 3.2 mm (0.16λ0), where λ0 is the wavelength of free space. The novel design of this configuration leads to wideband absorption with respect to a conventional absorber. Several physical parameters are also investigated, such as the dielectric constant, permittivity, permeability, impedance, and negative refractive index. The simulation and experimental results show from 13.60 to 16.14 GHz with 99.1% absorption, which is excellent agreement. The analysis of the proposed design indicates that it possesses the remarkable feature of being insensitive to polarization while also exhibiting high absorption even when the angle of incidence varies. For both the simulation and experiment, results are consistent with a frequency range of 13.60–16.14 GHz for normal incidence. Almost perfect absorption works well for solar cells, EM detection, and imaging applications.

This paper proposes a lightweight frequency selective surface polarization-insensitive wideband metamaterial absorber in C band and X band that employs only a few resistive elements. The proposed absorber is embodied with four quadrature slotted inner circular patch, which is horizontally and vertically bisected, and outer concentric copper rings of 0.035 mm thickness are attached with four lumped resistors placed at 90° apart. A slotted inner circular patch provides significant inductive and capacitive loading. The absorption bandwidth of 8.02 GHz with more than 90% absorption is observed from 5.69 to 13.71 GHz under normal incidence and maintains almost same absorptivity range under oblique incidence up to 45° in both transverse electric mode and transverse magnetic mode. The designed metamaterial absorber is fabricated and measured using free space measurement technique. The actual experiments and the simulated ones are in good agreement.

In order to solve the problems of low power transfer efficiency (PTE) and limited distance in magnetic coupling resonant wireless power transfer (MCR-WPT) technology. In this paper, based on the magnetic field control ability of metamaterials (MMs), the way to improve the performance of MCR-WPT systems is studied. First, the influence of MMs on the coupling of MCR-WPT system is theoretically analyzed by establishing an equivalent circuit model. Through a series of simulations and experiments, the relationships between the PTE and the array and placement of the MM slab are investigated. The results demonstrate that when one MM slab is placed in the middle, near the Tx coil or the Rx coil, the optimal PTE can be obtained by inserting one slab with $6 \times 6$, $1 \times 1$, and $6 \times 6$ arrays, respectively. Moreover, the systems with multilayer MM slabs are also studied. The measured PTEs on one, two, and three layers of MM slabs can increase by 20.6%, 29.3%, and 22.6%, respectively. The efficiency improvement capability of one MM slab is better than three slabs but worse than two slabs. This paper discusses the application of MMs in MCR-WPT systems, which has a certain reference significance.

Metamaterial lenses are appealing thin alternatives to conventional dielectric lenses. In this contribution we describe their design and application in two exemplary 77 GHz automotive radar sensors operating in monostatic and bistatic modes. The frontends are built around commercially available MMICs and small feed antennas are used in coordination with the six-layer printed circuit board-based realizations of metamaterial lenses. The design follows the principles of dielectric lenses, while the required local phase shift is obtained from a set of metasurface bandpasses. Their design uses a novel interpolation procedure to extract layout parameters for a given phase shift. Despite the small structural sizes due to the high frequency, the fabricated frequency-selective surfaces show very good performance in the required frequency range. Verification measurements were conducted on single bandpasses as well as on metamaterial lenses mounted on the radar frontend. The results agree very well with the simulation and confirm the applicability of thin lenses operating at mm-wave frequencies for automotive radar applications.

This article presents a flexible wearable KIT monopole antenna for biomedical application. A metamaterial unit cell is proposed to improve the antenna performance. The proposed antenna and the metamaterial are fabricated on 1 mm-thick polydimethylsiloxane substrate to operate in the ISM frequency band of 2.45 GHz. Integration of the metamaterial improves the gain and reduces the specific absorption rate (SAR) of the antenna. The overall dimension of the antenna with the metamaterial is 49 × 49 × 19 mm3. The designed antenna is investigated for the loading effect of the body by placing on the hand phantom model. Bending tolerances are also analyzed for x and y direction with various bend radii. Gain and SAR of the proposed antenna are 4.61 dBi and 0.868 W/kg. The results of the fabricated prototype show that the proposed wearable antenna is safe for biomedical applications.

This article presents wideband metamaterial cross-polarizer (MCP) structure for X-band applications. The proposed MCP consists of a splitted square-shaped resonating structure with two inner and one outer stub. It has an overall dimension of 8.6 mm × 8.6 mm. A wideband polarization conversion ratio (PCR) above 0.87 magnitude is achieved with a bandwidth of 3.49 GHz ranging from 8.8 to 12.29 GHz, which works for X (8–12 GHz) band. The PCR bandwidth of full width half maxima achieved is 4.55 GHz ranging from 8.5 to 13.05 GHz. Two distinct PCR peaks are observed at 9.44 and 11.47 GHz with PCR magnitude at 99.39 and 99.00% respectively. The normalized impedance and electromagnetic parameters (real and imaginary) curves proved the presence of metamaterial properties in the region of interest. Analysis of polarization conversion phenomena at two distinct frequencies is described with the help of electric field and current distribution. The structure is replicated using ANSYS HFSS 19.1 and measured inside anechoic chamber with the help of Vector Network Analyzer (VNA). The replicated and experimented responses obtained are almost similar to one another with adaptation due to fabrication liberality.

In this paper, the design of frequency reconfigurable planar antenna by incorporation of metasurface superstrate (FRPA-MSS) is presented using an artificial neural network. The dual-layer radiating structure is created on a 1.524 mm thick Rogers RO4350B substrate board (εr = 3.48, tan δ = 0.0037). The candidate antenna is designed and analyzed using a high-frequency structure simulator (HFSS) tool. The transfer matrix method is employed for the successful retrieval of electromagnetic properties of the metamaterial. Frequency reconfiguration is achieved by placing the metasurface superstrate onto the rectangular patch antenna. A simplified ANN approach has been employed for the design of metasurface incorporated proposed antenna. Presented prototypes are characterized through experimental measurements. It is found from the practical observations that the proposed antenna effectively reconfigures the tuning range from 5.03 to 6.13 GHz. Moreover, the presented antenna operates efficiently with agreeable gain, good impedance matching, and stable pattern characteristics across the entire operational bandwidth. The experimental results obtained validate the simulated performance.

In this paper, we present a linear to circular polarization converter integrated in a concrete structure to eliminate signal transmission problem originated from the concrete buildings in microwave regime. Two polarization converter samples and a control specimen made by traditional concrete are designed and their signal transmission responses are compared experimentally. Axial ratio values which can be calculated by the ratio between the co-polar transmission and cross-polar transmission results of the proposed samples are below 3 dB and highly sufficient for linear to circular polarization conversion activity. The operating frequency for the proposed sample 1 is between 6 and 6.5 GHz with 500 MHz of bandwidth. The proposed sample 2 exhibits dual-band operation covering frequency bands, 4.58–5.13 and 6.0–6.4 GHz with bandwidths of 550 and 400 MHz, respectively. Operating frequencies of the samples are in the WIMAX frequency bands. In addition, the liner to circular polarization converter design integrated to concrete has a huge potential to improve reflection and directivity parameters of many antennas if it is considered as a radome.

This paper presents a compact dual-band filtering antenna without extra employing of filter structures. The antenna is designed using a planar dual-composite right/left-handed (D-CRLH) transmission line unit cell, where the filtering function is achieved through current cancellation between the D-CRLH resonators. The antenna is designed to function at 3.0 and 5.1 GHz, which can serve different WLAN applications. The antenna is a co-planar waveguide fed with a very compact size of only 30 × 16 mm2. Compared to the conventional patch antenna, the antenna size is only 17% at 3.0 GHz and 31% at 5.1 GHz. Despite the small size, the antenna preserves a good omni-directional radiation pattern at the two resonant frequencies with a measured realized gain of 2 and 2.7 dB, respectively. At the stopband in-between the two resonant bands, the reflection coefficient is almost 0 dB at 4.25 GHz and complete non-radiation is proved with a −11 dB measured realized gain. The different antenna filtering functions are verified by full-wave simulation and measurements.

An analysis about the backscattering characteristics of a metamaterial coated magnetodielectric sphere covered with a metasurface has been presented. The effects of various types of metamaterial coatings and surface reactances of lossless metasurface upon the backscattering cross-section of a metamaterial coated magnetodielectric sphere covered with a metasurface have been studied. It is shown that the negligible backscattering cross-section from a double near-zero metamaterial coated magnetodielectric sphere can be enhanced significantly by using specific types of lossless metasurfaces. These types of enhanced backscattering cross-section find applications in the radar detection problems. The proposed theory is also extended to the lossy double negative metamaterial coated magnetodielectric sphere covered with a lossless metasurface. During the study, it is found that for a specific part of the lossy double negative metamaterial bandwidth, two specific types of lossless metasurfaces can be used to reduce the backscattering cross-section as compared to the backscattering cross-section of a lossy double negative metamaterial coated magnetodielectric sphere without metasurface.

Sensors based on metamaterial absorbers are very promising when it comes to high sensitivity and quality factor, cost, and ease of fabrication. The absorbers could be used to sense physical parameters such as temperature, pressure, density as well as they could be used for determining electromagnetic properties of materials and their characterization. In this work, an attempt has been made to explore the various possible applications of these sensors. Metamaterial-based sensors are very popular for its diverse applications in areas such as biomedical, chemical industry, food quality testing, agriculture. Split-ring resonators with various shapes and topologies are the most frequently used structures where the sensing principle is based on electromagnetic interaction of the material under test with the resonator. Overcoming the design challenges using metamaterial sensors involving several constraints such as cost, compactness, reusability, ease in fabrication, and robustness is also addressed.

The progressions in the field of wireless technology can be highly attributed to the development of antennas, which can access high data rates, provide significant gain and uniform radiation characteristics. One such antenna called the Vivaldi antenna has attracted the utmost attention of the researchers owing to its high gain, wide bandwidth, low cross-polarization, and stable radiation characteristics. Over the years, different procedures have been proposed by several researchers to improve the performance of the Vivaldi antennas. Some of these different approaches are feeding mechanisms, integration of slots, dielectric substrate selection, and radiator shape. Correspondingly, the performance of a Vivaldi antenna can be increased by including dielectric lens, parasitic patch in between two radiators, corrugations, as well as metamaterials. This paper gives a systematic identification, location, and analysis of a large number of performance enhancement methods of Vivaldi antenna design depicting their concepts, advantages, drawbacks, and applications. The principal emphasis of this article is to offer an outline of the developments in the design of Vivaldi antennas over the last few years, where the most important offerings, mostly from IEEE publications, have been emphasized. This review work aims to reveal a promising path to antenna researchers for its advancement using Vivaldi antennas.

The plane wave diffraction by a planar junction consisting of a thick metallic sheet and a lossy double-negative metamaterial slab is studied by using the Uniform Asymptotic Physical Optics approach. This approach assumes the radiation integral as a starting point and uses the physical optics surface currents as sources to be integrated. The integral is manipulated by taking advantage of useful approximations and evaluations, and re-formulated in order to apply an asymptotic procedure able to generate a closed-form approximate solution in the framework of the Uniform Geometrical Theory of Diffraction. Accordingly, advantages and drawbacks result from the application of the proposed solution. The jumps of the geometrical optics field are compensated. Implementation and handling of the computer code are facilitated by the evaluation of well-known functions and parameters. No differential/integral equations or special functions must be computed.

In this work, we propose a broadband, polarization-insensitive and wide incident angle stable metamaterial absorber (MA) based on the resistive film. The absorber consists of a three-layer structure with each layer of dielectric substrate printed with different shapes of resistive film. The multilayer structure not only extends the absorption bandwidth but also maintains high absorption under large wave incident angles. Numerical simulation shows that the absorptivity of a normal incident wave is above 90% in the frequency range 2.34–18.95 GHz, corresponding to a relative absorption bandwidth of 156%. Moreover, the whole MA structure has a total thickness of 11.3 mm, corresponding to 0.09 λ0 at its lowest absorption frequency. Due to the high symmetry of the structure, the absorber has good polarization insensitivity. In addition, for both transverse electric and transverse magnetic incidence, the proposed absorber achieves an absorptivity of more than 80% at incident angles of up to 45° and thus has good stability for wide incident angles. The absorption principle of the absorber is analyzed by the surface current and power loss density distribution. Parameter analysis is also performed for bandwidth optimization. Due to its advantages of wideband absorption with high efficiency, the proposed absorber has the potential to be applied to the energy-harvesting and electromagnetic stealth fields.

To prevent far-field radiation characteristics degradation while increasing bandwidth, an attempt has been made to design and fabricate a microstrip antenna. An electromagnetic band gap (EBG) structure, including a layer of a metallic ring on a layer of Rogers 4003C substrate, is used. For a better design, a patch antenna with and without the EBG substrate has been simulated. The results show that the bandwidth can be improved up to 1.6 GHz in X-band by adding the EBG substrate. Furthermore, using this structure, a dual-band antenna was obtained as well. Finally, to validate the simulation results, a comparison has been done between simulation data and experimental results which demonstrate good agreement.

For the requirements of low mutual-coupling MIMO antennas for WLAN, a new complementary split-ring resonator (CSRR) unit cell is introduced in this paper. A microstrip-fed Vivaldi antenna array is designed for WLAN applications, where compact triple-band gap-complementary split-ring resonator unit cells are loaded between two antennas to examine the effect of unit cells on the rate of mutual-coupling reduction. By inserting the CSRR, the final design offered an improvement in decoupling by 8.5, 10.5, and 18 dB at 3.65, 4.9, and 5.8 GHz, respectively, compared with the reference antenna. By suppressing surface waves, antenna gain and front-to-back ratio are improved.