Metamaterial absorber (MMA) is now attracting significant interest due to its attractive applications, such as thermal detection, sound absorption, detection for explosive, military radar, wavelength detector, underwater sound absorption, and various sensor applications that are the vital part of the internet of things. This article proposes a modified square split ring resonator MMA for Ku-band sensing application, where the metamaterial structure is designed on FR-4 substrate material with a dielectric constant of 4.3 and loss tangent of 0.025. Perfect absorption is realized at 14.62 GHz and 16.30 GHz frequency bands, where peak absorption is about 99.99% for both frequency bands. The proposed structure shows 70% of the average absorption bandwidth of 420 MHz (14.42–14.84 GHz) and 480 MHz (16.06–16.54 GHz). The metamaterial property of the proposed structure is investigated for transverse electromagnetic mode (TEM) and achieved negative permittivity, permeability, and refractive index property for each absorption frequency band at 0°, 45°, and 90° polarization angles. Interference theory is also investigated to verify the absorption properties. Moreover, the permittivity sensor application is investigated to verify the sensor performance of the proposed structure. Finally, a comparison with recent works is performed, which shows that the proposed MMA can be a good candidate for Ku-band perfect absorber and sensing applications.

A novel modified-segmented split-ring based symmetric metamaterial absorber is introduced in this paper for X, Ku, and K band applications. The perfect absorption was achieved with a total of 1.91 GHz absorption bandwidth using the conventional FR4 substrate without resistive lumped elements. EM waves were applied in TEM mode at both normal and oblique incidence up to 90° and the same absorptance was found at 11.23 GHz, 14.18 GHz, 17.37 GHz, and 19.18 GHz with the maximum of 85.51%, 99.13%, 98.19%, and 90.8% absorptance respectively. This absorption performance was proved for both co-and crosspolarization analysis. Double negative values of permittivity and permeability up to 17.37 GHz and single negative values of either permittivity or permeability at 19.18 GHz were achieved. An equivalent circuit analysis also proved its performance capability, which makes it a perfect metamaterial absorber. Finally, the comparison of the design with recently published works in terms of unit cell size, absorption band, maximum polarization angles, and cross-polarized absorptivity proved it as a better candidate for the potential use as a perfect absorber. INDEX TERMS Wideband, metamaterial absorber, modified segmented split-ring, X Ku and K band, triple band.

In this article, a symmetric split ring resonator (SRR) based metamaterial (MTM) is presented that exhibits three resonances of transmission coefficient (S21) covering S, C, and X-bands with epsilon negative (ENG) and near zero index properties. The proposed MTM is designed on an FR4 substrate with the copper resonator at one side formed with two square rings and one circular split ring. The two square rings are coupled together around the split gap of the outer ring, whereas two split semicircles are also coupled together near the split gaps. Thus, gap coupled symmetric SRR is formed, which helps to obtain resonances at 2.78 GHz, 7.7 GHz and 10.16 GHz with desired properties of the MTM unit cell. The MTM unit cell's symmetric nature helps reduce the mutual coupling effect among the array elements. Thus, different array of unit cells provides a similar response to the unit cell compared with numerical simulation performed in CST microwave studio and validated by measurement. The equivalent circuit is modelled for the proposed MTM unit cell in Advanced Design System (ADS) software, and circuit validation is accomplished by comparing S21 obtained in ADS with the same of CST. The effective medium ratio (EMR) of 10.7 indicates the compactness of the proposed MTM. A test antenna is designed to observe the effect of the MTM over it. Numerical analysis shows that the proposed MTM have an impact on the antenna when it is used as the superstrate and helps to increase the gain of the antenna by 95% with increased directivity. Thus, compact size, high EMR, negative permittivity, near zero permeability and refractive index makes this MTM suitable for S, C and X band applications, especially for antenna gain with directivity enhancement.

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In this research paper, the sensing capabilities of a tri circle split ring resonator shaped metamaterial is shown within the X-band frequency range for detection of various oil samples both theoretically and experimentally. Mathematical modelling was used to analyze the sensor efficiency for the various oil samples. A new sample holder has been made for the proposed sensor structure, and it showed significant performance. The simulated and measured transmission coefficient has been revealed in this study and monitoring the shift of resonance frequency and sensitivity of the metamaterial sensor for different oil samples. Since the dielectric constants of the oil samples differ, hence the resonance frequency is shifted. The obtained result revealed that the proposed sensor can detect a wide range of liquids, including (i) coconut and extra virgin coconut oils, (ii) olive and extra virgin olive oils, (iii) clean and waste engine oils, (iv) sunflower and canola oils. The resonance frequency has shifted to about 210, 230, 170, and 200 MHz for the above-mentioned oil samples, respectively. The sensitivity of the proposed MTM sensor is -83 dB (mg/L) which is a new analysis and quite significant as a potential sensor structure. Surface current and electric field distributions were used to deduce the sensing process. Since the recommended sensor is cheap and highly sensitive; so, it can be used in a variety of fields, such as detection of various liquids, microfluidic sensing, and industrial applications. INDEX TERMSMetamaterial (MTM); Split ring resonator (SRR); Tri circle; Dielectric constant; Mathematical modelling.

<span>The 12 elements antenna array for GPS system having high gain with circular polarization is presented in this paper. The circularly polarized antenna is very suitable for the use of various wireless systems such as Global Positioning System with operating frequency is 1.27 GHz with AR is less than 3 dB between 82˚ and 140˚.The antenna consists of twelve main radiation patches connected in parallel. The antennas array are designed on the Rogers RT5880 substrate with a dielectric constant (εr) of 2.2 and thickness is 0.787 mm. The antenna is excited with an inset feed line and it operates in L-band with a resonant frequency of 1.27 GHz.</span>

This paper reports a central spiral split-rectangular-shaped metamaterial absorber surrounded by a polarization-insensitive ring resonator for s-band applications. The rated absorption is 99.9% at 3.1 GHz when using a three-layer structure where the top and ground are made of copper and the center dielectric material is a commonly used FR-4 substrate. The central split gaps have an impact on the unit cell by increasing high absorption, and an adequate electric field is apparent in the outer split ring gap. At 3.1 GHz, the permittivity and permeability are negative and positive, respectively, so the proposed unit cell acts as an epsilon negative (ENG) metamaterial absorber. In a further analysis, Roger4450B was used as a substrate and obtained excellent absorption rates of 99.382%, 99.383%, 99.91%, and 95.17% at 1.44, 3.96, 4.205, and 5.025 GHz, respectively, in the S- and C-band regions. This unit cell acts as a single negative metamaterial (SNG) absorber at all resonance frequencies. The S11 and S21 parameters for FR-4 and Rogers4450B were simulated while keeping the polarization angle (θ and φ) at 15, 30, 45, 60, 75, and 90 degrees to measure, permittivity, permeability, reflective index, absorption, and reflection. The values of the reflective index are near zero. Near-zero reflective indexes (NZRI) are widely used in antenna gain propagation. The unit cell fabricated for the FR-4 substrate attained 99.9% absorption. S-band values in the range of (2–4) GHz can be applied for low-frequency radar detection.

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