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We proposed a novel electromagnetic-based chemical sensor that is realized by using a metamaterial absorber. The metamaterial absorber comprises a split-ring-cross resonator (SRCR) and a microfluidic channel. The SRCR can generate LC resonance that is very sensitive to changes in the effective dielectric constant around the capacitive gap. In addition, microfluidic channels can change the effective dielectric constant of the dielectric substrate by using an infinitesimal quantity of a liquid on the order of microliters. The proposed chemical sensor can detect the electrical properties of any unidentified liquids injected into the channels, as well as concentration changes in the liquids. The performance of the proposed sensor is demonstrated using the absorption measurements of a fabricated prototype sample with waveguides. In addition, the relationship between the absorption frequency and chemical concentration is demonstrated.

In this study, we demonstrated a new class of frequency-switchable metamaterial absorber in the X-band. Eutectic gallium-indium (EGaIn), a liquid metal alloy, was injected in a microfluidic channel engraved on polymethyl methacrylate (PMMA) to achieve frequency switching. Numerical simulation and experimental results are presented for two cases: when the microfluidic channels are empty, and when they are filled with liquid metal. To evaluate the performance of the fabricated absorber prototype, it is tested with a rectangular waveguide. The resonant frequency was successfully switched from 10.96 GHz to 10.61 GHz after injecting liquid metal while maintaining absorptivity higher than 98%.

In this paper, we present three ultra-thin frequency selective surface (FSS) microwave absorbers on a single layer, that have three remarkable features. First, the various absorbing bandwidths can be obtained in our absorber by adjusting the two absorbing peaks, which are produced by two different resonance effects on the FSS. By manipulating the dimension parameters, we design the dual-band, 3-dB and 10-dB band absorbers. We achieved the absorber's thickness of $0.039\lambda_{\rm g}$ with the single layer due to high loss of inter-digital capacitor patterns on the FSS. Additionally, the proposed absorbers are insensitive to polarized electromagnetic (EM) waves because of the symmetric structure of the FSS. In this study, the absorber mechanism and transmission line (TL) modeling for the absorber design are studied. Each of the proposed absorbers is analyzed by using the TL equivalent circuit model and full-wave analysis. The loss factor is studied in order to demonstrate the origin of losses, and a parametric study is conducted to explain how to vary the absorbing bandwidths. The performances of each proposed absorber are also experimentally demonstrated.

In this letter, a novel frequency tunable metamaterial absorber is proposed for wireless humidity sensor applications made with natural cork. Natural cork has excellent hygroscopicity and its electrical properties can be changed depending on the moisture content. In this work, the absorption ratio of the proposed absorber are simulated and measured in different moisture content ( ${\rm M} = 0\% $ , 1.44%, 5.88%, 13.32%, 18.8%) of the cork substrate. The resonant frequency changed from 4.92 GHz in the dry ( ${\rm M} = 0\% $ ) state to 3.49 GHz in the wet ( ${\rm M} = 18.8\% $ ) state; the measured absorptivity is higher than 90% in all moisture content values. To the best of our knowledge, it is the first metamaterial absorber using natural cork.

In this letter, a novel, flexible inkjet-printed metamaterial absorber is proposed. The unit cell consists of a miniaturized Jerusalem-cross resonator and a completely conductive bottom. Because the conductive patterns are inkjet-printed using silver nanoparticle inks on paper, the proposed metamaterial absorber is flexible. It is also eco-friendly because it does not produce any chemical waste. In this letter, the working principle of the proposed miniaturized unit cell is explained, and parametric simulations are described. The inkjet-printing process is delineated, and the silver nanoparticle inks and paper used are characterized. The performance of the proposed absorber is demonstrated with a full-wave simulation and measurements at the $X$ -band. The experimental results show that the absorption rate at 9.09 GHz is greater than 99% at the normal incidence. Angular and polarization insensitivity are also experimentally demonstrated.

A polarization-independent ultrawideband metamaterial absorber is proposed for X-band applications. High absorptivity over an ultrawide spectrum is achieved by the combination of an artificial impedance surface (AIS) and a resistor-capacitor (RC) layer. In addition, the unique hexagonal shape of an AIS and RC layer enables polarization insensitivity. A circuit analysis is introduced based on a transmission-line model and shows good agreement with the full-wave analysis. Fabrication tolerance issues are considered with parametric studies in the electromagnetic simulation. The proposed absorber is fabricated on low-cost FR4 substrates, and its absorption performance is experimentally demonstrated at different angles and polarizations of incident electric fields.

In this study, a novel ultra-wideband antenna with a tri-band notch capability is proposed. The proposed antenna can reject worldwide interoperability for microwave access (WiMAX, 3.3–3.7 GHz), wireless local area network (WLAN) IEEE802.11a/n (5.15–5.825 GHz), and international telecommunication union (ITU, 8.025–8.4 GHz) bands. The band notch capability is achieved by merely a split ring resonator (SRR) and complementary-SRR (CSRR) patterns. The SRR under the radiating patch, the CSRR loaded on the radiating patch, and the CSRRs on the ground of the CPW feeding reject the WiMAX, WLAN, and ITU bands, respectively. The simulation and measurement results demonstrate the performance of the proposed antenna.

In this paper, a novel ultra wide band(UWB) antenna with tri-band notch capability is proposed. The proposed antenna can reject WiMAX(3.3~3.7 GHz), WLAN IEEE 802.11a/n(5.15~5.825 GHz), and ITU(8.025~8.4 GHz) bands. Band rejection capability is achieved only split ring resonators(SRRs) and complementary SRRs(CSRRs). The SRR under the radiating patch, the CSRR loaded on the radiating patch, and the CSRRs on the ground of the CPW feeding reject the WiMAX, WLAN, and ITU bands, respectively. The simulation and measurement results demonstrate the performances of the proposed antenna.

In this paper, we propose a novel microfluidic tunable metamaterial (MM) absorber printed on a paper substrate in silver nanoparticle ink. The metamaterial is designed using a periodic array consisting of square patches. The conductive patterns are inkjet-printed on paper using silver nanoparticle inks. The microfluidic channels are laser-etched on polymethyl methacrylate (PMMA). The conductive patterns on paper and the microfluidic channels on PMMA are bonded by an SU-8 layer that is also inkjet-printed on the conductive patterns. The proposed MM absorber provides frequency-tuning capability for different fluids in the microfluidic channels. We performed full-wave simulations and measurements that confirmed that the resonant frequency decreased from 4.42 GHz to 3.97 GHz after the injection of distilled water into the microfluidic channels. For both empty and water-filled channels, the absorptivity is higher than 90% at horizontal and vertical polarizations.

This paper describes a tunable metamaterial (MM) absorber that incorporates novel microfluidic channels and is realized using inkjet printing on a photo-paper substrate. The fabricated sample demonstrated frequency-switching capability owing to distilled water flowing in the microfluidic channels. In addition, the resonant frequency was changed from 4.42 to 3.97 GHz when the empty channels were filled with de-ionized water. An analysis of the results suggests that microfluidic technology is a simpler and more effective way to achieve tuning functionality. The proposed structure is the first microfluidic absorber based on a photo-paper substrate.

In this paper, a novel inkjet-printed metamaterial absorber is proposed for the first time. The proposed absorber consists of circular Jerusalem-Cross resonators and it is printed on a thin paper substrate. The performance of the proposed absorber is validated through EM simulation and measurement. Flexibility and high absorptivity are achieved in X-band.

In this paper, we present a novel electronically switchable metasurface that provides absorption and reflection modes depending on bias voltages of pin diodes. The metasurface is designed by a periodic split ring resonator loading the pin diode. When the pin diodes turn on, the metasurface is working as the absorber. When the pin diodes turn off, the metasurface is working as the reflector. For a reliable operation, bias networks are designed as well. The performance of the proposed metasurface is demonstrated from both full-wave simulation and measurement. At 10.97 GHz, the metasurface shows 99.4% absorptivity and 100% reflectivity at the absorptivity and reflection modes, respectively.

In this paper, a novel wideband metamaterial (MM) absorber is proposed. The proposed absorber is composed of a hexagonal MM structure and a resistor-capacitor (RC) layer, with an air gap between the two layers. The additional RC layer comprises a series resistor and capacitor; this layer and an air gap have an important effect on the wider bandwidth. The proposed absorber shows absorbing properties over a very wide bandwidth. The performance of the proposed absorber is demonstrated by simulation and measurement results.

In this paper, three different unit cells are designed on the basis split-ring-cross resonators, and each unit cell has an absorption rate greater than 90% at incident angles of 0 degrees, 30 degrees, and 45 degrees, respectively. They are non-periodically placed in three different zones on the curved surface. Therefore, the proposed conformal metamaterial absorber can achieve a high absorption rate. The performance of the proposed absorber is compared with that of a metallic curved surface and a conformal metamaterial absorber with the same unit cells. (C) 2013 Optical Society of America

In this paper, we present a novel electromagnetic metamaterial which is able to electronically switch a reflector and absorber. For the absorbing mode, a split ring resonator is employed as an electric LC resonator. The reflector mode is achieved by switching the current path off. The performance is successfully demonstrated both by a full-wave simulation and measurement. At 10 GHz, high absorption is obtained when the switch is the on-state, while the perfect reflection is obtained when the switch on the off-state.

A novel active metasurface is proposed in this paper. The proposed metasurface can be electronically switched between the reflection and the absorption modes by a tunable component, such as a PIN diode. When the PIN diode is in the on-state, the proposed metasurface exhibits near-perfect absorptivity at 10 GHz. On the other hand, when the PIN diode is in the off-state, the proposed metasurface exhibits near-perfect reflectivity over a wide bandwidth at 10 GHz. A unit cell is designed to include a DC bias network, which yields reliable performance.