• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.29 no.4
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• pp.241-246
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• 2018

In this study, we proposed a wideband frequency tunable metamaterial absorber using a switchable ground plane (SGP). We proposed two fire retardant or flame resistant 4 (FR4) substrate structures for the SGP. An SGP is placed at the middle layer, between the top pattern and the bottom ground plane. The SGP can either be made ground or reactive, by switching the PIN diode ON/OFF. As the frequency is determined by the substrate thickness, the frequency can be switched from the SGP. The proposed absorber is demonstrated by full-wave simulations and measurements. When the SGP is turned on, an absorptivity higher than 90% is achieved from 3.5 GHz to 11 GHz. When the SGP is turned off, an absorptivity higher than 90 % is achieved from 1.7 GHz to 5.2 GHz.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.23 no.7
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• pp.840-843
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• 2012

In this paper, the authors present a new design for a dual-band metamaterial(MTM) absorber that utilizes resonant-magnetic inclusion of a split-ring resonator(SRR). The proposed MTM unit cell is constructed by two open complementary split-ring resonators(OCSRRs) and an SRR arrangement. To avoid the need for metallic back plate a planar array of SRRs for resonant-magnetic inclusion is placed facing toward the incident wave propagation direction. Each unit cell is printed on the two sides of a FR-4 substrate. A prototype absorber was fabricated with a planar array of $39{\times}39$ unit cells, and measured. The proposed backplane-less absorber can be used for microwave applications.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.5 no.1
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• pp.26-32
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• 2012

This paper presents a metamaterial absorber unit sell structure with four-element electric-LC resonators (ELC). In order to enhance the operating bandwidth of the proposed absorber unit cell two pairs of ELC resonators with a different size are used. The proposed unit cell shows negative permittivity and permeability when the electric field is parallel to the capacitive gap and the magnetic field is normal to the plane of ELC resonator. The simulated results show peak absorbance over 90% at two frequencies of 8.53 and 9.08 GHz, respectively.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.26 no.1
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• pp.1-15
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• 2015

In this invited paper, the authors give an overview of the new design technology for a metallic backplane-less metamaterial(MM) absorber and discuss a selection of examples. In contrast to a common MM absorber structure, the metallic pattern layer of the presented structure is placed facing toward the incident wave propagation direction to reduce the radar cross section(RCS) due to the metallic pattern itself at frequencies other than the targeted absorption frequency bands. The ability of the MM backplane-less absorber to exhibit broadband absorption performance and irregular surface applications will be discussed.

• ETRI Journal
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• v.34 no.1
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• pp.126-129
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• 2012

An ultra-thin hexagonal microwave metamaterial absorber is described. It can absorb any polarized transverse electromagnetic wave because of its hexagonal shape. In spite of its very thin structure, almost $0.028{\lambda}g$, the absorber achieved 99% absorptivity at 11.35 GHz in experimental results because of the increased coupling losses, showing good agreement with simulation results. In addition, this high absorbance is unchanged for any polarized waves with the same frequency.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.25 no.3
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• pp.339-347
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• 2014

In this paper, the authors present a new design for a broad-band metamaterial(MTM) absorber that utilizes flexible substrate. The proposed MTM unit cell is constructed by a electric-inducive-capacitive(ELC) resonator and a cut-wire on the same side of the flexible polyimide substrate. To reduce the radar cross section at frequencies other than the targeted frequency bands, the metallic pattern layer of the proposed structure is placed facing toward the incident wave propagation direction. A prototype absorber was fabricated with a planar array of $33{\times}45$ unit cells. Our experiments showed that the proposed absorber exhibits a peak absorption rate of 92 % and 93 % at 9.06 GHz and 15.0 GHz, respectively, and 75 % of the full-width at half-maximum(FWHM) bandwidth is achieved. The proposed backplane-less MTM structure can be used for a broad-band microwave absorber and irregular surface applications.

• Journal of electromagnetic engineering and science
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• v.14 no.3
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• pp.314-316
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• 2014

This letter presents two types of metamaterial-inspired absorbers adopting resistive trumpet structures at the X band. The unit cell of the first type is composed of a trumpet-shaped resonator loading a chip resistor, a metallic back plane, and a FR4 (${\varepsilon}_r=4.4-j0.02$) substrate between them (single-layer). The absorption rate is 99.5% at 13.3 GHz. The full width at half maximum (FWHM) is 95 % at 11.2 GHz (from 5.9 to 16.5 GHz). The size of unit cell is $5.6{\times}5.6{\times}2.4mm^3$. The second type has been optimized with a $7{\Omega}$/square uniform resistive coating, removing the chip resistors but leading to results comparable to the first type. The proposed absorbers are almost insensitive to polarizations of incident waves due to symmetric geometry.

• Current Optics and Photonics
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• v.6 no.3
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• pp.252-259
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• 2022

In this paper, a dual-function dynamically tunable metamaterial absorber is proposed. At frequency points of 1.545 THz and 3.21 THz, two resonance peaks with absorption amplitude of 93.8% (peak I) and 99.4% (peak II) can be achieved. By regulating the conductivity of photosensitive silicon with a pump laser, the resonance frequency of peak I switches to 1.525 THz, and that of peak II switches to 2.79 THz. By adjusting the incident polarization angle by rotating the device, absorption amplitude tuning is obtained. By introducing two degrees of regulation freedom, the absorption amplitude modulation and resonant frequency switching are simultaneously realized. More importantly, dynamic and continuous adjustment of the absorption amplitude is obtained at a fixed resonant frequency, and the modulation depth reaches 100% for both peaks. In addition, the sensing property of the proposed MMA was studied while it was used as a refractive index sensor. Compared with other results reported, our device not only has a dual-function tunable characteristic and the highest modulation depth, but also simultaneously possesses fine sensing performance.

• Journal of IKEEE
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• v.24 no.1
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• pp.347-353
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• 2020

In this paper, the durability of an electromagnetic metamaterial absorber is verified in a temperature varying condition mimicking a maritime environment for the purpose of applying it to reduce the radar cross section of an integrated mast of the next-generation destroyer. To validate the durability, the reflectance of the electromagnetic metamaterial absorber was measured after storing it in a chamber that can control the temperature according to Procedure I of Method 501.7 included in MIL-STD-810H. Before and after the environmental test, both of the measured reflectances were retained less than -10 dB over the X band, that can guarantee the stealth functionality.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.359.1-359.1
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• 2016

The electromagnetic (EM) properties of media, such as propagation, focusing and scattering, strongly rely on the electric permittivity and the magnetic permeability of media. Recently, artificially-created metamaterials (MMs) composed of periodically-arranged unit cells with tailored electric permittivity and magnetic permeability have drawn wide interest due to their capability of adjusting the EM response. MM absorbers using the conventional sandwich structures usually have very high absorption at a certain frequency, and the absorption properties of MMs can be adjusted simply by changing the geometrical parameters of unit cell. In this work, we suggested an incident-angle-independent broadband perfect absorber based on resistive layers. We analyze the absorption mechanism based on the impedance matching with the free space and the distribution of surface currents at specific frequencies. From the simulation, the absorption was expected to be higher than 96% in 1.4-6.0 GHz. The corresponding experimental absorption was found to be higher than 96% in 1.4-4.0 GHz, and the absorption turned out to be slightly lower than 96% in 4.0-6.0 GHz owing to the irregularity in the thickness of resistive layers.