Nowadays, low-frequency electromagnetic interference (<2.0 GHz) remains a key core issue that plagues the effective attenuation performance of conventional absorption devices prepared via the component-morphology method (Strategy I). According to theoretical calculations, one fundamental solution is to develop a material that possesses a high e' but lower e″. Thus, it is attempted to control the dielectric values via applying an external electrical field, which inducts changes in the macrostructure toward a performance improvement (Strategy II). A sandwich-structured flexible electronic absorption device is designed using a carbon film electrode to conduct an external current. Simultaneously, an absorption layer that is highly responsive to an external voltage is selected via Strategy I. Relying on the synergistic effects from Strategies I and II, this device demonstrates an absorption value of more than 85% at 1.5-2.0 GHz with an applied voltage of 16 V while reducing the thickness to ≈5 mm. In addition, the device also shows a good absorption property at 25-150 °C. The method of utilizing an external voltage to break the intrinsic dielectric feature by modifying a traditional electronic absorption device is demonstrated for the first time and has great significance in solving the low-frequency electromagnetic interference issue.

A Voltage-Boosting Strategy Enabling a Low-Frequency, Flexible Electromagnetic Wave Absorption Device.

Reactive matching is extended to wide bandwidths using the impedance property of LC-ladder filters. In this paper, we present a systematic method to design wideband low-noise amplifiers. An SiGe amplifier with on-chip matching network spanning 3-10 GHz delivers 21-dB peak gain, 2.5-dB noise figure, and -1-dBm input IP3 at 5 GHz, with a 10-mA bias current.

A 3-10-Ghz low-noise amplifier with wideband LC-ladder matching network

This work was supported by National Basic Research Program of China
(Project No. 2013CB933301) and National Natural Science Foundation of
China (Project No. 51272038). L.V.B. was supported by China Postdoctoral
Science Foundation. A.O.G. was supported by the Volkswagen
Foundation (Germany) and via the Chang Jiang (Yangtze River)
Chair Professorship (China). G.P.W. acknowledges support from the
Center for Nanoscale Materials, a U.S. Department of Energy Office of
Science User Facility, and support by the U.S. Department of Energy,
Office of Science, under Contract No. DE-AC02-06CH11357. In addition,
the authors acknowledge financial support obtained from the Virtual
Institute for Theoretical Photonics and Energy. This review is part of the
Advanced Optical Materials Hall of Fame article series, which recognizes
the excellent contributions of leading researchers to the field of optical
materials science.

/pdf/broadband-metamaterial-absorbers-1ivwczjh1w.pdf

Broadband Metamaterial Absorbers

In this paper, we designed a novel core-shell composite for microwave absorption application in which the α-Fe2O3 and the porous CoFe2O4 nanospheres served as the core and shell, respectively. Interestingly, during the solvothermal process, the solvent ratio (V) of PEG-200 to distilled water played a key role in the morphology of α-Fe2O3 for which irregular flake, coin-like, and thinner coin-like forms of α-Fe2O3 can be produced with the ratios of 1:7, 1:3, and 1:1, respectively. The porous 70 nm diameter CoFe2O4 nanospheres were generated as the shell of α-Fe2O3. It should be noted that the CoFe2O4 coating layer did not damage the original shape of α-Fe2O3. As compared with the uncoated α-Fe2O3, the Fe2O3@CoFe2O4 composites exhibited improved microwave absorption performance over the tested frequency range (2-18 GHz). In particular, the optimal reflection loss value of the flake-like composite can reach -60 dB at 16.5 GHz with a thin coating thickness of 2 mm. Furthermore, the frequency bandwidth corresponding to the RLmin value below -10 dB was up to 5 GHz (13-18 GHz). The enhanced microwave absorption properties of these composites may originate from the strong electron polarization effect (i.e., the electron polarization between Fe and Co) and the electromagnetic wave scattering on this special porous core-shell structure. In addition, the synergy effect between α-Fe2O3 and CoFe2O4 also favored balancing the electromagnetic parameters. Our results provided a promising approach for preparing an absorbent with good absorption intensity and a broad frequency that was lightweight.

Coin-like α-Fe2O3@CoFe2O4 Core–Shell Composites with Excellent Electromagnetic Absorption Performance

Ieee transactions on antennas and propagation

In this paper, a compact two-port MIMO antenna is designed, which uses a shared orthogonally fed slot-loop, loaded with split-ring resonators (SRRs). The SRRs reduce the operating frequency of the slot-loop, leading to miniaturized antenna footprint of 0.059λ2 (λ being the operating wavelength). Also the SRRs significantly enhance the inter-element isolation (>20 dB) in the working band. The proposed two-element MIMO slot-loop antenna exhibits bi-directional broadside radiation pattern with realized gain > 2 dBi in the operating band. Also the evaluated MIMO performance metrics like envelope correlation coefficient (ECC), channel capacity loss (CCL) and total active reflection coefficient (TARC), indicate satisfactory diversity performance. The design concept is validated by experiments on a fabricated prototype of the proposed MIMO antenna.

A compact two-port MIMO antenna with enhanced isolation using SRR-loaded slot-loop

In this article, a wideband low‐profile endfire circularly polarized (CP) antenna using magnetoelectric dipole is proposed. Designing a wideband electric dipole element is easy and well‐studied in the literature. However, designing a compact wideband magnetic dipole element is still a challenge. In this paper, the impedance bandwidth (IBW) of the magnetic dipole is enhanced by reducing the resonance frequency of higher‐order mode half‐TE310 with the help of rectangular slots placed at the null of mode half‐TE310. By combining the resonance frequency of mode half‐TE110 and mode half‐TE310, the magnetic dipole can yield a larger IBW (6.86–7.67 GHz, 11.14%) with smaller planar dimensions of 1.259λ0 × 0.363λ0 × 0.038λ0 (λ0 is the free space wavelength at the centre frequency). To generate a wideband endfire CP wave, a horizontally polarized electric dipole with a feed line is combined with the vertically polarized magnetic dipole. The measured IBW and axial ratio bandwidth (ARBW) are 11.65% and 12.02%, respectively, with a measured peak endfire gain of 5 dBic. The overall dimension of the proposed wideband low‐profile endfire CP antenna is 1.11λ0 × 0.66λ0 × 0.033λ0.

Wideband low‐profile endfire circularly polarized antenna using mode superposition technique

In this paper an ultra-thin polarization-independent compact metamaterial absorber has been proposed where the unit cell contains single fractal shaped square structure. The geometrical dimensions of the fractal structure have been designed in such a way that the structure exhibits absorption at 4.17 GHz and 11.16 GHz. Due to the four-fold symmetry of the structure, the absorber is polarization-independent in nature. The proposed structure has been studied under oblique incidences for TE and TM polarizations where it behaves as absorber upto 45° incident angles in both the cases. The structure is only 1.6 mm thick (∼ λ0/17 with respect to higher absorption frequency), making it ultra-thin in nature.

An ultra-thin polarization independent compact fractal shaped metamaterial absorber

A Novel EBG grounded PIFA has been designed for Universal Mobile Telecommunication System (UMTS) frequency band (2.1 GHz) with good directivity. In this paper a uniplanar compact Electromagnetic Band Gap (UC-EBG) structure is designed to use as ground for a Planar Inverted F Antenna (PIFA), to improve its radiation pattern and suppress the surface waves. The proposed EBG grounded PIFA has shown improvement over conventional PIFA in directivity, front to back ratio and radiation pattern. The front to back ratio has been improved from 8.75 dB to 15.80 dB.

Novel EBG grounded PIFA for improved directivity in mobile communication bands

In this paper, a low-profile tunable bandstop frequency selective surface (FSS) is presented for S-band applications The FSS consists of square loops connected through varactor diodes across the diagonals By controlling the reverse voltage of the varactors, the resonance frequency can be tuned for a wide frequency range Full-wave simulation shows 21% tuning range from 231 GHz to 279 GHz with respect to lower resonance frequency The novelty of the design lies in its four-fold symmetry, which makes the structure polarization-insensitive The FSS is also angularly stable under oblique incidence for both TE and TM polarizations Additionally, an equivalent circuit model has been introduced to explain the resonance mechanism of the proposed FSS The structure is also fabricated and measured, where good agreement is observed between simulated and measured responses

Kumar Vaibhav Srivastava

Papers

A compact two-port MIMO antenna with enhanced isolation using SRR-loaded slot-loop

Wideband low‐profile endfire circularly polarized antenna using mode superposition technique

An ultra-thin polarization independent compact fractal shaped metamaterial absorber

Novel EBG grounded PIFA for improved directivity in mobile communication bands

A tunable bandstop frequency selective surface with polarization-insensitive characteristic