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 novel technique to enhance the bandwidth of substrate integrated waveguide cavity backed slot antenna is demonstrated. The feeding technique to the cavity backed antenna has been modified by introducing offset feeding of microstrip line along with microstrip to grounded coplanar waveguide transition which helps to excite TE 120 mode in the cavity and also to get improvement in impedance matching to the slot antenna simultaneously. The proposed antenna is designed to resonate in X band (8–12 GHz) and shows a resonance at 10.2 GHz with a bandwidth of 4.2% and a gain of 5.6 dBi, 15.6 dB front to back ratio and −30 dB maximum cross polarization level.

Bandwidth enhancement of substrate integrated waveguide cavity backed slot antenna by offset feeding technique

In this letter, a dual-band tunable bandstop frequency selective surface (FSS), which is capable of exhibiting independent tuning for the top and bottom layers, has been presented. The proposed design comprises periodic patterns of cross diagonals printed on the opposite sides of a thin substrate, where the varactor diodes are mounted symmetrically. Both the layers use novel biasing circuitries to independently regulate their corresponding responses, thereby resulting in two tunable stopbands. Each of these two stopbands has wide bandwidths (having fractional bandwidths of 110.71%) as well as offers large tuning ranges of 128.21% (with respect to their center frequencies). Furthermore, the geometry is low profile, polarization insensitive, and angularly stable. A prototype has been fabricated, and the varactors have been modulated through parallel biasing. The experimental results show a reasonable agreement with the theoretical responses, thus confirming the proposed concept.

A Dual-Band Tunable Frequency Selective Surface With Independent Wideband Tuning

A triple band circular polarized monopole antenna for GNSS/UMTS/LTE

A polarisation-independent switchable absorber/reflector based on active frequency selective surface (AFSS) has been reported. The FSS design consists of diagonally connected circular loops on which semiconductor switches (PIN diodes) have been mounted. By controlling the bias voltage of the PIN diodes, the structure shows perfect reflection in ON state while exhibits single band absorption during OFF state. The proposed design is four-fold symmetric, thereby realising polarisation-insensitive behaviour, unlike the earlier reported AFSS designs. Furthermore, a prototype of the proposed structure has been fabricated where the PIN diodes have been biased through a novel biasing technique. The measured result also shows good agreement with simulated response under normal incidence.

https://ietresearch.onlinelibrary.wiley.com/doi/pdf/10.1049/el.2016.1193

Polarisation-independent switchable absorber/reflector

In this paper, the concept of cross-correlation Green's functions (CGF) is used in conjunction with the finite difference time domain (FDTD) technique for calculation of envelope correlation coefficient (ECC) of any arbitrary MIMO antenna system over wide frequency band. Both frequency-domain (FD) and time-domain (TD) post-processing techniques are proposed for possible application with this FDTD-CGF scheme. The FDTD-CGF time-domain (FDTD-CGF-TD) scheme utilizes time-domain signal processing methods and exhibits significant reduction in ECC computation time as compared to the FDTD-CGF frequency domain (FDTD-CGF-FD) scheme, for high frequency-resolution requirements. The proposed FDTD-CGF based schemes can be applied for accurate and fast prediction of wideband ECC response, instead of the conventional scattering parameter based techniques which have several limitations. Numerical examples of the proposed FDTD-CGF techniques are provided for two-element MIMO systems involving thin-wire half-wavelength dipoles in parallel side-by-side as well as orthogonal arrangements. The results obtained from the FDTD-CGF techniques are compared with results from commercial electromagnetic solver Ansys HFSS, to verify the validity of proposed approach.

Application of Cross-correlation Greens Function along with FDTD for Fast Computation of Envelope Correlation Coefficient over Wideband for MIMO Antennas

Kumar Vaibhav Srivastava

Papers

Bandwidth enhancement of substrate integrated waveguide cavity backed slot antenna by offset feeding technique

A Dual-Band Tunable Frequency Selective Surface With Independent Wideband Tuning

A triple band circular polarized monopole antenna for GNSS/UMTS/LTE

Polarisation-independent switchable absorber/reflector

Application of Cross-correlation Greens Function along with FDTD for Fast Computation of Envelope Correlation Coefficient over Wideband for MIMO Antennas