Narrow Results

The design and characterization of perfect metamaterial absorbers (MAs) based on simple configurations including square- and triangle-shapes, which operate in X-band frequency region are numerically and experimentally investigated. The proposed MAs provide perfect absorption with the polarization angle independency. In X-band waveguide, the absorption rates are 99.69% and 99.97% at the resonance frequencies of 10.57 GHz and 10.93 GHz for the square- and triangle-shaped MAs, respectively. In addition, the same configurations are numerically tested under free space boundary conditions to compare and discuss the obtained results. The suggested MAs enable myriad potential application areas for security and stealth technologies in X-band including wireless communication.

A novel compact coplanar waveguide (CPW)-fed planar monopole antenna with triple-band operation is presented for simultaneously satisfying the LTE 2600, WiMAX, WLAN and X-band applications. It is printed on a single-layered FR4 substrate. In this paper, the proposed antenna, which occupies a small volume of $30\times 28\times 0.8$mm³ including the ground plane, is simply composed of a CPW-fed monopole with U-, L- and T-shaped slots. By carefully selecting the lengths and positions of both L-shaped and U-shaped slots, a good dual notched band characteristic at center-rejected frequencies of 3.10GHz and 4.50GHz can be achieved, respectively. The T-shaped slot is etched on the radiating element to excite a resonant frequency in the 7GHz band. Then, to prove the validation of the typical design, a prototype model is fabricated and measured. The experimental result shows that the three frequency bands of 2.31–2.80GHz (490MHz), 3.37–3.84GHz (470MHz) and 5.04–7.94GHz (2900MHz) can successfully cover the desired bandwidths of LTE2600/WiMAX (3.50/5.50GHz)/WLAN (5.20/5.80GHz) and the X-band communication systems (7.1-GHz operation). The principal applications of the X-band are radar, aircraft, spacecraft and mobile or satellite communication system. Nearly omnidirectional and bidirectional radiation patterns of the triband antenna are observed in both H- and E-planes, respectively. In addition, a reasonable gain over the operating bands has been obtained. Indeed, the good agreements between simulation and measurement results have validated the proposed structure, confirming its potential for multiband wireless communication services.

A compact frequency band reconfigurable dual-mode antenna utilizing both Koch fractal geometry and circular complementary split ring resonators (CSRRs) is presented in this paper. The proposed antenna can be electrically switched into both dual- and single-band resonance modes. A Koch curve derivative novel fractal curve is used to design the patch boundary of the antenna. Two optimized circular CSRRs are loaded inside the antenna geometry to achieve double-band resonance. The antenna operates at both 5.1GHz (upper WLAN band) and 9.6GHz ($X$-band) in dual resonance mode and resonates only at 8GHz ($X$-band) in single resonance mode. A properly biased RF-range PIN diode placed at the slotted ground plane reconfigures the antenna in two operating modes by switching into its ON–OFF states. The antenna is fabricated on cost-efficient epoxy (FR-4) substrate consuming the maximum dimension of $0.34\lambda \times 0.32\lambda$ which is much more compact than the conventional rectangular patch antennas designed for similar bands. Stable radiation characteristics with reduced cross-polarization are achieved at all the resonant bands of the antenna. A prototype of the proposed antenna is fabricated and measured. The simulated results are in good agreement with the measured ones.

Porous flower nickel oxide@polyaniline (NiO@PANI) composites as excellent microwave absorption (MA) materials in the X-band were synthesized via a two-step strategy in this work. The porous NiO flower is uniformly dispersed and homogeneous in particle size after Ostwald ripening process. Coating conductive PANI on the surface of porous NiO microspheres could improve interfacial polarization and dielectric loss property that will lead to a great improvement of MA properties. Electromagnetic (EM) parameters of NiO@PANI composites with different NiO contents were investigated by a vector network analyzer and the reflection loss (RL) values with varied thickness were also calculated. The results showed that the effective absorption bandwidths ($\mathrm{\text{RL}}<-10$dB) of all NiO@PANI composites can cover the whole X-band. Especially, the NiO@PANI${}_{0.1}$ composite is able to attenuate microwave energy in the X-band with the thickness of 2.5mm. The NiO@PANI${}_{0.2}$ has a maximum RL of $-32.8$dB at 10.1GHz and the effective absorption bandwidths cover 4.64GHz (11.12–15.76GHz) at 2.0mm. The excellent MA absorption performance may be ascribed to the polarization effect, dielectric loss and structure of porous flower-like NiO@PANI. Our work confirms that the synthesized NiO@PANI composite is an attractive candidate as a highly efficient MA material in the X-band.

Ultrathin multi-walled carbon nanotubes (MWCNTs) buckypapers inserted with Mn nanopowder were fabricated via vacuum filtration method, at a lower manufacturing cost and easier operation. The buckypapers were characterized structurally using scanning electron microscopy, energy-dispersive spectrometer and X-ray diffraction. Electromagnetic interference (EMI) shielding effectiveness (SE) of MWCNTs buckypapers inserted with Mn nanopowder (0–30wt.%) were tested in X-band (8.2–12.4GHz). When the blended Mn nanopowder content is 20wt.%, the buckypaper exhibits much higher EMI SE of average value up to 42dB with the thickness of only 0.11mm. Further, this buckypaper is flexible and lightweight, and can be integrated with resin matrix composites. Thus, the results and techniques promise a simple and effective approach to achieve lightweight and ultrathin composite films for a wide application prospect in the field of EMI shielding and microwave absorption.