Ultra-wideband Electromagnetic Wave Research Articles

Constructing Core-Shell NiCo2O4@PPy nanocomposites with controllable dielectric properties toward wide-band microwave absorption

Nickel cobaltate@polypyrrole composite nanomicrospheres (NiCo2O4@PPy) were successfully synthesized by in situ oxidation polymerization on the surface of NiCo2O4 microspheres with polypyrrole layer as a shell. The impedance matching can be optimized by modulating the amount of polypyrrole, so as to obtain the best wave absorption performance. Furthermore, the full absorption of multiple bands can be realized under different thickness. The absorption mechanism of EMW is specifically analyzed, that is, the appropriate impedance matching and the large dielectric and magnetic losses caused by the electromagnetic synergistic effect generated by the heterogeneous interface of NiCo2O4 and PPy. NiCo2O4@PPy-0.8 achieves remarkable impedance matching in a wide frequency range compared with other samples, thus obtaining superior absorption performance. When the thickness of NiCo2O4@PPy-0.8 is 2.3 mm, the effective absorption bandwidth (EAB, RL exceeding −10 dB) at 10 wt% loading reaches 7.14 GHz (ranging from 10.86 GHz to 18 GHz, covering the whole Ku band), and the minimum reflection loss (RLmin) is −57.85 dB. This work provides an encouraging method for lightweight ultra-wideband electromagnetic wave absorption of multilayer structures based on nickel-cobalate matrix.

Statistical Features of Georadar Signals Obtained by Probing Horizontal Layered Media in Permafrost

Relevance. To study the structure and properties of rock masses in the permafrost zone, such a method of geophysics as ground penetrating radar is successfully used. The existing methods of GPR measurements make it possible to obtain large volumes of reliable data on the layered structure of permafrost rocks. The methodological support for processing and interpreting data is developed much worse. Thus, manual and semi-automatic methods are used to identify the in-phase axes of georadar signals confined to the boundaries of rock layers, which significantly slows down the process of cameral work. Existing methods for automating the selection of in-phase axes of georadar signals do not always successfully cope with this task, since the statistical characteristics of georadar traces obtained by probing a horizontally layered media are very variable. The purpose of the research is to establish the statistical features of georadar signals that form the in-phase axes obtained by probing horizontally layered media in permafrost. Research methods – statistical analysis of the results of field georadar measurements in the Anabar region of the Republic of Sakha (Yakutia) at the site of the Mayat diamond deposit (AO Almazy Anabara) using the GPR OKO ABDL-Triton. Conclusions. The research of the amplitude characteristics of GPR signals that form the in-phase axes showed the presence of a random component, which significantly affects the recorded GPR wave field. Using the results of field measurements of horizontally layered media as an example, a change with increasing depth of the main statistical characteristics, as well as the distribution of amplitude values (normal–uniform–normal) was established. The results obtained will be very useful both in interpreting georadar measurement data and in improving the accuracy of modeling the propagation of ultra-wideband electromagnetic waves in horizontally layered media, and can also be used to refine the previously developed model of a georadar section of a frozen rock mass.

A Novel Ultrathin Checkerboard Inspired Ultrawideband Metasurface Absorber

A cost-effective, conformal, polarization-insensitive, light-weight, ultrathin, and ultrawideband electromagnetic wave absorber covering the entire Ku, K, and Ka bands and the lower V band is presented in this article. The absorber consists of a single layer of inkjet printed resistive metasurface laid over a flexible paper supported by a grounded foam. A novel metasurface pattern is designed by combining a checkerboard inspired symmetrical structure around a central square patch. The notable features of the proposed absorber are its ultrathin thickness of 2.17 mm (0.09<inline-formula><tex-math notation="LaTeX">$\boldsymbol{\lambda _l}$</tex-math></inline-formula> at the lowest operating frequency) for achieving a fractional bandwidth of 117&#x0025; with a small radar cross section and its suitability for conformal applications. It exhibits more than 90&#x0025; absorptivity over a frequency range from 11.87 to 45.28 GHz for all the angles of polarization and is also angularly stable. The theoretical, simulation, circuital, and experimental analysis validates the various features exhibited by the absorber.

FeNi nanoparticles embedded reduced graphene/nitrogen-doped carbon composites towards the ultra-wideband electromagnetic wave absorption

A unique reduced graphene oxide (rGO)/nitrogen doped carbon (N-C)/FeNi hybrid was successfully synthesized via a green and environmentally friendly process by means of one pot method. The morphology, phase structure, composition and electromagnetic (EM) wave absorption behavior of all hybrids were studied in detail. All rGO/N-C/FeNi hybrids are composed of rGO sheets on which there are nitrogen doped carbon and FeNi nanoparticles, and the novel structure endows the absorber with multiple scattering and reflection, interfacial polarization, dipole polarization and so on, further bringing remarkable EM wave absorption behavior. Moreover, the complex permittivity of rGO/N-C/FeNi hybrids is able to be controlled through changing the amount of GO. All results show that the rGO/N-C/FeNi-3 hybrid displays a substantial improvement in EM wave absorption performance compared with other hybrids. The minimum reflection loss (RLmin) value is −68.87 dB at 12.08 GHz with the thickness of 2.5 mm and the largest effective absorption bandwidth (EAB) achieves 6.88 GHz at 2.2 mm with RLmin value of −14.73 dB at 12.16 GHz. Our research proves that the unique structure and composition have the potential to elevate EM wave absorption performance.

Study of plasma-based stable and ultra-wideband electromagnetic wave absorption for stealth application

A plasma-based stable, ultra-wideband electromagnetic (EM) wave absorber structure is studied in this paper for stealth applications. The stability is maintained by a multi-layer structure with several plasma layers and dielectric layers distributed alternately. The plasma in each plasma layer is designed to be uniform, whereas it has a discrete nonuniform distribution from the overall view of the structure. The nonuniform distribution of the plasma is the key to obtaining ultra-wideband wave absorption. A discrete Epstein distribution model is put forward to constrain the nonuniform electron density of the plasma layers, by which the wave absorption range is extended to the ultra-wideband. Then, the scattering matrix method (SMM) is employed to analyze the electromagnetic reflection and absorption of the absorber structure. In the simulation, the validation of the proposed structure and model in ultra-wideband EM wave absorption is first illustrated by comparing the nonuniform plasma model with the uniform case. Then, the influence of various parameters on the EM wave reflection of the plasma are simulated and analyzed in detail, verifying the EM wave absorption performance of the absorber. The proposed structure and model are expected to be superior in some realistic applications, such as supersonic aircraft.

Application of Coupled-Wave Wentzel-Kramers-Brillouin Approximation to Ground Penetrating Radar

This paper deals with bistatic subsurface probing of a horizontally layered dielectric half-space by means of ultra-wideband electromagnetic waves. In particular, the main objective of this work is to present a new method for the solution of the two-dimensional back-scattering problem arising when a pulsed electromagnetic signal impinges on a non-uniform dielectric half-space; this scenario is of interest for ground penetrating radar (GPR) applications. For the analytical description of the signal generated by the interaction of the emitted pulse with the environment, we developed and implemented a novel time-domain version of the coupled-wave Wentzel-Kramers-Brillouin approximation. We compared our solution with finite-difference time-domain (FDTD) results, achieving a very good agreement. We then applied the proposed technique to two case studies: in particular, our method was employed for the post-processing of experimental radargrams collected on Lake Chebarkul, in Russia, and for the simulation of GPR probing of the Moon surface, to detect smooth gradients of the dielectric permittivity in lunar regolith. The main conclusions resulting from our study are that our semi-analytical method is accurate, radically accelerates calculations compared to simpler mathematical formulations with a mostly numerical nature (such as the FDTD technique), and can be effectively used to aid the interpretation of GPR data. The method is capable to correctly predict the protracted return signals originated by smooth transition layers of the subsurface dielectric medium. The accuracy and numerical efficiency of our computational approach make promising its further development.

Designing an ultra-wideband electromagnetic waves receiver with new architecture for RF and wireless applications

This paper demonstrates an electromagnetic waves receiver (EMWR) with new architecture for finding the good performances at the very wide frequency range of 2.8 to 10.8 GHz. The proposed device applies conventional pulse position modulation (PPM) scheme for modulation. The combination of 8th–8th-order derivative of Gaussian pulse is used as impulse received signal. The EMW receiver circuit with core chip dimension of 32 × 10−3 mm2 was modeled in a 90 nm CMOS technology. The output amplitude pulse yielded 200 mV peak-to-peak under a supply voltage of 2.2 V. This circuit consumes 12 pJ/pulse at 0.5 GHz pulse-repeating frequency. The designed device can be employed in the transceiver systems in presence the multipath channel for 2.8 GHz to 10.8 GHz. Results express that the proposed system not only decrease the interference with narrowband (NB) systems, but is also robust against NB interference at the operating frequency of 7 GHz. Regarding to results, the EMWR can be used in radio frequency (RF) and wireless receiver applications.

Graphene as a high impedance surface for ultra-wideband electromagnetic waves

The metals are regularly used as reflectors of electromagnetic fields emitted by antennas ranging from microwaves up to THz. To enhance the reflection and thus the gain of the antenna, metallic high impedance surfaces (HIS) are used. HIS is a planar array of continuous metallic periodic cell surfaces able to suppress surface waves, which cause multipath interference and backward radiation in a narrow bandwidth near the cell resonance. Also, the image currents are reduced, and therefore the antenna can be placed near the HIS. We demonstrate that graphene is acting as a HIS surface in a very large bandwidth, from microwave to THz, suppressing the radiation leakages better than a metal.

A numerical study of time-reversed UWB electromagnetic waves in continuous random media

We investigate superresolution effects on ultrawideband (UWB) electromagnetic waves (EM) produced by time-reversal (TR) arrays in continuous random media. The investigation is done via numerical simulations employing the finite-difference time-domain (FDTD) method. A Gaussian random background medium is considered. We compare the effect of statistical parameters, viz. variance, and correlation length, on the focusing resolution of transmitted waves by the TR array (TRA). The effect of depolarization is also briefly considered.

Direction‐of‐arrival estimation for ultra‐wideband EM pulses with an interferometry

AbstractIn this paper, we present an interferometry for the direction‐of‐arrival estimation of ultra‐wideband electromagnetic waves. The interaction between the antennas composing the interferometer is calculated by using the finite‐difference time‐domain (FDTD) method, and taken into account in the analysis. We propose a new signal processing scheme for wideband pulses, and demonstrate its effectiveness using a typical wideband pulse. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 37: 17–18, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10811

DOA estimation of ultra-wideband EM waves with MUSIC and interferometry

We propose a direction-of-arrival (DOA) estimation technique for ultra-wideband electromagnetic waves, which allows for the effect of antenna mutual coupling. This technique is comprised of ultra-wideband interferometry, multiple signal classification (MUSIC), and databases. The effectiveness of our scheme is demonstrated through numerical examples.