Bartlomiej Salski

A Broadband Absorber With a Resistive Pattern Made of Ink With Graphene Nano-Platelets

A novel type of a broadband flexible electromagnetic absorbing panel made of a resistive pattern printed on a dielectric spacer backed by a conducting surface is investigated in this paper. It is shown that an appropriate choice of the shape and sheet resistance of the pattern allows extending an absorption spectrum up to an octave and beyond, which is very competitive over alternative solutions. The pattern is made of ink with graphene nano-platelets, which allows achieving expected sheet resistance with decent repeatability, what is confirmed with measurements undertaken with the DC point probe and microwave dielectric resonator techniques. An exemplary sample of the proposed absorber is manufactured and characterized, indicating a very good agreement between theoretical study and experiments.

An FDTD Model of Graphene Intraband Conductivity

A novel finite-difference time-domain (FDTD) model of magnetized graphene gyrotropic conductivity is proposed in this paper. The model, derived with the aid of auxiliary differential equations, takes into account intraband electron transitions, which are prevailing over interband conductivity terms up to terahertz frequencies. It is shown on the basis of equivalent circuit representation that a static magnetic bias changes a Drude dispersion characteristic of graphene into an extended Lorentz model supplemented with an additional branch accounting for the induced gyrotropy. The proposed FDTD updated equations are successfully validated with analytical results available in the literature. Computational efficiency of the algorithm is also tested.

Electromagnetic Inspection of Carbon-Fiber- Reinforced Polymer Composites With Coupled Spiral Inductors

This paper presents a new type of an electromagnetic sensor for nondestructive testing of carbon-fiber-reinforced polymer composites. The sensor utilizes coupled planar spiral inductors operating typically in the range of 10-500 MHz. The method proposed here shows some similarity to the eddy current technique, but as will be shown, the principles of operation are different as the sensitivity to defects is mostly due to the magnetic field components tangential to the surface of a material. It is shown that the method is applicable to 3-D inspection of carbon-fiber-reinforced composites widely employed in the aerospace industry.

An Advanced SAR Simulator of Three-Dimensional Structures Combining Geometrical Optics and Full-Wave Electromagnetic Methods

Modern research in the field of synthetic aperture radar (SAR) technology requires intensive simulations. The most accurate solution would be achieved by applying full-wave electromagnetic (EM) simulations. However, such an approach requires extremely huge computational efforts, mainly due to the large dimensions of the considered objects with respect to a wavelength. For that reason, most of currently used radar simulators are based on an optical approach, such as geometrical optics (GO). Full-wave EM methods require much more computational resources and are usually applicable to the analysis of geometries no larger than several wavelengths. Nowadays, standard desktop computer platforms are still equipped with too small computational resources to carry out full-wave EM simulations of large scenes considered in radar applications. This paper presents a new concept of hybrid analysis, based on GO enhanced with full-wave EM simulations of larger facets-of the size of a few radar resolution cells. The SAR raw radar simulator described in this paper allows a complex and realistic simulation of any scene under radar observation to be performed. The scene can be defined using any computer-aided-design software generating digital terrain model (DTM). It also allows using real DTMs gathered with, e.g., light detection and ranging systems.

FDTD for Nanoscale and Optical Problems

In this article, we have demonstrated that many representative problems of optical technologies can be accurately and effectively solved with the commercially available FDTD software, provided that such software offers the flexibility applying partial analytical knowledge to the problems. This is the case with scalar 2-D or guided 2-D FDTD algorithms relevant to the analysis of PhCs or microstructured optical fibers, as well as periodic FDTD method applicable in the scatterometry of ICs. We have also demonstrated an effective approach of hybridizing the FDTD and scalar Fresnel approaches for accurate and effective modeling of lens imaging phenomena. We believe that further developments along these lines using FDTD methods, supported by the concurrent developments in computer technology, will lead to hybrid time-domain software tools becoming a breakthrough in optics and photonics.

Graphene-Based Dipole Antenna for a UHF RFID Tag

This paper describes design and measurements of RFID tag built of a graphene-based dipole antenna and a chip operating in the UHF band in accordance with the EPC Global Class 1 Gen. 2 standard. Several tags have been constructed and tested with a standard RFID reader to reveal that each one is fully operational, but the interrogation range for the graphene-based circuits has been limited in comparison to copper antennae. This can be attributed to increased sheet resistance of a graphene layer. However, it seems that for applications were the read range is not crucial the novel antenna can be an alternative to more expensive circuits printed with silver-based inks.

Tunable negative index metamaterial employing in-plane switching mode at terahertz frequencies

We analysed the response of a tunable liquid crystal metamaterial transducer in the terahertz frequency range. Tunability of scattering parameters is achieving by an in-plane switching (IPS) effect. The metamaterial structure is based on Ω-shape resonators. A full-wave analysis technique based on the finite-difference time-domain (FDTD) method was performed using the QuickWave 3D electromagnetic solver. Terahertz transmission properties of the metamaterial structure can be controlled by the director of the liquid crystal layer. The effective refractive index for operation frequency varies from negative to positive values. A novel approach to switching of metamaterial transducer by IPS mode is presented.

Simulation of a tunable metamaterial with nematic liquid crystal layers

Authors analyze response of tunable liquid crystal metamaterial transducer in microwave frequency range. Tunability of scattering parameters is achieving by reorientation of liquid crystal molecules. Metamaterial (MTM) structure is based on Ω-shape resonators. A full-wave analysis technique based on the finite-difference time-domain method (FDTD) was performed using QuickWave 3D electromagnetic solver. Microwave transmission properties of the metamaterial structure can be controlled by director of liquid crystal layer. Effective refractive index for operation frequency varies from negative to positive values.

Electrodynamic study of YIG filters and resonators

Numerical solutions of coupled Maxwell and Landau-Lifshitz-Gilbert equations for a magnetized yttrium iron garnet (YIG) sphere acting as a one-stage filter are presented. The filter is analysed using finite-difference time-domain technique. Contrary to the state of the art, the study shows that the maximum electromagnetic power transmission through the YIG filter occurs at the frequency of the magnetic plasmon resonance with the effective permeability of the gyromagnetic medium μr ≈ −2, and not at a ferromagnetic resonance frequency. Such a new understanding of the YIG filter operation, makes it one of the most commonly used single-negative plasmonic metamaterials. The frequency of maximum transmission is also found to weakly depend on the size of the YIG sphere. An analytic electromagnetic analysis of resonances in a YIG sphere is performed for circularly polarized electromagnetic fields. The YIG sphere is situated in a free space and in a large spherical cavity. The study demonstrates that both volume resonances and magnetic plasmon resonances can be solutions of the same transcendental equations.

Graphene-based dipole antenna for a UHF RFID tag

This paper describes the design and measurements of a remote frequency identification (RFID) tag built of a graphene-based dipole antenna and a chip operating in the ultrahigh-frequency (UHF) band in accordance with the EPC Global Class 1 Gen. 2 standard. A custom-designed antenna has been designed first. Then, it was used to construct several tags that have been tested with a standard RFID reader to reveal that each one is fully operational, although the interrogation range for the graphene-based circuits has been limited in comparison to copper antennas. This can be attributed to increased sheet resistance of a graphene layer and-in the case of tags fabricated on paper-also to significant dielectric losses of the substrate material. However, it seems that for applications where the interrogation range is not crucial the novel antenna can be an alternative to much more expensive circuits printed with silver-based inks.