Pawel Kopyt

Improvement of terahertz field effect transistor detectors by substrate thinning and radiation losses reduction

Phenomena of the radiation coupling to the field effect transistors based terahertz (THz) detectors are studied. We show that in the case of planar metal antennas a significant portion of incoming radiation, instead of being coupled to the transistors, is coupled to an antenna substrate leading to responsivity losses and/or cross-talk effects in the field effect based THz detector arrays. Experimental and theoretical investigations of the responsivity versus substrate thickness are performed. They clearly show how to minimize the losses by the detector/ array substrate thinning. In conclusion simple quantitative rules of losses minimization by choosing a proper substrate thickness of field effect transistor THz detectors are presented for common materials (Si, GaAs, InP, GaN) used in semiconductor technologies.

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.

Planar antennas for integration with FET-based THz radiation detectors

This paper presents a design of planar antennas integrated with MOSFETs to form a THz radiation detector. The antennas have been developed on thin substrates in order to increase the detector responsivity through eliminating substrate modes responsible for electromagnetic power losses.

Towards a multiphysics simulation system for microwave power phenomena

Microwave power phenomena pose a great chellange to the computational electromagnetics specialists as accurate modelling of all the effects calls for employing a number of numerical tools that span several disciplines and are coupled together. In this paper, the authors present three hybrid multiphysics systems designed to solve coupled EM-thermal problem and compare simulation results with measurements. The described systems use as their building blocks EM and CFD tools popular in the market. The consequences of using two different numerical algorithms for EM and thermal part of calculations are also discussed.

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.

Remotely Powered Wireless Dual-Band Sensing System for Aircraft EMC Environment

In this paper, a wireless measurement system designed to monitor temperature inside a slat of an aircraft is presented. Both measurement signals and supply power for sensors installed on the remote part are transmitted by means of electromagnetic waves, which allows the system to work without connecting cables. The power delivered to the remote part is sufficient for a general-purpose microcontroller and separate platinum resistor thermal sensors, which significantly enhaces flexibility of the solution in comparison to other wireless sensing approaches based on a single dedicated ultralow power IC. Care was taken to maintain compliance of the system with RTCA/DO160E electromagnetic compatibility norms defined for aeronautic electronic equipment as well as with U.S. and European norms for general-purpose electronic devices.

A one-dimensional semi-analytic model of the microwave heating effect in verification of numerical hybrid modeling software

In this paper a semi-analytic model of the microwave heating effect has been briefly presented. The paper illustrates also an application of the model in verification of the computational accuracy of a commercially available electromagnetic simulator coupled with an FDTD-based thermal solver prepared by the author. In a series of simulations the behavior of the numerical model has been verified against the semi-analytic model for media of various losses as well as different relationships between temperature and the medium properties. The obtained results confirm the expectations based on the known properties of the computational methods employed in the numerical model.

Electric Properties of Graphene-Based Conductive Layers from DC Up To Terahertz Range

This paper describes results obtained using a hybrid measurement methodology employed to investigate electric properties of thin conductive layers based on graphene nanoplatelets in the frequency band spanning from dc up to terahertz range. As many as four different measurement methods were employed to cover the band of interest, including the terahertz time-domain spectroscopy and the Fourier-transform infrared spectroscopy besides resonator techniques applicable in the microwave band and the four-point dc technique. Raw measurement data obtained using these approaches were processed and based on the results a relationship between frequency and sheet resistance for various types of new graphene-based conductive layers was extracted. Eventually, several models that help to explain the observed behavior of each of the analyzed conductive inks were proposed.

Ferromagnetic Resonance Revised – Electrodynamic Approach

Resonance in a ferromagnetic sphere, known in the body of literature as the mode of uniform precession, has recently been proven to be magnetic plasmon resonance (MPR). This finding has prompted research which is presented in this paper on the relation between the Q-factor at the MPR and the ferromagnetic resonance (FMR) linewidth ΔH, which is a parameter of magnetized gyromagnetic materials. It is proven in this paper that ΔH can be unequivocally determined from the Q-factor measured at the MPR, if all losses in the resonance system are properly accounted for. It can be undertaken through a rigorous but simple electrodynamic study involving the transcendental equation, as proposed in this paper. The present study also reveals that electric losses have a substantially reduced impact on ΔH due to the large magnetic to electric energy storage ratio at the MPR. Theoretical results are supported by measurements of the Q-factors on a monocrystalline yttrium iron garnet (YIG) sphere.