Propagation Characteristics Of Electromagnetic Waves Research Articles

New aspects of UHF PD diagnostics on gas-insulated systems

Gas insulated switchgears (GIS) have been increasingly introduced as main substation equipment since the late 1960s thanks to their high reliability, safety, and compactness. The UHF method to diagnose partial discharge (PD) is broadly employed in the field as an advanced insulation diagnostic technology. There are three primary factors related to the PD signal detection characteristics using this UHF method; namely the frequency spectrum of the PD signal itself inside GIS, the propagation characteristics of the PD signal inside the GIS tank, and the detection characteristics of the sensor measuring the PD signal. Accordingly, to further improvement of the diagnostic technique based on the UHF method, the PD phenomenon itself and its propagation characteristics should be clarified and the measurement system refined. From these perspectives, the present study reviewed the recent and latest findings concerning the PD phenomenon and its propagation characteristics inside GIS as well as the PD measurement system verification methods and diagnostic technologies, and summarized typical examples. Firstly, with regard to the PD phenomenon, measurement up to the high frequency band exceeding 10 GHz (even 30 GHz) clarified that the rise time of the PD current waveform is several tens of picoseconds, shorter than previously known. In the case of PD in micro-defects inside the epoxy insulator, however, the rise time is relatively long, in the order of nanoseconds, and a crack is the most critical defect. Subsequently, with regard to UHF PD diagnostics/monitoring technology, a novel technique using PD current waveform characteristics has been developed, and a more advanced PD diagnostic algorithm has been established by clarifying the influence of the shape and GIS internal structures on the electromagnetic wave propagation characteristics. Less uncertain and simplified calibration and verification technologies are also proposed both for a single UHF sensor and the entire UHF measurement system. These new technologies and further advanced studies in future are expected to make the UHF method more convenient and sophisticated.

The Simulation Study of Electromagnetic Wave Propagation Characteristics in Closed GIS Tank

Partial discharge (PD) detection using UHF signal is a well known advanced detecting method in GIS and has been actively studied. Numerical simulation using finite difference time domain (FDTD) algorithm is performed to investigate the transmission characteristics of W-M waves excited by partial discharge through straight closed tank of a GIS bus in. The time domain decaying characteristics and frequency domain resonance characteristics is studied in this paper. The simulation results shown that for the closed tank, E-M waves attenuate little during transmission and distribute oscillating in the tank. The distributions are symmetrical at 0 degree and 180 degrees and the energy at the two types of degrees is the same.

Numerical analysis of propagation characteristics of electromagnetic wave in lossy left-handed material media

The propagation characteristics of electromagnetic wave in lossy left-handed materials (LHM) are studied using finite-difference time-domain (FDTD) method base on auxiliary differential equation (ADE) technology. The LHM medium is realized with lossy Drude models for both the negative electric permittivity and the negative magnetic permeability. The discretized ADE-FDTD equations are derived in detail. The incident wave used in the simulation is a multiple cycle m-n-m pulses source. The term of Poynting's vector ExHy was calculated. These numerical results demonstrate conclusively that the phase velocity direction of electromagnetic wave propagation and the direction of the Poynting vectors are anti-parallel in LHM. The amplitude of electric field is reduced with the enhancive distance of LHM slab. It is also demonstrated that the energy of electromagnetic wave in the LHM slab is obviously attenuated, and the attenuation of energy becomes stronger with the angular plasma frequency ωp increasing. These results indicate that LHM stealth is effective in theory, and reasonable selection of the large negative index of refraction can greatly enhance its effectiveness.

Investigation on the placement effect of UHF sensor and propagation characteristics of PD-induced electromagnetic wave in GIS based on FDTD method

Using ultra-high-frequency (UHF) method in practical partial discharge (PD) detection can be affected by the positioning and placement of the UHF sensor. This in turn can affect the PD diagnosis. To ensure optimal performance of the sensor and understand the propagation process of electromagnetic (EM) wave, there is a need to fully analyze how the sensor's placement affects the output signal and the attenuation of EM wave in various positions and directions. As the previous researches are mainly concentrating on the radial component of the UHF signal, the propagation of the signal components in axial and radial directions and that perpendicular to the radial direction of the GIS tank are investigated in detail in this paper. Firstly, the attenuation of UHF signals at different radial positions of a GIS model is analyzed using the finite difference time domain (FDTD) method. Then, secondly, the coupled signals in the three directions are calculated respectively. By comparing the signal received for different directions and circumferential angles, the peak to peak value (Vpp) and cumulative energy of the coupled voltage in each case are considered both in the time and frequency domain. As well, the attenuation characteristics and rules are summarized, based on which a new method for circumferential and axial location is proposed. The investigation on the propagation and the detection mechanism of EM wave in GIS provides a significant understanding of the application of UHF sensor and actual PD detection.

Electromagnetic characterization of a computational asymmetric analysis for wireless networks

While sensor networks research for terrestrial applications has made significant strides in the past few years, the literature has relatively few examples of papers that have validated the feasibility and reliability issue, for the performance of Wireless Sensor Networks (WSNs) for underground applications. The propagation characteristics of electromagnetic (EM) waves in soil, and significant differences from propagation in air, prevent straightforward characterization of the underground wireless channel. Fundamentals, such as the dielectric permittivity and magnetic permeability, are required to solve the propagation of EM waves in soil. To this end, in this paper, we proposed a new model, Asymmetric Mixture Homogenization, based on the representative volume element concept, to characterize the dielectric permittivity of soil according to the composition of soil, and layout the foundation for efficient communication in this new environment. Further, in this paper we validated that with the latest wireless network system being used for terrestrial applications, challenges exists for the WSN to be used for underground applications. Experiments are performed to examine the link-level quality and received signal strength parameter between under-soil and above soil sensor nodes. The theoretical analysis and the experimental results prove the feasibility for the realization of WSN in underground applications.

Dispersion effects in Fakir's bed of nails metamaterial waveguides

The propagation characteristics of electromagnetic waves in waveguides implemented using the “Fakir's bed of nails” are investigated both analytically and numerically. The classical metal walls of a parallel-plate waveguide are replaced by a Fakir's bed of nails metamaterial having arbitrary pin lengths on both walls; treated as a homogenized effective spatially dispersive dielectric. A modal analysis of the electromagnetic fields is presented for the first time, and dispersion expressions for the propagating modes are derived analytically and independently validated with full-wave numerical simulations. An equivalent transmission line model is also given, and similarities with the classical metal-dielectric-metal structure commonly used in optics are discussed.

Propagation characteristics of THz electromagnetic waves in time varying un-magnetized plasma

This paper has built the one-dimensional model of the time-varying un-magnetized plasma, and the finite different time domain (FDTD) algorithm is used to calculate the reflection and transmission coefficients, as well as the absorption rate of terahertz (THz) electromagnetic waves in time-varying plasma. The relation between the frequency of the THz wave and the propagation characteristic influenced by rise time, electron density, temperature, and depth of time-varying plasma plate is analyzed. Results demonstrate that the reflection coefficient is mainly influenced by plasma rise time and electron density. The absorption rate increases with decreasing rise time, increasing depth and electron density. Furthermore, the THz electromagnetic wave is an effective tool for the communication of reentry vehicle and high density plasma diagnosis because of its strong penetrability in high density plasma.

Investigation on Propagation Characteristics of PD-induced Electromagnetic Wave in T-Shaped GIS Based on FDTD Method

Investigation on Propagation Characteristics of PD-induced Electromagnetic Wave in T-Shaped GIS Based on FDTD Method

Investigation of propagation characteristics of electromagnetic waves through eccentric core optical fibers

The propagation characteristics of electromagnetic waves through eccentric core optical fibers have been discussed making use of scalar wave equation in conjunction with Graf's addition theorem for cylindrical Bessel's functions. The system under investigation consists of three media with eccentric location of the inner core region. This makes the system birefringent and lifts up the degeneracy present in the corresponding structure with cylindrically symmetric inner core region. Furthermore, the birefringence increases with the increase in eccentricity up to an allowed limit dictated by the geometrical parameters of the system and makes the propagation truly single mode single polarization.

Experimental studies of slow wave based on the surface waves in a two-dimensional metamaterials waveguide

In this paper, we study the slow propagation characteristics of surface electromagnetic waves according to theoretical analysis in the MNG (μ-negative)-DPS (double-positive)-MNG waveguide, which is composed of two-dimensional (2D) metamaterials. The dispersion curves of this waveguide vary with circuit parameter (unit capacitors) of MNG metamaterial. At the cutoff frequency of the dispersion curve the group velocity of electromagnetic wave is equal to zero in theory. So we can obtain slow propagation of the surface waves at different cutoff frequencies just by changing the unit capacitor of the MNG metamaterial. Theoretical analysis also shows that the step changes in slow waves are obtained at some fixed frequencies through changing the unit circuit parameters. The experimental results are in good agreement with simulation results.

Grain Moisture Content Measurement System Based on Time-Domain Transmission Technology

To measure the grain moisture content with time-domain transmission technology (TDT), electromagnetic wave propagation characteristics was studied to find the relationship of electromagnetic wave propagation and the dielectric parameters of grain. Basic structure of measurement sensor was designed to be coaxial transmission line based on TDT theories. The main parameters of the sensor were calculated. The measurement circuit was designed based on processing theories of high frequency electromagnetic signals. Grain samples with different moisture contents were measured by both TDT system and the standard drying method. The results show that TDT system with Quadratic curve measurement model is of desired measurement accuracy.

Analysis and Mechanism of Impact of GPR Detection Effect Result from Soil Water Content

Using the ground-penetrating radar (GPR) system with the different frequencies and neutron probe, combing with radar image interpretation and the amplitude spectrum, the impact of GPR detection effects on the soil taxonomy and underground pipe were analyzed. The results indicate that when the soil content is 17.02%, the effect on soil taxonomy of 750MHZ antenna is better than 400MHZ, but the effect on underground pipe is same. As soil water content increases to 25.333%, the soil taxonomy of two antennas’ detection tends to same, and “fake stratifications” existed. The soil water content accelerates to 36.389%, the detection effect on soil taxonomy and underground pipe is so poor. Attenuation mechanism and propagation characteristics of the high electromagnetic wave were presented to interpret those phenomena. The above analysis shows that the soil water content is one of the main prerequisites for the applications of GPR. Some indicators could be provided to nondestructive test in land consolidation project quality by GPR from this research.

Self-consistent simulation on discharge characteristics in a ring dielectric line typed surface wave plasma apparatus

A self-consistent simulation tool for a microwave-excited surface wave plasma is developed. The plasma is treated as a dispersive medium and the finite-difference time-domain method is used to analyze the propagation characteristics of electromagnetic waves in the plasma. Plasma parameters such as electron temperature, electron density and space potential are calculated based on the fluid model of plasmas. In this paper, the microwave propagation characteristics and the distributions of plasma parameters are investigated at Ar gas pressures of 10 and 30 mTorr in a ring dielectric line typed surface wave driven plasma apparatus. The simulation tool is evaluated by comparing the simulation results with the experimental results.

Study on Electromagnetic Wave Propagation Characteristics in Rotating Environments and Its Application in Tire Pressure Monitoring

During parameter acquisition of rotating components, wireless data transmission is an efficient way. In this paper, electromagnetic (EM) wave propagation characteristics in rotating environments are preliminarily studied in order to provide a strong theoretical support for developing high-performance radio monitoring systems in rotating environments. The mathematical formulation of signal wave propagation between the transmitting antenna and the receiving antenna in time-dependent rotating motion is derived. The Doppler frequency shift and the EM wave polarization characteristics in rotating environments are presented and analyzed. The two-ray propagation model in rotating environments is proposed, and the validity of the model is verified by experimental results. Taking tire pressure monitoring system (TPMS) as a typical example, key parameters affecting wireless data transmission from a rotating transmitting antenna are investigated, and system performance enhancement strategies are proposed. Power transmission tests were conducted on a TPMS operating at different frequencies and different rotating radii relative to wheel rotation axis. The test results show that the path loss and the path loss fluctuation sharpness increase with the operating frequency and the rotating radius. Moreover, the path loss for most rotation angle values decreases drastically at lower frequencies and lower radii. Wireless data transmission tests were implemented for both the improved TPMS and the old TPMS. The test results show that the receiving probabilities of successful data frame transmission are improved greatly.

Characteristics of Plane Wave Propagation in Biaxially Anisotropic Gyrotropic Media

Propagation characteristics of electromagnetic waves at the interface between an isotropic regular medium and a biaxially anisotropic gyrotropic medium are investigated. The results indicate that the reflection and refraction properties of electromagnetic waves are closely dependent on the dispersion relation of the gyrotropic media, and that anomalous total reflection and negative refraction may occur. The existence conditions of total transmission are also considered. It is found that total transmission arises when the TE-polarized incident waves are normal to the interface and the physical parameters of the two media are chosen properly, which are quite different from the existence conditions of total transmission at the anisotropic left-handed material interface. Numerical results are given to validate our theoretical analysis.

Wireless distributed functional electrical stimulation system

BackgroundThe control of movement in humans is hierarchical and distributed and uses feedback. An assistive system could be best integrated into the therapy of a human with a central nervous system lesion if the system is controlled in a similar manner. Here, we present a novel wireless architecture and routing protocol for a distributed functional electrical stimulation system that enables control of movement.MethodsThe new system comprises a set of miniature battery-powered devices with stimulating and sensing functionality mounted on the body of the subject. The devices communicate wirelessly with one coordinator device, which is connected to a host computer. The control algorithm runs on the computer in open- or closed-loop form. A prototype of the system was designed using commercial, off-the-shelf components. The propagation characteristics of electromagnetic waves and the distributed nature of the system were considered during the development of a two-hop routing protocol, which was implemented in the prototype’s software.ResultsThe outcomes of this research include a novel system architecture and routing protocol and a functional prototype based on commercial, off-the-shelf components. A proof-of-concept study was performed on a hemiplegic subject with paresis of the right arm. The subject was tasked with generating a fully functional palmar grasp (closing of the fingers). One node was used to provide this movement, while a second node controlled the activation of extensor muscles to eliminate undesired wrist flexion. The system was tested with the open- and closed-loop control algorithms.ConclusionsThe system fulfilled technical and application requirements. The novel communication protocol enabled reliable real-time use of the system in both closed- and open-loop forms. The testing on a patient showed that the multi-node system could operate effectively to generate functional movement.

Propagation characteristics of time reversal pulsed electromagnetic waves in double negative materials

With the full time-domain electromagnetic simulation technique, the time-domain propagation properties such as the temporal pulse waveform, the pulse compression and the electric field distribution inside the material are comparably investigated by transmitting the time-reversal pulsed electromagnetic wave and the pulsed electromagnetic wave through the double negative material of the Smith structure, respectively. The results show that after the time-reversal pulsed electromagnetic wave passes through the double negative material, the received electromagnetic wave exhibits remarkable spatial and temporal focusing at the location of the initial excitation. The most interesting physical phenomenon is that the peak values of the electric field inside the double negative material become smaller and tend to be uniform in the magnitude. These novel physical phenomena would be very helpful for developing new electronic devices and systems with double negative materials for the purpose of high power applications.

Broadband Electromagnetic Modeling of Woven Fabric Composites

We demonstrate a new method for predicting the broadband electromagnetic (EM) wave propagation characteristics of woven fabric composites. The method combines a rigorous EM model with effective media theory to predict the EM properties of structural composites from dc to 50 GHz. Experimental results are provided that demonstrate the validity of the method. We also describe the presence of large narrow band electromagnetic resonances that occur above 30 GHz. These resonances, which are shown to be guided mode resonances, can be predicted by solving a simple dispersion relation.

Delay spread of electromagnetic waves along random rough surface

This paper is concerned with a numerical analysis of propagation characteristics of electromagnetic waves traveling along two-dimensional (2D) random rough surface (RRS). Ray searching algorithm is based on 2D discrete ray tracing method, and the field distribution corresponding to each searched ray is computed by using source and image diffraction coefficients. Numerical computations are carried out for total field distributions along RRS as well as delay profiles at an arbitrary observation point which is far from a source antenna. Detailed discussions are made on the effect of directivity of source or receive antenna to the delay spreads of received powers.

3D Polarized Channel Modeling and Performance Comparison of MIMO Antenna Configurations With Different Polarizations

We propose a three-dimensional (3D) polarized MIMO channel model, which takes into account 3D power angular spectrum and comprehensive propagation characteristics of electromagnetic waves excited by polarized antennas. Based on the model, we derive a close form expression of the spatial correlation as a function of the physical parameters representing both characteristics of arbitrary antennas and propagation environment in 3D space. The spatial correlation expression allows to use the Von Mises Fisher (VMF) distribution, resulting in a more accurate and general channel model. Through simulation, we evaluate and compare performance, in terms of the spatial correlation and capacity, of 2 × 2 MIMO configurations with different polarizations, i.e., V/V, V/H, and slanted ±45° polarizations, as a function of critical input parameters including elevation angle, antenna orientation, antenna spacing, cross-polarization discrimination (XPD), and signal-to-noise ratio (SNR). The effect of the parameters on the performance is analyzed, and verified in certain cases through the literature.