Electromagnetic Wave Propagation Effects Research Articles

Quantitative assessment to the impact of InSAR ionospheric and tropospheric corrections on source parameter modelling: application to the 4th nuclear test, North Korea

SUMMARYAlthough many studies have revealed that the atmospheric effects of electromagnetic wave propagation (including ionospheric and tropospheric water vapour) have serious impacts on Interferometric Synthetic Aperture Radar (InSAR) measurement results, atmospheric corrections have not been thoroughly and comprehensively investigated in many well-known cases of InSAR focal mechanism solutions, which means there is no consensus on whether atmospheric effects will affect the InSAR focal mechanism solution. Moreover, there is a lack of quantitative assessment on how much the atmospheric effect affects the InSAR focal mechanism solution. In this paper, we emphasized that it was particularly important to assess the impact of InSAR ionospheric and tropospheric corrections on the underground nuclear explosion modelling quantitatively. Therefore, we investigated the 4th North Korea (NKT-4) underground nuclear test using ALOS-2 liters-band SAR images. Because the process of the underground nuclear explosion was similar to the volcanic magma source activity, we modelled the ground displacement using the Mogi model. Both the ionospheric and tropospheric phase delays in the interferograms were investigated. Furthermore, we studied how the ionosphere and troposphere phase delays could bias the estimation of Mogi source parameters. The following conclusions were drawn from our case study: the ionospheric delay correction effectively mitigated the long-scale phase ramp in the full-frame interferogram, the standard deviation decreased from 1.83 to 0.85 cm compared to the uncorrected interferogram. The uncorrected estimations of yield and depth were 8.44 kt and 370.33 m, respectively. Compared to the uncorrected estimations, the ionospheric correction increased the estimation of yield and depth to 9.43 kt and 385.48 m, while the tropospheric correction slightly raised them to 8.78 kt and 377.24 m. There were no obvious differences in the location estimations among the four interferograms. When both corrections were applied, the overall standard deviation was 1.16 cm, which was even larger than the ionospheric corrected interferogram. We reported the source characteristics of NKT-4 based on the modelling results derived from the ionospheric corrected interferogram. The preferred estimation of NKT-4 was a Mogi source located at 129°04′22.35‘E, 41°17′54.57″N buried at 385.48 m depth. The cavity radius caused by the underground explosion was 22.66 m. We reported the yield estimation to be 9.43 kt. This study showed that for large-scale natural deformation sources such as volcanoes and earthquakes, atmospheric corrections would be more significant, but even if the atmospheric signal did not have much complexity, the corrections should not be ignored.

Plasma Instability Modeling With Mixed Wave/Diffusion Field Behavior

Recent efforts have extended fluid dynamic modeling to include low-electrical-conductivity (wavelike) electromagnetic field effects in plasmas. Here, we present results of a new study to explore and illustrate the capability of resolving such effects in the development of plasma instabilities. Recent work[1, 2] has explored the development of an efficient numerical procedure for simulating the coupled fluid dynamic and full electromagnetic (Maxwell) equations. This system of equations is more general than the resistive magnetohydrodynamic (MHD) model. The physical advantage to this system is that the inclusion of the displacement current and charge separation effects extends fluid dynamic modeling of plasmas to include regions of extremely low (or zero) electrical conductivity, where the electromagnetic fields possess a wave nature. Capturing the correct physical behavior of plasma instabilities in the limit of extremely low electrical conductivity is of significance for modern aerospace applications, including energy bypass arrangements for scramjet propulsion using magnetohydrodynamic augmentation, due to the extremely low electrical conductivity of the aerospace environment. The results depicted in this paper illustrate the potential for the numerical method realized in Ref. 1 to effectively resolve this behavior in cases where the MHD approximation may not be valid due to an exceedingly low electrical conductivity. A new study was initiated to explore more fully the capabilities to resolve regions of both low and high electrical conductivity using this numerical scheme. The problem selected for this study was the classic MHD KelvinHelmholtz instability. The initial and boundary conditions are provided in Ref. 2. A periodic box is initialized with two fluids of different density moving in opposite directions. An initial small perturbation is applied to the interfaces between the fluids, seeding an instability. A 256x256 grid size using a Roe solver for the coupled system of Navier-Stokes and full Maxwell equations was used, as detailed in [1, 2]. Three cases were explored: Case A was assigned a zero electrical conductivity, σ = 0 (purely hydrodynamic), Case B was given a small electrical conductivity of σ = 1, and Case C was given a very high conductivity of σ = 10 6 . Case A provides a hydrodynamic benchmark. Case B permits an investigation of a simulation that includes the effects of electromagnetic wave propagation in the plasma evolution. Case C effectively realizes the magnetohydrodynamic approximation. Results for the simulations are presented in a unique fashion in Fig. 1. For each subfigure, three spacetime isosurfaces of the density (blue, green and orange corresponding to the color range) have been depicted. Isosurfaces are the same for all three presented subfigures. Time flows from right (initial conditions) to left (final solution). For Case A, the fluid achieves a highly chaotic solution. The propagation of the initial disturbance at the interfaces between the two fluids is clear, as well as their development into a highly turbulent flow. Case B possesses an extremely low electrical conductivity, and therefore is not subject to the magnetic diffusion approximation of MHD. In fact, electromagnetic wave propagation was visible in this solution. The presence of a finite electrical conductivity provides some diffusion, but it does not match very well to the MHD prediction. However, the conductivity is large enough to abate the low-wavelength instabilities somewhat, and provide stability to the flow. Case C realizes the magnetohydrodynamic limit, where the magnetic field tends to stabilize the flow and strongly suppresses low-wavelength instabilities. A much more organized series of flow structures evolve through time to the final state. The magnetic field is effectively “frozen” to the fluid with such a large electrical conductivity, and the field strongly diffuses with little wave propagation.

Electromagnetic Modeling of Dielectric Mixtures

Electromagnetic modeling of dielectric materials allows us to study the effects of electromagnetic wave propagation and how such electromagnetic fields influence and interact with them. Dielectric materials are composites or mixtures, which often are made up of at least two constituents or phases. Modelling the electromagnetic behaviour of dielectric mixtures is crucial to understand how geometrical factors (shape and concentration), electromagnetic properties of inclusions and background medium, influence the permittivity of the overall material. The aim of this work is to develop new analytical models for dielectric mixtures, in order to describe their electromagnetic behaviour and design them with desired electromagnetic properties, for specific required applications. In particular, in this paper a new general expression for the effective permittivity of dielectric mixture is presented. The mixtures consist of inclusions, with arbitrary shapes, embedded in a surrounding dielectric environment. We consider the hosting environment and the hosted material as real dielectrics, both of them as dispersive dielectrics. The proposed analytical models simplify practical design tasks for dielectric mixtures and allow us to understand their physical phenomena and electromagnetic behaviours.

Advanced CAD tool for noise modeling of RF/microwave field effect transistors with large gate widths

In the millimeter-wave frequency range, electromagnetic (EM) effects can significantly influence a device behavior. As the core of modern communication systems, active devices such as field effect transistors (FETs) require up-to-date models to accurately integrate such effects, especially in terms of noise performance since most of communication systems operate in noisy environments. Furthermore, to keep low-noise amplification over a wide frequency band, the transistor noise resistance Rn must be substantially reduced to make the system insensitive to impedance matching. Since this can be realized through large gate-width devices, a novel large gate-width FET noise model is proposed which efficiently integrates EM wave propagation effects, one of the most important EM effects in mm-wave frequencies.

Self-consistent electrodynamics of large-area high-frequency capacitive plasma discharge

Capacitively coupled plasmas (CCPs) generated using high frequency (3–30 MHz) and very high frequency (30–300 MHz) radio-frequency (rf) sources are used for many plasma processing applications including thin film etching and deposition. When chamber dimensions become commensurate with the effective rf wavelength in the plasma, electromagnetic wave effects impose a significant influence on plasma behavior. Because the effective rf wavelength in plasma depends upon both rf and plasma process conditions (e.g., rf power and gas pressure), a self-consistent model including both the rf power delivery system and the plasma discharge is highly desirable to capture a more complete physical picture of the plasma behavior. A three-dimensional model for self-consistently studying both electrodynamic and plasma dynamic behavior of large-area (Gen 10, >8 m2) CCP is described in this paper. This model includes Maxwell’s equations and transport equations for charged and neutral species, which are coupled and solved in the time domain. The complete rf plasma discharge chamber including the rf power delivery subsystem, rf feed, electrodes, and the plasma domain is modeled as an integrated system. Based on this full-wave solution model, important limitations for processing uniformity imposed by electromagnetic wave propagation effects in a large-area CCP (3.05×2.85 m2 electrode size) are studied. The behavior of H2 plasmas in such a reactor is examined from 13.56 to 200 MHz. It is shown that various rectangular harmonics of electromagnetic fields can be excited in a large-area rectangular reactor as the rf or power is increased. The rectangular harmonics can create not only center-high plasma distribution but also high plasma density at the corners and along the edges of the reactor.

On the Experimental Evaluation of Wireless Multihop Networks

In wireless multihop networks, nodes cooperate to forward data packets. After years of simulation-based research, the next step is the evaluation of this paradigm under real-world conditions. However, due to the distributed nature of such a network in combination with the complex effects of electromagnetic wave propagation, it is extremely difficult to perform these experiments systematically. In this paper, we introduce a bundle of techniques and tools to tackle the fundamental problems of the control and analysis of such experiments.

Electromagnetic field nonuniformities in large area, high-frequency capacitive plasma reactors, including electrode asymmetry effects

Electromagnetic wave propagation effects can give rise to important limitations for processing uniformity in large area, radio-frequency (rf) capacitive plasma reactors. The electromagnetic wavefield solution is derived for a capacitive, high-frequency, cylindrical reactor with symmetric or asymmetric electrode areas containing a uniform plasma slab. It is shown that only two distinct electromagnetic modes are necessary and sufficient to determine the electromagnetic fields everywhere within the reactor except close to the sidewalls. The first mode gives rise to the interelectrode rf voltage standing wave effect associated with high frequencies in large area reactors, and the second mode gives rise to the telegraph effect associated with asymmetric electrode areas, which necessitates the redistribution of rf current along the plasma to maintain rf current continuity. This work gives a unified treatment of both effects which have previously been studied separately, experimentally and theoretically, in the literature. The equivalent circuit of each mode is also derived from its respective dispersion relation. Examples of this electromagnetic wavefield solution show that both modes can cause nonuniformity of the plasma rf potential, depending on the reactor geometry, excitation frequency and plasma permittivity and sheath width, which has consequences for large-area plasma processing.

Advantages of Semiconductor Device Simulator Combining Electromagnetic and Electron Transport Models

Physical simulation of semiconductor devices at high frequencies involves not only semiconductor transport issues but also electromagnetic wave propagation issues. In order to obtain the nonlinear and the large-signal characteristics of the semiconductor devices, an electromagnetic model should replace the traditional quasi-static model in the device simulator. In this paper, the advantages of a semiconductor device simulator combining an electromagnetic and an electron transport models are presented. This study is based on a semiconductor device simulator that couples a semiconductor model to the 3D time-domain solution of Maxwell's equations. The electromagnetic wave propagation effects on the millimeter-wave FETs are thoroughly analyzed. The use of the electromagnetic model over the conventional quasi-static model provides the actual device response at high frequencies. It also shows the nonlinear energy build-up along the device width whereas the quasi-static model provides a linear increase of energy. The combined model is capable of predicting the device nonlinearity and harmonic distortion of amplifier circuits at large signal.

Flexible microwave system to measure the electron number density and quantify the communications impact of electric thruster plasma plumes

An advanced microwave interferometric system operating in the Ku (12–18 GHz) band has been implemented for use in very large vacuum chambers to determine the effects of electromagnetic wave propagation through a plasma plume created by a space electric propulsion thruster. This diagnostic tool is used to nonintrusively obtain the local electron number density as well as provide information necessary for understanding impact to communications and other spacecraft electromagnetic systems. The use of a nonintrusive electromagnetic measurement provides highly accurate line integrated density and avoids problems caused by intrusive measurement techniques. If the plasma is symmetrical, local plasma density can also be determined accurately using well known inversion techniques. A network analyzer acts as a transmitter and receiver while a two axis positioning system maps the amplitude and phase variation of a transmitted signal over one plane of the plasma plume. The utilization of a 6 m×9 m vacuum chamber effectively minimizes plasma boundary effects, but the longer cable path lengths have required a frequency conversion circuit to reduce power loss and phase uncertainty at high frequencies. Two studies are presented: the first is a measurement of the local electron density in the plume of a 1 kW arcjet and the second is a measurement of attenuation in the plume of a stationary plasma thruster. Both the arcjet and SPT emit a steady state conical unmagnetized plasma that is radially symmetric. The arcjet peak density is 1015–1016 m−3 along centerline and the SPT peak density is 1016–1017 m−3 along centerline.