An electromagnetics course with EMC applications for computerengineering students

When computer engineering students follow a different (separate) program of study from the electrical engineering students, only a single course in engineering electromagnetics can be accommodated in the computer engineering (CE) core program. An outline for a course on electromagnetics for computer engineering is given combining traditional electromagnetics topics with definitions, concepts, and discussions drawn from EMC. In this way engineering electromagnetics is made relevant and vital for the CE student. Specific EMC topics are included as they arise in a presentation based on a standard engineering electromagnetics text. Shielding, radiated emissions, susceptibility, the electromagnetic environment, EMC test methods, open sites, shielded anechoic rooms, screen rooms, TEM cells, and EMC test antennas are discussed. The goal of the computer engineering electromagnetics course is to prepare the student for a full-scale EMC course to be taken as an elective in the final undergraduate year or the first year of graduate study     

Animating transmission-line transients with BOUNCE

This paper presents the program BOUNCE for animating transients on transmission lines. BOUNCE is used for classroom demonstrations of fundamental concepts such as traveling wave, reflected wave, reflection from an unmatched load, and transmission through junctions and branches. BOUNCE provides a "laboratory" for students to use in verifying homework exercises solved with a lattice diagram. BOUNCE is used to demonstrate fundamental principles of logic design, such as ringing because of mismatch at high-impedance gate inputs, the effect of gate-input capacitance, and the effect of logic-gate rise time. BOUNCE graphically demonstrates the transition to the sinusoidal steady state and the concept of a standing wave, as the result of an unmatched load, as an introduction to solving transmission lines with phasors. This paper describes the operation of the BOUNCE program and then discusses various classroom demonstrations and the associated homework exercises.     

Unconditionally stable Crank-Nicolson scheme for solving two-dimensional Maxwell's equations

The Crank-Nicolson method is an unconditionally stable, implicit numerical scheme with second-order accuracy in both time and space. When applied to solve Maxwell's equations in two-dimensions, the resulting matrix is block tri-diagonal, which is very expensive to solve. The Douglas-Gunn algorithm is used to subdivide the update procedure into two sub-steps. At each sub-step only a tri-diagonal matrix needs to be solved for one field component. The other two field components are updated explicitly in one step. The numerical dispersion relations are given for the original Crank-Nicolson scheme and for the Douglas-Gunn modification. The predicted numerical dispersion is shown to agree with numerical experiments, and its numerical anisotropy is shown to be much smaller than that of the ADI-FDTD.     

Graphics for visualizing RCS as a function of frequency and angle

Over the past few years, the David Florida Laboratory (DFL) has conducted extensive measurements of the radar cross section (RCS) of simple, "canonical" targets, and of scale models of real-life targets. Software has been written for computer-controlled acquisition of the RCS, over a wide frequency band, as a function of the angle of incidence on the target. This article presents specialized graphics formats which have been developed to effectively visualize the RCS. Different color palettes for depicting RCS values are compared. The RCS can be graphed as a "color map" in a rectangular format, with the angle on the x axis and the frequency on the y axis. But the RCS as a function of the incidence angle is better perceived when plotted in a polar format, with the angle around the circumference and the frequency along the radius. Moreover, when the radius is proportional to the frequency, RCS color maps display striking geometric patterns, related to the basic scattering mechanisms of the target. This feature provides a useful analytic and pedagogical tool.<>     

Challenges facing quantification of rat locomotion along beams of varying widths

Optoelectronic motion capture systems have been widely used to investigate temporal gait parameters in humans and animals in order to understand function and behavioural attributes of different pathologies, e.g. Parkinson's disease (PD). The aim of the present paper was to investigate the practicality of utilising this system to investigate the effects of a unilateral 6-hydroxydopamine (6-OHDA) lesion on rat locomotion while walking on beams of varying widths (graduated, narrow, and wide). Temporal gait parameters of ten male Lister Hooded rats (five controls and five hemiparkinsonian) were observed using passive markers placed in locations that were representative of their four limbs and their body axis. The results demonstrate that marker-based motion capture can provide an effective and simple approach to quantifying temporal gait parameters for rat models of PD. They also reveal how the width of the path affects the locomotion in both experimental cohorts. Such measurements can be compared with human motion analysis to explore correlations between the animal model and human behaviour, which is an important step for translational medicine.     

Longwall roof control through a fundamental understanding of shield–strata interaction

Real-time and non-real-time software has been developed that encapsulates a fundamental understanding of the interaction between a longwall powered support (shield) and the surrounding strata based on the interpretation of the leg pressure data within each load cycle. A load cycle is the change in support pressure with time from setting the shield against the roof to the next release and movement of the support. It is now possible to automatically identify when a shield has too low a set pressure, and when a shield is faulty and/or has an inadequate capacity for the conditions. The use of this software has the potential to significantly reduce or even eliminate roof control problems on a longwall face with significant benefits to both productivity and safety. By automatically identifying potential causes of roof control problems and offering solutions, the software has the potential to aid longwall automation. A Beta test version of the real-time software has been successfully working at BMA's Broadmeadow Mine in Australia for some time and several Australian mines have benefited from expert off-line analyses using the software. The software can also be used to isolate the many interconnected factors affecting roof control on a longwall face, which will enable their quantification, and is therefore a powerful research tool.     

Study of multiple draw-zone interaction in block caving mines by means of a large 3D physical model

Current production level design guidelines in block caving mines are based on the concept of interaction of movement zones and the spacing of draw-points at which mass flow is achieved. The limit of the isolated movement zone (IMZ) interaction has been determined by observations of the flow of sand and finely fragmented caved rock. This paper presents a study of the mechanisms and limit of IMZ interaction in coarse fragmented caved rock using a large 3D physical model. Results showed that when drawing from multiple draw-points, the unmoved zone between IMZs is characterised by an increase in vertical load and a decrease in horizontal load. However, it was observed that the unmoved zones between the movement zones of adjacent draw-points did not enter the flow zone, despite draw-points being spaced at less than 1.2 times the width of the IMZ. This result is in marked contrast to previous findings obtained in sand models, where movement zones have been observed to interact at draw-point spacings up to 1.5 times the width of the IMZ. The major reasons for the differences between the two different model results was found to be that significant stress arching and less induced vertical stress during flow was observed in the gravel model, in contrast to limited stress arching and more induced vertical stress in the sand models. It is hypothesised that significant stress arching would occur in block caving mines, and therefore that the results obtained in the gravel model maybe more representative of full-scale conditions. Movement zones in block caving mines may therefore not interact at draw-point spacings greater than the width of the isolated movement zone.     

Precision radar cross-section measurements for computer codevalidation

Precision measurements of the radar cross section (RCS) of simple rod and cylinder targets for all angles of incidence in a plane containing the long axis of the target are presented. The RCS is presented as a contour map as a function of the frequency and the incidence angle. These extensive measured RCS data are used as a reference for validating numerical computations. Wire-grid models of the rod and cylinder targets are constructed using commonly accepted guidelines. It is shown that the resulting RCS is in error by less than 2 dBm² for segments of length as long as λ/5, and that the wire grid is capable of precisely determining the resonant frequencies of the wire. A comparison of the RCS of the rod computed using the finite-difference time-domain method with the measured RCS suggests a cell-size correction. Thus, the surface of the conducting object is considered to be 1/4 cell away from the surface of cells designed as perfectly conducting. This quarter-cell margin guideline greatly improves the agreement between the finite-difference time-domain (FDTD) RCS of the rod and cylinder targets and the measured RCS     

Comparison of Computed RF Current Flow on a Power Line With Full Scale Measurements

Reradiation of an MF/AM broadcast transmitter's signal by a power transmission line can cause serious pattern distortion. A computer model of a power line, developed and tested against scale model measurements over highly conductive ground, has been used to assess the pattern distortion to be expected from a power line proposed for construction, to identify those towers on an existing power line which carry strong RF currents, and to design "detuningn devices to suppress such currents. The accuracy of the computer model's "predictions" is tested in this paper against full-scale measured RF current flow on the skywires of a real power line. A toroidal current probe is described which is suitable in the MF band for current measurement on a large steel lattice structure such as a power line tower. Instrumentation is described for the measurement of either current magnitude only, or of both magnitude and phase. Thus the current flowing on a power line tower is readily measured by this method. Measurements of skywire current are compared with computations using a highly conductive "perfect" ground model, and using the Sommerfeld-Norton ground model for "lossy" ground of conductivity 10 millisiemens/metre and relative permittivity 15. The two ground models result in similar current distributions, with the peaks and minima in the standing wave pattern at the same positions on the skywire. The lossy ground model results in somewhat less current flow due to the damping introduced into the resonant behaviour of the power line.     

Effect of dam removal on habitat use by spawning Atlantic salmon

By impeding migration and degrading habitat downstream, dam construction has caused population declines in many migratory fish populations. As part of the landlocked Atlantic salmon (Salmo salar) restoration program in Lake Champlain, the Willsboro Dam was removed from the Boquet River, NY in 2015 providing an opportunity to study the effects of dam removal on spawning habitat quality and availability. Spawning habitat surveys were conducted downstream of the dam site in 2014, 2016 and 2017, and in historical spawning grounds upstream in 2016 and 2017. The habitat used was characterized by measuring depth, water velocity, and substrate size at each redd. Mean habitat use did not differ between upstream and downstream sites for any variables in 2016 and only differed for depth in 2017. However, the variance in depth and substrate used for spawning were lower at the upstream site in 2016, likely due to an abundance of habitat. In the downstream site, the mean and variance in depth at redds decreased after dam removal as did the variance in substrate size, increasing the habitat suitability of redds. When compared to literature data, habitat used upstream of the former dam was of medium quality in both 2016 and 2017, and improved downstream from low to medium quality in both column velocity and substrate size after dam removal. This study illustrates that positive shifts in the quality of habitat used can occur rapidly following dam removal by allowing access to suitable spawning habitat upstream and improving habitat downstream.