Figure of merit for low frequency anechoic chambers based onabsorber reflection coefficients

Return loss as a function of frequency and angle of incidence is studied to determine the effectiveness of the absorbing material used in an anechoic chamber. This alone is not enough to determine a figure of merit for an anechoic chamber or to compare the figure of merit for one anechoic chamber to that of another. While the information gained from return loss calculations and measurements as a function of angle of incidence is valuable, an overall measure of anechoic chamber effectiveness is necessary in order to compare different designs. In this paper, a new chamber figure of merit which is based on the decay time of the chamber is introduced. This decay time is, in turn, based on the average power absorbed by the chamber walls. The resulting model is simple and does not require intensive numerical computation. Calculations of the figure of merit for anechoic chambers which contain different types of absorbing materials are shown, and calculated and measured values of decay time for a primary standards calibrations facility are compared     

A sophomore capstone course in measurement and automated data acquisition

A novel multidisciplinary course (Engineering Applications III) was developed that integrates knowledge gained and tools acquired from the introductory freshman circuits, mechanics, and C/C++ courses. It is built around the concepts associated with automated data acquisition systems. This three-quarter-hour, laboratory-intensive course uses a suite of data acquisition equipment located in the computer aided teaching laboratory at the University of Denver, Denver, CO. The presentation format is two lectures and one three-hour laboratory per week. The lectures are designed to cover material that directly supports the laboratories. Early in the course, laboratories explore the subsystems of an automated data acquisition system. The students then learn the operation of a PCMCIA (personal computer memory card international association) data acquisition card, write C/C++ programs to control the data acquisition, learn the operation of analog-to-digital and digital-to-analog converters, and learn the use of the C/C++ commands provided for controlling these subsystems. These concepts are introduced while doing typical experiments dealing with the measurement of temperature and strain and the evaluation of a temperature controller.     

Finite-difference time-domain analysis of the Celestron-8 telescope

Electromagnetic interference analyses of large complex systems demand large computational resources and give limited information on general types of systems. A finite-difference time-domain (FDTD) code was used to determine the response of a “generic” optical system to microwave radiation. A plane wave with a Gaussian pulse excitation was used along with “point sensors” within the system model to determine time and frequency response. In the low-frequency region, ramped sinusoidal excitation from a point within the sensor was used to determine angles of high sensitivity and field distributions within the sensor. From these field distributions, resonance modes were identified that are similar to those found in a simple cylindrical cavity     

Use of equivalent boundary conditions for the solution of a classof strip grating structures

Equivalent boundary conditions for an electromagnetic strip grating are used to derive reflection and transmission coefficients for a boundary value problem consisting of three nonconducting media where the strip grating exists at one of the planar boundaries. The results are used to generate data for a number of cases where data and/or theories exist. The theory presented compares favorably with the literature cited for the limiting condition that the period of the grating be small when compared with the free-space wavelength of the radiation     

Mathcad

Discusses the use of Mathcad software in an electrical engineering course. It is used to solve problems in electromagnetism such as electrostatics, plane wave propagation, antennas and transmission lines     

Using Mathcad in electromagnetics education

Mathcad is an effective learning tool in electromagnetics courses. Use of Mathcad by students in such courses at the University of Denver incorporate four essential ingredients needed for the successful integration of computer aided learning into a curriculum component: (1) involvement by the student in establishing what is to be analyzed by the computer; (2) a general purpose tool rather than concept-specific software; (3) a user friendly interface; and (4) effective integration of the computational tool(s) into the course. This paper gives examples of the use of Mathcad in the subject areas of electrostatics, plane wave propagation, transmission lines, antennas, and advanced topics     

Comparison of electromagnetic absorber used in anechoic andsemi-anechoic chambers for emissions and immunity testing of digitaldevices

The absorber used in anechoic and semi-anechoic chambers employed for emissions and immunity testing of digital devices is examined. Using reflectivities obtained by the method of homogenization, the advantages and disadvantages of urethane pyramids, twisted-pyramids, wedges, as well as ferrite tiles, ferrite grids, and “hybrid” combinations of urethanes and ferrites, are determined. General reflectivity guidelines are also presented for comparing absorber used for the electromagnetic compatibility (EMC) testing of digital devices from 30 to 1000 MHz     

Analysis of composite walls and their effects on short-pathpropagation modeling

For short-propagation paths, correctly representing reflections of electromagnetic energy from surfaces is critical for accurate signal-level predictions. In this paper, the method of homogenization is used to determine the effective material properties of composite materials commonly used in construction. The reflection coefficients for block walls and other types of materials calculated with these homogenized effective material properties are presented. The importance of accurately representing the reflections for signal-level prediction models is also investigated. It is shown that a 5-10-dB error in received signal strength (RSS) can occur if the composite walls are not handled appropriately. Such accurate predictions of signal propagation over a short distance is applicable to microcellular personal communications services deployments in urban canyons as well as indoor wireless private branch exchanges and local-area networks     

Using MathCad in understanding the induction motor characteristics

Computer-aided multimedia education is increasingly popular within the classroom and laboratory. The applications of market-ready mathematical and database programming software for teaching engineering course outline is well appreciated. This article shows how MathCad can be used to introduce electrical machine characteristics simulated at different possible control modes. The undergraduate students require minimum knowledge of a programming language. The examples presented in the article show how MathCad software can be used to simplify some of the characteristics of the three-phase and one-phase induction machine. The result of introducing math software as a teaching tool at the third- and fourth-year level have been accepted and are now used as part of the practical sessions for the electrical machine and other credited courses at Birzeit University, West Bank and Gaza in the Palestine