ELECTROMAGNETICS LABS AT NDSU
Laboratory Status and Goals as of Summer 1998:
Electromagnetic Compatibility, Applied Electromagnetics,and Optical Communications
With a course in applied electromagnetics (EE 351) as a prerequisite, all EE students are required to take a junior-year laboratory that includes two hands-on transmission-line and waveguide experiments based on slotted-line measurements. Two other laboratory experiences in this class are devoted to using the computer to make the necessary calculations to study transmission-line impedance matching techniques, power transmission and losses, and similar topics. Students can also choose from the following elective courses in electromagnetics: Designing for Electromagnetic Compatibility (EMC) (EE 455/655), Optical Signal Transmission (EE 457/657), Electromagnetic Theory and Applications (EE 751), and Advanced Topics in Electromagnetics(EE 755).
Most of these courses in electromagnetics also include a laboratory component. For instance, the EMC course (EE 455/655) includes several experiments dealing with such phenomena as crosstalk, the effect of frequency on the response of passive components, common-mode filtering, radiated and conducted emissions, and the measurement of narrowband and broadband signals. Elementary fiberoptics experiments are included in the optical signal transmission course (EE 457/657).
The graduate courses include laboratory components through class demonstrations and/or student projects. Typical topics include measuring the input impedance of antennas and characterizing microstrip devices such as couplers, filters, etc.
Current hands-on experiments in EE 314 involve using a slotted line to investigate the effect of load and characteristic impedances on the system VSWR. Single and double stub tuners are used to match the load to the line, and students are able to see the effect of such matching on the VSWR. In addition, unknown load impedances are measured with the slotted line. Although these experiments illustrate important concepts, our new network analyzer will soon allow very useful measurements to be made of both one- and two-port devices yielding the scattering parameters for these devices. This means that quantities such as VSWR, impedance, reflection coefficient, and gain (or attenuation) can measured over a wide frequency range. Such an instrument not only is easier to use than a slotted-line, but it facilitates the vital understanding of the frequency dependence of such measurements. In general this instrument lets the student measure the efficiency of a device and its impact on other components of the system under study. Not only can the students study the frequency dependence of a circuit but they also can view its interaction with its neighboring components by studies in the time domain. It is anticipated that new experiments will include looking at the effect of impedance mismatches in both the time and frequency domains as well as investigating the effect of using tuners to decrease the VSWR, and observing the bandwidth of those tuners. In addition, the input impedance and reflection coefficient of cascaded transmission lines will be investigated, as will attenuation loss for various transmission lines. Other experiments that may be developed include measuring the characteristic impedance for various transmission line structures (coax, waveguide, twin lead, microstrip, strip line, etc.,) as well as measuring the scattering parameters of lumped elements and transmission line filters.
Laboratory Capability: Electromagnetic Compatibility
The course "Designing for Electromagnetic Compatibility"was first offered at NDSU in 1991. At that time, NDSU was one of the few universities in the United States to offer a course on EMC. As such, the course was well received by students, faculty, and industry. This course involves a laboratory component, which typically includes an introduction to the use of the spectrum analyzer and antennas, as well as experiments on crosstalk, the effect of frequency on the response of passive components, common-mode filtering, radiated and conducted emissions, and the measurementof narrowband and broadband signals.
The EMC laboratory at NDSU was recently upgraded through the addition of a shield room. The purpose of this room is really twofold. It is used to shield out the noisy RF environment caused by intentional and unintentional radiators so that students can measure the radiated and conducted noise being emitted from electronic devices undertest. In doing this, they not only learn measurement techniques, but also will be able to observe the effect of using noise suppression techniques in the products. Secondly, students will observe the immunity level of electronic devices under test by creating electric and magnetic fields inside the room and noting how the devices work in the presence of this noise. Again, they can observe the effect of incorporating various "hardening" methods.
Laboratory Capability: Optical Communications
Laboratory capability in the optical communications course is in the process of being upgraded through the addition of a Newport Projects in Fiber Optics kit and a professional optical table. This will be incorporated partially into the existing fiber optics course. It also will be used in a proposed senior elective course in fiber optic measurements. Students will conduct experiments with optical fiber components to study the optical power budget, coupling and alignment losses, attenuation, dispersion, transmission of information, and characteristics of the source and detector.
Laboratory Capability: Applied Electromagnetics
The Department of Electrical Engineering has a wide assortment of equipment available for undergraduate student use for general instruction and for use in basic and applied electromagnetics. Of particular interest to this project are items such as slotted lines, oscillators and signal generators, power meters, frequency meters, stub tuners, cable assemblies, etc., that will continue to be used as needed. Spectrum analyzers and antennas are available that are used in the EMC course to provide students the opportunity to see and hear what the ambient electromagnetic environment is in a typical residential area. These devices are also used tomeasure the electromagnetic emissions from electronic products. A scalar network analyzer is also available which has been used in efforts to measure the frequency response of passive components.
In addition to hardware, significant computing capabilities exist in the Department. In addition to the many computer clusters available to all NDSU students, the Department of Electrical Engineering also provides its students with twenty-four hour access to a dedicated computer cluster. This cluster is equipped with general purpose computing tools such as MATLAB, EXCEL, etc., as well as with EE-specific tools used such as PSPICE. The Department recently acquired the HP 85180A High-Frequency Structure Simulator software, which analyzes the electrodynamic behavior of passive structures. It computes scattering parameter response and electromagnetic field distributions for passive, three-dimensional structures. This powerful software provides students the opportunity to compare simulated results with those measured in the laboratory.