EMC education has long been a pioneering effort
in engineering schools around the world. The costs of creating
a laboratory coupled with a lack of instructors with training
and experience in EMC has substantially constrained the development
of courses that teach this vital field. The annual award of a
$10,000 grant by the IEEE EMC Society to an academic institution
for the establishment of a course in the principles and practices
of EMC has done much to improve the situation. In June 2003, we
were pleased to learn from John Howard that the grant for that
year had been awarded to The Citadel in Charleston, South Carolina.
This article details the elements of the course and laboratory
that were consequently created.
The Citadel was founded in 1842, and the Department of Electrical
and Computer Engineering was established there in 1941. It offers
two coeducational, undergraduate-only programs. The daytime program
educates students in a military setting as members of the South
Carolina Corps of Cadets. The evening program is offered in a
nonmilitary environment to students from the Coastal South Carolina
region, and is typically populated by students who are returning
to school after significant work experience or military service.
The Citadel has been supportive of the effort to offer EMC education
and began by granting funds for the purchase of a new Agilent
spectrum analyzer with an optional tracking generator installed.
The department was able to obtain the donation of a surplus 8.5X20X8-ft.
shielded chamber from a local military installation, and the school
committed significant resources for the reconstruction and refurbishment
of the room. Surplus absorptive material donated by NASA was installed
to deaden the response of the chamber. A ground-floor classroom
was converted to permanently house this laboratory.
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| Instructor Tom Jerse (standing) shows
Cadets Dave Coisson, Ivan Puhalo, and Derek Hall (from left)
how to use a spectrum analyzer for making radiated-emission
measurements. |
The course instructor, Tom Jerse, has extensive industrial experience
in EMC design practice, troubleshooting, and education obtained
both at Hewlett-Packard and Boeing. One of his primary goals in
entering academia was to create an ongoing EMC course, and his
first step was to earn a Ph.D in EMC under Clayton Paul at the
University of Kentucky.
The course ELEC 425, “Interference Control in Electronics,”
was added to The Citadel catalog as a permanent senior elective.
The word “electromagnetic” was deliberately omitted
from the course title because it tends to strike fear in many
students. With the aid of the IEEE EMC Society grant, the course
was first offered during the spring semester 2004 in two sections.
Eighteen students enrolled in the day section and twelve enrolled
in the evening. These numbers represent approximately 90% of the
students who were eligible to take the course. The prerequisites
for the ELEC 425 course are all required junior-level courses:
a one-semester introduction to electromagnetics, a course in linear
systems, and a second course in digital design. The electromagnetics
course primarily covers electrostatics along with Faraday’s
Law. A few of the students had taken an elective course during
the summer that discusses time-harmonic fields, but two of the
lectures in the EMC course were used to bring everyone up on concepts
such as wave propagation and wave impedances. This material was
well supported by our textbook, Introduction to Electromagnetic
Compatibility, by Clayton R. Paul.
The primary thrust of the course is to provide the students with
the principles of good EMC design practice backed by enough relevant
theory to explain their basis. A second goal is to provide a serviceable
background, sufficient for those who might wish to engage in the
graduate study of EMC. As a one-semester course, the scope of
the EMC field had to be narrowed. The context of electronic product
design was chosen for the exposition of the design practices.
Areas such as frequency management and the effects of interference
in communications systems and multi-emitter platforms were not
covered. Because EMC design is in many ways the orchestration
of current flow, its visualization became a major theme of the
course.
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| Setting up a test sample for a radiated
emissions experiment. |
The IEEE EMC Society funds were used to help outfit our laboratory.
A broadband biconalog antenna and preamplifier were purchased
for use in the anechoic chamber along with a line impedance stabilization
network (LISN) to measure conducted emissions. Probes and cables
were obtained, and a small portion of the funds was used to acquire
a commercial software package that enables the creation of animated
3D plots of time-varying functions for use in explaining some
of the field concepts.
A vital part of the course was the use of the laboratory for a
series of experiments that reinforced the theory as only practice
can. Because the three-hour course as scheduled does not explicitly
allocate time for a laboratory, several mini-labs were included.
The students were divided into teams of three, and each experiment
took approximately twenty minutes to perform. Only two lecture
periods were allocated for mini-labs, but with the number of labs
and the relatively large enrollment, several of the teams worked
at other arranged times to complete the experiments. The incorporation
of the optional tracking generator in our spectrum analyzer facilitates
experiments involving crosstalk, current distribution, and shielding
effectiveness measurements.
The course material encompassed the following areas:
1) Introduction and motivation for EMC study
Although a few of the evening students had encountered EMI problems
in their work or military experience, the majority of students
needed to learn the vital importance of EMC for the reliability
and marketability of electronic products. Several real-world anecdotes
where the reliability, safety, or cost of a product was dramatically
compromised by EMI, served to motivate interest in the material.
2) Government regulations
Because the course emphasis is placed on design techniques, the
coverage of regulations was relatively brief. The students learned
the various categories of EMC regulations and the Class-B limits
for both radiated and conducted emissions.
3) Measuring radiated emissions
The difference between near- and far-field measurements was presented,
along with measurement procedures that account for antenna factors,
preamplifier gains, and cable losses. A laboratory experiment
quantifying and comparing to regulatory limits the emissions from
a battery-powered digital clock circuit reinforced the concepts.
4) Crosstalk
Crosstalk was presented primarily from the point of view of signal
integrity, but in doing so the basic principles of controlling
radiated emissions were revealed. The material included common-impedance
coupling, situations where electric-field coupling dominates,
magnetic field coupling, and mixed coupling. The students were
provided MATLAB routines written by the instructor that computed
the mutual inductances and capacitances between a specified array
of parallel conductors. Homework assignments had the students
adjust the geometry of various configurations to discern some
general principles about the relationship of layout to crosstalk.
A laboratory experiment demonstrated the effect of termination
impedances on crosstalk.
5) Cables: Applications and side effects
This section introduced twisted pair, ribbon cables, and various
types of shielded cable and characterized them in terms of crosstalk
and radiated emissions. Substantial attention was paid to the
practical aspects of grounding and potential problems such as
ground loops. Key to this discussion was the development of an
intuitive understanding of the frequency-dependent distribution
of return current over multiple paths, with the important role
played by the skin effect. The characteristics and applications
of ferrite devices were also presented.
6) EMC characteristics and layout of digital circuits
The impacts of circuit layout on signal integrity and radiated
emissions were discussed. As with cables, an understanding of
the distribution of return current flow was the most crucial skill
developed. Original analysis software based on the Partial-Element
Equivalent Circuit (PEEC) method that generates current maps proved
helpful in this task. Some basic transmission line theory was
introduced, and MATLAB software for computing the characteristics
of various microstrip and stripline configurations was provided
for numerical experiments. Several decoupling arrangements and
their potentially resonant behavior were also covered.
7) Conducted emissions and immunity
This section detailed the need for and methods of controlling
conducted emissions as well as their measurement with a LISN.
Practical aspects of power-line filter design and installation
were discussed. Various transient suppression devices were contrasted
to illustrate their use in product protection.
8) Radiated immunity
After a discussion of the relatively dense electromagnetic environment
that exists today, the theorem of reciprocity was invoked to show
that the techniques learned to control emissions also enhanced
radiated immunity. Nonlinear effects such as rectification and
their exacerbation by resonances were also presented.
9) Shielding
This section began with Schellkunoff’s transmission line
analogy for analyzing the penetration of an electromagnetic wave
through a shield wall. Next, a surface current model was presented
to enable the students to visualize and quantify the effects of
apertures. Finally, the concept of transfer impedance and the
physical design parameters that influence it on a shield seam
were given. Colorful field plots made using a method-of-moments
program were presented to demonstrate the concepts of reflection,
diffraction, and resonance.
The Student Evaluation of Instruction forms
completed by the students at the end of the term showed the appreciation
felt by the students for the course. Twenty-eight of the thirty
students “strongly agreed” and the other two “agreed”
with the statement “I learned a lot in this course.”
Written comments reflected the feeling among the students that
they were given the opportunity to learn valuable real-world material
that is less commonly taught, and statements of gratitude including
“A good use of IEEE funds” were frequent.
The Citadel appreciates the support of the IEEE EMC Society that
hastened the development of this popular senior elective. It will
be offered every spring semester. Work is ongoing to refine and
create additional experiments, and a student programmer has been
enlisted to enhance and modernize the user interface of various
analysis programs. This development activity will enable additional
numerical analysis experiments to be given to the students as
homework in order to give them a better sense of the dependence
of EMC behavior on various physical parameters. EMC
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