RMCEMC September Meeting |
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Our last meeting was... A View of Electromagnetic Life above 100 MHz (An Experimentalist’s Intuitive Approach)
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the presentation here Date : September 25 2003 Location : Front Range Community College Westminster, CO Pesenter :Dr. Bud Hoeft - Bio What we saw: Interest in electromagnetic life above 100 MHz has increased in the past decade, primarily due to an increase in high speed digital electronics and telecommunications. In this frequency regime, many of the usual simplifying assumptions are no longer true and the EMC engineer must adopt a new way of looking at the problems. If the problem involves a high level (>0.7 V) modulated culprit signal, the semiconductors become non-linear, rectify the signal and the effect of the culprit signal can be analyzed by analyzing the effect of the modulation envelope. The EMC engineer must be aware of the long and short of it, namely, the dimensions of the circuit/system in terms of wavelengths. Little things mean a lot, particularly when they are parasitic reactances. Small parasitics that can be ignored at lower frequencies can be significant impedances and admittances above 100 MHz. In designing circuits and making measurements, it is important to keep things small. Another way of saying this is “If you can’t do it correctly, do it quickly.” Life is absorbing above 100 MHz, that is, most losses are proportional to some power of frequency, therefore, they can become dominant effects at the higher frequencies. Besides losses in the conductors and dielectrics, circuits can have significant losses through radiation and through leaks in the shields. At high data rates, the pulses are short and the risetimes are fast. Therefore, timing becomes very important and close attention must be paid to skew in differential signals. Dispersion is often also evident at these frequencies. Instead of components connected by wires, the EMC engineer should visualize the circuit/system as a world made up of transmission lines. Another way of visualizing the circuit/system configuration is to use the acoustic to electromagnetic wave analogy. Because of the differences in the propagation velocity, most things in life are acoustically small and they scatter, interact and absorb acoustic energy in an analogous way to how they react to electromagnetic energy.
Dr. Bud Hoeft
received a B.S. and M.S. in physics from the University of Wisconsin and a PhD
in physics and biophysics from Pennsylvania State University. In 1979, he
completed a 25-year R&D career in the U.S. Air Force working on acoustical
noise control, bionics, nuclear weapon simulation, pulse power technology and
international R&D coordination. He joined BDM, where he was primarily
concerned with helping designers build and test systems that are hard to
electromagnetic effects. In 1994, he retired from BDM and became a private
consultant. Dr. Hoeft is a Certified EMC Engineer. He has presented numerous
papers and tutorials on shielding and electromagnetic effects at IEEE-EMC, NEM,
Zurick-EMC, Wroclaw-EMC, IEE-EMC, Lightning and IICIT symposia. In 2001, he
was appointed Distinguished Lecturer of the IEEE EMC Society for 2001 and
2002. Contact Information: Dr. Lothar (Bud) O. Hoeft Consultant, Electromagnetic Effects 5012 San Pedro Ct. NE Albuquerque, New Mexico 87109-2515 Voice/Fax: (505) 889-9705 |
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