EMC Engineers Gather on Lake Michigan
2005 IEEE Symposium on Electromagnetic Compatibility
Martin Rowe, Senior Technical Editor -- Test & Measurement World, 8/10/2005 11:24:00 AM
Randall Vaughn gives a presentation on circuit-to-circuit interference.
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TUESDAY, AUGUST 9. This year’s IEEE EMC Symposium (August 8-12, Chicago, IL. www.emc2005.org) features more than 200 technical papers presented as open forums, technical sessions, and tutorials. Tutorials commenced yesterday with topics such as “Fundamentals of EMC Design,” "EMC Directive in Europe,” "Fundamentals of Signal Integrity,” and “Basic Antenna and Probe Use.”
Tuesday’s session opened with the Keynote address, “Advanced Wireless Systems, Seamless Mobility, and EMC,” by Gary Graube, corporate VP at Motorola’s Government and Enterprise Mobility Solutions Business. Graube is not an EMC engineer, but he’s well aware of how emerging technologies are placing new challenges on EMC design.
Graube’s talk centered on “The device formerly called a cell phone” that now takes photos, views Web pages, plays music, and connects to just about any network—GSM, CDMA, infrared, USB, or Ethernet. He described the EMC design challenges caused by ever-shrinking consumer products. For example, consumers don’t want antennas sticking up, so designers now put them inside phones. But, that creates huge EMC issues because the transmitted signal can interfere with device operation, and the device must be able to detect weak incoming signals while rejecting EMI generated by its internal components.
Graube also pointed to EMC challenges faced by automotive electronics designers. “Broadband is coming to the automotive industry,” he told the attendees, “and broadband signals are increasing in speed.” For example, vehicles will be able to get information on traffic conditions. Governments will one day control traffic signals based on traffic conditions and change traffic patterns in the event of an emergency. This kind of communication brings new EMC issues, because these devices must not interfere with each other.
Technical program
Tuesday’s technical program featured sessions on EMC measurements. The technical session featured two papers on EMI measurements above 1 GHz. Andrew Marvin (University of York, UK) presented highlights of his paper, “Toward Evaluating the Shielding Effectiveness of Enclosures with Contents at Frequencies above 1 GHz.” Marvin and co-author Yong Cui experimented with a 480x480x120-mm enclosure that contained a board that radiated EMI. They found that the position of the board inside the enclosure greatly affected the emissions that radiated outside the enclosure. They measured emissions by rotating the enclosure and by scanning across a rectangular area.
Following Marvin, Alexander Kriz of ARC Seibersdorf Research (Germany) presented, “Validating Anechoic Chambers Above 1 GHz Using a Reciprocal Site VSWR Technique." He pointed out that EMI antennas take on different characteristics above 1 GHz, and this affects your ability to validate the EM fields inside a chamber. Kriz showed test results for three test methods, pointing out the advantages and disadvantages of each.
An open forum on EMC measurements featured nine papers on topics such as loop antennas, calibration, magnetic-field measurements, and noise on AC mains lines produced when equipment powers on and off.
Other presentations included one on circuit-to-circuit interference by Randall Vaughn (photo). His experiments showed how changing components can change a circuit’s EMC characteristics.
EMC consultant Doug Smith, a perennial presenter, demonstrated how a common ground between two chassis creates interference from one chassis to the other. Smith used a SPICE simulation to model two equipment chassis placed 1 cm apart and connected to a common ground. By exciting one chassis with a 1-V, 150-ohm source, he was able to create current on the unexcited chassis. The capacitance between the two chassis and the inductance on the ground wires creates a resonant circuit that, at the resonant frequency, produces current in the unexcited chassis that exceeds the current produced by the voltage source.
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