Knowledge Is Key to Accurate EMF Measurements

The plethora of electromagnetic sources permeating our environment is making EMC measurement an increasingly important application for the test and measurement industry. Unfortunately, effective and accurate electromagnetic field (EMF) measurements can be difficult to make.

Test vendors offer a variety of capable instruments and related equipment that can help with EMI troubleshooting, EMC precompliance and compliance test, and electromagnetic susceptibility (EMS) measurements; they also offer software that helps automate immunity and emissions testing and documentation.¹

Nevertheless, rapid success in your EMC measurement projects can depend on theoretical knowledge beyond what’s embedded in your instruments and EMC measurement software. Fortunately, 2014 is seeing the debut of one new book and one soon-to-be revised book; the latter will be used in an upcoming seminar on EMC measurement that provides theoretical and practical training.

The new book, Electromagnetic Field Standards and Exposure Systems, by Eugeniusz Grudzinski and Hubert Trzaska, is published by SciTech Publishing, an imprint of the Institution of Engineering and Technology and part of the SciTech Series on Electromagnetic Compatibility (Figure 1). (In the United States, the book is available from Stylus Publishing, the distributor for IET/SciTech Publishing.)

Figure 1. Electromagnetic Field Standards and Exposure Systems Courtesy of Stylus Publishing

In a forward to the book, series editor Alistair P. Duffy, Ph.D., wrote, “Managing error budgets is important in all measurement activities. Within an EMC environment, however, this is especially vital for improving both accuracy and precision of any results.”²

Grudzinski currently is head of the EMF Standards and Measurements Lab at the Wroclaw University of Technology. He has authored many publications in the field of EMF metrology. Trzaska is head of the EM Environment Protection Lab at the Wroclaw University of Technology, devoting his research to the practical aspects of EMF metrology. He holds more than 50 patents in the field of EMF measurements and standards.

Calibration Standards

In their preface to the book, Grudzinski and Trzaska stated, “Electromagnetic field measurements are among the least accurate of all measured phenomena.” They said that one of the key factors limiting the accuracy of EMF measurements is the class of EMF standards used: A calibrated instrument cannot be more accurate than the standard used to calibrate it.

This book addresses the need to establish measurement standards for electromagnetic fields (EMF) to produce accurate results. Although the book provides a review of fundamental properties of EM fields and the simple antennas that can generate and receive such fields, the main focus is the analysis of the accuracy of measurements and field standards using a range of radiating structures. Through real-world laboratory examples, the book provides readers with the information they need to ensure proper instrument calibration and to take into account external environmental factors that affect measurement accuracy.

In the introduction, Grudzinski and Trzaska wrote, “Nowadays civilization may be characterized by the rapid growth of applications of the number and power of EMF sources in, for instance, telecommunications, industry, science, medicine, and domestic uses.” This growth, they said, necessitates the accurate measurement of the electric field (E), magnetic field (H), and power density in three main areas:

Free propagating EM waves in telecommunications, radiolocation, radio navigation, radio astronomy, geophysics, and related areas. Such measurements relate to antennas with respect to radiation pattern, gain, and calibration.
EMI to assure undisturbed coexistence of devices and systems. These measurements must take into account additional sources of EMI such as electric motors, combustion engines, overhead power lines, information networks and devices, and atmospheric discharges.
Biosphere exposure measurements relating to labor safety. Such measurements, in close proximity to EMF-generating devices and systems, can help ensure environmental and general public protection.

In addressing these areas, the authors covered topics ranging from the theoretical (Maxwell’s equations) through the practical (E-field probing of an object under test in a TEM cell).

Book Featured at Seminar

The revised book is Controlling Radiated Emissions by Design by Michel Mardiguian. The third edition is scheduled to be published March 31. Donald L. Sweeney, a senior EMC engineer and president of D.L.S. Electronic Systems, said he has considered the book to be the ideal textbook for his “EMC By Your Design” seminars since the first edition was published in 1992. D.L.S. is a compliance laboratory that offers testing and consulting for EMC, wireless, product safety, and environmental certification.

In the preface to the second edition, Mardiguian wrote, “In 1999, after seven years and six reprints, this book, although quite successful, started to show its age. Interestingly, most of the EMI aspects of the future that we were anticipating in the first edition are actually happening.” At the request of the publisher, he continued, “I prepared this fully revised edition. The quantum jump that we are witnessing at the end of the century, almost unprecedented in the history of electronic engineering, poses a severe challenge to the EMC discipline, which this new edition will hopefully help to win.”³

Well into the second decade of the new century, it became time to update the book yet again. Sweeney at D.L.S., who contributed to many parts of the new third edition, said that all 13 chapters have been updated to present new examples and otherwise address the newer technologies that have come along since 2001, especially those related to the increasing clock speeds.

Sweeney said he will be using the new third edition at his seminar scheduled for April 8-10 in Northbrook, IL. The seminar will provide an introduction to EMC and what you need to know about FCC, Canadian, European, military, and other EMC regulations. Covering topics such as noise paths, grounding, cabling, passive components, and E and H fields from simple circuits, it will offer guidance on general strategies for low-emissions product designs. A workshop involving a real-life product will give attendees an opportunity to determine the product’s EMC parameters and calculate the emissions characteristics of circuit boards, the power supply, I/O lines, and enclosures.

The seminar will address practical as well as theoretical issues, with attendees having the opportunity to apply proprietary software to EMC problem solving.

Automation and Accuracy

And indeed, sophisticated instruments and software will play a key role as vendors roll out ever more capable automated EMC test systems. Yet in Field Standards and Exposure Systems, Grudzinski and Trzaska cautioned that automation can come at the expense of accuracy. “The most accurate stand-ardizations still require an individual, discrete approach,” they wrote, adding that with the rapid development of new technologies, better-educated people will make it possible to bring to reality solutions to problems “that are, as yet, unforeseen.”

You can rest assured that EMC requirements will become increasingly stringent. In Mardiguian’s second edition of Controlling Radiated Emissions by Design, he wrote that in the first part of the 20th century, EMI was a concern for wire and radio telecommunications, with adverse affects ranging from annoyance (such as poor television reception) to danger (for example, from impaired air navigation systems). Typical EMI sources included natural atmospheric noise, motor commutators, fluorescent lights, automobile ignition systems, and overhead power lines. “The ‘policing of airwaves’ was a manageable task,” he concluded.

Subsequently, RF sources proliferated with the emergence of digitally operated devices, and as the number of offenders has grown exponentially, so too has the number of potential victims. Mardiguian wrote in 2001, “EMI control must be incorporated in the design stage of a product rather than postponed until the day of prequalification or final acceptance testing.”

That’s as true today as it was in 2001, and resources like Mardiguian’s Third Edition, Grudzinski and Trzaska’s Field Standards and Exposure Systems, and the D.L.S. “EMC By Your Design” seminars can help meet the EMC challenges of tomorrow.

References

Lecklider, T., “Exposing the EMI Menace,” EE-Evaluation Engineering, January 2014, p. 14.
Grudzinski, E. and Trzaska, H., Field Standards and Exposure Systems, Stylus Publishing, 2014.
Mardiguian, M., Controlling Radiated Emissions by Design, Second Edition, Kluwer, 2001.