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"It is difficult to determine what is meant by a high level. Some have defined any electromagnetic field that exceeds 100 V/m as a high field."

—William Radasky

More IEC Standards to Address High-Power Electromagnetic Transients

A new family of standards has been developed to address the threat of intentional EMI. The standards, which address high-power electromagnetic (HPEM) transients and disturbances caused by high-altitude electromagnetic pulses (HEMP) due to intentionally produced HPEM transients, are designed to help manufacturers and facility owners protect their equipment from the effects of these disturbances.

HPEM involves any situation in which electronic equipment may be exposed intentionally or otherwise to EM pulsed or continuous fields at high levels, according to William Radasky, president of Metatech Corp. (Goleta, CA).

"It is, of course, difficult to determine what is meant by a high level, however. Some in the community have defined any electromagnetic field that exceeds 100 V/m as a high field." Typical cases of concern include the EM fields generated close to a cloud-to-ground lightning strike, or the fields generated close to an airport or naval ship radar, he says. "A surprising producer of HPEM is electrostatic discharge (ESD).

"The fields produced within 10 cm of an arc may exceed 1 kV/m. This high-frequency field can penetrate the case of an electronics enclosure, potentially interfering with the circuits inside," says Radasky.

To develop its standards for these transients, IEC Subcommittee 77 has referenced existing IEC EMC standards wherever possible to minimize duplication. The current development of standards and reports includes 17 active projects or publications. In addition, IEC 61000-5-1 and IEC 61000-5-2 will be maintained by subcommittee 77C.

Among the newest standards is IEC 61000-1-3, "The Effects of High-Altitude EMP (HEMP) on Civil Equipment and Systems," which provides information concerning the effects of HEMP on electrical and electronic equipment and systems. The information is based on effects observed during high-altitude nuclear testing and from tests performed in HEMP simulators.

IEC 61000-1-5, "High Power Electromagnetic (HPEM) Effects on Civilian Systems," will produce an IEC technical report that discusses the effects of HPEM fields on civilian systems. It will illustrate the general protection principles that can be applied to protect systems. IEC 61000-2-X, "Environment," contains four projects that describe the HPEM environment.

For HEMP, two separate standards cover radiated and conducted emissions. The first standard, "Description of HEMP Environment—Radiated Disturbance," 61000-2-9, contains definitions and the radiated parameters for the early, intermediate, and late HEMP waveforms. "Description of HEMP Environment—Conducted Disturbance," IEC 61000-2-10, describes the conducted environment applicable for categories of conductors for different positions and illumination cases, statistically taken into account. "Classification of HEMP Environment," IEC 61000-2-11, is also included.

"Classification provides guidance for equipment manufacturers to help them decide on the proper immunity test levels appropriate for their equipment," says Radasky. "It also provides system designers with guidance regarding construction methods and protective measures needed to achieve defined environmental classes."

Another new Part 2 project, "High Power Electromagnetic (HPEM) Environments—Radiated and Conducted," IEC 61000-2-13, defines the current and near-future HPEM environments that are a potential threat to civil systems, including both the radiated and conducted environments. This standard will likely become the basis for defining appropriate protection methods in the future, according to Radasky.

"HEMP Simulator Compendium," IEC 61000-4-32, has been approved for publication. This standard will allow potential simulator users to evaluate the adequacy of available simulators for testing large systems. IEC 61000-4-33, "Measurement Methods for High-Power Transients," will identify appropriate sensor calibrations and measurement methods.

Some of the standards already published include: IEC 61000-4-23, "Test Methods for Protective Devices for HEMP and Other Radiated Disturbances"; IEC 61000-4-24, "Test Methods for Protective Devices for HEMP Conducted Disturbance"; and IEC 61000-4-25, "HEMP Immunity Test Methods for Equipment and Systems."

This EM environment, which is now commonly referred to as intentional EMI, has recently gained much interest. However, the new term, Radasky says, does not imply any particular motive of the user. For more information, contact Radasky at wradasky@aol.com.

Australia Defers RF Exposure Regulations

The Australian Communications Authority (ACA) has decided to defer its human exposure regulations. Regulations to limit human exposure to radio-frequency electromagnetic radiation (EMR) from all radiocommunications transmitters will be postponed until early 2003. Application of the EMR requirements to apparatus-licensed transmitters was slated to begin in July 2002.

"ACA has decided that it would be prudent to apply the remaining measures to introduce human-exposure regulations in a holistic manner," says Chris Zombolas, technical director for EMC Technologies Pty Ltd. (Tullamarine, Victoria, Australia).

ACA is now considering the adoption of two other options. One proposal includes changing its standard to match an existing one. The standard, "Radiocommunications (Electromagnetic Radiation) Human Exposure," would incorporate the limits of the new radiation protection standard, "Radiation Protection Standard Maximum Exposure Levels to Radiofrequency Fields—3kHz to 300 GHz," which was developed by the Australian Radiation Protection and Nuclear Safety Agency (ARPANSA). The ARPANSA standard would apply to devices with integral antennas.

In addition, ACA would apply EMR limits and compliance arrangements for installed transmitters licensed under the apparatus and spectrum licensing systems.

During the deferral period, ACA will also consider integrating recent international developments in testing methodology.

"ACA believes that the deferral will provide an opportunity to develop and implement a better and more comprehensive regulatory arrangement for both industry and the community," says Zombolas. Visit http://www.aca.gov.au/standards/emr/index.htm for more information.

Company News

MET Labs has acquired an EMC and telecom testing facility formerly operated by BABT and TÜV Product Service. The Santa Clara, CA, facility was originally the corporate test facility for Seimens. MET's agreement with TÜV provided for the transfer of the facility, equipment, customer information, and selected staff.

The new test site provides wire-line and fiber-optic test capabilities. Included with the acquisition is a 10-m semianechoic test chamber, which provides the ability to conduct ambient-free 3- and 10-m EMC measurements. The chamber includes a screen room for support equipment and an automated test system.

MET plans to add a wireless testing lab. In addition to traditional intentional radiators and spread-spectrum transmitters, the lab can test microwave point-to-point and point-to-multipoint systems up to 38.5 GHz.

Standard Proposed for Validation of Computed Modeling

"Important technological advances have
accelerated the arrival of CEM applications."

—Andrew L. Drozd

The need for appropriate standards and guidelines for computational electromagnetics (CEM) computer modeling and simulation has been a topic of much discussion within the electromagnetic community in recent years, according to Andrew L. Drozd, IEEE Project 1597.1 Working Group chair and president, and chief scientist for Andro Consulting Services (Rome, NY).

"CEM encompasses a broad range of applications such as the analysis of printed circuit board (PCB) radiated and conducted emissions and immunity, assessing system-level EMC, and predicting the radar cross section (RCS) of complex structures, and automated target recognition (ATR) and imaging simulations."

Concerns exist regarding the lack of well-defined methodologies to achieve code-to-code or even simulation-to-measurement validations within a consistent level of accuracy, Drozd said at the IEEE EMC Conference in Minneapolis. The concerns, he said, have been prompted by the development and use of new CEM computer codes over the past 20 years.

Drozd discussed an IEEE project that is under way to guide the validation of CEM application models. The proposed standard, he said, is intended to address concerns and provide a method for validating
CEM codes and models.

Although CEM codes have their basis in Maxwell's equations in one form or another, their applicability and associated accuracies depend on a number of factors, he said. Factors include applied physics, numerical solver approach, mathematical basis functions, canonical modeling primitives, inherent modeling limitations and built-in approximations, desired observables (current or scattered fields), and other factors such as analysis frequency and time or mesh discretization. "All of these factors affect accuracy, solution convergence, and overall validity of computer models," he said.

Concerns arise when the results of predictions using one type of CEM code do not consistently agree with the results of other codes or measurement benchmarks, which he says makes it difficult to determine which method is correct.

The need for a CEM standard has been influenced by several factors, including the growing complexity and sophistication of military and commercial system designs and the need to ensure a balanced, cost-effective electromagnetic environmental effects (E³) program in which computer analysis effectively complements measurements. "Important technological advancements in computer hardware and use of structured code have accelerated the arrival of CEM technologies and applications, as we know them today," Drozd said.

The IEEE "Standard for Validation of CEM Computer Modeling and Simulation" is a four-year project to develop a standard for the validation of CEM computer modeling and simulation codes in differing applications.

The standard, IEEE 1597.1, is designed to provide a basis for analytical and empirical validation of CEM codes and configurations. The standard addresses several key areas, including validation by use of canonical models and validation by simulation versus measurement.

The standard is intended to address concerns over the lack of well-defined methodologies to achieve code-to-code or simulation-to-measurement validations within a consistent level of accuracy, and provide a method for validating CEM codes and models.

A companion project, IEEE 1597.2, will develop a recommended practice for use in CEM computer modeling and simulation applications to guide the EMC design of PCBs to large, complex systems. The standard will address general guidelines for creating CEM models and the development of modeling methodologies for small- to large-scale canonical systems, platforms, or composite models. In addition, it will look at methodologies for developing and applying collaborative, multidisciplinary engineering modeling schemes and computation of uncertainty for modeling applications.

FM and TV Emissions:

Standard Set for Overdue Overhaul

The standard for measuring emissions from FM and TV broadcast receivers, which was last updated in 1990 when UHF and nonwireless remotes were added, is undergoing an overhaul. The next draft of the standard is slated to go to the committe for ballot in November 2002. If all comments are resolved, the standard is expected to be published in the spring of 2003.

The standard, IEEE 187, sets measurement methods for receivers in the frequency range of 150 kHz to 2 GHz. The current standard fails to address A/V, video, component video, and digital input/outputs to TV. In addition, it does not address Advanced Television Systems Committee (ATSC) tuners (high-definition digital tuners). The current standard also requires a different turntable setup than ANSI C63.4. The new standard will harmonize the testing requirements, according to Dave Traver of Sony Electronics (San Diego). Traver is chair of Working Group 187.

The new standard will include or reference all TV requirements. It includes a conducted emissions test and references the TV broadcast receiver tests required in FCC Part 15. In addition, the new standard specifies a test method and signal for ATSC tuners (a color bar with moving element) and eliminates the requirement for the currently required time-consuming radiated method of measuring a local oscillator. The local oscillator is now measured with a direct connection to the measurement receiver.

According to Traver, the direct connection reduces test time from the previous 4–6 hours to 1 hour or less. The updated standard will include test procedures for radiated emissions, conducted emissions, and local oscillator measurement. Tests that will be referenced include noise figure, peak picture sensitivity, selector switch isolation, and cable compatibility.

FYI

An article in CE's May/June 2002 issue titled "Specific Absorption Rate Requirements for Australia" contains an error. The RCM mark is not permitted to be used on radio products at this stage. It is allowed only for general electrical products. "The long-term aim of the mark is to extend its application across the broad scope of products to include telecom and radiocom, but this will not occur until various legal and administrative difficulties are resolved," says Chris Zombolas of EMC Technologies Pty Ltd. (Australia). According to Zombolas, the incorrect material in the article relating to the RCM mark was drawn directly from the ACA regulation that appears on the ACA Web site.