System Resistance to Electromagnetic Interference

Electromagnetic Interference (EMI) is the disruption of operation of an electronic device when it is in the vicinity of an electromagnetic field in the radio frequency (RF) spectrum. Many electronic devices fail to work properly in the presence of strong RF fields. The disturbance may interrupt, obstruct, or otherwise degrade or limit the effective performance of the circuit. The source may be any object, artificial or natural, that carries rapidly changing electrical currents.

Electromagnetic Compatibility (EMC) is the ability of systems, equipment, and devices that utilize the electromagnetic spectrum to operate in their intended operational environments without suffering unacceptable degradation or causing unintentional degradation because of electromagnetic radiation or response. It involves the application of sound electromagnetic spectrum management; system, equipment, and device design configuration that ensures interference-free operation; and clear concepts and doctrines that maximize operational effectiveness (DAU 2010, Chapter 7)

Electromagnetic Interference

Narrowband and Broadband Emissions

EMI is categorized into two types in order to help in analyzing conducted and radiated interference effects: narrowband and broadband. These type of emissions are defined as follows:

1. Narrowband Emissions

   A narrowband signal occupies a very small portion of the radio spectrum… Such signals are usually continuous sine waves (CW) and may be continuous or intermittent in occurrence… Spurious emissions, such as harmonic outputs of narrowband communication transmitters, power-line hum, local oscillators, signal generators, test equipment, and many other man made sources are narrowband emitters. (Bagad 2009, G-1)

2. Broadband Emissions

   A broadband signal may spread its energy across hundreds of megahertz or more… This type of signal is composed of narrow pulses having relatively short rise and fall times. Broadband signals are further divided into random and impulse sources. These may be transient, continuous or intermittent in occurrence. Examples include unintentional emissions from communication and radar transmitters, electric switch contacts, computers, thermostats, ignition systems, voltage regulators, pulse generators, and intermittent ground connections. (Bagad 2009, G-1)

TEMPEST

TEMPEST is a codename used to refer to the field of emission security. NSA investigations conducted to study compromising emission (CE) were codenamed TEMPEST. TEMPEST is defined in National Security Telecommunications Information Systems Security Issuance (NSTISSI)-7000 as:

Electronic and electromechanical information-processing equipment can produce unintentional intelligence-bearing emanations, commonly known as TEMPEST. If intercepted and analyzed, these emanations may disclose information transmitted, received, handled, or otherwise processed by the equipment. (NSTISS 1993, 3)

These compromising emanations consist of electrical, mechanical, or acoustical energy intentionally or unintentionally emitted by sources within equipment or systems which process national security information. Electronic communications equipment needs to be secured from potential eavesdroppers while allowing security agencies to intercept and interpret similar signals from other sources. The ranges at which these signals can be intercepted depends upon the functional design of the information processing equipment, its installation, and prevailing environmental conditions.

Electromagnetic Compatibility

Spectrum

Each nation has the right of sovereignty over the use of its spectrum and must recognize that other nations reserve the same right. It is essential that regional forums are provided for the discussion and resolution of spectrum development and infringement issues between bordering and proximal countries that might otherwise be difficult to resolve. The oldest, largest and unquestionably the most important of these is the International Telecommunication Union. One hundred ninety-three Countries are members of the ITU. Spectrum is managed at a global level through the International Telecommunications Union (ITU) agency within the United Nations. As described in Chapter 3 of the NTIA Manual: "The International Telecommunication Union (ITU)...is responsible for international frequency allocations, worldwide telecommunications standards and telecommunication development activities" (NTIA 2011, 3-2). The broad functions of the ITU are the regulation, coordination and development of international telecommunications.

The Spectrum allocation process is conducted by many different international telecommunication geographical committees. Figure 1 shows the various international forums represented worldwide.

Figure 1. International & Regional Spectrum Management Forums. (SEBoK Original)

Assigning frequencies is very complicated as shown in the Radio Spectrum allocation chart in figure 2. Frequencies sometimes are used in the commercial world that are actually assigned to US government Agencies such as the Department of Defense. One such incident occurred when an automatic garage door vendor had installed their doors on a number of homes near a government installation using the same frequency as the installation. Random opening and closing of the doors created a problem for the vendor that could have been avoided.

Four ITU organizations affect spectrum management: the World Radio-communication Conference (WRC), the Radio Regulations Board (RRB), the Radio-communications Bureau (RB), and the Radio-communication Study Groups (RSG) (Stine and Portigal March 2004). The WRC meets every four years to review and modify current frequency allocations. The RB registers frequency assignments and maintains the master international register. The RRB approves the Rules of Procedures used by the BR to register frequency assignments and adjudicates interference conflicts among member nations. The SG analyzes spectrum usage in terrestrial and space applications and makes allocation recommendations to the WRC. These regulations have treaty status. Most member nations generally develop national frequency allocation polices that are consistent with the Radio Regulations (RR). Nations are still sovereign and may operate systems, provided that nation does not cause interference and is willing to accept interference.

Most countries have a single government agency to perform the spectrum management function. In contrast, the Communications Act of 1934 established a dual management scheme for the United States. In this scheme, the Federal Communications Commission (FCC) is responsible for all non-government usage and the President is responsible for federal government usage. The FCC is directly responsible to Congress. By executive order, the President delegates the federal government spectrum management to the National Telecommunications and Information Administration (NTIA), which is placed under the Secretary of Commerce. The dual approach was selected so that decisions concerning commercial interests would be made only after considering their impact on government systems, and so that government usage supported commercial interests.

The FCC regulates all non-federal government telecommunications using Title 47 of the Code of Federal Regulations. (For example, see (FCC 2009, 11299-11318).) The FCC is directed by five Commissioners appointed by the President and confirmed by the Senate for five-year terms. The Commission staff is organized by function. The responsibilities of the six operating Bureaus include processing applications for licenses, analyzing complaints, conducting investigations, implementing regulatory programs, and conducting hearings (http://www.fcc.gov).

The NTIA performs spectrum management function through the Office of Spectrum Management (OSM), governed by the Manual of Regulations and Procedures for Federal Radio Frequency Management. The IRAC develops and executes policies, procedures, and technical criteria pertinent to the allocation, management, and usage of spectrum. The Spectrum Planning and Policy Advisory Committee (SPAC) reviews the reviews IRAC plans with regard to a balanced consideration of manufacturing, commerce, research, and academic interests. Within the Department of Defense, the spectrum planning and routine operation activities are cooperatively managed. Spectrum certification is a mandated process that ensures (1) the frequency band usage and type of service in that band are in conformance with the appropriate national and international tables of frequency allocations, (2) the equipment conforms to all applicable standards, specifications, and regulations, and (3) approval is provided to expend funds to develop equipment dependent upon wireless communications.

Host Nation Coordination (HNC)/Host Nation Approval (HNA)

In peacetime, international spectrum governance requires military forces to obtain host nation permission to operate spectrum-dependent systems and equipment within a sovereign nation. As an example international governance is honored and enforced within the United States by the U.S. departments of state, defense and the user service. In wartime, international spectrum governance is not honored between warring countries; however, the sovereign spectrum rights of bordering countries must be respected by military forces executing their assigned missions.

Accordingly, as another example, HNA is solicited by U.S. Naval forces to use spectrum-dependent systems and equipment in bordering countries' airspace and/or on bordering countries' soil. HNA must be obtained before the operation of spectrum-dependent systems and equipment within a sovereign nation. The combatant commander is responsible for coordinating requests with sovereign nations within his or her area of responsibility. Because the combatant commander has no authority over a sovereign nation. The HNC/HNA process can be lengthy and needs to be started early in the development of a system. Figure 2 is a spectrum example.

Figure 2. The Radio Spectrum (Department of Commerce 2003). Released by the U.S. Department of Commerce. Source is available at http://www.ntia.doc.gov/files/ntia/publications/2003-allochrt.pdf (Retrieved September 15, 2011)

Radiation Hardness

Radiation Hardening techniques are used for designing electronic devices and systems in order to resist damage or malfunction caused by ionizing radiation (van Lint and Holmes Siedle 2000). Electronics in systems can be exposed to ionizing radiation in the Van Allen radiation belts around the Earth’s atmosphere, cosmic radiation in outer space, gamma or neutron radiation near nuclear reactors, and electromagnetic pulses (EMP) during nuclear events.

A single charged particle can affect thousands of electrons, causing electronic noise that subsequently produces inaccurate signals. These errors could affect safe and effective operation of satellites, spacecraft, and nuclear devices. Lattice displacement is permanent damage to the arrangement of atoms in element crystals within electronic devices. Lattice displacement is caused by neutrons, protons, alpha particles, and heavy ions. Ionization effects are temporary damages that create latch-up glitches in high power transistors and soft errors like bit flips in digital devices. Ionization effects are caused by charged particles.

Most radiation hardened components are based on the functionality of their commercial equivalents. Design features and manufacturing variations are incorporated to reduce the components' susceptibility to interference from radiation. Physical design techniques include insulating substrates, package shielding, chip shielding with depleted boron, and magneto-resistive RAM. Logical design techniques include error-correcting memory, error detection in processing paths, and redundant elements at both circuit and subsystem levels (Dawes 1991). Nuclear hardness is expressed as susceptibility or vulnerability for given environmental conditions. These environmental conditions include peak radiation levels, overpressure, dose rates, and total dosage.

Practical Considerations

EMI/EMC is difficult to achieve for systems to operate world wide because of the different frequencies products are designed to operate in each of the telecommunication areas. Billions of US Dollars have been spent in retrofitting US DoD equipment to operate successfully in other countries.

References

Works Cited

Bagad, V.S. 2009. Electronic Product Design, 4th ed. Pune, India: Technical Publications Pune.

DAU. 2010. Defense Acquisition Guidebook (DAG). Ft. Belvoir, VA, USA: Defense Acquisition University (DAU)/U.S. Department of Defense (DoD). February 19, 2010.

NSTISS. 1993. Tempest Countermeasures for Facilities. Ft. Meade, MD, USA: National Security Telecommunications and Information Systems Security (NSTISSI). 29 November, 1993. NSTISSI No. 7000.

NTIA. 2011. Manual of Regulations and Procedures for Federal Radio Frequency Management, May 2011 Revision of the 2008 Edition. Washington, DC, USA: National Telecommunications and Information Administration, U.S. Department of Commerce.

Stine, J. and D. Portigal. 2004. An Introduction to Spectrum Management. Bedford, MA, USA: MITRE Technical Report Spectrum. March 2004.

Van Lint, V.A.J. and A.G. Holmes Siedle. 2000. Radiation Effects in Electronics: Encyclopedia of Physical Science and Technology. New York, NY, USA: Academic Press.

Primary References

DAU. 2010. Defense Acquisition Guidebook (DAG). Ft. Belvoir, VA, USA: Defense Acquisition University (DAU)/U.S. Department of Defense (DoD). February 19, 2010.

Additional References

None.

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