As the density of the electromagnetic environment continues to increase, the concern about its effects from sources producing EMI also increases. Advances in technology and the number of products produced are having a significant effect on the efforts aimed at maintaining the required operation and interoperability of products and systems used in our society. These events had added challenges for those who are responsible for keeping pace with the effort needed to maintain the required level of electromagnetic compatibility (EMC) in these products and systems.
EMI sources, both natural and man-made, that compose the EME can be categorized into several primary categories. Some of these classifications of sources are listed below.
(1) Ambient EME that is composed of numerous sources of which the most significant are:
- Television transmissions both analog and digital
- Radio AM, FM, and Satellite
- Solar Magnetic Storms which peak on a eleven year cycle
- Lightning which occurs as a very high voltage and high current event
- Utility power grid transmission lines which have high voltage, low current, and low frequency characteristics. In this category is also the new technology of Broadband over Power Lines (BPL) digital signals.
- Other ambient EME sources include airport port radar, telecom transmissions, electrostatic discharge (ESD), and white noise. Also in this category is the earth’s magnetic field flux which has a value of about 500 milligauss.
- Some other major product and system’s emissions sources include switching mode power supplies, arc welders, motor bushes, and electrical contacts
(2) High Powered Electromagnetic Pulse (HEMP) threats which are intended to disable electrical and electronic equipment. These sources are designed to be utilized by terrorist and military organizations. Currently existing HEMP devices include the following:
- Intentional Electromagnetic Interference (IEMI) source – a high powered pulse device utilized by combat, sabotage and terrorist organizations
- High Altitude Nuclear Electromagnetic Pulse (HNEMP) – produced by the detonation of a nuclear device high above the earth’s atmosphere
- High Powered Microwave Weapon (HPM) – a device utilized by the military as a combat weapon
- E-Bomb – a HEMP weapon employed by the military to disrupt an enemy’s intra structure that is delivered by an aircraft.
- EMP Cannon – a military tactical weapon
(3) Power Quality degradation factors can effect the operation of equipment that is powered by a mains power source. These mains degradation factors include:
- Voltage surges, sages, dips, spikes, and high and low voltage
- Brownouts and blackouts
- Power line faults
- Electrical Fast Transitions (EFT)
- Electrical noise superimposed on the mains power line
These power quality degradation factors can occur simultaneously or independently, during any time interval.
(4) Railroad and Mass Transit Systems have some unique types of EMI source problems. These include:
- Propulsion system’s high voltage and high current operational mode emissions
- Train signaling systems and their associated computer operating codes
- Third rail shoes arcing broadband emissions
- High voltage contact switching arcing broadband emissions
- Train control system’s emissions
- Track train control circuits
- Right away emission sources
(5) Medical equipment utilized in medical facilities has numerous EMI sources. Some of the more prominent of these are listed below:
- Life support equipment such as ventilators, cardiac defibrillators, infusion pumps, etc.
- Patient telemetry and assistance equipment which includes electrocardiographs and motorized wheelchairs
- Electrical surgical units and their associated support equipment
- Magnetic Resonance Imagine (MRIs) systems
- X-ray units, both therapeutic and diagnostic
- Gamma Beam Electron Accelerators and Therapeutic equipment
SOURCES AND THEIR MOST SIGNIFICANT EFFECTS
(1) Ambient (EME) – Can affect sensitive electronic equipment in the vicinity of the EMI sources. The closer the sensitive electronic equipment is to the EMI source, the higher the source’s radiated power level, and its in-band frequency the greater is the probability that the EMI will cause an interference problem.
In the case of the effects of ESD on sensitive electronic systems it can cause upsets, burn outs, and latch-ups in these units.
(2) High Powered Electromagnetic Pulse effects – High powered electromagnetic sources can totally destroy an electrical and electronic equipment’s function.
As an example, an HNEMP device detonation above the earth’s atmosphere of the United States can totally immobilize the whole of the continental United State’s infrastructure. IEMI, HPM, E-Bombs, and EMP Cannons can be utilized to disable electronic systems at specific locations.
(3) Power Quality distortions and transits that are present on the power main systems can affect the normal operation of the equipment that it supplies power. Transits such as power surges are capable of destroying interface electronic circuits. EFTs can cause electronic circuit upset conditions.
(4) Railroad and Mass Transit Systems have one primary source of EMI and that is the transit and railroad engine’s propulsion systems, which operates with high voltages, currents, and magnetic field levels. They have been known to affect other facilities that contain sensitive electrical equipment that are located near the railroad or mass transit systems right away. These propulsion systems have had EMI associated problems with other elements of their systems. Train control electronics can be affected by EMI sources such as third rail and other broadband frequency arcing sources if they are not adequate designed for EMC.
(5) Medical equipment and facilities sources include patient monitoring systems
Those are very susceptible to EMI interactions. The human body signals that they monitor are very weak. They are measured in unites of microvolts and micro-amps. Among other devices that are susceptible to EMI are hearing aids, wireless patient monitoring systems, magnetic resonance imaging systems, implantable cardiovascular devices, drug pumps, and portable diagnostic meters. As new technologies are developed and enter the marketplace at a fast pace the list will grow.
As new devices and new technologies enter the marketplace, many operating at lower power levels and higher frequencies that make will make these devices more susceptible to EMI effects. This will also increase the number of EMI sources in the EME. The Functional Safety of a product (a hazard resulting from an EMI induced failure in the operation of a product) becomes of increasing concern. EMI factors are important consideration that must be taken into account when evaluating the reliability and quality assurance status of electrical and electronic products and systems.
Fortunately the steady pace in the evolution of harmonized globally based EMC regulatory certification compliance requirements is resulting in the minimizing of the increase in the new generation of safety hazards and their associated safety risks as the density of the EME increases. EMC Engineers have the responsibility of insuring that electrical and electronic products placed on the market are safe and their EMC design requirements have been met.
Anthony A. DiBiase is the president of Spec-Hardened Systems, an EMC and Product Safety consulting company. He is a graduate of the Rochester Institute of Technology and holds a BSEE. He has presented seminars on EMC topics and has written several articles on that subject. He can be reached at SHSESC@aol.com