Glossary

The absorbing clamp method of measurement is a standard method of measuring the interference power levels on cables connected to electronic devices using groups of ferrite rings. Without an antenna, simple emission measurements can be made from 30 MHz to 300 MHz.

The CE marking (also known as CE mark) is a mandatory conformity mark on many products placed on the single market in the European Economic Area (EEA) Related to the EMC and LVD directives. The CE marking certifies that a product has met EU consumer safety, health or environmental requirements.

Conducted Emission (CE) The potential EMI that is directly coupled through conduction from one device to another. It may be generated inside equipment and transferred through power lines, I/O lines, or control leads. Governing bodies impose limits conduction interference levels.

Test of a devices susceptibility to the potential EMI that is directly coupled through conduction from one device to another. Typical test are the burst immunity test, the surge immunity test, and the radiated immunity test.

The connection or bonding of an equipment case, chassis, bus, or frame to a conductive object or structure to ensure a common potential. In home electrical systems, Earthing is key to ensuring proper operation of protection relays and surge arresters. The term ground and grounding are used in US electrical engineering to represent electrical equipment that is securely bonded to the ground (i.e. that on which we stand) for safety reasons. In the UK the equivalent terms are earth and earthing.

A high polymer compound with the property of viscoelasticity.

An oscillating wave of electromagnetic radiation (energy) comprising electric and magnetic field components.

A material or structure with a very low reflection coefficient, which dissipates a portion of incident electromagnetic energy into internal heat, i.e. the ferrite tiles or pyramid-shaped resistive elements used in anechoic chambers.

The capability of equipment or systems to be used in their intended environment within designed efficiency levels without causing or receiving degradation due to unintentional EMI.

Any electromagnetic disturbance, phenomenon, signal, or emission that causes, or is capable of causing, undesired responses or degradation of performance in electrical or electronic systems and equipment. EMI is a more generalized term for RFI.

A violent transfer of electric charge between bodies of different electrostatic potential in proximity or through direct contact. It is called electro static discharge since it is accompanied by an arc discharge. The impulsive electromagnetic waves generated by ESD, or "static electricity" as it is more commonly known, can greatly affect electronic equipment.

A United States government agency that supervises, licenses and controls electronic and electromagnetic transmission standards. FCC rules are located in Title 47 of the Code of Federal Regulations. The FCC, under rule part 15 and 18 states that electronic devices including computers, manufacturing, scientific and medical equipment need to either be verified to not cause harmful emissions or need to be certified to not cause harmful emissions. A declaration of conformity from manufacturers stating that the emissions limits are within the FCC rules can greatly simplify the verification and/or certification process.

Powdered magnetic material called Ferrites in the form of beads, rods and blocks used to absorb and attenuate conducted interference on wires, cables and harnesses.

When two or more different sorts of metal come into contact in the presence of an electrolyte a galvanic couple is set up as different metals have different electrode potentials. The electrolyte provides a means for ion migration whereby metallic ions can move from the anode to the cathode. This leads to the anodic metal corroding more quickly than it otherwise would.

The connection of an electric circuit or equipment to Earth or a conductive body of relatively large extent in place of Earth. The term ground and grounding are used in US electrical engineering to represent electrical equipment that is securely bonded to the ground (i.e. that on which we stand) for safety reasons. In the UK the equivalent terms are earth and earthing.

Microwaves are electromagnetic waves with wavelengths ranging from as long as one meter to as short as one millimeter, or equivalently, with frequencies between 300 MHz and 300 GHz. This broad definition includes both UHF and EHF bands, as well as the entire SHF band (3 to 30 GHz, or 10 to 1 cm). Waves in this frequency range are widely used in cellular and satellite communications because of their ability to penetrate the ionosphere, and their resistance to atmospheric attenuation due to rain, fog, snow etc..

Standards developed for the United States armed forces. Standards concerning EMC are in the MIL-STD 460 series. Related to these military standards, there are also Department of Defense (DOD) Standards and National Security Agency (NSA) Standards.

Open Area Test Site (OATS) An outdoor test facility location, free of reflecting objects except a ground plane (normally laid with chicken wire), where radiated emission tests for electronic devices may be carried out.

Bombarding an EUT with modulated electromagnetic radiation in an anechoic chamber is a commonly used standard test method for radiated fields above 80 MHz, while the induced RF (EMI introduced via wiring) test method is used below 80 MHz, because the wavelength of the radiated field as compared to the mechanical dimensions of the EUT may be much longer, making the EUT less susceptible to internal interference and more likely to have interference transmitted into it through its connected wires.

Desired or undesired electromagnetic energy that is propagated into or across space, either as a transverse electromagnetic wave (Radiative) or by capacitive or inductive coupling (Conductive). This propagation can either intentional or accidental. Radio law considers this to be radiation.

Shield gaskets are used to fill and electronically bond and seal leaky apertures between mating panel member parts in order to maintain a minimum shielding effectiveness over a defined frequency spectrum. When dealing with the very short waves in the GHz spectrum, even a gap of a few centimeters between metal plates can dramatically reduce the shielding effectiveness of an enclosure. That is where gaskets come in. Shape, installation method and electrical corrosion are all factors which must be considered when selecting a shield gasket.

Shielding effectiveness (SE) is a parameter used for shielding evaluation, which is defined as the ratio between the field strength, at a given distance from the source, without the shield interposed and the field strength with the shield interposed. Though the shielding effectiveness of metallic plates is not infinite, they can approach very large values. The effectiveness of a shield is the sum total of two effects, reflection losses and absorption losses, plus a correction factor to account for reflections from the back surfaces of the shield.

An anechoic chamber is needed in order to test immunity to electromagnetic field radiation, and measure radiated emissions. A method to convert an existing room into a low-cost, simple anechoic chamber by lining the walls, floor an ceiling with absorbing material such as ferrite tiles to reduce the reflection of electromagnetic waves was invented. This "quiet zone", with its electromagnetic field constant, can be used to test immunity and measure free space emissions.

Underwriters Laboratories® is an American independent product safety certification organization that has been testing products and writing standards for safety for products and equipment such as waterproofing, alarms and theft deterrent systems, chemicals, electrical components and electronic equipment. There are places in the United States where it is forbidden to sell such products that do not bear the UL seal. There are many products that bear the UL seal because whether or not a product bears the UL seal can often times determine whether or not a product will be insured.

In Japan, Emissions control is performed on a voluntary basis, under the supervision of the Voluntary Control Council for Interference by Information Technology Equipment (VCCI). The VCCI was formed in December 1985 by four Japanese industry associations in response to a government request that electronics manufacturers participate in the control of electromagnetic interference (EMI). The Japanese Telecommunications Technology Council presented the Ministry of Post and Telecommunications with standards based on the internationally recognized CISPR 22 recommendations, and industry responded by organizing the VCCI as the mechanism to implement a voluntary EMI-control program.