| A | B | C | D | E | F | G | H | I | J | K | L | M |
| N | O | P | Q | R | S | T | U | V | W | X | Y | Z |

A

Abrasion Resistance
The resistance of a material to wearing away by contact with a moving abrasive surface. Usefulness of standard tests very limited. Abrasion resistance is a complex of properties: resilience, stiffness, thermal stability, and resistance to cutting and tearing.

Absorption Loss
Attenuation of an electromagnetic wave or energy encountered in penetrating a shield caused by the induction of current flow in the barrier and the resulting IR loss. Usually stated in dB (decibels).

Ambient Electromagnetic Environment
That electromagnetic field level existing in an area and emanation from sources other than the system under test.

Attenuation
A reduction in energy. Attenuation occurs naturally during wave travel through transmission lines, waveguides, space or a medium such as water, or may be produced intentionally by inserting an attenuator in a circuit or a shielding absorbing device in the path of radiation. The degree of attenuation is expressed in decibels or decibels per unit length.

Attenuator
An arrangement of fixed and/or variable resistive elements used to attenuate a signal by a desired amount.

C

Cold Flow
Continued deformation under stress.

Compression Deflection
When a compressive load is applied to certain materials, such as solid elastomers, the material is deformed but the volume of the material remains constant.

Compression Set
The decrease in height of a specimen which has been deformed under specific conditions of load, time, and temperature. Normally expressed as a percentage of the initial deflection (rather than as a percentage of the initial height).

Conductivity
Capability of a material to conduct electrical currents.

Cross Coupling
Coupling of the signal from one channel to another where it becomes an undesired signal.

D

Decibel (dB)
A convenient method for expressing voltage or power ratios in logarithmic terms. The number of such units of attenuation, N is where

.........................P /P is a unitless power ratio. N can also be expressed in terms
.........................of a voltage ratio E /E as follows:

Depth of Penetration
Distance which a plane wave must travel through a shield to be attenuated 1/e, or approximately 37 percent of its original value. (Also called "skin depth"). It is a function of the shield's conductivity and permeability and the wave's frequency.

Degradation
An undesired change in the operational performance of a test specimen. Degradation of the operation of a test specimen does not necessarily mean malfunction.

Durometer
An instrument for measuring the hardness of rubber. Measures the resistance to the penetration of an indentor point into the surface of the rubber.

E

Elasticity
The property of an article, which tends to return to its original shape after deformation.

Elastic Limit
The greatest stress which a material is capable of developing without a permanent deformation remaining after complete release of the stress. Usually this term is replaced by various load limits for specific cases in which the resulting permanent deformations are not zero but are negligible.

Elastomer
A general term for elastic, rubber-like substances.

Electrical or E-Field
A field induced by a high impedance source, such as a short dipole.

Electromagnetic Compatibility (EMC)
A measure of an equipment's ability to neither radiate nor conduct electromagnetic energy, or to be susceptible to such energy from other equipment or an external electromagnetic environment.

Electromagnetic Interference (EMI)
Undesired conducted or radiated electrical disturbances, including transients, which can interfere with the operation of electrical or electronic equipment. These disturbances can occur anywhere in the electromagnetic spectrum.

Emanation
Undesired electromagnetic energy radiated or conducted from a system.

Elongation
Increase in length expressed numerically as a fraction or percentage of initial length.

G

Gasket-EMI
A material that is inserted between mating surfaces of an electronic enclosure to provide low resistance across the seam and thereby preserve current continuity of the enclosure.

Ground
A reference plane common to all electronic, electrical, electromechanical systems and connected to earth by means of a ground rod, ground grid, or other similar means.

H

Hardness
Relative resistance of rubber surface to indentation by an indentor of specific dimensions under a specified load. (See Durometer). Numerical hardness values represent either depth of penetration or convenient arbitrary units derived from depth of penetration. Devices for measuring rubber hardness are known as durometers and plastometers. Durometers are used most commonly. The higher the durometer number, the harder the rubber, and vice versa.

Hardness Shore A
Durometer reading in degrees of hardness using a Type A Shore durometer. (Shore A hardness of 35 is soft; 90 is hard).

Hertz
An international designation for cycles per second (cps).

I

Insertion Loss
Measure of improvement in a seam, joint or shield by the addition of a conductive gasket. Usually stated in dB.

Interference
Any electromagnetic phenomenon, signal or emission, man-made or natural, which causes or can cause an undesired response, malfunctioning or degradation of performance of electrical or electronic equipment.

Internal Loss
Attenuation of electromagnetic energy by the reflection and re-reflection of electromagnetic waves within a shield or a barrier. Usually stated in dB.

M

Magnetic or H-Field
An induction field caused predominantly by a current source. Also called a low impedance source, such as may be generated by a loop antenna.

Malfunction
A change in the equipment's normal characteristics which effectively destroys proper operation.

P

Permeability (Electrical)
The capability of a material to be magnetized at a given rate. It is a non-linear property of both the magnetic flux density and the frequency of wave propagation.

Permeability (Mechanical)
A measure of the ease with which a liquid or gas can pass through a material.

Permanent Set, Stress and Strain Relaxation
Permanent Set is defined as the amount of residual displacement in a rubber part after the distorting load has been removed. Stress Relaxation, or Creep, is a gradual increase in deformation of an elastomer under constant load with the passage of time, accompanied by a corresponding reduction in stress level.

Plane Wave
An electromagnetic wave which exists at a distance greater than a wavelength from the source, where the impedance of the wave is nearly equal to the impedance of free space -377 ohms.

R

Radio Frequency Interference (RFI)
Used interchangeably with EMI. EMI is a later definition, which includes the entire electromagnetic spectrum, whereas RFI is more restricted to the radio frequency band, generally considered to be between the limits 10 kHz to 10 GHz.

Relative Permeability
Magnetic permeability of the shield material relative to the permeability of free space.

Reflection Loss
Attenuation of the electromagnetic wave or energy caused by impedance mismatch between the wave in air and the wave in metal.

Relative Conductivity
Conductivity of the shield material relative to the conductivity of copper.

Resilience
The ratio of energy given up on recovery from deformation to the energy required to produce the deformation - usually expressed in percent.

S

Shield
A metallic configuration inserted between a source and the desired area of protection which has the capability to reduce the energy level of a radiating electromagnetic field by reflecting and absorbing the energy contained in the field.

Shielding Effectiveness
A measure of the reduction or attenuation in electromagnetic field strength at a point in space caused by the insertion of a shield between the source and that point. Usually stated in dB.

Shielding Increase
The difference of an electromagnetic field amplitude emanating through a seam (measured under fixed test conditions) with and without the gasket in the seam, with the force joining the seam remaining constant. The difference is expressed in dB based on voltage measurements.

Skin Effect
Increase in shield resistance with frequency because of crowding of current near the shield surface because of rapid attenuation of current as a function of depth from the shield surface.

Stress Relaxation
When a compressive load is applied to a material such as an elastomer, there is an initial deflection followed by a slow relaxation process whereby some of the load is relaxed. This process continues until the compressive load is balanced by the cohesive strength of the material.

Surface Treatment
Coating or plating of mating surfaces of a junction.

Susceptibility
Measure of the degradation of performance of a system when exposed to an electromagnetic environment.

T

Total Shielding Effectiveness
The difference of an electromagnetic amplitude emanating from a source within an enclosure, and that from a source in free space. The difference is expressed in dB based on voltage measurements.

Tear Strength
The force per unit of thickness required to initiate tearing in a direction normal to the direction of the stress.

Tensile Strength and Elongation
Tensile Strength is the force per unit of the original cross sectional area which is applied at the time of the rupture of the specimen during tensile stress. Elongation is defined as the extension between benchmarks produced by a tensile force applied to a specimen, and is expressed as a percentage of the original distance between the marks. Ultimate elongation is the elongation at the moment of rupture. Tensile Stress, more commonly called "modulus" is the stress required to produce a certain elongation.

Thermal Conductivity (k)
Thermal conductivity (k) is an intrinsic property of a homogeneous material, which describes the material's ability to conduct heat. This property is independent of material size, shape or orientation.

Thermal Impedance (ø)
The thermal impedance (ø) of a material is defined as the sum of its thermal resistance and any contact resistance between it and the contacting surfaces, as defined by the equation:
(ø) = R material + R contact