A
Absorption Loss: Reduction of electromagnetic energy as it penetrates a shield, caused by current induction and heat dissipation (I²R loss), typically measured in decibels (dB).
Ambient Electromagnetic Environment: Electromagnetic field present in a given area, originating from sources unrelated to the system being tested.
Attenuation: Energy reduction during wave transmission, either naturally through mediums or by using attenuators or shielding devices, quantified in decibels.
Attenuator: A device designed to reduce signal strength using resistive elements.
C
Cross Coupling: Unintended transfer of a signal from one channel to another.
Conductivity: The ability of a material to conduct electrical current.
D
Decibel (dB): A logarithmic unit used to express voltage or power ratios.
Degradation: Unwanted change in a test specimen’s performance, not necessarily a malfunction.
Dielectric Loss Tangent: Measure of a material’s ability to convert electromagnetic energy into heat.
E
Electromagnetic Compatibility (EMC): A system’s ability to neither emit nor be affected by external electromagnetic energy.
Electromagnetic Interference (EMI): Disruptive electrical disturbances affecting the performance of electronic equipment.
Emanation: Unintended emission of electromagnetic energy from a system.
Electromagnetic Waves: Classified into magnetic (H-field), electric (E-field), and plane waves based on their properties and sources.
Electromagnetic Pulse: A brief, high-intensity burst of electromagnetic energy.
G
Gasket-EMI: A material used in electronic enclosures to maintain electrical continuity across seams.
Ground: A reference plane in electrical systems connected to the earth.
H
Hertz: A unit measuring frequency, defined as cycles per second.
I
Insertion Loss: The improvement in shielding performance with the use of a conductive gasket, expressed in decibels.
Interference: Any external electromagnetic phenomenon that degrades the performance of electronic equipment.
Immunity: The ability of a device to resist external EMI without malfunctioning.
Impedance: The opposition to current flow in a circuit when voltage is applied.
M
Malfunction: A significant deviation from normal operation leading to system failure.
N
NRL Arch: A Naval Research Laboratory method to assess material reflectivity for electromagnetic absorption.
P
Permeability: A material’s ability to be magnetized.
Permittivity: The ability of a material to store electrical energy.
R
Radio Frequency (RF): Electromagnetic radiation frequencies, generally above 10 kHz.
Radio Frequency Interference (RFI): A subset of EMI focused on radio frequencies between 10 kHz and 10 GHz.
Reflection Loss: Energy reduction due to impedance mismatch between an electromagnetic wave in air and one in metal.
Relative Conductivity: Shield material’s conductivity compared to copper.
Relative Permeability: Shield material’s magnetic permeability compared to free space.
S
Shield: A metallic barrier that reduces electromagnetic energy by reflecting or absorbing it.
Shielding Effectiveness: Reduction in electromagnetic field strength caused by a shield, measured in decibels.
Skin Depth: The distance electromagnetic waves penetrate a shield before being significantly attenuated.
Skin Effect: Increased resistance due to higher current concentration near a conductor’s surface as frequency increases.
Surface Treatment: Coating or plating applied to a junction’s mating surfaces.
Susceptibility: A system’s vulnerability to performance degradation in the presence of external electromagnetic energy.
V
Volume Resistivity: Resistance that accounts for material thickness, typically measured in ohm-cm.
W
Wave Impedance: The ratio of electric to magnetic field intensity in an electromagnetic wave.
Wavelength: The distance over which a sinusoidal wave repeats its shape.
EMI Shielding Mechanical Terms
A
Abrasion Resistance: The ability of a material to resist wear caused by contact with an abrasive surface. Standard tests have limited value due to the complexity of factors such as resilience, stiffness, thermal stability, and resistance to cutting and tearing.
C
Cold Flow: The gradual deformation of a material under stress.
Compression Set: The reduction in height of a material after being deformed for a specific duration under load and temperature, expressed as a percentage of its initial deflection.
Compression Strength: The capability of a material to bear compressive forces that reduce its size.
Compression Modulus: A measurement of the force required to stretch a material sample, used to define the material’s elastic properties.
Conversion Coating: A chemically-created protective layer on metal, typically compliant with MIL-DTL-5541 standards. Type 1 involves hexavalent chromium (CR3), and Type 2 involves trivalent chromium (CR6).
CBRN: Abbreviation for Chemical, Biological, Radiological, and Nuclear exposure, a modern equivalent to NBC.
CVCM: Measurement of outgassing in the form of collected volatile condensable materials.
D
Durometer: A device that measures the hardness of rubber by evaluating resistance to penetration.
Density: The relationship between an object’s mass and its volume.
E
Elasticity: The ability of a material to return to its original shape after deformation.
Elastic Limit: The maximum stress a material can endure without permanent deformation after the stress is released.
Elastomer: A term used for materials with elastic, rubber-like properties.
Elongation: The increase in length of a material, expressed as a percentage of its original length.
EPDM: A type of synthetic rubber (ethylene propylene diene monomer) used in harsh environments, including NBC applications.
F
Fatigue Strength: The stress range a material can withstand without breaking after repeated cycles of loading.
Ferrex: A tin-plated, copper-clad stainless steel wire.
Flammability Rating: Classification of plastics based on how they burn under various conditions, standardized by UL-94.
Flexural Strength: The stress a material experiences before breaking during bending.
Flexural Modulus: The ratio of stress to strain in a material when subjected to bending forces.
Fluorosilicone: A silicone compound with fluorinated chains that improves oil and fuel resistance.
FEA: Finite Element Analysis, a software-based method for predicting mechanical behavior under various loads.
G
Galvanic Corrosion: The oxidation or corrosion of dissimilar metals in contact with each other in the presence of an electrically conductive medium.
Galvanic Compatibility: The degree to which dissimilar metals resist corrosion in a shared environment.
Gravimetric Weight Loss: The amount of metal lost due to corrosion when two different metals are in contact.
H
Hardness: The resistance of a material, such as rubber, to surface indentation, measured using a durometer.
Hardness Shore A: A specific durometer scale for measuring rubber hardness, where lower values indicate softer materials and higher values indicate harder materials.
HDT (Heat Deflection Temperature): The temperature at which a polymer begins to deform under a specified load.
Hygroscopic: The ability of a material to absorb and retain moisture from the environment.
I
Izod Impact: The amount of kinetic energy required to fracture a material during an impact test.
L
LOI (Limited Oxygen Index): The minimum oxygen concentration, as a percentage, required to sustain the combustion of a polymer.
M
Modulus of Elasticity: The ratio of stress to strain within the elastic limit of a material.
Monel: An alloy primarily composed of nickel and copper, with small amounts of iron, manganese, carbon, and silicon.
N
NBC: Refers to exposure to Nuclear, Biological, and Chemical agents.
O
Outgassing: The release of gas that was previously trapped or dissolved in a material.
P
Permeability: The ability of a material to allow liquids or gases to pass through it.
Permanent Set, Stress, and Strain Relaxation: Permanent set refers to the residual deformation in a material after removing a load, while stress relaxation (creep) describes the gradual deformation over time under a constant load.
R
Resilience: The percentage of energy recovered by a material after deformation.
RoHS Compliant: Refers to compliance with the Restriction of Hazardous Substances directive (European Directive 2002/95/EC), which limits certain hazardous materials in electronic products.
S
SAE: The Society of Automotive Engineers, which develops standards for EMI gasket testing.
Shear Modulus: The ratio of shear stress to shear strain in a material.
Surface Treatment: The application of a coating or plating to improve the mating surfaces of a junction.
Specific Gravity: The ratio of a material’s density to that of a reference substance.
T
Tear Strength: The force required to initiate and propagate tearing in a material.
Tensile Set: The residual elongation of a material after being stretched and allowed to relax.
Tensile Strength and Elongation: Tensile strength refers to the force required to break a material under tension, while elongation measures the material’s extension during that process. Ultimate elongation is the point at which the material breaks.
TML (Total Mass Loss): The weight loss of a material due to outgassing.
Thermal Conductivity: The ability of a material to conduct heat.
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