Why EMI Shielding||
EMI & RFI Shielding Benefits
The EMI Shielding Process||
Free Production Masking
Shielding Characteristic of Metals||
Glossary of EMI Shielding Terms
Not sure how to talk the talk? Consult VTI’s glossary to improve your grasp of the language of vacuum technologies. From “A” to “W,” learn the difference between conductive susceptibility and surface resistivity, along with many more definitions that illustrate the world of vacuum technologies.
Absorption - Dissipation or loss of electromagnetic energy
in passing through a material substance.
Absorptive Loss - The portion of incident radiation absorbed
by a material.
Amplitude - The magnitude such as peak, rms, or average of a changing quantity such as a voltage or
current from its zero value.
Aperture - A hole or seam in an electronic equipment enclosure
through which internal or external electromagnetic fields may couple.
Attenuation - The decrease in amplitude of a signal during
its transmission from one point
to another. It may be expressed
as a ratio or by extension of the term, in decibels.
Barrier - A partition for the insulation or isolation of
1. Firmly connecting together various elements, shields or housings
of a device to prevent potential differences and possible interference.
2. A method used to produce good electrical contact between metallic
parts of any device.
3. The means employed to obtain an electromagnetically homogenous
mass having an equipotential surface.
Buss - A metallic electrical conductor used to make a common
Conductance - A measure of the ability of a material to
conduct electrical current. The
reFIProcal of the resistance of the material, expressed in siemens
Conducted Susceptibility - The tendency of a piece of equipment
to have its performance degraded in response to noise on its connecting
Conductivity - The ability of a material to conduct current. The reFIProcal of resistivity.
Contact Resistance - The resistance in ohms between two
objects in contact with each other.
Corrosion - A chemical action which causes gradual destruction
of a surface of a metal by oxidation, electrolysis, or chemical
Coupling - The association of two or more circuits of systems
in such a way that power may be transferred from one to another.
Crosstalk - Interference caused by stray electromagnetic
or electrostatic coupling of energy from one circuit to another.
Cure To change the physical properties of a material by
chemical or physical process through the action of a catalyst such
as heat, pressure moisture or chemical reaction.
Decibel (db) - The standard unit for expressing transmission
gain or loss and relative power levels. Decibels indicate the ratio of power output
to power input: db=10.log
(P1/P2) One decibel is 1/10 of a bel.
Deflection - A dimensional change of a material as a result
of stress. Deflection of
elastomers occurs with the application of compressive force.
Dielectric Strength - The maximum potential gradient that
an insulting (dielectric) material can withstand before it breaks
down (volts per mil).
Dynamic Range - The ratio of the maximum level capability
of a system to its least detectable or smallest level (e.g., maximum
signal level to system noise level).
E-Field - Abbreviation for electrical field. Electromagnetic field having the electric component
more than the magnetic component.
Electrical Ground -
1. A metallic connection with the earth to establish ground potential.
2. The voltage reference point in a circuit. There may or may not be an actual connection
to the earth, but it is understood that a point in the circuit said
to be at ground potential could be connected to the earth without
disturbing the operation of the circuit in any way.
Electrical Noise -
1. Any unwanted disturbance within a dynamic electrical system.
(e.g., undesired electromagnetic radiation in a transmission channel
2. Any unwanted electrical disturbance or spurious signal which
modifies the transmitting, indicating, or recording or desired data.
Electrolytic Corrosion Corrosion which occurs when a net
DC current flows between two metals in the presence of a conducting
fluid (electrolyte). The
rate of corrosion depends upon the amount of current and the nature
of the electrolyte. Compare Galvanic Corrosion.
Electromagnetic Having both magnetic and electrical properties.
Electromagnetic Compatibility (EMC) Capability of electronic
equipment or systems to operate with a defined margin of in the
intended operational environment at designed levels or efficiency
without degradation due to interference.
Electromagnetic Interference (EMI) Electromagnetic phenomena
which, either directly or indirectly, can contribute to a degradation
in performance of a electronic system. (The terms radio interference,
noise, EMI and RFI have been employed at various times in the same
Electromagnetic Pulse (EMP) Broadband, high-intensity,
transient electromagnetic fields such as those produced by lightning
and nuclear explosions.
Electrostatic Charge An electric charge accumulated on
an object, usually by friction between two objects or by transfer
from another object.
EMC Isolation The technique for producing a high electrical
resistance between an integrated-circuit component and the substrate
in which it is form.
Emission Electromagnetic energy propagated from a source
by radiation or conduction.
Enclosure Any electrical or electronic device housing.
Faraday Shield A network of parallel wires connected to
a common conductor at one end to provide electrostatic shielding
without affecting electromagnetic waves. The common conductor is usually grounded.
Field Strength The strength of an electromagnetic field. The measurement may be of either the electric or the magnetic
component of the field, and may be expressed as V/m, A/m, or W/m2;
any one of these may be converted to the others.
Galvanic Corrosion Corrosion which occurs between two
dissimilar metals in the presence of moisture or some other electrolyte. Under these conditions, an electrochemical cell is form
and current will flow from one metal to the other carrying tons
of the metal with it. Compare
Gasket, EMI A material or combination of materials, which
conducts electricity and which is used to ensure a continuous low-impedance
contact between two surfaces which conduct electromagnetic energy.
Go/No-Go A test technique in which the object tested is
required to perform in a specified manner. If it performs, it passes (Go); If it does not
perform, it fails, (No-Go). (e.g.;
a tapped hole which will (Go) or will not (No-Go) accept a particular
screw thread gage).
Ground A reference potential, used as a common return
for an electrical or electronic circuit and from which signal and
power voltages are measured.
H-Field Abbreviation for magnetic field. Electromagnetic field in which the magnetic
component is more intense than the electrical component.
Hertz (H/z) A unit of frequency equal to one cycle per
Impedance Control The design technique of suppressing
unintentional radiation by providing matched impedance conduction
paths for electronic signals.
Incidental Receiver Device which responds to unintended
Insertion Loss The difference between the power received
at the load before and after the insertion of apparatus at some
point in line.
Interference Any undesirable electromagnetic emission
or nay electrical or electromagnetic disturbance, phenomenon, signal
or emission, man-made or natural, which causes or can cause undesired
response, malfunctioning, or degradation of the electrical performance
of electrical or electronic equipment.
Magnetic Field or H-Field The low-impedance, or magnetic,
component of an electromagnetic wave. A magnetic field induces current in a shield and is measured
in amperes per meter. Compare
Electric Field or E-Field.
Magnetic Permeability The ratio of the magnetic induction
of a substance to the magnetizing field to which it is subjected.
Ohm A unit of electrical resistance equal to the resistance
of a circuit element in which a potential difference of one volt
produces a current of one ampere.
Ohm-cm A unit of material volume resistivity.
Ohms/Square A unit of material surface resistivity.
Permeability, Magnetic A relative measure of the ability
of a material to serve as a path for magnetic times of force based
on air=1. Permeability is the magnetic induction B in test (gauss)
divided by the magnetizing force H in ampere per meter (oersteds).
Plane Wave An electromagnetic wave in which all points
normal to the direction of propagation are in phase.
Radiated Emission Radiation of electromagnetic fields
Radiated Susceptibility Tendency of an electric deice
to respond with degraded performance to radiated noise.
Radiation Electromagnetic energy, such as light waves,
x-rays, infrared and thermal waves traveling through a medium or
Radio Waves (or Hertzain Waves) Electromagnetic waves
in the frequency range of 10kHz to 100 Ghz propagated in space without artificial guide.
Reflection The redirection of electromagnetic energy due
to reflection at the air metal boundary of a shield impedances.
1. That part of a transmission loss due to the reflection of power
at any discontinuity.
2. The ratio in decibels of the power incident upon the discontinuity.
3. The ratio in decibels of the power incident upon the discontinuity,
to the difference between the powers incident upon reflected from
Re-reflective Loss Losses from electromagnetic-barrier
interactions due to internal barrier discontinuities.
Relative Conductivity A comparative measure of electrical
conductivity based copper =1.
Shield Also called shielding. A screen or other housing (usually conductive)
placed around devices or circuits to reduce the effect of electric
or magnetic fields around them.
Shielding Effectiveness The relative reduction of radiated
electromagnetic energy levels occasioned by the use of an enclosure
either to contain or exclude the energy.
Shield-Seal A material which provides both EMI and environmental
Skin Depth In a current-carrying conductor, the depth
below the surface at which the current density has decreased one
level below the current density at the surface; that is, the field
has decreased to 1/e (36.8%) of its surface value, also called depth
1. The frequency components that make up complex waveform. The band of frequencies necessary for transmission of a given
type of intelligence.
2. The range of frequencies considered in a system.
Square Wave A square or rectangular shaped periodic wave
which alternately assumes two fixed value of near equal time duration
in which the transition time is negligible in comparison with the
Static Discharge or Electrostatic Discharge Electric are
caused by a potential gradient which is due to turboelectric charge
Stress Relaxation The decrease in stress after a given
time at constant deflection.
Surface Resistivity The resistance of a material between
two opposite sides of a unit square of its surface, commonly expressed
in ohms per square.
Susceptibility The undesired response of electronic equipment
to emissions, interference, or transients, or to signals other than
those to which the equipment is intended to be responsive.
Transmission Line A path from one place to another, used
for directing the transmission of electromagnetic energy.
Volume Resistivity The electrical resistance between opposite
faces of a 1 centimeter cube of material, commonly expressed as
Waveguide A system of material boundaries capable of guiding
electromagnetic waves. A
transmission line comprising a hollow conducting tube within which
electromagnetic waves are propagated on a solid dielectric or dielectric-filled
Wavelength In a periodic wave, the distance between the
point of corresponding phase of two consecutive cycles. The wavelength (X) is related to the phase velocity
(y) and frequency (f) by the formula X=v/f.
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EMI Shielding||Benefits of
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