VTI Vacuum Technologies Inc.

Why EMI Shielding|| EMI & RFI Shielding Benefits
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Shielding Characteristic of Metals|| FAQ|| Glossary

Glossary of EMI Shielding Terms

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 electric circuits.

Bonding -
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 electrical connection.

Conductance - A measure of the ability of a material to conduct electrical current. The reFIProcal of the resistance of the material, expressed in siemens (mhos).

Conducted Susceptibility - The tendency of a piece of equipment to have its performance degraded in response to noise on its connecting wires.

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 contamination.

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 or device).

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 context).

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 Electrolytic Corrosion.

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 second (l/s).

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 electromagnetic energy.

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 into space.

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 through space.

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 impedance’s. Compare Absorption.

Reflective Loss –
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 the discontinuity.

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 sealing.

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 penetration.

Spectrum –
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 duration item.

Static Discharge or Electrostatic Discharge – Electric are caused by a potential gradient which is due to turboelectric charge separation.

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 ohms-centimeters (ohm-cm).

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 conductor.

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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Why EMI Shielding||Benefits of Shielding||The Shielding Process
Free Production Masking||Shielding Characteristic of Metals||FAQ||Glossary