·Guide Shield
A shield that includes the input circuit of an amplifier.

·Decoupling Network
An electrical circuit used to decouple energy between two circuits.

·Susceptibility
Refers to the ease with which components, devices, or systems experience performance degradation due to electromagnetic interference. Susceptibility indicates the degree of immunity deficiency.

·Gasket
A rubber gasket used to block electromagnetic waves or environmental intrusion at seams; available in practical, shielding, or composite types.

·Coupling Path
A path through which all or part of the electromagnetic energy from a specific source is transferred to another circuit or device.

·Coupling Clamp
A device with a defined shape and characteristics used to couple interference signals to the equipment under test without direct connection.

·Coupling Plane
A metal plate used to simulate electrostatic discharge to objects near the equipment under test.

·Coupling Network
An electrical circuit designed to transfer energy from one circuit to another.

·Ghost
An interference pattern that appears on a TV screen when broadcast signals are reflected by buildings or other structures and received out of sync.

·Harmonic
In a Fourier series of a periodic physical quantity, components of orders higher than the first; the first-order component is called the fundamental wave.

·Common Impedance Coupling Noise
Noise caused when currents from two different circuits flow through a shared impedance.

·Board-Band EMI
An electrical disturbance that spans multiple octaves or subdecades in the frequency spectrum. Because the spectral components are close together, they cannot be separated by a receiver.

·Ground Reference Plane
A metal plate used as a common voltage reference point for the equipment under test, test equipment, and auxiliary devices. Also known as the earth reference plane.

·Ground Loop
A loop formed between signal lines and ground or earth, in which a common voltage is induced by electromagnetic fields. Such loops may also form via stray capacitance even without conductive connections.

·Ground
A part of a circuit, device, or system that serves as a common potential reference point. It is grounded to the earth to prevent electrical shock hazards.

·Near Field Region
The region encompassing electrostatic and magnetostatic fields and inductive electromagnetic fields before transitioning to the plane wave region. In this region, wave impedance varies depending on the source (e.g., high for rod antennas, low for loop antennas), but it gradually approaches 377 ohms with distance. The field strength attenuates proportionally to the square or cube of the distance near the source and transitions into a far-field plane wave attenuating linearly with distance.

·Degradation
In immunity testing, this refers to an undesirable change in the operational performance of the equipment under test. It does not necessarily mean malfunction or catastrophic failure.

·Air Discharge Method
A method of electrostatic discharge testing in which the charged electrode of an ESD simulator is slowly brought near the equipment under test and discharged through an arc (spark).

·Interal Immunity
The ability of a device, equipment, or system to operate without performance degradation in the presence of electromagnetic interference appearing at its regular input terminals or antenna.

·Inner Noise
It refers to noise generated inside electronic devices, such as thermal noise from resistors, shot noise from semiconductors, and other inherent circuit noises caused by fluctuations in current and voltage.

·Normal Mode Noise
Noise that occurs between power lines or signal terminals. Since both signal and noise voltages are applied in series to the load, it is also called longitudinal voltage noise or differential mode noise.

·Noise Margin
In digital circuits, it defines the allowable noise level to prevent malfunction due to external noise. It is generally defined as the difference between the output level of a device and its input threshold level. Also known as operating margin.

·Noise Cut Transformer
A high-performance isolation transformer for power supplies that blocks both common-mode and normal-mode high-frequency noise. It uses double shielding and isolation to reduce capacitive coupling between the primary and secondary windings, and special cores to suppress electromagnetic coupling.

·Cross-talk
The phenomenon where a signal leaks into another circuit due to induction. The term originated from telephone transmission.

·Dipole Antenna
A half-wavelength antenna split at the electrical center point for connection to a transmitter.

·Frequency Band
The range between upper and lower frequencies where the response drops by 3 dB.

·Antistatic Material
A material that prevents static charge buildup, with a surface resistivity between 10 and 10⁶ ohms per meter.

·Decibels
A logarithmic unit representing power level ratios, defined as 10 times the logarithm of the power ratio. For voltage or current, it is 20 times the logarithm of the ratio. For field strength, 1 V/m or 1 A/m is defined as 0 dB; for example, 120 dB corresponds to 1 V/m.

·Ductive Coating
A low-resistance coating applied to plastic or similar cases to reduce internal emissions. It contains conductive fillers like silver, copper, nickel, or carbon dispersed in a binder. Carbon-based types are also used to enhance antistatic damping.

·Electro Conductive Plastics
Plastics mixed with conductive fillers such as metal or carbon, mainly used for electromagnetic shielding of electronic device enclosures or for static electricity countermeasures.

·Dropout
A condition involving a few hertz of cycle interruption or short-circuit state caused by a brief power outage.

·Decoupling Circuits
Circuits used during equipment testing to prevent test energy from spreading to other devices operating on the same power source. Also known as decoupling networks or back filters.

·Differential mode Voltage
The voltage that appears between two conductors in a defined pair. Also referred to as normal mode, line-to-line mode, symmetrical mode, or transverse mode.

·Random Noise
Noise whose amplitude and timing are unpredictable. Thermal noise and shot noise are typical examples.

·Level
The average or weighted value of a varying quantity such as power or electromagnetic field, calculated over a defined time using a specified method.

·Ripple Content
A physical quantity obtained by removing the DC component from the ripple.

·Pulsating
A periodic physical quantity whose average value is not zero.

·Monopole Antenna
An antenna placed on a ground plane to produce a radiation pattern similar to that of a dipole antenna.

·Mini Bus
A power bus with low characteristic impedance, consisting of insulated layers with power and return planes on both sides, used in high-speed logic circuits to supply stable power without fluctuation.

·Varistor
A semiconductor device with nonlinear voltage characteristics, used to absorb surges.

·By-pass Capacitor
A capacitor that bypasses high-frequency components and is used for noise suppression. Typically, ceramic or film capacitors are used.

·Biconical Antenna
A dipole antenna with a pair of conical basket-shaped elements, designed for broadband operation as a constant-impedance transmission line. Used for emission measurements and energy optimization in the 25–200 MHz range. For frequencies up to 1 GHz, log-periodic or log-spiral antennas are also used.

·Reflection Loss
In EMI, this refers to energy loss due to impedance mismatch between an electromagnetic field and a metal barrier. It is a key component of shielding effectiveness.

·Radiated Emission
Emission consists of both radiation and conduction. This term refers to the propagation of signals or interference from sources other than conduction. While legally termed “radiation,” it is commonly referred to as “radiated emission.”

·Balun
A device that converts balanced voltage to unbalanced voltage or vice versa.

·Bus
A common conductor or line used to transmit information or energy between functional units.

·Burst
A series of pulses repeated at fixed time intervals.

·ransfer Impedance
A figure of merit indicating the shielding performance of a cable, defined as the ratio of coupled voltage to surface current, with units of ohms per meter.

·Parallel Stripline
A parallel-plate transmission line used to generate electromagnetic waves for immunity testing.

·Bond
A temporary or permanent connection between two metal parts with low impedance.

·Stray Capacity
When the length of a line is not negligible compared to the wavelength, voltage and current in the circuit no longer change uniformly. In such cases, the circuit is referred to as a distributed-constant circuit.

·Rise Time
The time it takes for a pulse to rise from a specified lower value to an upper value—typically from 10% to 90% of its peak value.

·Intermodulation
A phenomenon that occurs in devices or transmission media with nonlinear characteristics, where new frequency components are generated from multiple spectral components of the input signal, causing mutual interference.

·Sag
A sudden drop in power supply voltage.

·Selectivity
A measure of a receiver’s ability or function to distinguish between desired and undesired signals.

·Screen
A metallic material used to minimize the intrusion of electromagnetic fields into a specific area.

·Stripline
A terminated transmission line composed of two parallel plates that propagates TEM-mode electromagnetic waves to generate a defined test field.

·Spike
A relatively short-duration unidirectional pulse.

·Spectrum Analyzer
A specialized receiver designed to analyze amplitude versus frequency data and display it on an oscilloscope.

·Spectrum
The decomposition of electromagnetic waves by wavelength, typically displayed with frequency on the horizontal axis and field strength or energy level on the vertical axis.

·Spurious Radiation
Unwanted electromagnetic radiation emitted from transmission or reception equipment, other than the intended electromagnetic waves.

·Spurious Response
The response of an electronic device to energy outside the designed reception band through its input terminals.

·Inter-system Interference
Interference caused by electromagnetic disturbances generated by the system itself.

·Signal-to-Noise Ratio
The ratio of signal level to electronic noise level in a circuit, measured under specified conditions.

·Shield Room
A specially designed room or enclosure with metal walls to isolate the interior from external electromagnetic environments—intended to prevent performance degradation from external interference and to contain internal emissions.

·Shield Effectiveness
The ability of an infinitely large metal plate to block electromagnetic waves. Theoretically expressed by the classical Gelkroth formula: Shielding Effectiveness = Reflection Loss + Absorption Loss + Multiple Reflection Correction.

·Site Attenuation
The frequency attenuation characteristics of a measurement site, influenced by antennas and surroundings, which must remain within specified limits to ensure consistent emission measurements.

·Surge
A transient wave of voltage, current, or power in a circuit lasting several seconds.

·Antenna Factor
The ratio of the electric field strength of radiated noise to the received voltage measured by an antenna. It includes effects from antenna mismatch and transmission loss.

·Antenna
A transducer that either emits radio frequency power from a signal source into the air or receives electromagnetic waves and converts them into electrical signals.

·Elastomer
A material with high elasticity, such as natural or synthetic rubber, derived from polymer compounds.

·Continuous Wave
A continuously transmitted electromagnetic wave that remains constant in steady state and can be modulated or interrupted to convey information.

·Audio Rectification
A phenomenon where high-frequency signals beyond a device’s response range are demodulated due to the nonlinear characteristics of components like transistors or ICs, affecting the output—also known as audio frequency rectification.

·Open Site
A measurement location for emission testing of electronic devices, defined by technical standards as a flat ground area free from surrounding structures that reflect radio waves.

·External Immunity
The ability of a device, equipment, or system to operate without malfunction when exposed to electromagnetic interference entering through standard input terminals or antennas.

·Umbrella Directive
A comprehensive directive requiring that electrical/electronic devices used in member countries meet common emission and immunity standards. It is called an umbrella directive because it defines overarching requirements.

·Far Field Region
The region where the distance between the transmitter and receiver is large compared to the wavelength, causing electromagnetic waves to behave as plane waves. In this region, field strength is inversely proportional to distance, and electromagnetic energy is equally carried by electric and magnetic fields, with a wave impedance of 377 ohms.

·Induction Field
A dominant electric or magnetic field present in the near-field region.

·Immunity
Defined as the ability of a circuit, device, or system to withstand interference. While the U.S. uses the term “susceptibility” as the opposite, the IEC adopts “immunity.” In Japan, it is also referred to as noise resistance or interference rejection capability.

·Emission
Electromagnetic energy radiated or conducted from a source.

·Artificial Noise
Noise generated by man-made sources, including radio or radar transmissions, engine ignition systems, motors, switches, fluorescent lights, induction heating, welding machines, computers, and peripherals.

·Artificial Hand
An electrical network that simulates the impedance of a human hand between a handheld device and ground under average usage conditions.

·Artificial Mains Network
A network inserted into the power supply line of the equipment under test, providing a defined load impedance over a specified frequency range for disturbance measurement and isolating the test equipment from the power source.

·Incoherent Noise
Broadband noise in which the amplitude and/or phase of adjacent frequency components vary randomly. Typical examples include noise from discharge tubes or corona discharge.

·nterface Port
A connection point used for information exchange between electronic devices, typically referring to terminals or connectors for interface cables.

·Threshold Level
In digital circuits, the voltage level used to distinguish discrete values. For TTL logic circuits, this is typically around 400 mV.

·Impulse
Refers to an electrical pulse with a very short duration. Mathematically, it is defined as a pulse with infinite amplitude, infinitesimal duration, and finite area.

·Magnetic Shield
A shielding method using magnetic materials to concentrate magnetic flux and prevent magnetic field influence on surrounding areas.

·Natural Noise
Electromagnetic noise caused by natural phenomena such as cosmic, geophysical, or meteorological events—examples include lightning and galactic noise.

·Mains Terminal Interface Voltage
The disturbance voltage measured at the power cable terminals of a device, representing conducted interference transmitted externally. Measurement is regulated using an LISN (Line Impedance Stabilization Network).

·Electrical Application Voltage
A Japanese law enacted in 1960 by the Ministry of Communications to prevent electric shock, fire hazards, and electromagnetic interference from electrical appliances.

·Conducted Emission
Electromagnetic energy transmitted through conductors, which may be desirable or undesirable. Undesirable emissions are referred to as conducted interference.

·Transfer Impedance
The voltage appearing between two defined points in a shielding circuit, excluding the current flowing through a defined cross-section. According to IEC, it is the ratio of longitudinal voltage per unit length on the outer conductor surface to the current inside the line. Higher values indicate greater electromagnetic leakage and coupling.

·Current Probe
A device used to measure current flowing through a conductor without breaking the conductor or affecting the circuit’s impedance.

·Voltage Dip
A sudden drop in voltage at a point in an electrical system, followed by recovery within a few cycles to a few seconds.

·Voltage Unbalance
A condition in a multiphase system where the effective values or phase angles of voltages between phases are not equal.

·Voltage Surge
A transient voltage that propagates along a line or circuit, characterized by a rapid rise followed by a gradual fall.

·Power Line Filter
A filter used to eliminate normal-mode and common-mode noise transmitted through power lines, improving conducted emission suppression and immunity.

·Power Filter
A filter that removes conducted noise from power lines, typically composed of LC elements. It is a low-pass filter that allows commercial frequencies to pass. Available as standalone units, onboard types, or inlet socket types.

·Field Strength
Applied to far-field electromagnetic measurements. If one component (electric or magnetic) is measured, the other can be calculated using the wave impedance of 377 ohms. In the near field, both components must be measured separately.

·Electromagnetic Wave
Radiated energy consisting of electric and magnetic fields generated by oscillating charges. Commonly referred to as radio waves.

·Anechoic Chamber
A measurement room with electromagnetic absorbers on the shielded walls to suppress both incoming external waves and internal reflections. Also called a radio wave anechoic chamber, it allows emission measurements of electronic devices without environmental interference.

·Electromagnetic Wave Absorber
A material that converts electromagnetic energy into another form to prevent reflection. Common types include pyramid-shaped foam, ferrite tiles, or hybrids, used in anechoic chambers.

·Isolation Transformer
A transformer used to electrically isolate circuits. When used in power lines, it can break ground loops.

·ESD Simulator
A simulator used for electrostatic discharge (ESD) testing.

·Commutation Notch
A brief voltage variation in AC caused by the commutation process in converters, much shorter than the AC cycle.

·Sweep
The continuous variation of frequency across a defined range.

·Quasi-peak Detection
A detection method used in EMI measurements that evaluates interference by considering the repetition and duration of signals.

·Peak-Value Detection
A detection method that captures the peak value of noise without time constants. Used in MIL standards for measuring ignition noise.

·Common-Mode Noise
Noise that propagates in phase on both lines of a transmission pair, as opposed to differential-mode noise. It can convert into differential noise and appear as interference at input terminals.

·Common-Mode Choke
A choke coil with two windings on a single core, wound in opposite directions to cancel differential currents and block common-mode noise.

·Corona
고Ionization of air around a conductor caused by high voltage.

·Coherent Noise
Broadband noise with a defined relationship between amplitude and phase of adjacent frequency components. Clock signals and radar are typical sources.

·Cross Modulation
A phenomenon where energy from one transmitter modulates the received signal of another transmitter.

·Clock Signal
A pulse train used in digital circuits to control timing and gate operations, typically generated by dividing a fixed-frequency oscillator.

·Click
An electromagnetic disturbance measured using a defined method, with a duration shorter than a specified limit.

·Test Site
A measurement location that meets specific conditions for accurately measuring radiated electromagnetic fields from a device under test.

·Transceiver
A portable radio device that combines both transmitting and receiving functions in a single unit.

·Transient
A short, non-periodic variation between two steady states.

·Wave Impedance
The ratio of electric field strength to magnetic field strength in an electromagnetic wave, denoted as Z.

·Pulse
A rapid change in a physical quantity over a short time, followed by a quick return to its initial value.

·Ferrite Beads
Cylindrical ferrite cores with wire passed through them, used to attenuate high-frequency components in the wire.

·Polarization
A term used to describe the vector direction of a radiated electromagnetic field.

·Average Detect
A detection method where the detector’s charge/discharge time constant is set below the inverse of the bandwidth. The output voltage indicates the average value of the modulation envelope of the input signal. Commonly used for narrowband signals and often combined with quasi-peak detection to evaluate mixed broadband and narrowband noise.

·Plane Wave
A wave in which the electromagnetic field layers are parallel planes. It occurs when the wave source is infinitely distant.

·Balanced Line
A transmission line above ground where two conductors have equal voltage magnitudes with opposite polarity and equal currents flowing in opposite directions.

·Surface Resistance
The resistance between opposite sides of a square plate, which theoretically remains constant regardless of the square’s size. Also called sheet resistance or area resistance.

·Skin Effect
The tendency of alternating current to flow near the surface of a conductor as frequency increases.

·Fourier Envelope
The envelope in the frequency domain obtained from the Fourier transform or series of a time-domain function.

·Flicker
A visual impression of instability caused by light stimuli whose intensity or spectral distribution fluctuates over time.

·Filter
A circuit that allows desired signal frequencies to pass while blocking EMI. It may have low-pass, high-pass, or band-pass characteristics.

·Narrow-Band EMI
Electromagnetic interference with a bandwidth narrower than that of an EMI receiver or spectrum analyzer.

·Cross Modulation
A phenomenon in nonlinear devices or transmission media where new frequency components—sums and differences of integer multiples of input frequencies—are generated, causing mutual interference.

·Whitter Wave
A low-frequency electromagnetic wave generated by lightning that travels along Earth’s magnetic field lines to the opposite hemisphere and returns to the surface. It induces a whistling sound in signal lines, hence the name.

·Absorbing Clamp Method
A measurement method using a clamp made of ferrite rings to determine the maximum radiated disturbance power from a device via its power line. It allows simple measurement without using an antenna.

·EEE(Electromagnetic Environment Effects)
Refers to all types of electromagnetic environmental influences, including EMC, EMI, RFI, and EMP. Also known as "E".

·EFT(Electro Fast Transient)
Describes a fast electrical transient phenomenon.

·EMC(Electro Magnetic Compatibility)
The ability of equipment, devices, or systems to function satisfactorily in their electromagnetic environment without exceeding acceptable levels of electromagnetic interference.

·EMI Receiver
A heterodyne receiver specifically designed to measure electric or magnetic field strength, conducted voltage, or current on lines. It uses quasi-peak detection as a standard.

·EMI(Electro Magnetic Interference)
Defined as electrical or electronic disturbances that cause performance degradation, malfunction, or failure of equipment. It generalizes the concept of RFI.

·EMP(Electro Magnetic Pulse)
A general term for pulses of electromagnetic energy. Those caused by lightning are called LEMP; those from nuclear explosions are NEMP.

·EN(European Norm)
A harmonized European standard developed by CENELEC, based on IEC/CISPR standards. Since 1989, TC110 has been working to establish immunity requirements not originally included in EU norms.

·ESD(Electro Static Discharge)
The discharge of electric charge between objects with different static potentials. The resulting impulse can significantly disrupt electronic devices.

·EUT(Equipment Under Test)
Refers to the device being tested. For components, the term DUT (Device Under Test) is used.

·IEC(International Electrotechnical Commission)
A global organization that reviews and sets standards in the electrical field. National standards adopt IEC specifications wherever possible. Committees such as CISPR and TC77 handle EMI/EMC, and TC65/WG4 manages immunity standards (IEC 801 series).

·IEV(International Electrotechnical Vocabulary)
Section 161 of the IEC standard lists related terminology.

·ISM Equipment(Industrial, Scientific and medical Equipment)
Devices designed to generate and use RF energy for purposes other than telecommunication—such as industrial, scientific, medical, household, or similar uses.

·ITE(Information Technology Equipment)
Devices or systems designed to handle secondary pulse waveforms and perform tasks like speech processing, computing, data transformation, storage, filing, classification, retrieval, and image playback.

·LISN(Line Impedance Stabilization Network)
A circuit inserted between the test equipment and its power supply to ensure consistent conditions for measuring conducted emissions. Known as an Artificial Mains Network in CISPR terminology.

·MIL(Military Standard)
U.S. joint military standards across the Army, Navy, and Air Force. EMC-related standards include the MIL-STD-460 series. Additional standards come from the Department of Defense and NSA.

·NVLAP(National Voluntary Accrediting Program)
A U.S. program run by NIST to accredit testing labs in various fields. Since 1985, it has included EMI testing facilities.

·RADHAZ(Radiation Hazards)
Zones where radiation poses risks to humans, animals, weapons, or fuel.

·RFI(Radio Frequency Interference)
Electromagnetic disturbances within the radio frequency spectrum (10 kHz to 40 GHz), potentially affecting systems such as communication, radar, satellite, and broadcasting.

·SAE(Society of Automotive Engineers)
A U.S.-based professional organization that publishes numerous standards for automotive components and testing. ISO also issues standards for vehicle EMC with 12V or 24V power supplies.

·SG(Signal Ground)
The signal ground line, typically the DC 0V line, abbreviated as SG.

·TEM Cell
A chamber formed by expanding a coaxial cable section, with a tapered outer box and flat inner conductor terminated at 50 Ω. It is used for immunity testing by placing the device under test within this electromagnetic field space.

·ULStandards(Underwriters Laboratories Standards)
U.S. safety standards for materials and products, established by the nonprofit UL in 1894. Although privately developed, products without UL certification are practically non-sellable in the U.S.

·UPS(Uninterrupted Power Supply)
A power system that continues supplying power to equipment even during power outages.

·VDE(Verband Deutscher Electrotechniker)
The Association of German Electrical Engineers, which publishes EMI standards such as 0871, 0875, and 0877. These often also appear as DIN standards with dual numbering.