The nominal level of radiated and conducted electromagnetic signals and noise existing at a specified location. This is usually considered to be a function of the entire electromagnetic environment including atmospheric noise and interference generated from within the measuring set-up.
Amplitude Modulation (AM)
The amplitude of an AM signal carrier varies according to the baseband signal source (modulating signal). The nominal bandwidth of an AM signal is twice that of the highest frequency contained in the baseband signal.
A room lined with absorbing material to reduce the reflection of electromagnetic waves. A full anechoic chamber is designed to simulate a free-space environment. It should have absorber material on all surfaces, including the floor. A semi-anechoic chamber should have absorbing material on the walls and ceiling only. The floor should be without absorbing material so that it is reflective to create a ground plane effect.
An antenna is a transducer through which electromagnetic waves are coupled from a transmitter to space and from space to a receiver. Some of the design parameters of an antenna include gain, bandwidth, beamwidth, directivity, radiation pattern, impedance, phase and polarization.
Antenna directivity (maximum or peak gain) is a measure of how well an antenna radiates in its intended direction as compared to an isotropic radiator. The Half-Power Beam Width (HPBW) of an antenna is the radiated beam width, measured in degrees, between the half-power points (3 dB points of the main lobe). The HPBW of an antenna design may be different for the azimuth than for the elevation. An omni-directional antenna provides equal radiation levels in all directions.
Antenna Factor (AF)
The term (AF) is used to define the antenna calibration relationship required for making accurate radiated emission measurements. The unknown electric field strength (E in V/m) is obtained by multiplying the voltage (V in volts or uVolts) at the measuring receiver by the (AF), allowing for attenuation (A) in the connecting cable. AF = E/V, the conversion can be expressed in dB by: E(dBμV/m) = V(dBμV) + AF(dB/m) + A(dB)
Antenna Front-to-Back Ratio
Front-to-Back Ratio is the difference in dB between the peak gain of an antenna and the radiation from the back of the antenna (typically 180 degrees from peak gain).
Antenna gain is generally referenced to an isotropic radiator (radiates equally in all directions) as 10 log (numerical gain), and is expressed in dBi. Gain may also be referenced to a half-wave dipole, depending on the antenna's application.
Antennas exhibit different feed-point impedances (resistive and reactive components), depending on their design, proximity to surrounding objects, and height above ground. For example, the half wave center-fed dipole exhibits an impedance of about 70 Ohms at 1/2 wavelength above ground. However, the input/output impedances of most RF connectorized devices is 50 Ohms. Therefore it is necessary to ensure proper matching in order to achieve efficient transfer of power. The Voltage Standing Wave Ratio (VSWR) provides a good indication of impedance match, with a perfect match resulting in a ratio of 1.0:1.
The polarization of an electromagnetic wave is determined by the orientation of the electric field (E) vector with respect to the direction of wave propagation.
· Linear Polarization
The antenna is designed to radiate and receive electromagnetic waves where the E-vector remains in a straight line as it moves in the direction of propagation. These antennas may be oriented or designed for horizontal or vertical polarization. The dipole and slot antennas form the basis of all linearly polarized antenna designs.
· Circular Polarization
The antenna is designed to radiate and receive electromagnetic waves where the E-vector rotates with time along the direction of wave propagation. All circularly polarized antennas are divided into two main categories: 1. Antennas polarized by the physical structure of their radiating aperture, such as the spiral and the helix. Right-hand (R-H) and left-hand (L-H) polarization are determined by the screw sense of these designs. 2. Antennas with orthogonal elements that are combined in phase quadrature such as the crossed dipole with external 90 degree hybrid coupler. This type of antenna can produce right-hand and left-hand circular polarization simultaneously.
· Cross Polarization
This condition exists when the wave polarization is orthogonal to the polarization of the receiving antenna. The polarization mismatch can result in large signal transfer losses. For example, a circular polarized wave has equal vertical and horizontal components, each with one-half of the radiated power. Therefore there is a 3 dB loss when the wave is coupled to a linearly polarized antenna. Losses between vertical and horizontal linear polarizations or between R-H and L-H circular polarizations can approach infinity, theoretically. However, due to other antenna design factors, these are typically at least 20 dB.
An opening in a shielded enclosure that may become the source of leakage for electromagnetic energy. This is most common in joints, seams and penetrations such as switches, connectors, and lamps/LEDs. Typically, the maximum dimension of an aperture should be less than 1/20 wavelength of the highest frequency of interest in order to avoid emissions.
The amount of reduction or loss in signal level (voltage, current, or power) offered by a device such as an attenuator, filter, or shielded enclosure. This quantity is generally expressed in decibels (dB).
Characterized by equal charge and discharge time constants resulting in readings of the average voltage level of the measured emission.
Used for FCC, MIL-STD testing, receive/transmit. A broadband linear polarized dipole antenna used to measure and produce electric fields from approximately 30 MHz to 300 MHz.
Antenna Used for FCC, MIL-STD testing, receive/transmit. A combination (hybrid design) of a biconical and a log periodic antenna with an automatic crossover network. It has a frequency range from about 26 MHz to 2 GHz.
To provide a fixed union between two objects that results in electrical conductivity between them. The union may occur either from physical contact between conducting surfaces of the objects or from the addition of a firm electrical connection.
An emission that has a spectral energy distribution that is wide compared to a referenced bandwidth, such as that of the susceptible receptor or the measuring receiver. This is usually defined using the 3 dB bandwidths. The unit for broadband signal measurements using EMI receivers is usually dBuV/MHz.
Signals that are identical in amplitude and phase at both inputs; the potential or voltage that exists between neutral and ground. Most electronic equipment requires it to be close to 0 V and not to exceed 1⁄2 V.
The component of the signal current that induces electric and magnetic fields that do not cancel each other. For example, in a circuit with one outgoing signal conductor and one ground conductor, the common-mode current is the component of the total signal current that flows in the same direction on both conductors. It is the primary source of EMI in many electronic systems.
Common-Mode Noise or Interference
This type of conducted emission travels in the same direction in both wires and returns through the ground plane or structure. In power and signal systems that have a single reference to ground or single-point ground, CM noise is capacitively coupled to the ground plane or structure. Because of this capacitive coupling, CM noises are generally high frequency (above approximately 2 MHz).
Conducted Emission (CE)
The potential ElectroMagnetic Interference (EMI) that is directly coupled through conduction (with attenuation) from one network or device to another. It may be generated inside equipment and transferred through power lines, I/O lines, or control leads.
Conducted Susceptibility (CS)
The determination or measurement of a device's capability to function in the presence of undesirable conducted EMI. This usually involves conduction through the I/O cables, signal leads, or power lines.
Conical Log Spiral Antenna
This antenna design receives or generates fields with circular rather than linear polarization. It is widely utilized for military susceptibility tests but is not suitable for commercial IEC/CISPR testing. This antenna has the capability of covering specific frequency ranges such as 200 MHz to 1 GHz or 1 GHz to 10 GHz.
A nonlinear interference where the modulation product of an interfering signal is present along with that of the desired signal. This is usually a type of adjacent channel interference.
Crosstalk results from the coupling of conducted emissions between two pairs of wires, one pair carrying emissions from a source and the other pair connected to a susceptible device. In a printed circuit board (PCB), crosstalk involves interaction between signals on two different electrical nets. The one creating crosstalk is called an aggressor, and the one receiving it is called a victim. Often, a net is both an aggressor and a victim.
An EMI measuring sensor designed to clamp around an electrical conductor, wire, wire pair, or cable harness. Current probes are used to measure the conducted emission (AC and DC) currents on power leads and signal lines. They can also help to locate and quantify ground loops.
A frequency ratio of 10 to 1, such as 1 Hz to 10 Hz, 10 kHz to 100 kHz, or 30 MHz to 300 MHz. One decade is equal to 3.32 octaves.
Logarithmic representation of a ratio measurement. Although it expresses the ratio of two power levels, it may be used for other electrical ratios across the same or equal impedances. It is most commonly used for expressing power, voltage and current ratios as follows: Power Ratio dB = 10 log (P1/P2), Voltage Ratio dB = 20 log (V1/V2), Current Ratio dB = 20 log (I1/I2).
Decibel (dB) Units of Measurement
dBW = decibels (power level) referenced to 1 Watt. dBmW = decibels (power level) referenced to 1 milliWatt; often used across 50 ohm input for receivers. dBV = decibels (voltage level) referenced to 1 volt across 50 ohms. dBuV = decibels (voltage level) referenced to 1 microvolt across 50 ohms. dBuV/m = decibels (voltage level) referenced to 1 microvolt per meter; used for electric field intensity measurement. dBuV/m/MHz = decibels referenced to 1 microvolt per meter per MHz; used for broadband field intensity measurement.
Detector (detection methods for EMI measurements)
The detector is used as the final stage of demodulation in a superhetrodyne receiver. It is used to recover the envelope of the input or baseband signal from the intermediate frequency (IF) components or carrier. The following detectors are commonly used in EMI receivers to meet various test specifications:
· Peak or Direct-Peak Detection
Characterized by rapid charge and slow discharge characteristics. The rise time is generally less than the reciprocal of the widest IF bandwidth and the discharge time provides enough delay to allow for full response of the receiver output functions. This method is required for testing EMI emissions to Military Specifications.
· Slideback Peak
An indirect-peak reading method with a controlled bias voltage used to represent the emission signal level. This method is not suitable for transient or single-shot pulses. In most cases it has been replaced by the direct-peak method.
Characterized by controlled charge and discharge time constants along with controlled predetection bandwidths to provide weighted readings corresponding to the type of signal measured or the EMI degrading effects. This method is used by CISPR and through harmonization of ANSI and adoption by the FCC.
· Root-Mean-Square (RMS)
This method of detection provides readings that are proportional to emission signal power at the detector's input.
Differential Mode Noise or Interference
This type of conducted emission is propagated out of one wire and returned on the other. This noise is generated by clock signals or switching waveforms in power supplies. DM noise amplitudes are usually minimal above 2 MHz because line-to-line and line-to-ground capacitance and wiring inductance tend to filter this type of noise.
An antenna with its gain, radiation pattern, and impedance defined at or near resonance of one-half wavelength. The antenna is split at its electrical center for connection to a transmission line. The radiation pattern is maximum at right angles to the axis of the antenna.
Acronym for Electrical, Electronic, and Electromechanical Parts. An effective EEE parts program is designed to achieve optimum safety, reliability, maintainability, on-time delivery, and performance of hardware. The resulting reduction in parts-related failures can save program resources through decreased failure investigation and maintenance costs.
Effective Radiated Power (ERP)
The product of a transmitter power output and the antenna gain, taking into consideration any losses from the transmission line, connectors, couplers, etc.
Electric Field (E)
The potential gradient of a radiated wave measured in V/m or Volts per meter.
Electromagnetic Compatibility (EMC)
The capability of equipment or systems to be used in their intended environment within designed efficiency levels without causing or receiving degradation due to unintentional EMI. EMC generally encompasses all of the electromagnetic disciplines.
Electromagnetic Disturbance (EMD)
Any electromagnetic phenomenon that may degrade the performance of equipment and/or a system. NOTE: An electromagnetic disturbance may be an electromagnetic noise, an unwanted signal, or a change in the propagation medium itself.
Electromagnetic Emissions (EME)
Electromagnetic radiation including intentional or non-intentional and conducted or radiated emissions.
Electromagnetic Environment (EME)
The entirety of all electromagnetic phenomena existing at a given location. This includes all conducted and radiated emissions. The Department of Defense (DoD) definition: it is the sum of electromagnetic interference; electromagnetic pulse; hazards of electromagnetic radiation to personnel, ordnance, and volatile materials; and natural phenomena effects of lightning and static.
Electromagnetic Environmental Effects (EEE) or (E³)
As defined by the Department of Defense (DoD), there are many types of E3 that can affect the electromagnetic compatibility (EMC) of a system. This group of EMC disciplines is used to properly address the EMC environment over the system's life cycle. The American National Standards Institute (ANSI C63.14) has been adopted by the DoD to serve as a standard dictionary for definitions commonly used pertaining to E3. This group includes the following: Electromagnetic Environment (EME), Electromagnetic Compatibility (EMC), Electromagnetic Interference (EMI), Electromagnetic Vulnerability (EMV), Electromagnetic Pulse (EMP), Hazards of Electromagnetic Radiation to Personnel (HERP), Hazards of Electromagnetic Radiation to Ordnance (HERO), Hazards of Electromagnetic Radiation to Fuel (HERF), Lightning, Precipitation static, Electrostatic discharge (ESD), Emission Control.
Electromagnetic Field (EMF)
A condition produced in space by the joint interaction of oscillating electric and magnetic fields which move independently of the charges or poles from which they originate. Per Maxwell’s equations, a varying electric field produces a varying magnetic field and vice versa. They are in phase and time quadrature. The cross product of the electric field upon the magnetic field produces the power density directional flow known as the Poynting vector.
Electromagnetic Interference (EMI)
Any electromagnetic disturbance, phenomenon, signal, or emission that causes, or is capable of causing, undesired responses or degradation of performance in electrical or electronic equipment. EMI is characterized by the following categories for test and measurement purposes:
- 1. Conducted Emissions
- 2. Radiated Emissions
- 3. Conducted Susceptibility
- 4. Radiated Susceptibility.
Coupling Paths Electromagnetic Interference (EMI)
Coupling Paths EMI is produced by a source emitter and is detected by a susceptible victim via a coupling path. This may involve one or more of the following coupling mechanisms:
- 1. Conduction electric current
- 2. Radiation electromagnetic field
- 3. Inductive coupling magnetic field
- 4. Capacitive coupling
Electromagnetic Pulse (EMP)
A broadband, high-intensity, short-duration burst of electromagnetic energy. In the case of nuclear detonations, the electromagnetic pulse signal consists of a continuous spectrum with most of its energy distributed throughout the lower frequencies of 3 Hz to 30 kHz. Such an intense single-pulse transient electromagnetic wave may be generated when a nuclear device is detonated or it may be generated by non-nuclear means. This intense wave may damage semiconductor components and signal processing circuitry that is found in electronic and electrical equipment.
Electromagnetic Radiation (EMR)
The emission of energy in the form of electromagnetic waves. It consists of oscillating electric and magnetic fields propagating at the speed of light. It includes gamma radiation, X-rays, ultraviolet, visible light, infrared radiation, radar, and radio waves. The two major categories are: Ionizing Radiation capable of causing ionization of gas molecules; includes x-rays, gamma rays, and electromagnetic particles. Non-Ionizing Radiation does not cause ionization of gas molecules. It includes sources such as RF, antennas, microwave ovens, infrared and visible light.
Electromagnetic Vulnerability (EMV)
The characteristics of electrical or electronic equipment/systems that cause them to suffer degradation or failure in performance as a result of electromagnetic interference.
Electrostatic Discharge (ESD)
A transfer of electric charge between bodies of different electrostatic potential in proximity or through direct contact.
A field originating from a non-fluctuating voltage source where no displacement current is contained.
A circuit or device containing series-inductive and parallel-capacitive components that provide a low impedance path for high-frequency noise around a protected circuit.
An EMI Receiver is a tunable, sensitive Voltmeter used to measure electric and magnetic field strengths. Most are similar to specialized spectrum analyzers, but are characterized by having preselectors, several detector functions, a housing shielding effectiveness of at least 90 dB and other unique additions. The frequency coverage of high-end receivers is typically 30 Hz to 22 GHz. Measurement bandwidths are variable to cover broadband and narrowband measurements. For EMI testing, they are used to measure conducted emissions (via LISN or R-F current probe) and radiated emissions (via antennas).
In EMI applications, this term applies to unintentional radiators, particularly those that are the source of interference. Otherwise, the term refers to the intentional radiators such as transmitter antennas.
Equipment Under Test (EUT) or Device Under Test (DUT)
The test equipment or item(s) being tested.
A conductive material used to contain or control an electric field. It is placed between the primary and secondary windings of a transformer to reduce coupling capacitance and common-mode noise. The shield provides electrostatic shielding while passing electromagnetic waves. No ground is needed.
Ferrite Material (Ferrites)
Powdered magnetic (permeable) material in the form of beads, rods and blocks used to absorb conducted interference on wires, cables and harnesses. Made by calcining a combination of metal oxides sintered into tiles. Material only a few millimeters thick absorbs low frequencies. Tiles may be used with dielectric materials or as a hybrid combination with dielectric pyramids. Acting as a lossy resistance and with increased self inductance, ferrites convert the associated EMI magnetic-flux density into heat (an exothermic process). One benefit of this, in contrast to filters, which perform by reflecting EMI in their stopbands, is that ferrites do not reflect EMI which otherwise could enhance radiation and disturb other victims.
Fields (Near Field, Far Field)
Near the source, field properties are determined primarily by source characteristics. Far from the source, field properties depend mostly on the medium through which the field propagates. Near to Far Field transition distance from the emitter: r = l/2p (this is approx. 1/6 wavelength), for D < l/2 r = D2/2l, for D 3 l/2 r = 2l, often used at low frequencies. Where r is the near/far field interface distance (distance from antenna at which the E and H fields begin to decrease as 1/r), p is pi (3.14), and D is the length of the radiating antenna element (or aperture dimension) in terms of wavelength l. Note: Very close to the source, the field is called the induction field (reactive or quasi-static field, non-radiating E or H field may provide strong coupling at low frequency and close proximity to source). Farther away, it is called the Fresnel region or near field (radiated field components decrease as 1/r3), and still farther from the source is the Fraunhofer region or far field (radiated field components decrease as 1/r). The far field wave impedance, E/H = 377 ohms (this is the characteristic impedance of the medium for air or free space).
Field Strength (FS)
The radiated voltage per meter (V/m) or current per meter (A/m) corresponding to electric (E) or magnetic (H) fields, respectively.
A device for blocking the flow of EMI current while passing the desired 50/60/400-Hz current. In communications circuits, it suppresses unwanted frequencies, noise, or separates channels.
A beryllium copper electrical gasket used to bond metal panel members on doors, sills, or covers.
Finite Difference Time Domain (FDTD)
The FDTD technique is commonly used for the simulation of a printed circuit board (PCB) and its associated components and connectors within the interior of the shielded enclosure or box. It is a time domain technique that easily supports multiple frequencies with a single simulation using a differential time domain numerical modeling method.
This is a mathematical technique for converting a function in the time domain to its equivalent representation in the frequency domain. For example, if the manufacturer's specifications or measured data are not available for a transmitter's modulation characteristics, a Fourier analysis may be used for determining the envelope of the specific type of modulation.
Frequency Domain Finite Differences (FDFD or FD)
FDFD/FD solves equations for electromagnetic fields at points in closed regions using a specialized form of Householder's Method of Modified Matrices. FD boundaries are specified by the UTD modeling elements.
Frequency Modulation (FM)
The instantaneous frequency of an FM signal carrier varies according to the baseband information source, while the carrier remains constant in amplitude. The rate at which the carrier varies from its center frequency is determined by the modulating frequency, while the frequency deviation (the amount of frequency variation) is proportional to the modulating signal's amplitude.
Electrical noise voltage fluctuations in a ground plane sharing common-impedance return from many PCB logic gates.
The connection of an electric circuit or equipment to Earth or a conductive body of relatively large extent in place of Earth. The connection or bonding of an equipment case, chassis, bus, or frame to a conductive object or structure to ensure a common potential.
Horn Antenna (Standard Gain)
Used for FCC, MIL-STD testing, receive/transmit. A linearly polarized microwave antenna covering test segments within the frequency range of 18 GHz to 40 GHz. The design consists of a flaring circular or rectangular metal waveguide shaped like a horn to direct radio waves in a beam.
The ability of equipment and/or system to perform without degradation in the presence of an electromagnetic disturbance.
The ratio between the power received at a specified load before and after the insertion of a filter at a given frequency. It is an indication of the attenuation provided by a filter.
A hypothetical antenna with equal radiation intensity in all directions. It is commonly used as a reference for expressing the directive characteristics of actual antennas.
The effect of unwanted energy due to one or more emissions upon the reception in a radio communication system, manifested by any performance degradation, misinterpretation, or loss of information, which could be extracted in the absence of such unwanted energy.
A Line Impedance Stabilization Network (LISN) is an electrical network used between the power mains and the test article for isolation in measuring conducted emissions. It ensures test measurement repeatability by stabilizing the power line and test article input impedances (which vary with frequency) at 50 ohms.
The following log relationships are most commonly used to convert magnitude to decibels (See Decibel dB): log (AB) = log A + log B, log (A/B) = log A log B, log (An) = n log A.
Log Periodic Antenna
Used for FCC, MIL-STD testing, receive/transmit. A broadband, linear polarized antenna used in the frequency range of 300 MHz to 2 GHz. The electrical lengths and element spacings are chosen in such a way that the bidirectional radiation pattern, impedance, and other antenna properties are repeated for several frequencies. The bandwidth is approximately the ratio of the longest dipole element to the shortest.
Used for FCC, MIL-STD testing. An antenna consisting of one or more complete turns of a conductor; usually tuned to resonance by a variable capacitor connected to the terminals of the loop. It is capable of measuring magnetic-field strengths at frequencies of 20 Hz to 2 MHz.
Low Pass Filter
A filter providing low insertion loss in its passband (DC to a 3-dB cutoff frequency) and significant insertion loss in its stopband (above the cutoff frequency to some defined upper frequency).
Magnetic Field Strength (H)
A radiated wave’s current gradient measured in amperes/m. 1 A/m = 0.0125 oersteds and 1 oersted = 79.6 A/m
1 weber = 108 Maxwell = 108 Lines.
Magnetic Flux Density (B)
Tesla (T) = 1 weber/m2 = 104 gauss. 1 gauss = 1 line/cm2 = 1 maxwell/cm2 = 7.936 x 105 A/m.
Method of Moments (MOM)
The MOM technique is commonly used for analysis of radiated electric field emissions caused by common-mode currents on the enclosure or box, connectors, and cables resulting from the PCB emissions.
An emission with a spectral energy distribution that is narrow compared to a referenced bandwidth, such as that of the susceptible receptor or the measuring receiver. This is usually defined using the 3 dB bandwidths. The unit for narrowband signal measurements using EMI receivers is usually dBuV.
Undesirable electrical signals that are present in a circuit or equipment. This becomes interference if the result is a degradation in performance. Whenever possible, noise should be controlled at the source to avoid extensive interference problems.
A frequency ratio of 2 to 1, such as 1 Hz to 2 Hz, 10 kHz to 20 kHz, or 500 MHz to 1000 MHz. 3.32 octaves is equal to one decade.
Open Area Test Site (OATS)
A test facility location, free of reflecting objects except a ground plane, where radiated emission tests may be carried out per CISPR 22 (FCC, Parts.15B, EN55022 and other test standards). A site attenuation test must be carried out to confirm that radiated pickup from a source to a receiving antenna falls within 4 dB of the theoretical range.
The capacitive leakage across a component such as a resistor, inductor, filter, isolation transformer, or optical isolator that adversely affects high-frequency performance.
The extent to which a material can be magnetized; often expressed as the parameter relating the magnetic-flux density induced by an applied magnetic-field intensity. A measure of how much better a material is as a path for magnetic lines of force, compared to air which has a permeability of one. The ratio of the flux density B to the magnetic field strength H in vacuum is called the permeability of free space.
Phase Modulation (PM)
In a phase modulated signal, the reference phase of the carrier varies in proportion to the instantaneous amplitude of the modulating baseband signal. This is similar to FM, but the frequency deviation is proportional to the frequency instead of the amplitude of the modulating source.
A precision EMI measuring sensor which clamps onto a wire, wire pair, coaxial line, cable, harness or strap carrying current, intentional or interference. Snap-on current probes are used to measure the normal-mode current in a single wire or the common-mode current in a wire pair, coax or an entire bundle or harness. Current probes cover the 100 Hz to 1 GHz spectrum in two or three units.
·Electric Field Probe
Small (usually 10-30 cm) monopoles feeding a FET amplifier for monitoring the E-field used often for diagnostic purposes. Some probes are passive and contain no amplifier. RF leakage sniffing at seams, gaps, slots, and apertures of a metal housing is one of many uses.
Radiated Emission (RE)
Desired or undesired electromagnetic energy that is propagated into or across space, either as a transverse electromagnetic wave or by capacitive or inductive coupling.
Radiated Susceptibility (RS)
The determination or measurement of a device's capability to function in the presence of undesirable radiated EMI from external electromagnetic sources.
Radiation (Ionizing, Non-Ionizing)
The non-conduction propagation of a signal from a source emitter. The radiation field is predominant over the induction field at distances defining the near and far field areas. Ionizing Radiation is capable of causing ionization of gas molecules; it includes x-rays, gamma rays, and electromagnetic particles. Non-Ionizing Radiation does not cause ionization of gas molecules; it includes sources such as RF, antennas, microwave ovens, infrared and visible light.
Radiation (Non-Ionizing RF Field Exposure) Safety Limit
The earliest limit in the U.S. was 10 mW/cm. This was based on studies of the level of an incident wave needed to double the average human body's base metabolic rate from the normal 100 W thermal dissipation. Considering frequency effects, this safety level has now been lowered for most frequencies. The average grounded adult resonates at approximately 30 to 34 MHz. The frequency is higher for children.
Radio Frequency (RF)
A frequency at which coherent electromagnetic radiation of energy is useful for communications. Radio frequencies are designated as very low.
Radio Frequency (RF) Compatibility
The ability of antenna-connected RF receiver and transmitter subsystems operating within a system to function properly without performance degradation caused by antenna-to-antenna coupling.
Radio Frequency Interference (RFI)
RFI is considered a part of the EMI spectrum, with interference signals being within the radio frequency (RF) range. This term was once used interchangeably with EMI.
A device that receives conducted or radiated electromagnetic emissions. In EMI applications, a receptor has the potential of being susceptible to undesired interference. It is considered to be a victim if it is susceptible to EMI from the emissions received.
The AC component of the output of a DC signal. The term typically refers to the residual line-frequency-related AC part in the output of a DC power supply that arises as a result of incomplete or inadequate filtering. The amount of filtering depends on the ripple frequency and the load resistance. As load resistance decreases, more filtering is required.
An omni-directional monopole antenna (usually 41 inches or 1.04 meters in length, adjustable) with counterpoise is commonly used for measuring radiated emissions in the 10 kHz to 30 MHz frequency range.
This is a measure of the selectivity (attenuation versus frequency) of a bandpass filter. The shape factor is usually defined as the ratio of the 60 dB and 6 dB bandwidths.
A room made free from EMI by applying shielding to the floor, walls, and ceiling, and by suppressing interference entering through the power lines. Typical construction shields from 70 dB to 140 dB from 10 kHz to 10 GHz.
The relative capability of a shield to screen out undesirable electric and magnetic fields and plane waves. The measurement is the ratio of the signal received without the shield to the signal received inside the shield.
A material that maintains shielding effectiveness across a seam or gap in an electronics enclosure. It can be made from a variety of materials including fabric-wrapped foam, wire mesh, stamped metal, and elastomer.
Signal integrity is the ability of a signal to generate correct responses in a circuit. A signal with good signal integrity has digital levels at required voltage levels at required times.
Slew rate is the edge rate (rate of change of a signal voltage with respect to time). 1/0 specifications (such as PCI) state the two voltages between which the slew rate is measured.
The inability of equipment/systems to perform without degradation in the presence of an electromagnetic disturbance. Susceptibility is often characterized as a lack of immunity. The threshold of susceptibility is the level of interference at which the test article begins to show a degradation in performance. This is often frequency dependent.
Susceptibility Degradation Criteria
A delineation of the essential safety and performance characteristics for a device under test (DUT) and the allowed degradation of these characteristics during susceptibility testing.
The electromagnetic noise environment in which a device or equipment can operate satisfactorily.
Difference between the threshold of susceptibility for a device or equipment and the environmental levels to which it is exposed.
Pertaining to or designating a phenomenon or a quantity that varies between two consecutive steady states during a time interval that is short in comparison to the time-scale of interest.
Transverse Electromagnetic (TEM) Cell
A chamber that maintains its characteristic impedance throughout its volume. Cable assemblies, connectors, and electronic devices may be placed inside the cell for testing purposes such as for measuring radiated emissions.
Uniform Theory of Diffraction (UTD)
The UTD analysis technique is useful for direct rays, reflected rays, diffractions from edges and corners, and waves around curved surfaces. UTD uses modeling elements of flat plates, cylinders of elliptical cross-section, and the end caps of each cylinder that may be tilted.
Voltage Standing Wave Ratio (VSWR)
A measure of the degree to which a load is impedance matched to its transmission line. A perfect match has a VSWR of 1.0 while an imperfect match has a greater standing wave ratio value.