Ampere is the SI unit of electric current and is one of the seven SI base units. In practical terms, the ampere is a measure of the amount of electric charge passing a point in an electric circuit per unit time with 6.241 × 1018 electrons, or one coulomb per second constituting one ampere
Electric charge A physical property of matter which causes it to experience a force when near other electrically charged matter. Electric charge comes in two types, called positive and negative. Two positively charged substances, or objects, experience a mutual repulsive force, as do two negatively charged objects. Positively charged objects and negatively charged objects experience an attractive force. The SI unit of electric charge is the coulomb, although in electrical engineering it is also common to use the ampere-hour.
uninterruptible power supply uninterruptible power source, UPS or battery/flywheel backup, is an electrical apparatus that provides emergency power to a load when the input power source, typically the utility mains, fails. A UPS differs from an auxiliary or emergency power system or standby generator in that it will provide instantaneous or near-instantaneous protection from input power interruptions by means of one or more attached batteries and associated electronic circuitry for low power users, and or by means of diesel generators and flywheels for high power users
tesla is the SI derived unit of magnetic field B (which is also known as “magnetic flux density” and “magnetic induction”). One tesla is equal to one weber per square meter, and it was defined in 1960 in honour of the inventor, physicist, and electrical engineerNikola Tesla. The strongest fields encountered from permanent magnets are from Halbach spheres which can be over 5 T.
Transformer is a device that transfers electrical energy from one circuit to another through inductively coupled conductors—the transformer’s coils. A varying current in the first or primary winding creates a varying magnetic flux in the transformer’s core and thus a varying magnetic field through the secondary winding. This varying magnetic field induces a varying electromotive force (EMF), or “voltage”, in the secondary winding. This effect is called mutual induction.
volt is the SI derived unit of electromotive force, commonly called “voltage”. It is also the unit for the related but slightly different quantity electric potential in a point (voltage as related to a reference ground) and electric potential difference (also called “electrostatic potential difference.
Voltage informal term for electric potential difference and is also called electric tension. Voltage is a measure of the energy of electricity, specifically, it is the energy per unit charge. A voltage may represent a source of energy (electromotive force), or it may represent lost or stored energy (potential drop).
Attenuation Loss of energy (i.e. conversion to heat) as radiation passes through a lossy (absorptive) medium (expressed in dB). Function of the properties of the medium. In contrast to insertion loss or reflectivity.
Compatibility Refers to the problem of a transmitter on a device causing interference to a receiver, or receivers on the same device (such as may be encountered on satellites, aircraft, or automotive vehicles).
dB Down The portion of incident energy which is reflected from a surface. A flat metal surface reflects all incident radiation. Measured in dB which is a logarithmic measure of the portion of energy reflected as compared to that reflected from a flat metal plate of the same area
Decibel A logarithmic ratio (base 10) between two quantities denoted as “”dB.”” In terms of energy reflection: dB = 10 x LOG(power reflected/power reflected by metal plate)
Dielectric A medium through which electric attraction or repulsion may be sustained – an insulator.
Electromagnetic Phenomenon related to the propagation of electric and magnetic energy. Defined by frequency in the Electromagnetic Spectrum. Electric and Magnetic energy is coupled. Meaning you cannot have one without the other. Described as Electromagnetic fields.
Electromagnetic Compatibility Refers to the problem of a transmitter on a device causing interference to a receiver, or receivers on the same device
Electromagnetic fields A vector field of Electromagnetic energy. The Magnetic (H) and Electric (E) fields generated by any system of electric charges. A low current, high voltage, source will generate mainly an ELECTRIC FIELD. A high current, low voltage, source will generate mainly a MAGNETIC FIELD.
Electromagnetic waves An electromagnetic wave can be thought of as propagating electric and magnetic fields. An electromagnetic wave propagates with the electric field and magnetic field perpendicular to each other.
EMC Refers to the problem of a transmitter on a device causing interference to a receiver, or receivers on the same device
Frequency The number of cycles per second. Units: Hertz (Hz) 1-cycle. KiloHertz (1000 cycles), MegaHertz (106 cycles), GigaHertz (109 cycles
Harmonic A signal present in a complex period waveform which is a multiple of the fundamental frequency, i.e. l st harmonic 2f, 2nd Harmonic 3f.
IMPEDANCE The ratio of electric to magnetic field (E/H) With waves, The wave impedance depends on the distance from the source.
The closer the values of the impedance of two materials, the less reflectivity will occur at their boundaries. If there is an impedance match there will be no reflectivity.
INSERTION LOSS IL – Ratio of input power to transmitted power. Loss of power passing through a material which includes reflection and attenuation.
LOSSY The ability of a material to attenuate or absorb energy.
MICROWAVE electromagnetic waves that refers to the frequency range of 700 MHz to 40 GHz in the electromagnetic spectrum.
PERMEABILITY Measure of the magnetic characteristics of a material. A measure of the effect of a nearby magnet on a material.
Radio Frequency Interference Refers to the problem of a device being susceptible to having its function compromised by interference from nearby high powered transmission.
WATTS Voltage X current (AMPS).
WAVELENGTHS The wavelength is the distance between two positive (or negative) peaks.
Ambient Level- The nominal level of radiated and conducted electromagnetic signal
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.
Anechoic Chamber- 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.
Attenuation- 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).
Average- Characterized by equal charge and discharge time constants resulting in readings of the average voltage level of the measured emission.
Bonding – 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.
Broadband Emission- An emission that has a spectral energy distribution that is wide compared to a referenced bandwidth, such as that of the suseptible 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.
Common Mode –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 as close to 0 V and not to exceed 1⁄2 V.
Common-Mode Current- 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 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.
DecadeA 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.
Decibel (dB) Units of Measurement
dBW = decibels (power level) referenced to 1 watt.
dBm = 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.
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.
Electromagnetic Disturbance (EMD) – Any electromagnetic phenomenon that may degrade the performance of equipment and/or 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 total of electromagnetic phenomena existing at a given location. This includes all conducted and radiated emissions. The 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 Field (EMF)- 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 electric 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 Poynting’s vector.
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 – electric field
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; includes sources such as RF, antennas, microwave ovens, infrared and visible light.
Electrostatic Discharge (ESD)-A transfer of electric charge between bodies of different electrostatic potential in proximity or through direct contact.
EMI Filter 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.
Equipment Under Test (EUT) or Device Under Test (DUT)The test article(s) or item(s) being tested.
Faraday Shield-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.
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.
Filter- 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.
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 (amount of the frequency variation) is proportional to the modulating signal’s amplitude.
Grounding- 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.
Immunity- The ability of equipment and/or system to perform without degradation in the presence of an electromagnetic disturbance.
Insertion Loss- 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.
Interference – 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.
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
1 oersted = 79.6 A/m
Magnetic Flux-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.
Noise- 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.
Parasitic Capacitance-The capacitive leakage across a component such as a resistor, inductor, filter, isolation transformer, or optical isolator that adversely affects high-frequency performance.
Permeability-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 with respect 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.
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.
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 – 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; includes sources such as RF, antennas, microwave ovens, infrared and visible light.
Radiation (Non-Ionizing RF Field Exposure)-2 Safety Limits – 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 basal 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 man 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: <30 kHz, low: 30 to 300 kHz, medium: 300 to 3,000 kHz, high: 3 to 30 MHz, very high: 30 to 300 MHz, ultrahigh: 300 to 3,000 MHz, superhigh: 3 to 30 GHz, and extremely high: 30 to 300 GHz.
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.
Shape Factor- 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.
Shielded Room- A room made free from EMI by applying shielding to the floor, walls, and ceiling, and by suppressing interference entering through the power lines.
Shielding Effectiveness – 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.
Transient – Pertaining to or designating a phenomenon or a quantity that varies between two consecutive steady states during a time interval short compared with the time-scale of interest.