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Key Terms - ABCD

Absorber Materials which absorb acoustical energy or electromagnetic energy then dissipate this energy as heat within the structure of the materials
Absorption Loss The attenuation of an acoustical or electromagnetic wave as it passes through a shield
Acoustics The science of the production, control, transmission, reception and effects of sound and the phenomenon of hearing
Acoustical Treatment The use of acoustical absorbents, acoustical isolation, or any changes or additions to the structure to correct acoustical faults or improve the acoustical environment
Airborne Sound Sound transmitted through air as a medium rather than through solids or the structure of a building
Alternating Current Electric current that periodically reverses direction. Abbreviated AC.
Ambient The value of radiated and conducted signals and noises existing at a specified location
  The instrument noise floor or sensitivity level when referring to RF measurements
Ampere The unit of current. It is the current flowing through one ohm of resistance at one volt potential
Analog Being continuous or having a continuous range of values, not discrete steps
Anechoic Room A room whose boundaries effectively absorb all incident sound or RF over the frequency range of interest, thereby creating essentially free field conditions
Antenna A device employed as a means for radiating or receiving electromagnetic energy
Aperture An opening in a shield through which electromagnetic energy passes
Attenuation A reduction in energy
  Occurs naturally during wave travel through transmission lines, waveguides, space or a medium such as copper, or may be produced intentionally by inserting an attenuator in a circuit or an absorbing device in the path of radiation. The amount of attenuation is expressed in decibels or dB.
Attenuator An arrangement of fixed and/or variable resistive elements used to attenuate a signal by a desired amount

Background Noise The ambient noise level above which signals must be presented for sources measured.
Band Pass Filter A wave filter with a single transmission band, neither of the cutoff frequencies being zero or infinite. The filter attenuates frequencies on either side of this band
Bus Bar Power or ground distribution components. May consist of a length of brass with multiple screw connections for distribution
Bypass Device A shunt (parallel) path around one or more elements of a circuit. A secondary channel that permits routing of surge currents to earth ground

CapacitanceThe property of a system of conductors and dielectrics which permits the storage of electricity when a potential difference exists between the conductors
CapacitorA device which stores a charge of electricity
Center Frequency That frequency which corresponds to the center of a frequency span (spectrum analyzer)
Coaxial CableDesignating a two conductor high frequency transmission line, the outer conductor shielding the inner. Radio frequency transmission applications include radar, medical, electronics, and laboratory instrumentation. A vital link in these transmission systems is the RF coaxial connector. The connector's primary function is to attach and disconnect coaxial cable
Cold Solder JointA soldered connection where the surfaces being bonded have moved relative to one another while the solder was solidifying. This condition also can be caused by uneven or inadequate heating of the joint, or by improper surface preparation. Such cold joints are usually dull and grainy in appearance. These joints eventually cause failure to the system.
Conductive Interference Undesired signals that enter or leave equipment along a conductive (wire or metallic) path
Co-Planar The orientation for two magnetic loop antennas per MIL-STD-285. The two antennas are in the same plane oriented at any angle in a plane perpendicular to the shielding wall
CounterpoiseA system of wires or other conductors, forming a system of conductors for a grounding system; usually buried below ground
CouplingAny means of joining separated masses of any media so that sound energy is transmitted between them
CoronaA luminous discharge due to ionization of the gas surrounding a conductor around which exists a voltage gradient exceeding a certain value. A type of discharge, sometimes visible, in the dielectric of an insulation system caused by an electric field
CorrosionChemical action which causes destruction of the surface of metal by oxidation or other chemical combinations such as sulfating
CurrentThe flow of electrical charge from one point to another
Cutoff FrequencyThe frequency below which electromagnetic energy will not propagate readily in a waveguide

Damping Any means of dissipating or attenuating vibrational energy within a vibrating medium. Usually the energy is converted to heat
Decibel Ten times the logarithm (to the base 10) of the ratio of two mean square values of sound pressure, voltage or current. The abbreviation for decibels is dB
Dielectric Any insulating medium which intervenes between two conductors
Diffuse Field A sound field in which the sound pressure level is the same everywhere, and the flow of energy is equally probable in all directions
Direct Current Electric current that flows in one direction. Abbreviated DC
Dynamic Range The maximum measurable range of the test equipment. Usually the range between the reference level and the noise floor of the instrument

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Information presented is subject to change as product enhancements are made. Contact ETS-Lindgren Sales Department for current specification.