6.5 KiB
| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| Anechoic chamber | 2/2 | https://en.wikipedia.org/wiki/Anechoic_chamber | reference | science, encyclopedia | 2026-05-05T09:03:19.715865+00:00 | kb-cron |
Waves of higher frequencies have shorter wavelengths and are higher in energy, while waves of lower frequencies have longer wavelengths and are lower in energy, according to the relationship
λ
=
v
/
f
{\displaystyle \lambda =v/f}
where lambda represents wavelength, v is phase velocity of wave, and
f
{\displaystyle f}
is frequency. To shield for a specific wavelength, the cone must be of appropriate size to absorb that wavelength. The performance quality of an RF anechoic chamber is determined by its lowest test frequency of operation, at which measured reflections from the internal surfaces will be the most significant compared to higher frequencies. Pyramidal RAM is at its most absorptive when the incident wave is at normal incidence to the internal chamber surface and the pyramid height is approximately equal to
λ
/
4
{\displaystyle \lambda /4}
, where
λ
{\displaystyle \lambda }
is the free space wavelength. Accordingly, increasing the pyramid height of the RAM for the same (square) base size improves the effectiveness of the chamber at low frequencies but results in increased cost and a reduced unobstructed working volume that is available inside a chamber of defined size.
=== Installation into a screened room === An RF anechoic chamber is usually built into a screened room, designed using the Faraday cage principle. This is because most of the RF tests that require an anechoic chamber to minimize reflections from the inner surfaces also require the properties of a screened room to attenuate unwanted signals penetrating inwards and causing interference to the equipment under test and prevent leakage from tests penetrating outside.
=== Chamber size and commissioning === At lower radiated frequencies, far-field measurement can require a large and expensive chamber. Sometimes, for example for radar cross-section measurements, it is possible to scale down the object under test and reduce the chamber size, provided that the wavelength of the test frequency is scaled down in direct proportion by testing at a higher frequency. RF anechoic chambers are normally designed to meet the electrical requirements of one or more accredited standards. For example, the aircraft industry may test equipment for aircraft according to company specifications or military specifications such as MIL-STD 461E. Once built, acceptance tests are performed during commissioning to verify that the standard(s) are in fact met. Provided they are, a certificate will be issued to that effect. The chamber will need to be periodically retested.
=== Operational use === Test and supporting equipment configurations to be used within anechoic chambers must expose as few metallic (conductive) surfaces as possible, as these risk causing unwanted reflections. Often this is achieved by using non-conductive plastic or wooden structures for supporting the equipment under test. Where metallic surfaces are unavoidable, they may be covered with pieces of RAM after setting up to minimize such reflection as far as possible. A careful assessment may be required as to whether the test equipment (as opposed to the equipment under test) should be placed inside or outside the chamber. Typically most of it is located in a separate screened room attached to the main test chamber, in order to shield it from both external interference and from the radiation within the chamber. Mains power and test signal cabling into the test chamber require high quality filtering. Fiber optic cables are sometimes used for the signal cabling, as they are immune to ordinary RFI and also cause little reflection inside the chamber.
=== Health and safety risks associated with RF anechoic chamber === The following health and safety risks are associated with RF anechoic chambers:
RF radiation hazard Fire hazard Trapped personnel Personnel are not normally permitted inside the chamber during a measurement as this not only can cause unwanted reflections from the human body but may also be a radiation hazard to the personnel concerned if tests are being performed at high RF powers. Such risks are from RF or non-ionizing radiation and not from the higher energy ionizing radiation. As RAM is highly absorptive of RF radiation, incident radiation will generate heat within the RAM. If this cannot be dissipated adequately there is a risk that hot spots may develop and the RAM temperature may rise to the point of combustion. This can be a risk if a transmitting antenna inadvertently gets too close to the RAM. Even for quite modest transmitting power levels, high gain antennas can concentrate the power sufficiently to cause high power flux near their apertures. Although recently manufactured RAM is normally treated with a fire retardant to reduce such risks, they are difficult to eliminate.
== See also == Soundproofing Vibration isolation Buffer (disambiguation) Damped wave Damping ratio Damper (disambiguation) Electromagnetic reverberation chamber Reverberation room Sensory deprivation GTEM cell
== References ==
== External links ==
360-degree video of an anechoic chamber Pictures and description of an acoustic anechoic chamber Archived 4 March 2019 at the Wayback Machine Anechoic Chambers, Past and Present How RF Anechoic Chambers Work Archived 17 April 2012 at the Wayback Machine Video tour of an EMC/RF Test facility. Including the largest anechoic test chamber in the southern hemisphere Some examples Antenna Testing For An Anechoic Chamber Millimeter Wave Inc's Radio/MM Wave anechoic chamber Archived 21 December 2012 at the Wayback Machine Bell Labs' Murray Hill anechoic chamber Anechoic chamber for millimeter wave designs Archived 22 June 2018 at the Wayback Machine "Acoustics Anechoic Chamber". The UK's National Measurement Laboratory. National Physical Laboratory. Archived from the original on 29 September 2007. Retrieved 22 February 2011. Anechoic chambers at Apple Inc. campus used to test their mobile device products, via WaybackMachine Photos from building an anechoic chamber in CTU, Prague Sound examples The sound of clothes inside an anechoic chamber Hallucinations in anechoic chambers: the science behind the claim Listen to a subdued balloon burst in an anechoic chamber