MI Technologies is the leading supplier of Compact Ranges for RF and Microwave test and measurement. The anechoic chambers that house our Compact Range equipment are a vital part of the test and measurement system, providing a secure, radiation-free test environment. MI Technologies is proud to team with a number of quality suppliers to provide structures, absorber and other equipment needed to meet your Compact Range and anechoic chamber requirements.
Anechoic chambers are commonly used in acoustics to conduct experiments in nominally "free field" conditions. All sound energy will be traveling away from the source with almost none reflected back. Common anechoic chamber experiments include measuring the transfer function of a loudspeaker or the directivity of noise radiation from industrial machinery. In general, the interior of an anechoic chamber is very quiet, with typical noise levels in the 10–20 dBA range.
Full anechoic chambers aim to absorb energy in all directions. Semi-anechoic chambers have a solid floor that acts as a work surface for supporting heavy items, such as cars, washing machines, or industrial machinery, rather than the mesh floor grille over absorbent tiles found in full anechoic chambers. This floor is damped and floating on absorbent buffers to isolate it from outside vibration or electromagnetic signals. A recording studio may utilize a semi-anechoic chamber to produce high-quality music free of outside noise and unwanted echoes.
The internal appearance of the radio frequency (RF) anechoic chamber is sometimes similar to that of an acoustic anechoic chamber, however, the interior surfaces of the RF anechoic chamber are covered with radiation absorbent material (RAM) instead of acoustically absorbent material. The RF anechoic chamber is typically used to house the equipment for performing measurements of antenna radiation patterns, electromagnetic compatibility (EMC) and radar cross section measurements. Testing can be conducted on full-scale objects, including aircraft, or on scale models where the wavelength of the measuring radiation is scaled in direct proportion to the target size. Coincidentally, many RF anechoic chambers which use pyramidal RAM also exhibit some of the properties of an acoustic anechoic chamber, such as attenuation of sound and shielding from outside noise.
The RAM is designed and shaped to absorb incident RF radiation (also known as non-ionising radiation), as effectively as possible, from as many incident directions as possible. The more effective the RAM is the less will be the level of reflected RF radiation. Many measurements in electromagnetic compatibility (EMC) and antenna radiation patterns require that spurious signals arising from the test setup, including reflections, are negligible to avoid the risk of causing measurement errors and ambiguities.
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/ƒ where lambda represents wavelength, v is phase velocity of wave, and ƒ 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 2λ - 4λ, where λ 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.