Anechoic chamber

Recently, the term has been extended to other radio frequency (RF) and sonar anechoic chambers, which eliminate reflection and external noise caused by electromagnetic waves.

Anechoic chambers range from small compartments the size of household microwave ovens to ones as large as aircraft hangars.

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 can be very quiet, with typical noise levels in the 10–20 dBA range.

[5] As a result, the component of the reflected waves R along the direction of I that escapes the gaps A (and goes back to the source of sound), denoted R', is notably reduced.

Even though this explanation is two-dimensional, it is representative and applicable to the actual three-dimensional wedge structures used in anechoic chambers.

This mesh floor is damped and floating on absorbent buffers to isolate it from outside vibration or electromagnetic signals.

Designs are becoming ever more complex with a single device incorporating multiple technologies such as cellular, WiFi, Bluetooth, LTE, MIMO, RFID and GPS.

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.

An RF anechoic chamber is usually built into a screened room, designed using the Faraday cage principle.

[citation needed] At lower radiated frequencies, far-field measurement can require a large and expensive chamber.

[citation needed] RF anechoic chambers are normally designed to meet the electrical requirements of one or more accredited standards.

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.

The following health and safety risks are associated with RF anechoic chambers: 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.

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.

Although recently manufactured RAM is normally treated with a fire retardant to reduce such risks, they are difficult to eliminate.