An electromagnetic compatibility (EMC) or anechoic chamber is a highly specialized piece of test equipment used in the testing of electronic devices against regulatory standards concerning both radiated and conducted radio frequency (RF) emissions and immunity.
EMC or anechoic chambers are designed to create an enclosure with an extremely high level of shielding attenuation against electromagnetic interference.
The word ‘anechoic’ means simply ‘without echo’. An anechoic chamber is a box, chamber or room designed to completely absorb reflections of either sound or electromagnetic waves.
The key characteristic of an anechoic chamber is that it’s designed to absorb reflections of waves within the chamber instead of having them bounce off the walls which would cause an echo. If designed and assembled correctly, these chambers also do a great job at keeping waves from entering the chamber, specifically they provide shielding from outside interference. This combination means that a person or detector exclusively hears direct sounds, no reverberant sounds, in effect simulating being inside an infinitely large room.
If you’ve ever shouted ‘echo!’ in a large room, you’ve probably noticed some kind of reverberation and you’ve heard your voice repeat a few times. To avert this phenomena, anechoic chambers are lined on the inside with materials that are designed to completely absorb all sound waves therefore eliminating any and all reflections.
In today’s industries, anechoic chambers are used for performing EMC measurements according to a variety of published EMC standards. There are many different fields of application, including consumer electronics, automotive, aerospace, military, medical, telecommunications, research & development and others. Different organizations around the world develop and publish standards, resulting in different requirements and consequently different chamber types.
There are many types of anechoic chambers that are designed for different types of applications. A few of the most common uses and types are for things like audio recording, radiated emissions testing, radiated immunity testing, wireless transmitter (RF) testing, antenna testing and specific absorption rate (SAR) testing.
An anechoic chamber’s primary application is to determine whether a product or device complies with emission and immunity limits defined in specific industry standards. Nevertheless, depending on your industry, anechoic chambers can be used for testing according to a wide variety of EMC standards such as CISPR, IEC/EN, MIL-STD 461 and RTCA DO-160.
EMC anechoic chambers, principally those with conductive floors called semi-anechoic chambers or SAC, are essentially used for testing radiated emissions (RE) in the frequency range from 30 to 1000 MHz and radiated immunity (RI) from 26 or 80 MHz to 1000 MHz, with extensions to 6 GHz, 18 GHz, or even 40 GHz with RE measurements becoming more frequent.
RF SHIELD TECHNOLOGY
The chamber itself will almost always be a shielded room or Faraday cage, meaning that it is an isolated RF environment that is not disturbed by external interference and in turn does not disturb the external environment itself. The shielding specification is typically defined from 10 kHz to 18 GHz and sometimes to 40 GHz with acceptance testing methods described in IEEE 299 [1] or EN 50147-1 [2] and the user will typically define the required shield attenuation levels.
It is a near RF-impenetrable metal box, that offers electric and magnetic field shielding effectiveness up to 100 dB over a wide range of frequencies. It is good for emissions testing because no signals or ambient noise from the outside can penetrate it, making it much easier to measure the emissions generated only by the equipment under test. At the same time, it is also good for immunity testing because no signals generated inside the enclosure can escape to the outside, possibly causing harmful interference to equipment or personnel located nearby.
One of the main applications for an RF chamber is measuring the emissions of a product to determine if it complies with the limits defined in specific industry standards. Other uses for RF anechoic chambers include radiated emissions testing, radiated immunity testing, wireless transmitter testing, antenna testing and specific absorption rate testing.
Remember that there are different types of shielding materials and configurations for anechoic chambers and each of them have different shielding performance levels. If your application requires maximum shielding effectiveness, then you may want to consider shielding material that is double electrically isolated. This shielding has two layers of metal (one on the inner surface and one on the outer surface), typically connected at only the main grounding point of the chamber. If anything needs to be mounted to either the inside or outside of the chamber then the mounting screws selected should be keep short enough to penetrate just the first shielding layer and not go through the second.
Other components of the shielded room are the door, whose quality and size will significantly influence the overall cost and performance of the shielded room, as well as RF filtering for electrical, data and other cabling that must be present in the room.
Are you in the process of installing an EMC anechoic chamber? Don’t hesitate to contact us for more information. Even if you are not entirely sure what you’re looking for, our account managers are always ready to answer your questions either by phone, e-mail or during an introductory meeting.
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References:
Eadie, A. (2016, June 29). The Anechoic Chamber Guide For EMC and RF (Wireless) Testing.
