Anechoic chamber
It is a known fact that certain scientific experiments and manufacturing procedures need to be carried out in a closed space with no external factors interrupting the process. Such chambers are often vaccuum, or immune external electromagnetic radiations or sound waves.
While manufacturing electronic devices it is necessary for the device to be shielded from external electromagnetic waves and also to make sure that the device’s electromagnetic waves don’t affect other electronic devices. Electronic manufacturers should make sure that an electronic device performs to the required level by conducting certain tests to determine its ground capabilities and shielding capacities. This test is called ElectroMagnetic Compatibility (EMC) test and should be done in specially designed chambers called anechoic chambers.
Anechoic chamber is simply a room that is designed in a way such that any sound wave or electromagnetic wave in the room is absorbed and is immune to external sources of sound. At first these chambers were made to minimize reflection and reverberations in a room but now it has also been designed to reduce external noise and reflections in radio frequencies and are used to test radars, antennas and so on. These chambers vary in size. From that of a small microwave ovens to a large airport hangers, the size of anechoic chambers vary.
Anechoic chambers are usually used to conduct experiments in ‘free field’ condition. Free field condition means that there are no reflected signals.That is, any sound wave from the source will not be reflected back. This is achieved by carefully designing the wall of the chamber in a way such that reflections die down almost immediately. Walls composed of wedges are used in anechoic chambers. When the incident light hits on the wall, a series of reflected waves are formed which bounce up and down in the gap between the wedges. This creates a standing wave pattern and as a result the reflected waves are dissipated.
The interior of an anechoic chamber is usually quiet with the noise level in the range of 10-20 dBA. The best anechoic chamber had a noise level of -9.4 dBA until Microsoft constructed an anechoic chamber in 2015 with a noise level of -20.6 dBA. Human ear can only detect sounds above 0 dBA. Thus when a person enters these chambers, he would feel that the chamber is devoid of sounds.
While constructing an anechoic chamber, proper ventilation should be provided if a person is going to spend a good amount of time inside the room. Construct an air inlet and outlet and keep them apart from one another as far as possible. For allowing natural light to enter the chamber, window glass can be covered with sheets of slightly sealed acoustic glass and double window glazing so as not to disturb the acoustic properties of the room.
Test and supporting equipment configurations should expose as little metal surfaces as possible since metallic surfaces cause unwanted reflections. The test equipment, if possible, should be places outside the chamber. If experiments are conducted in high RF frequencies, people are not allowed inside the chamber owing to health reasons. People are sometimes not allowed to enter the room so that unwanted reflections are not caused.