Electromagnetic reverberation chamber

An electromagnetic reverberation chamber (also known as a reverb chamber (RVC) or mode-stirred chamber (MSC)) is an environment for electromagnetic compatibility (EMC) testing and other electromagnetic investigations. Electromagnetic reverberation chambers have been introduced first by H.A. Mendes in 1968. A reverberation chamber is screened room with a minimum of absorption of electromagnetic energy. Due to the low absorption very high field strength can be achieved with moderate input power. A reverberation chamber is a cavity resonator with a high Q factor. Thus, the spatial distribution of the electrical and magnetic field strengths is strongly inhomogeneous (standing waves). To reduce this inhomogeneity, one or more tuners (stirrers) are used. A tuner is a construction with large metallic reflectors that can be moved to different orientations in order to achieve different boundary conditions. The Lowest Usable Frequency (LUF) of a reverberation chamber depends on the size of the chamber and the design of the tuner. Small chambers have a higher LUF than large chambers. The concept of a reverberation chambers is comparable to a microwave oven. The notation is mainly the same as in the IEC standard 61000-4-21. For statistic quantities like mean and maximal values, a more explicit notation is used in order to emphasize the used domain. Here, spatial domain (subscript s {displaystyle s} ) means that quantities are taken for different chamber positions, and ensemble domain (subscript e {displaystyle e} ) refers to different boundary or excitation conditions (e.g. tuner positions). A reverberation chamber is cavity resonator—usually a screened room—that is operated in the overmoded region. To understand what that means we have to investigate cavity resonators briefly. For rectangular cavities, the resonance frequencies (or eigenfrequencies, ornatural frequencies) f m n p {displaystyle f_{mnp}} are given by f m n p = c 2 ( m l ) 2 + ( n w ) 2 + ( p h ) 2 , {displaystyle f_{mnp}={frac {c}{2}}{sqrt {left({frac {m}{l}} ight)^{2}+left({frac {n}{w}} ight)^{2}+left({frac {p}{h}} ight)^{2}}},} where c {displaystyle c} is the speed of light, l {displaystyle l} , w {displaystyle w} and h {displaystyle h} are the cavity's length, width and height, and m {displaystyle m} , n {displaystyle n} , p {displaystyle p} are non-negative integers (at most one of those can be zero). With that equation, the number of modes with an eigenfrequency less than a given limit f {displaystyle f} , N ( f ) {displaystyle N(f)} , can be counted. This results in a stepwise function. In principle, two modes—a transversal electric mode T E m n p {displaystyle TE_{mnp}} and a transversal magnetic mode T M m n p {displaystyle TM_{mnp}} —exist for each eigenfrequency.