An Electromagnetic Reverberation Chamber (RC) is a screened room or shielded enclosure formed by highly conductive walls, equipped with tuners (stirrers) to conduct radiated immunity testing to ensure EMC Compliance. It is designed to provide high field strength (V/m) with statically uniform electromagnetic field distribution within the chamber for EMC testing. The chamber can create high field strengths up to several hundred or thousands of V/m (e.g., 200V/m - 7000V/m or higher) for radiated immunity testing. Some standards, like the DO-160 (200 V/m), require high field strengths. Reverberation chambers can also be used for emission measurement testing.

Figure 1: Inside look of a reverberation chamber. The walls are highly conductive. The vertical mode stirrer (tuner) changes electromagnetic boundaries to ensure a (statistically) homogeneous field distribution.

The electromagnetic reverberation chamber is ideal for performing EMC Tests. Various EMC standards, including MIL-STD 461E, RTCA DO 160D, IEC 61000-21, and ISO 11452-11, allow the use of reverberation chambers for EMC certification testing. This chamber can also be used to evaluate the shielding effectiveness of materials and cables, determine the total radiated power of a DUT, and be used in antenna measurement, the channel modelling of mobile communication, the omnidirectional sensitivity test for mobile devices & the base stations, and more.

Construction and working principle of Electromagnetic reverberation chamber:

The Reverberation Chamber (RC) is an enclosure constructed with conducting walls (Figure 1) of aluminum or galvanized steel. The highly conductive walls create a highly reflective environment within the chamber, where electromagnetic waves bounce off all surfaces with minimal energy loss. Due to the low energy loss during reflection, the chamber can create very high field strength (V/m) inside the chamber with moderate input power for performing radiated immunity testing.

Inside the chamber, because of electromagnetic wave reflection from the walls, the electromagnetic field distribution is strongly inhomogeneous (standing waves). This inhomogeneity can be reduced by changing the electromagnetic boundary of the chamber. Changing the electromagnetic boundary of the chamber will change the standing wave pattern (i.e., will change electromagnetic field distribution inside the chamber), thereby creating a statistically uniform field environment inside the chamber for EMC testing. This is usually done with mode stirrers or tuners that are installed in the chamber.

There are two main techniques to reduce inhomogeneity (i.e., to change the boundary of the chamber to create a statistically uniform field distribution).

• Mode Stirred Chamber: Generating a uniform field environment by using one or more tuners (stirrers) inside the chamber. This reverberation chamber is called a mode-stirred chamber (MSC). The mode stir technique is mostly used in the reverberation chamber (Figure 1&2). 
• Vibrating Intrinsic Reverberation Chamber: Generating a uniform field environment by vibrating the walls of a shielded tent instead of using stirrers (tuners). This chamber is called the vibrating intrinsic reverberation chamber (VIRC).

In this way, the reverberation chamber can create a uniform field with high field strength inside the chamber. This chamber can be used to conduct both EMC emission and immunity testing.

Mode-Stirred Chamber (MSC)

A Mode-Stirred Chamber (MSC) is an enclosure constructed with perfectly conducting walls fitted with tuners (stirrers). A tuner (stirrer) is a rotating paddle with large metallic reflectors that can be moved to various orientations to change the effective boundary of the chamber. This can help achieve a uniform electromagnetic field environment inside the chamber. To efficiently stir the field patterns, the chamber can use two stirrers - horizontal and vertical (Figure 2). The material of the tuner (stirrer) is the same as that of the chamber wall (usually aluminum or galvanized steel). The Lowest Usable Frequency (LUF) of the mode-stirred chamber depends on chamber size and the tuner design. Small chambers have a higher LUF compared to large chambers. 

Figure 2: A mode-stirred chamber (MSC) with a horizontal and vertical stirrer, used in EMC emission testing

The stirrer system is driven by a stepper motor. The motor is controlled by the computer through a motor control unit to ensure the efficient performance of the chamber. The computer is loaded with software that automatically tunes the stirrers and controls the instruments to collect the measurement data of DUT (device under test) and analyze the measured results (Figure 2). 

Vibrating Intrinsic Reverberation Chamber (VIRC)

The VIRC is a tent made from a conductive fabric. In this chamber, instead of using the conventional paddle wheel (i.e., stirrers), the walls of the tent are vibrated/shaken (typically between 5 and 20 Hz), see Figure 3. The vibration of the walls’ alters the chamber's boundary and effectively changes the standing wave pattern, resulting in a more uniform electromagnetic field distribution inside the chamber. The VIRC is the most affordable version of a reverberation chamber (RC). This chamber is easy to mount and can be assembled and disassembled quickly at the customer's location within a matter of hours.  

Figure 3: Vibrating intrinsic reverberation chamber (VIRC)
Benefits of a Reverberation Chamber (RC) over Anechoic Chambers: 

• RC provides a more realistic test environment and can generate a uniform field with very high field strength (V/m) using moderate input power. 
• RC can illuminate equipment under test (EUT) from all angles while radiated immunity test. 
• Low construction and repair costs since NO RF absorbers in the reverberation chamber. This chamber is a low-cost alternative to semi-anechoic chambers for EMC testing. 
• This chamber has good test repeatability in the radiated immunity test.
• RC has shorter testing times
• Also, compared to TEM Cell methods, the reverberation chamber has benefits such as a more realistic test environment, good test repeatability, and an easy-to-achieve high-field strength environment.

Limitations of Reverberation Chambers: 

At low frequencies, the size of the reverberation chamber becomes very large. Hence, the RC may not replace traditional test sites in the lower frequency bands.

Key features of Reverberation chambers:

• Screened environment, meaning no ambient signals
• The Electromagnetic reverberation chambers are available wide frequency range with customization features
• This chamber can Illuminate with all directions and polarisations (immunity test)
• Avail with a large working volume 
• Reverberation Tents are available with flexible and modular designs, and they can be easy to set and disassemble quickly 
• Available as a Turnkey Package – chamber, turntables, Antenna & mast, instrumentation and software
• Provide convenient solutions at a low cost.

Like an anechoic chamber, semi-anechoic chamber, TEM cell, and GTEM cell, the Electromagnetic Reverberation Chamber is another EMC test site/environment for conducting Electromagnetic compatibility (EMC) testing and other electromagnetic investigations.

Click here to view Reverberation Chambers from the leading manufacturers on EMC Directory.