Reverberation chamber – creating clarity from chaos
We test sensors and controllers under changeable electromagnetic conditions in our accredited reverberation chamber, which provides chaotic electromagnetic conditions and delivers clear results.
It is not only electric drive systems that make high demands on electromagnetic compatibility testing. The sensors and ECUs that are essential for the megatrend of “automated driving” – and which are nearly always safety-relevant – have to be particularly resistant to electromagnetic interference..
Upper limit of the frequency range
Technical concept of the reverberation chamber
Inhomogeneous conditions in the reverberation chamber
EMC testing involves carrying out conventional interference immunity tests, such as such as shielding effectiveness tests or antenna interference, usually in a homogeneous electromagnetic field. As stable environmental conditions are necessary for these tests, the measuring chamber is fitted with absorber materials on the walls, ceiling and floor to prevent reverberation as much as possible.
But in our reverberation chamber, exactly the opposite takes place. In this chamber, the antenna radiates its electromagnetic field either to fixed positions (tuning mode) or to a rotating “stirrer”, a metal construction that has irregularly shaped metal surfaces. One can think of this stirrer as a kind of mirror ball or whisk that reflects the electromagnetic radiation in all directions. This is then reflected again on the bare metal walls, the ceiling and on the floor of the measuring cabin and in this way forms a completely inhomogeneous electromagnetic field.
The reverberation chamber saves time and money
This maximum reflection of the interference waves makes good sense. Statistical methods have shown that a completely inhomogeneous field has almost the same effects on the test object as homogeneous interference fields that act on it from three sides. Therefore, with just one measurement in our reverberation chamber, we can generate practically the same results as three consecutive conventional antenna measurements. This saves a great deal of set-up and testing time, especially for interference immunity tests in which the OEMs specify test configurations from several orthogonal directions.
In principle, measurements can be made using a rotating stirrer or one that is moved by a stepper motor. However, based on the evaluation of previous measurement projects, we recommend using the rotating version in order to save time. If our engineers discover any abnormalities in the measurement results, additional measurements in stepping mode are required.
The reverberation chamber has a further advantage: its special design without an absorber means that the signal amplifiers require much less power to generate the same interference field strength than amplifiers used in other measuring chambers. Such reduced-power amplifiers with an output of 100 to 200 watts are much cheaper.
High level of flexibility in selecting the test
A comparison between the measurement results for antenna radiation in conventional chambers for measuring shielding effectiveness and the reverberation chamber showed that the results have a good correlation and are therefore comparable. This offers you, as our customer, two practically equivalent measurement alternatives, depending on which method of measurement your OEM customers define in their specifications. In the reverberation chamber, immunity to disturbances is measured in accordance with the well-known and proven standard ISO 11452-11.
The reverberation chamber also offers a high level of flexibility with regard to the devices under test (DUT). It can be used to test the EMC of cameras, other sensors, ECUs and combinations of these components without any problems. The reverberation chamber can accommodate test specimens up to the size of an electric motor plus an inverter. As the size of the device under test in relation to the size of the test chamber has an influence on the measurement results, we always take the influence of these variables into account for each measurement by applying a loading factor.
Service supports measurement methods
As usual, we offer an attractive service package for the reverberation chamber in addition to the actual measurements. Even before the measurements themselves are carried out, our continuous support begins with a preliminary consultation, which includes preparatory work and various specifications that contribute to a successful completion of the tests and measurements. Once you have instructed us on the characteristics of your test specimen, we will then carry out the testing process independently. On completion of the test, we will discuss the results with you in detail and, if required, we will support you in the further EMC optimisation of your components and systems.
Throughout the entire project, one of our permanently assigned engineers will accompany you – as is always the case at Mooser – and will be ready to answer all your questions and address your concerns. This person has undergone extensive in-house training and will also carry out the EMC tests in the reverberation chamber. After all, the measuring procedures themselves, the setting of the parameters and the assessment and evaluation of the results are very complex and demanding in this extraordinary testing environment. As one of only very few EMC service providers in Europe, we offer not only a reverberation chamber, but also a comprehensive service at the same time
Frequently asked Questions
In a conventional measuring chamber for carrying out shielding effectiveness tests, a constant electromagnetic field and thick absorber layers on the surfaces of the chamber ensure stable and homogeneous electromagnetic conditions. By contrast, in a reverberation chamber, electromagnetic chaos prevails.
In this type of chamber, a metal construction with irregularly shaped metal surfaces emits an electromagnetic field onto an element called a “stirrer”, which can be either fixed or rotating. This causes the electromagnetic radiation to be reflected in all directions, thus creating a completely inhomogeneous electromagnetic field.
If measurements from different directions are necessary, the reverberation chamber requires just one measuring process to deliver results that are comparable to several conventional antenna measurements from different directions. This saves a great deal of set-up and testing time.
“Reverberation” is a term in acoustics that describes sound that persists or echoes for a while due to reflection from surfaces even after the sound source itself has stopped. The multiple reflections from the stirrers, walls and floor in the reverberation chamber have the effect of creating an inhomogeneous electromagnetic field. DELETE – The German technical term for the reverberation chamber is Modenverwirbelungskammer.
Only two reverberation chambers are accredited in Germany. The results of measurements in these chambers are, of course, valid and reliable. One of these two accredited reverberation chambers can be found at Mooser in Ludwigsburg.
The components that are most often examined include cameras, other sensors, ECUs and combinations of these components The components that are most often examined include cameras, other sensors, ECUs and combinations of these components. The reverberation chamber is ideally suited for carrying out EMC testing on the components and systems used for automated driving. The special measuring chamber can accommodate test objects up to the size of an electric motor plus an inverter.
