Beamforming

Beamforming is a method for determining the position of sources of wave fields (for example, sound fields ). Corresponding devices are also called acoustic camera, microphone array or acoustic antenna. In acoustics, beamforming is most often used when measuring near the object to be measured, or only with great effort are possible, such as when landing aircraft or passing trains. Therefore, in the relevant literature and the very term "acoustic telescope " is introduced. The microphone assembly is then usually on a level surface. Usually annular cross-shaped, linear, spiral or quasi- randomly distributed arrays are used.

The term beamforming network ( BFN) antennas used in the electromagnetic radiation is in contrast, for a circuit which adjusts the radiation profile of the antenna to a desired geometric shaped contour ( see applications).

Principle of measurement

The measurement principle is explained using the example of acoustic arrays here. It consists in that the microphone array is focused to the different measurement points on the measurement object. This is done by one of the running time from the measurement point to the respective microphone corresponding time shift of the signals detected by this microphone. The time- corrected signals from all microphones are summed, resulting in a the particular measuring point yields assigned time signal. The sound sources at different positions is attenuated while because their signals are not completely corrected time and overlap partially destructive. In contrast, by the respective measuring point ( focal point ) is reinforced radiated sound. The quality of the beamformer is often increased by using more elaborate, digital filters.

The frequency range of beamforming array is downward limited by the array size, the larger the array, the lower its cut-off frequency. The upper limit of the frequency range is carried out by increasing the occurrence of apparent sound sources ( aliasing ). This is particularly seen in regularly spaced microphones and lead to misinterpretations. The cut-off frequency above which this phenomena occurs is the higher, the smaller the distance of the microphones relative to one another.

Most of the importance of the sound sources is shown in a color code, and superimposed on a conventional video image of the measuring object. In this way, the positions of the main sound sources can be easily detected. And frequency selective representations are possible.

Applications

• Sound source localization and assessment
• Hide from noise sources

• Beamforming with radio waves