Measurement Techniques

Far Field Measurement Technique

The far field measurement technique is as the name states measuring with your sensor far from the source. But how to define the word far in the far field measurement technique. As long as the source to sensor distance is more than a few times the maximum acoustic wavelength the source is considered in the far field. Any sound field is described by two complementary acoustic properties, the scalar value 'sound pressure' and the vector value 'particle velocity'. The Microflown is the only sensor which can physically measure the acoustic particle velocity directly. When three directional Microflown are placed perpendicularly, so one each in X,Y,Z direction, an Acoustic Vector Sensor ( AVS ) is created. Acoustic Vector Sensors are used in the far field to discrimenate sound sources by two main techniques: sound localization and sound mapping. Acoustic vector sensors are unique as they capture both amplitude and phase information. Thus, powerful signal processing routines can be applied detecting a larger number of airborne objects. A larger number of acoustic vector sensors working in a cooperative mode increase the accuracy of finding noise source positions substantially. Comparing to traditional techniques as for example sound pressure based beamforming arrays, AVS far field measurements can measure trully broad banded. Spacing between sensor wich is essential for sound pressure beamforming. The large spacing needed to measure low frequencies is practical situations not applicable. Using AVS independing on spacing between sensors a broad banded frequency range is applicable.