Near Field Acoustic Camera
Sound source localization is an important topic in the working field of sound & vibration, from the product development stage to the end off line control of products. The Microflown PU-based Near Field Acoustic Camera is a very fast and accurate system for sound source localization. The sound pressure can be seen as a result of an object making too much noise where the particle velocity is very well suited to localize the cause of why an object is making too much noise. The Near Field Acoustic Camera can be used in real operating conditions and in reverberant conditions, it is no longer needed to have, or create anechoic conditions. Unlike traditional techniques, the array of sensors does not consist only of sound pressure microphones, but of PU sound intensity probes. The Near Field Acoustic Camera measures the particle velocity directly, which means that there are no complex and inaccurate computation steps. Hence, the Microflown Acoustic Camera yields an accurate particle velocity map in the full audible frequency range, while maintaining a dynamic range of over 40 dB. The dynamic range is frequency independent, so for all frequencies the same high dynamic range can be reached.
Acoustic camera software can be equipped with two analysis methods. First method is based on direct measurement of sound pressure, and particle velocity at discrete sensor positions (DSV – Direct Sound field Visualisation). In this method the sound filed is visualized based on point measurements – all data in between measurement points is created as a result of interpolation. The second method is based on the Near Field Acoustic Holography (NAH). The NAH allows for finer interpolation and greater resolution in the obtained sound field visualizations. Furthermore, the NAH method allows for the extension of the measured plane. Thanks to this feature, the sound field can be calculated closer, or further away from the actual measured plane. Both methods can display absolute values for sound pressure, particle velocity, sound intensity, or sound power. The Acoustic Camera array, thanks the presence of two sound field visualisation techniques, can be used either as a planar array, or a scattered array with sensors positioned randomly around the surface of the studied noise source. This feature has significant consequences for how the equipment can be utilised. If you require a quick measurement, then a planar array coupled with the NAH processing will deliver the best results in a short time frame. However if you need a detailed examination of a complex problem in a noisy environment, then positing your sensor close to the measured surface, while using the DSV processing, would yield the best results.
All results, calculated through the Acoustic Camera system, can be visualized as a function of time, as phase information is maintained between all sensors in a given array. This means that non-stationary problems such as engine run-ups can be evaluated reliably in an unparalleled frequency range (20 Hz – 10 kHz). By looking into the time domain, transient noises like squeak & rattles can be easily detected for all frequencies. Furthermore, for applications involving rotating machinery, extensive order analysis functions are available. The Near Field Acoustic Camera introduces a fast, accurate and intuitive solution for this daily issue. Cars, aircrafts, consumer goods all can be tested nowadays with Near Field Acoustic Camera.
- Chapter 8: Near field acoustics (PDF)
Sound Power per RPM and Order
NAH | Near Field Acoustic Holography
- Standard probes
- Sources | VVS
- Velo Software