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Acoustic particle velocity sensors can be an alternative sensor category for end of line testing next to microphones, accelerometers or scanning laser vibrometers. As any other category of transducers, particle velocity sensors have their specific features. The acoustic particle velocity field is far less susceptible to background noise than the sound pressure field, allowing acoustic testing to be carried out in a manufacturing environment with significant background noise levels [2]. Close to a vibrating surface, acoustic particle velocity is a good estimate of the normal structural velocity, allowing non contact vibration measurements [4]. The results of some case studies will be summarized.

In [1] is shown that very close (distance smaller than L/2Π) to a vibrating and flat structure with typical size L, the normal particle velocity and the (normal) structural velocity coincide. It is shown that with an acoustic particle velocity sensor the normal acoustic particle velocity close to the surface can be measured and that this velocity coincides with the surface velocity that is measured with a laser vibrometer or accelerometer. In [1] it is also shown that in the very near field (contrary to the behavior in the near field) the particle velocity level doesn't depend upon frequency. Furthermore, in the very near field, there is a linear relationship between the particle velocity as measured and the structural velocity to be measured.