High-resolution absorption mapping with a pu surface impedance method.

Microflown Technologies, 6826 CC Arnhem, Arnhem, The Netherlands, .
The Journal of the Acoustical Society of America (Impact Factor: 1.5). 03/2010; 127(3):2003. DOI: 10.1121/1.3385194
Source: PubMed


The in situ method to measure the surface impedance with a pu probe documented is published in many publications. The method is based on the measurement of sound pressure (p) and particle velocity (u) close to an acoustic absorbing material. A loudspeaker at a defined distance is applied to generate a sound field with a known radiation impedance. The impedance of a small area (a few square cm(2)) with a known impedance is scanned with an ultraminiature pu probe very close to the surface. The area is made of steel with a cut-out, behind this a material with a known impedance is placed. In this paper the method is explained, the spatial accuracy of the measurement is examined, and a visualization technique is presented with a display of the spatial distribution (two dimensional picture) of the damping properties as function of frequency. Finally the high-resolution measurements are combined and compared with a method that covers a larger surface area.

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    ABSTRACT: The vibro-acoustic load during launch takes a big toll on space structures. In order to simulate the dynamic loading as encountered during launch, both shaker facilities and high sound pressure reverberant rooms are used. Acoustic particle velocity sensors offer interesting new opportunities, for measuring both the applied noise field as well as the structural responses. Single particle velocity sensors in a so-called U probe can be used for very near field vibration measurements. When they are combined with a microphone in a PU probe the full sound vector can be measured. The novel perspectives of using PU probes for reverberant room testing comprise: The classical control of the noise field and the measurement of the sound pressure level, and of acoustic quantities like the reverberation time may be complemented by making reference to the total acoustic energy. Arrays of U probes can be used to measure contactless surface vibrations at multiple measurement points simultaneously as an alternative to accelerometers or laser vibrometers. PU probes can be used to measure local acoustic quantities near the structure like sound radiation, acoustic impedance and energy. 3D sound fields around structures can be visualized. The degree of diffusion in a reverberation room can be better characterized. In this paper, the first experience with practical implementation and the results of recent measurements using the PU probe will be presented.
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