2010_asa_imp_mapping.pdf

Baltimore, Maryland NOISE-CON 2010 2010 April 19-21 High resolution absorption mapping with a pu surface impedance method Emiel Tijs a Microflown Technologies Zevenaar, The Netherlands Hans-Elias de Bree b Microflown Technologies / HAN University Arnhem, The Netherlands Eric Brand?o c LVA/UFSC (Federal University of Santa Catarina) CTC-UFSC Florianopolis-SC, Brazil ABSTRACT The in-situ surface impedance method with pressure-velocity probes is documented in many publications (see e.g. 1-6). 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 used to generate a sound field with a known radiation impedance. The impedance of a small area (a few square centimeters) with a known impedance is scanned with an ultra miniature pu probe very close to the surface. The area is made of steel with a cut-out, and 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 (2D picture) of the damping properties as function of frequency. a tijs@ b deBree@ c eric@lva.ufsc.br 1. INTRODUCTION The properties of many sound absorbing samples are not uniform. Often the material package itself is inconsistent, and adjacent structures influence the overall acoustic behavior. To get a better understanding of the mechanisms that create the absorption it is useful to have information about small material sections instead of one general absorption value of the entire structure. The pu surface impedance method consists of measuring the impedance in situ close to the surface with a combined sound pressure and particle velocity sensor. From the impedance above the material also the material’s surface impedance, r