Low frequency in situ metrology of absorption and dispersion of sound absorbing porous materials based on high power ultrasonic non-linearly demodulated waves |
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Authors: | Bernard Castagné de |
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Affiliation: | Laboratoire d’acoustique, UMR CNRS 6613, Université du Maine, avenue Olivier Messiaen, 72085 Le Mans Cedex 9, France |
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Abstract: | The present work is related to acoustic in situ free-field measurements of sound absorption in porous materials, such as cellular plastic foams, glass-wool or recycled felt materials. The emphasis is given towards fine metrology of absorption in view of potential industrial applications. A powerful ultrasonic array working at 40 kHz is used. It enables to measure absorption acoustical data down to 100 Hz due to the exploitation of the non-linear ultrasonic demodulation phenomenon in air. Fine measurements of acoustic absorption are compared to numerical predictions based on the “equivalent-fluid” model (when the squeleton frame is motionless), and to some measurements performed on a Brüel and Kjaer impedance tube. Dispersion curves are also measured and compared to the numerical predictions for some automotive felt materials which are compressed at various ratios. Data obtained with a dedicated portable instrument are also discussed for the same type of materials and configurations. |
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Keywords: | Acoustic in situ measurements Portable instrumentation Ultrasonic demodulation in air Non-linear high power ultrasonics Absorption coefficient Dispersion &ldquo Equivalent fluid&rdquo model Porous materials Automotive felts Compressed sound absorbing materials Noise reduction |
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