Sound absorption for low frequency noise has received much attention nowadays. Typical low frequency sound absorption structures, such as MPP (Micro-Perforated Plate), CPA (Compound Panel Absorber), BCA (Broadband Compact Absorber), are composed of thin plates.
A thin plate is also a narrow-band low frequency sound absorber. However the sound absorption coefficient of the thin plate close to its first vibrational mode is very small due to the low loss or damping factor of the structure. In some cases the plate vibration can even reduce the sound absorbing properties of a construction. So CHANG Daoqing, LIU Bilong and LI Xiaodong of Key Laboratory of Noise and Vibration Research, Institute of Acoustics, Chinese Academy of Sciences, carried out a series of studies and investigated how to improve the sound absorption coefficient of the thin plate and the MPP plate using the shunt damping technology.
In the study, the researchers investigate the sound absorbing properties of a thin micro-perforated plate (MPP) coated with piezoelectric material with shunt damping technology. They introduce the passive shunting technology to control the sound absorbing properties of the thin plate and micro-perforated plate. First they develop a theoretical model to predict the sound absorption coefficients of a thin plate attached with a piezoelectric patch and electrical circuits. Then they extend the model to analyze the sound absorption for a thin plate with micro perforations and piezoelectric material.
The numerical analysis and the experimental results both show that the sound absorption coefficient of the thin plate can be accurately controlled by tuning the shunting RL circuits to the first natural frequency of the vibrating plate. It is very important in some room acoustic cases that the sound absorption coefficient is within certain limits. The coupling between the electrical resonance and the flexible plate vibration induces another sound absorption peak that increases the sound absorbing bandwidth of the plate. This sound absorption peak can also be controlled to shift between the two maxima of the sound absorbing curve of the thin MPP. That just improves the sound absorbing properties of the thin MPP.
This research result was published on the recently issued journal of Journal of the Acoustical Society of America (Pages: 639–645, Vol. 128, No. 2, August 2010).