The radiation efficiency is defined as a ratio of radiated sound power to the correlative vibration velocity of a structure. The radiation efficiency of a plate is a significant indicator in noise and vibration control.

The reason for that is it not only gives information on the radiated sound power from the structure, but also on the response of a plate due to random excitation.

Much theoretical work has been devoted to the prediction of the radiation efficiency of the plate, but the influence of structural damping has not been taking into account in these research.

It has been reported during tests that a viscoelastic damping layer attached to a plate could increase the radiation efficiency significantly. This phenomenon is often stated to be due to that the damping treatment reduces the plate response significantly, while having less effect on the radiated sound.

This phenomenon, however, has not been well explained so far.

Researchers from the Institute of Acoustics of the Chinese Academy of Sciences have recently studied the radiation efficiency of damped plates. Numerical results show that the radiation efficiency of a plate is much influenced by structural damping below the critical frequency.

Modifications of the formulas given by Cremer for the infinite plate and Leppington for the finite rectangular plate are proposed to include the structural loss factor for frequencies below the critical frequency.

The results demonstrate that the radiation efficiency is influenced significantly by the structural loss factor for heavily damped plates.

When the structural loss factor of the plate varies from 5% to 10%, the increased radiation efficiency could reach 4 to 6 dB.

The results imply that the damping treatment to the plate could increase the radiation efficiency significantly. It also explain the phenomenon that the damping treatment may effectively reduce the response of a plate while it has less effect on the sound radiation of the plate.

Funding for the research came from the State Key Development Program for Basic Research of China (973 Program) Grant 2012CB720204 and NSFC Grant 11374326.

References:

KOU Yiwei, LIU Bilong, and TIAN Jing. Radiation Efficiency of Damped Plates (L). The Journal of the Acoustical Society of America (Vol. 137, No. 2, pp. 1032-1035, February 2015). DOI: 10.1121/1.4906186

Contact:

LIU Bilong

Key Laboratory of Noise and Vibration Research, Institute of Acoustics, Chinese Academy of Sciences, 100190 Beijing, China

Email: liubl@mail.ioa.ac.cn