Microperforation and microjet noise——The special contributions of Prof. Dah-You MAA in acoustics

This paper is concerned with two main contributions of Prof.Dah-You Maa in acoustics,namely,the microperforation and microjet noise.Microperforation has been proposed by Prof.Dah-You Maa,and are in common use in sound absorption and noise control.Micropeforated panels can be manufactured as non-fibrous broadband sound absorptive materials,which are often applied to general building acoustics and noise control engineering,in particular under the extreme conditions,for example,at high temperature and in the case of high speed flow.High sound absorption coefficients can be achieved in multiple ranges of low-frequencies,when acoustic cavities lie behind the panels.In jet noise control,the noise radiation can generally be reduced by 20~60 dBA in the audible frequency range by using micropores at the outlet of an air or steam jet nozzle.The fundamental theory and applied aspects provide the basis for improving acoustic techniques for jet noise control.