Acoustic impedance of perforated panels covered by membranes

In this paper, acoustical characteristic of a perforated panel with cover membranes is theoretically investigated. Based on the fundamental principle of acoustics, the expressions of reflecting the sound transmission of this construction are derived and the formulas of calculating the specific acoustic impedance are obtained, We also discuss the changes of specific acoustic resistance with some important parameters, such as the frequency, the thickness of air layer and the surface density of the membrane. A good agrecment between predicted results and measured data is illustrated.

Effect of Repainting Process on Atmospheric Corrosion Behavior of Perforated Panel

Steel structures are often painted to protect against corrosion. Repainting is one of the most important factors in maintaining the corrosion protection function of the coating. Various factors affect the life of the coating film, such as the surface preparation, the type of coating, and the number of coats. Surface preparation is important for the life of the coating film. However, appropriate surface treatment is difficult due to the complex shape of perforated panels, and it has been confirmed that corrosion progresses from the machined area. Therefore, appropriate pretreatment of the machined area is important for corrosion prevention. In this study, we investigated the effects of the repainting process on the atmospheric corrosion behavior of perforated panels. To reproduce the repainting process, a number of pretreatments were performed, such as salt spraying, blasting, and zinc phosphate treatment. In the salt spray test after pretreatment and painting, the corrosion progressed in cases with no zinc phosphate treatment and those left untreated for 48 h before painting. In addition, the coating film on the processed area was confirmed to be thin. These results suggested that appropriate pretreatment and sufficient thickness of the coating on the machined area would affect the occurrence of corrosion.

Diffusion and sound absorption properties of the quadratic residue diffuser structure with perforated panel

Acoustic structure study always is the academic research interest. Diffusion ab？sorbing structure（DiflFsorber） has good research value because it has both diflFusion property and sound absorption property. Quadratic residue diffusers（QRD） structure which had good diffusion property was combined with the perforated panel which had good sound absorption property in this study. According to standard AES-4id-2001, the diffusion experiments were carried out to study QRD structure and ones composited with perforated-panels which had1 mm-thickness and perforated percentage of 3%, 5%, 8% respectively. The polar coordinate diagrams of different structure were analyzed to derive the diffusion coefficients. Results showed that the composite structure still had good diffusion performance in the frequency range from100 Hz to 800 Hz. The reflection sound energy of composite structure reduced obviously in the perforated panel resonance frequency range where there was about 2 dB reduction averagely.The study result can provide the reference for the design and development of diifsorber.