Design of ParaMPA: a micro-perforated absorber Onursal Onen and Mehmet Caliskan Department of Mechanical Engineering Middle East Technical University 06531 Ankara, Turkey ABSTRACT Perforated absorbers with sub-millimeter size holes can provide high absorption coefficients. Various types and configurations of micro-perforated absorbers are now available commercially for different applications covering a wide area. This paper presents work to develop an effective single layer micro-perforated absorber from the commercial composite material Parabeam® with micro diameter holes drilled on one side. Parabeam® is used as a structural material made from glass fiber and epoxy, constitutes an upper, a lower plate and relatively closely spaced, thick fibers connecting the two plates. The paper outlines the analytical model developed for prediction of normal incidence absorption coefficients and finite element solution for 4 selected samples using commercial software MSC.ACTRAN. Results obtained from analytical model and finite element show good agreement. Different absorption characteristics can be obtained by variation of hole diameter, distance between holes and thickness of the intermediate air layer that includes the fibers, as from nature of perforated absorbers. Based on the developed models, a linear optimization is performed to obtain an efficient absorber configuration. Several different and interesting applications can be possible combining structural and absorption properties of the developed micro-perforated absorber. 1 INTRODUCTION Micro perforated absorbers are basically of metal, plastic or wooden panels (or membranes) with very small (micro size) holes drilled on panels and an air gap between the perforated panel and the wall or backing. Their major advantages lie in the flexibility in design, variety of materials, and high sound absorption coefficients with relatively low thicknesses compared with porous and fibrous absorbers. Micro perforated absorbers have been investigated as clean and health-friendly absorbing materials for almost two decades as an alternative to traditional fibrous and porous absorbers. Micro perforated absorbers are resistant to moist oil and dust and they can be built up from any rigid material available in thin plates. They can be painted or a simple surface finish can be applied. In this particular study, it is aimed to develop an effective single layer micro-perforated absorber from the commercial composite material Parabeam® with micro diameter holes drilled on one side. Parabeam® is special epoxy-cured glass fabric which naturally involves two layers of individual fabric. These layers are connected to each other with fiber groups that are woven inside the individual layers (Figure 1). After a special curing process, the structure turns into a structure with two plates at the bottom and top and an intermediate layer that is composed of thick fibers connecting the two plates through air in-between. Parabeam® shows good mechanical properties and is commonly used in marine industry and thin-walled