A study on the characteristic behavior of mass inclusions added to a poro-elastic layer

Heterogeneous (HG) blankets consist of a layer of poro-elastic media with small embedded masses that replicate the behavior of a distributed mass-spring-damper system. The concept of an HG blanket used to control the sound transmission through an aircraft double-panel system has already been developed and cited in the present literature. However, deficiencies in methodical property control exist; therefore, the prime objective of this research is to provide a simple method to predict and control material properties of the heterogeneous blankets through alteration of mass and stiffness parameters. Mass inclusion size, shape, and placement were varied. If optimized heterogeneous (HG) blankets targeted to specific applications are to be successfully developed, control of these parameters is necessary.This research offers a detailed analysis of the behavior of the mass inclusions, highlighting controlled stiffness variation of the mass-spring-damper systems inside the HG blanket. Characteristic parameters of the HG blanket like the “footprint,” “effective area,” and the “mass interaction distance” are defined and confirmed through mathematical calculations and experimental results. A novel, empirical approach to predict the natural frequency of different mass shapes embedded in porous media was derived and experimentally verified for many different types of porous media, including melamine foam, polyurethane, and polyamide. A maximum error of 8% existed for all the predictions made in this document.