Influence of foam structure and service environment on sound absorption characteristics of polyimide foams

The sound absorption properties of open-celled polyimide foams at room temperature and high temperatures were tested by an AWA6122A standing wave tube and a temperature controllable impedance tube, respectively. The sound absorption characteristics of polyimide foams at room temperature were analyzed by applying the rigid end model and Helmholtz resonator model. The effects of material structures (thickness, density and cell size) and material service environments (frequency of sound wave, ambient temperature and mechanical crushing) on the sound absorption coefficients (α) were investigated. The results showed that the models can predict the numerical relationship between the structure parameters and α. At frequencies below 1600 Hz the value of α increased with the increase of foam thickness and foam density and decreased with the increase of cell size. In contrast to untreated polyimide foams, the first resonant frequencies of mechanically crushed polyimide foams moved to higher frequencies and αincreased at higher frequencies. With an increase in temperature, at the same frequencies below 2000 Hz, the αof polyimide foams decreased and the first resonant frequencies trended to move towards higher frequencies. The experimental data indicated that the sound absorption properties of polyimide foams were significantly influenced by foam structures and service environments.