Considering the environmental pollution caused by waste rubber, some measures should be taken to improve the utilization rate of waste rubber. In this study, the effect of Ethylene Propylene Diene Monomer (EPDM) particles in the polyurethane (PU) foams on sound absorption behavior is investigated for improving sound environment within vehicles and reducing the environment pollution. EPDM of different contents and hardness are used as fillers for producing foams with different pore morphologies and sound absorption properties. The results show adds EPDM to foam would produce smaller pores, higher density and bigger air-flow resistivity. Simultaneously, there are better sound absorption properties of the PU foam composites in the medium frequency region and the better value can be obtained at the lower frequency with the content of EPDM increasing. The hardness of EPDM also shows better influence on sound absorption properties, especially in the medium frequency region. It means the foam pore morphologies have influence on sound absorption properties.
The normal modes cannot be extracted even in the Pekeris waveguide when the source-receiver distance is very close. This paper introduces a normal mode extraction method based on a dedispersion transform (DDT) to solve this problem. The method presented here takes advantage of DDT, which is based on the waveguide invariant such that the dispersion associated with all of the normal modes is removed at the same time. After performing DDT on a signal received in the Pekeris waveguide, the waveform of resulting normal modes is very close to the source signal, each with different position and amplitude. Each normal mode can be extracted by determining its position and amplitude parameters by applying particle swarm optimization (PSO). The waveform of the extracted normal mode is simply the waveform of the source signal; the real waveform of the received normal mode can then be recovered by applying dispersion compensation to the source signal. The method presented needs only one receiver and is verified with experimental data