Study the effect of thickness on the natural and resonant frequencies of polyurethane foams

In this paper, the effects of thickness variations on the natural and resonant frequencies of polyurethane foams have been studied. The governing Biot’s equations are solved using an analytical method, and the natural and resonant frequencies are presented alongside the variations in solid, fluid displacement, and pressure. By selecting the characteristics of three different foam samples from various references, the variations in the frequency characteristics of the foam with changes in thickness are investigated over a broad range, and specific results are provided. Based on the presented results, it is observed that as thickness increases, the solid and fluid natural frequencies, along with the resonant frequencies, shift to lower frequencies. Interestingly, the values of the natural frequencies at lower thicknesses are repeated at higher thicknesses, maintaining their values and nature while following a specific repetition rule.