Performance enhancement of polyurethane foam applied to optical fiber microphones

The application of polyurethane foam to optical fiber microphone sensitization is proposed. In this experiment, the Michelson interference system is used, and polyurethane foam is coated on the optical fiber of the signal arm. By changing the optical fiber material of the signal arm and the reference arm, four sets of comparative experiments are designed to test the sensitivity of the optical microphone. Through a scanning electron microscope (SEM) test and a pore size distribution test, the porous structure and non-closed cell structure characteristics, pore size range, etc., of the polyurethane foam were determined. The average sound absorption coefficient of the polyurethane foam is 0.66 through the sound absorption coefficient and sound insulation test. The sound absorption coefficient of each frequency band is above 0.2; the sound insulation is below 30 dB; and the overall sound insulation performance is poor, which can be regarded as an ideal sound absorption material. The sound-absorbing effect of polyurethane foam is better than that of nylon tight-packed materials in the frequency range of 500–2800 Hz, and it has a significant sensitization effect in this frequency band. In the frequency band above 2800 Hz, the sound-absorbing effect of nylon tight-packed optical fiber is better than that of polyurethane foam, and the optimal combination is determined by lateral comparison as signal arm (nylon tight-packed fiber + polyurethane foam) + reference arm (bare fiber). Finally, with different coating thicknesses as variables, the results show that the optical fiber microphone has the best sound collection effect when the coating thickness of polyurethane foam is 1.5 cm.