Analytical and experimental evaluation of magnetic field effect on sound transmission loss of MR-based smart multi-layered panels

Investigations are made to determine the effect of magnetic field on the Sound Transmission Loss (STL) of smart multilayered panels incorporating MR layers. The acoustic model of a multi-layered panel containing MR fluid is developed analytically using the elastic model with complex modulus for the MR layer. The STL of the panel is then calculated based on the analytical model. Experimental work comprises two major parts: rheology tests and acoustic (STL) measurements. Rheology tests are conducted using a MCR300 rheometer. Characteristics of the MR fluid (loss/storage moduli) are determined in magnetic fields where current varied within 0.2–1.8 Amp. Acoustic measurements are made with a special impedance tube equipped with a magnetic chamber designed and fabricated to apply the field on the MR fluid. Test samples are subjected to two external fields of 145 mT and 340 mT. Analytical results show that increasing the magnetic field from 0.2 A to 1.8 A raises the STL to 30 dB for a wide range of frequencies (f < 3 kHz). However, in some frequencies, especially those above 3 kHz, increasing the field leads to a decline in the STL values. In order to validate the analytical model, theoretical results are compared with those obtained from the experiments. Good agreement is found especially at frequencies below 2500 Hz.