Ultrasound absorption in magnetic nanofluids

V.V. Sokolov, V.V. Nadvoretskiy
Moscow State University of Instrument Engineering and Computer Science, RU

Keywords: magnetic nanofluid, ultrasound


Mechanisms of ultrasound absorption in magnetic nanofluids at the absence of external magnetic field are theoretically studied in the first part of the paper. The novel magnetodynamic mechanism of ultrasound absorption is introduced – it has relaxation nature and reflects the unique properties of magnetic nanofluids due to magnetic dipole moments of nanoparticles. It is demonstrated that the most probable channels of ultrasound energy dissipation are viscous, thermal and magnetodynamic. Comparison with existing experimental data is carried out and average sizes of nanoparticles as well as characteristic relaxation times are determined. Theoretical research of ultrasound absorption in magnetic nanofluids at the presence of external magnetic field is presented in the second part of the paper. The analytical formula for ultrasound absorption in magnetic nanofluid with prolate ellipsoids aggregates is derived. Experimental results for ultrasound absorption anisotropy in dodecane-based magnetic nanofluid are first demonstrated and they manifest the ultrasound absorption resonance at certain angle between wave vector and external magnetic field direction. Such unique results are explained by presented theory of ultrasound absorption in magnetic nanofluids with prolate ellipsoids aggregates.