Regensburg 2007 – wissenschaftliches Programm

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DY: Fachverband Dynamik und Statistische Physik

DY 16: Brownian motion and transport I

DY 16.3: Vortrag

Dienstag, 27. März 2007, 15:00–15:15, H3

Experimental characterization of a Brownian Motor based on Ferrofluids — •Jens Nawitzki and Achim Kittel — Institute of Physics, Energy and Semiconductor Research Laboratory, Carl von Ossietzky University of Oldenburg, 26111 Oldenburg, Germany

We characterize the dynamics of an experimental Brownian Motor. The Brownian Motor consists of a hollow plastic sphere filled with a ferrofluid. The orientation dynamics of the ferrofluids ferromagnetic particles ist strongly influenced by thermal fluctuations. The sphere is suspended on a thin filament in the center of two crossed pairs of Helmholtz coils. One of the pair forms a static magnetic field in x direction and the other on applies a time dependent magnetic field in y direction. The time dependent field consists of a harmonic oscillation with a higher harmonic of the basic frequency. The magnetic fields act as potential for the orientation of the ferromagnetic particles. Directed motion of the ferromagnetic particles manifests as a rotation around the z Axis. Through the viscous coupling of the particles with the ferrofluids carrier liquid and their combined effective action results in a macroscopic torque of the plastic sphere. We measure the torque by means of applying a countertorque to the sphere's suspension. The control parameters for the measurements are the amplitude, frequency and phase of the time dependent and the magnitude of the static magnetic field. The measurements are done with varying viscosities of the ferrofluid. We observe the dynamical behavior of the sphere under variation of the control parameters and compare the results with the theoretical expectations.