Dynamical sensitivity of a three-layer microsystem under the influence of the Casimir force in a ferrofluid

Abstract

Here, we investigated the actuation dynamics of a microsystem in the presence of Casimir and dissipative hydrodynamic forces having a ferrofluid as the intervening layer between components. It is shown that the Casimir force decreases as the concentration of the Fe₃O₄ nanoparticles of 10 nm diameter in the ferrofluid increases. In addition, changes in nanoparticle concentration leads to changes of the viscosity of the ferrofluid resulting to changes of the hydrodynamic forces. The latter is reflected by changes in the area of the velocity-position phase portraits. In the short distance limit, the autonomous microsystem with optical properties closer to metals shows a limited motion area in the phase space, which is increased as the concentration of nanoparticles decreases, leading also to an increased possibility for stiction and malfunction. By applying an external driven force, the microsystem reveals stable oscillation over large distances and, by increasing this force, the range of stable oscillation and the velocity of the moving component grows. However, by decreasing the driving frequency, the range of stable oscillation expands despite that the moving plate does not achieve high velocity. Finally, the driven microsystem can effectively sustain stable oscillation over an extended period and avoid stiction by using materials for components of low conductivity and/or using high concentration of nanoparticles. This is happening because in both cases the attractive Casmir force, which favors stiction, decreases.