Frequency response of cantilever beams immersed in viscous fluids with applications to the atomic force microscope: Arbitrary mode order

The frequency response of a cantilever beam is well known to depend strongly on the fluid in which it is immersed. In this article, we present a theoretical model for the frequency response of a rectangular cantilever beam immersed in a viscous fluid that enables the flexural and torsional modes of arbitrary order to be calculated. This extends the previous models of Sader and Green [J. Appl. Phys. 84, 64 (1998); 92, 6262 (2002)], which were formulated primarily for the fundamental mode and the next few harmonics, to the general case of arbitrary mode order by accounting for the three-dimensional nature of the flow field around the cantilever beam. Due to its importance in atomic force microscope applications, results for the thermal noise spectrum are presented and the influence of mode order on the frequency response investigated.