Eventos Anais de eventos
DINAME 2017
XVII International Symposium on Dynamic Problems of Mechanics
COUPLED FINITE ELEMENT MODEL FOR AN AFM CANTILEVER BEAM INCLUDING A PIEZOCERAMIC BASE ACTUATOR
Submission Author:
kleber rodrigues , SP
Co-Authors:
kleber rodrigues, Marcelo A. Trindade
Presenter: Marcelo A. Trindade
doi://10.26678/ABCM.DINAME2017.DIN17-0198
Abstract
The modeling and analysis of the Atomic Force Microscope (AFM) cantilever beam is essential to understand and to improve its operation. With approximately 140 µm , the cantilever beam has a probe tip at its free end, otherwise, at the clamped end, a PZT actuator is responsible to excite (depending on the operation mode) and move it in xyz directions. While the probe tip scans the sample surface, a laser beam detects its deflections sending a signal to a photo detector. Several operation modes may be used, depending on the sample characteristics and desired analysis. The tapping mode is a common operation mode, in which the cantilever beam vibrates in a frequency close to its resonance and softly touches the sample surface, while a feedback control system through the piezoceramic actuator is designed to keep the probe tip-sample distance constant. The error between the desired and achieved probe tip-sample distance is evaluated and minimized. Thus, the necessary quasi-static base motion is obtained and used to determine the topology of the sample surface. However, due to the tip-sample nonlinear interaction forces, the feedback control system may become unable to find the exact required base motion and, hence, from the point-of-view of the end user, the topology of the sample surface, observed as a colored pixel in a sample image, is poorly detected. Normally, this occurrence is identified by an abnormal image constructed by the xy plane pixels obtained from the AFM. In this work, the piezoceramic base actuator and the cantilever beam are modeled using the finite element method leading to a coupled system. Material and geometric properties of the cantilever beam and probe tip are obtained from a real AFM device, which enables the model validation. The tip-sample interactions are modeled using Lennard Jones potentials and numerical simulations are performed in order to understand the effects of changing the tip-sample distance, as well as the effects of changing the number of vibration modes of the cantilever beam.
Keywords
Piezoeletric coupling, Nonlinearities, Cantilever beam., Finite Element Model, Atomic Force Microscope
