Abstract

In this work the objective was to extract the properties of high viscosity liquids using the vibrational response of the micro cantilevers utilized in the atomic force microscopes (AFM). Such an aim could not be achieved using thermal excitation of the cantilever because the energy given to the cantilever in this method is not enough to allow it to have a recognizable response. Instead we proposed the frequency sweep and step excitation techniques and we proved that they can be use<;l to overcome such a limitation. These two methods are considered as two specific types of the acoustic excitation technique. The application of acoustic excitation to the cantilever in liquid resulted in many spurious peaks in the response, which make it impossible to identify the original cantilever response. Therefore, the first step of this study was to understand the real factors leading to this effect and to improve the design of the fluid cell. After achieving such a goal, we focused on the extraction of the fluid properties by comparing the theoretical analysis with the experimentally obtained results. During our study we implemented the previously established theory for the frequency sweep and we managed to develop the theory for the step excitation technique by ourselves. We proved that although both methods are successful in analysing high viscosity liquids, the step excitation technique was better than the frequency sweep method mainly in having an exact theoretical solution rather than a solution in the form of a series. This enabled us to increase the accuracy of the theoretically obtained results by diminishing the truncation error. In addition, for determination of the fluid properties from the frequency sweep data, three different methods were proposed. These were to determine the properties of the fluids through the whole frequency range using the phase response or the amplitude response or by using both responses at each excitation frequency. Finally, we explained how to extend our work in order to serve for the studies being made on the non-Newtonian fluids and we also mentioned few guidelines to help in focusing such efforts to achieve the best results expected.