A novel technique of microforce sensing and loading

Abstract

With remarkable reduction of the characteristic scales in researches of materials and structures, microforce sensing and loading is becoming an important and challenging issue in mechanical tests. On the one hand, miniaturization of the tested objects leads to serious problems of manipulating, grasping, and loading. On the other hand, the smaller a sample is, the smaller the forces have to be measured. Up to now, it is still a difficult task to measure such small forces. In this paper, a newly developed probe-type microforce sensor is described, which can be combined with a micromanipulator to perform microforce sensing and loading. A strategy call ladder or hierarchy force sensing and loading method is further suggested, by which the above combined system is used as a platform to calibrate other cantilever probes with finer resolutions, which may form a sequence of probe-type sequence microforce sensors to cover a broad range of forces to be measured from mN down to nN and even lower provided that proper spring constants are selected for these force sensors. In the preliminary studies, two probe-type microforce sensors are successfully developed with force sensing sensitivities of 705.4 nN/mV and 37.3 nN/mV, respectively. They are applied to calibrate atomic force microscope (AFM) cantilevers with various spring constants, and then one of these calibrated cantilevers is used as a more sensitive force sensor to calibrate other even softer cantilevers. Tests of real microscale objects, a single silk filament and a papilla on the lotus leaf surface, demonstrate excellent performance of the developed sensors.