Investigating the Use of Interference Fringe of Spherical Film for Detecting Micro-force.

Measuring Nano-Newton force is a difficult matter in biomedical domain and industrial field. A novel type of spherical film, with about 700 nm thickness and around 50 mm diameter, was used as sensing element to detect the nano-Newton (nN) level force. The spherical film is a kind of water-soluble film, and an interference fringe will be presented on its surface. Distortions are observed when nN-level particles are placed on the bottom of WSSF (water-soluble spherical film), which results in a width change of the interference fringe. From the variable of interference fringe, we can obtain the gravity of the particle or applied force. The relation among the nN-level force, the diameter of spherical film, and the change of interference fringe is investigated, and the least square method is utilized to obtain the equation among upon parameters. The error analysis of experimental and computational data showed that when controlling the force in the range of 65–1105 nN, the detecting error was in the range of −5.7%–6.2%.