Dynamic analysis of spherical film as sensing element for detecting micro-force

In order to realize the precise measurement of a micro-force in the biomedical domain and industrial fields, a type of spherical film, of about 700 nm thickness and 50 mm diameter, was used as sensing element to detect a nano-Newton (nN) level force. Distortions were observed when nN-level particles were placed on the spherical film or such level forces were applied on the spherical film. From the deformation of spherical film, we can obtain the gravity of the particle or applied force. A dynamic model of the spherical film was constructed using the ANSYS software. Adopting the orthogonal experimental method, we designed effective experimental parameters for numerical calculation and mainly focused on the relations among nN-level force, thickness and diameter of spherical film, and deformation parameters. Then a fitting formula describing the relationship between deformation, the thickness and diameter of the spherical film, and the loaded force was obtained from the experimental data using the least square algorithm. The error analysis of experimental and computational data showed that when controlling the force in the range of 20–160 nN, the detecting error was less than ±3.2%.