High-resolution force sensor based on morphology dependent optical resonances of polymeric spheres

Performance characteristics of a force sensor concept based on the morphology dependent resonance (MDR) shifts of micro-optical resonators have been investigated. Previous experimental studies have indicated that microsphere sensors with diameters ranging between 30 and 950 mu m may have force resolutions reaching 10(-5) N [T. Ioppolo et al., Appl. Opt. 47, 3009 (2008)]. In the present, we carry out a systematic analysis and experiments to investigate the sensitivity, resolution, and bandwidth limits of MDR-based force sensors. Expressions for MDR shifts due to applied force in the polar direction are obtained for microspheres of various dielectric materials in the diameter range of 300-950 mu m. The analyses are compared with experimental results for polymethylmethacrylate and polydimethylsyloxane (PDMS) microsphere sensors. The results show that the strain effect on MDR shifts is dominant over that of mechanical stress. It also indicates that force sensitivities of the order of a 1 pN are feasible using hollow PDMS spheres. The sensor bandwidths range between 1 kHz and 1 MHz, depending on the sphere material. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3054338]