Decay time control of mass diffusion in a transient grating using a fringe-tunable electrothermal Fresnel mirror

This paper reports a microelectromechanical systems (MEMS) mirror with electrothermal polymer actuators for the diffusion sensor. A compact and high-speed diffusion sensor is desirable for point-of-care testing because of its real-time monitorability and portability, and because diffusion coefficient reflects the abnormality of biological samples such as proteins. Herein, a fringe-tunable electrothermal Fresnel mirror (FEFM) is analyzed to maximize the mirror's angular shift while maintaining the repeatability of the actuator drive. The thermal-response-speed and temperature-distribution characteristics were examined. The proposed fabrication process contributed toward improving the yield and quality of the device. The diffusion coefficient was successfully measured using the fabricated FEFM. Moreover, by making the fringe spacing 7.1 times narrower than its initial value, the decay time of diffracted light became 50 times faster than that of the wider fringe, thereby showing reasonable agreement with theory. The results validated the development of a compact, high-speed diffusion sensor that realizes control of the decay time of the mass diffusion in a transient grating using an FEFM.