MEMS structure with tunable stiffness using the magnetorheological effect

This study presents a novel polymer MEMS structure with Fe
₃
O
₄
-glycerol fill-in. Thus, the concept of magnetorheological effect is exploited to increase the stiffness of polymer MEMS structure by applying a magnetic field. The stiffness enhancement by magnetic field is achieved through the following mechanisms: (1) distribution of the Fe
₃
O
₄
particles in glycerol would change from isotropic to anisotropic, and (2) the attraction between the aligned Fe
₃
O
₄
particles. Note the stiffness of structure could also be reduced by varying the direction of magnetic field. In applications, parylene beams with Fe
₃
O
₄
-glycerol fill-in have been fabricated and tested. Preliminary results show the critical buckling loads of beams increase from 0.6gw to 1.5gw (1% fill-in), 0.78gw to 2.3gw (3.8% fill-in), and 0.78gw to 2.6gw (5 % fill-in) by 5mT magnetic field. The resonant frequency of beam is reduced for 1.2 kHz in as magnetic field applied in x-direction. However, the resonant frequency of beam decreased for 2-3.3% as the magnetic field applied at y-and z-directions.