S M T L Surface Mechanics & Tribology Laboratory 3 rd Generation Device Design D S S S D D Driving/sensing setup allows for separate driving and sensing signal comb drives However, amplitude of the outer edge of the comb drive is limited by the comb fingers touching – the spoke of the comb drive bends and reduces the spacing between the fingers The ratio of the rotation of the specimen at the ring to the outer edge of the comb drive ranges from 1:2 to 1:4, depending on the device 60  m, 2 beam Device Multi-Axial Fatigue Device (  m   m   m) Theoretical Resonance Frequency (kHz) Experimental Resonance Frequency (kHz) 30x4x x4x x4x x4x x4x x4x

S M T L Surface Mechanics & Tribology Laboratory 3 rd Generation Maximum Stress These values for stress are based on the maximum deflection obtainable in vacuum – estimating an amplitude of 2  m at the end of the specimen The devices were run for >10 10 cycles and no fatigue damage was observed To increase the maximum stress and produce failure, an notch was introduced by FIB The stress concentration factor ranged from Stresses ranged from ~ 1 to 4 GPa Area notched with FIB The introduction of the notch reduced the stiffness and therefore resonance frequency of the device MUMPS 48 Chip  m Beam Device Multi-Axial Fatigue Device (  m   m   m) Est. Max von Mises Equivalent Stress (GPa) 30x4x x4x x4x x4x x4x x4x20.51 Multi-Axial Fatigue Device (  m   m   m) Unnotched (kHz) Notched (kHz) 30x4x252.30~46 40x4x245.42~40 50x4x238.83~29 60x4x231.24~29 Experimental Resonance Frequency

S M T L Surface Mechanics & Tribology Laboratory 4 th Generation Device Design Design now has a stiffer comb drive-ring structure The ratio of the rotation of the specimen at the ring to the outer edge of the comb drive is a little less than 1 More linear amplitude of comb drive along the spoke Allows for a 2 mm displacement at the end of the specimen beam Can therefore reach stress levels high enough to cause failure Multi-Axial Fatigue Device (  m   m   m) Theoretical Resonance Frequency (kHz) Experimental Resonance Frequency (kHz) 30x4x x4x x4x x4x x5x