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SUMMARY:Bistable microstructures under electrostatic loading - Dr Lior Med
 ina\, CUED
DTSTART:20210604T150000Z
DTEND:20210604T160000Z
UID:TALK157858@talks.cam.ac.uk
CONTACT:46601
DESCRIPTION:Bistable micro devices are distinguished by their ability to s
 tay in two different configurations at the same loading. Micro- and nanoel
 ectromechanical systems (MEMS/NEMS) incorporating bistable elements are ad
 vantageous in a variety of applications ranging from electrical and optica
 l switches\, variable capacitors and up to non-volatile memories and logic
 al elements. Behaviour of bistable structures under conventional mechanica
 l loading is a well-established topic in structural mechanics. However\, t
 he presence of nonlinear electrostatic forces is abundant in MEMS/NEMS\, a
 ffecting the stability of the structures\, and leading to new phenomena no
 t encountered in conventional large-scale structures.\nIn the present work
 \, incorporating both theoretical and experimental procedures\, two types 
 of bistable structures are considered\, initially curved clamped beams and
  imperfect circular plates (shallow caps). The beam is described by nonlin
 ear Kirchhoff model\, while the plate is modelled using Föppl von-Kármá
 n\, and Berger theories. The analyses are based on reduced order (RO) mode
 ls resulting from Galerkin’s decomposition with buckling modes of a stra
 ight beam\, or flat plate\, used as the base functions. Criteria of a symm
 etric limit point buckling\, non-symmetric bifurcation and latching are de
 veloped in terms of the geometric parameters of the structures and initial
  pre-stress. The RO model results are validated using nonlinear finite ele
 ments and finite differences analyses carried out in conjunction with the 
 “Riks” arc-length continuation method. The results also indicate that 
 reasonably low voltages can actuate micro plates having realistic dimensio
 ns\, suggesting the suitability of such elements in various applications. 
 Experimental results are found to be consistent with the beams buckling cr
 iteria\, predicted numerically as well as by the RO models. Theoretical an
 d experimental results collectively indicate that the nonlinearity of the 
 electrostatic loading has major influence on the structures behaviour. Bot
 h snap-through instability and symmetry breaking occur at lower voltages a
 nd smaller displacement when compared to the case of a purely “mechanica
 l” load. Moreover\, electrostatic forces result in appearance of additio
 nal pull-in instabilities. The study is also extended to examine the effec
 ts of dynamic actuation on micro beams. Among such actuations stand two in
  particular\, namely dynamic snap-through to a statically inaccessible sta
 ble equilibrium (dubbed as dynamic trapping)\, and a dynamic release effec
 t of a latched beam. For both cases\, corresponding experiments were carri
 ed out\, demonstrating both phenomena.
LOCATION:Online - Teams.  Please email div-c@eng.cam.ac.uk for the link
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