[mems-modsim] Re: dynamic Pull-in

[Eihab]

Hello,

    Dynamic pull-in should indeed be much lower 
than static pull-in. There are various ways to 
define dynamic pull-in, none of which seems 
agreed upon right now. So you will need to 
consider and define what you mean by it 
carefully. Loosely speaking, what we mean by 
dynamic pull-in is: when will a device pull-in 
once we add it's dynamics into consideration. 
Dynamics can change the device response in one of 
two ways: transients due to a sudden disturbance 
or magnification due to a resonant external 
excitation. Transients due to a step-voltage can 
decrease the pull-in voltage by 8%-16% below the 
static pull-in. Resonant external excitations can 
decrease the pull-in voltage by up to 75%. Check 
the first two references for the effect of 
transients only, check the third reference for both effects:

1) S. Krylov and R. Maimon, ``Pull-in dynamics of 
an elastic beam actuated by continuously 
distributed electrostatic force,'' J. Vib. 
Acoust., Vol. 126, pp. 332-–342, 2004.

2) D. Elata and H. Bamberger, ``On the dynamic 
pull-in of electrostatic actuators with multiple 
degrees of freedom and multiple voltage 
sources,”. J. Microelectromech. Systems, Vol. 15, pp. 131--140, 2006.

3) A. H. Nayfeh, M. I. Younis and E. M. 
Abdel-Rahman, ``Dynamic pull-in phenomenon in 
MEMS resonators,” Nonlinear Dynamics, Vol. 48, pp. 153–-163, 2007.

Regards,

Eihab

>Hi all,
>
>I am investigating a capacitive torsional 
>micromirror pull-in voltages in static and dynam 
>conditions. which is subjected to a step bios 
>voltage. Using MATLAB I plotted a 
>(voltage-displacement) diagram and found the 
>static pull-in. but finding the dynamic pull-in 
>it exactly lies on the static pull-in diagram 
>and gives the same pull-in voltage with a
>neglectible difference of about (0.5% lower). In 
>dynamic case I plot damped steady displacements 
>against voltages. It seems that dynamic pull-in 
>should be lower than static pull-in but here the 
>difference is negligible. it would be very kind 
>of you if told me whether I am true and if not 
>where I do have mistakes and if possible 
>introduced me  some references about it.
>
>Sincerely yours,
>Faraz Khatami
>
>
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