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Electric charge much lower than expected in plate capacitor
Posted 2020年8月17日 GMT-4 07:55 Electromagnetics, MEMS & Nanotechnology, Structural & Acoustics 4 Replies
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Hi there,
the charge I get from global evaluation is much lower than expected on my terminals.
My model is a bending beam, which should touch the bottom of a cavity by electrostatic attraction. I started off with electrostatics, but global evaluation of the terminal charge returns a 1E-9 smaller value.
Preliminary considerations are based on a plate capacitor ( Q = V * C ) with 30 V potential difference, 20 mm^2 plate area, 70 um plate distance and the relative permittivity is 80. This results in a charge of about 6.07 C. But global evaluation of the terminal charge returns 6.06E-9.
However, when I set the terminal constraints to charge, an electric field is not generated at all.
Any idea where I could be mistaken?
Thanks in advance,
Jonas
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Jonas,
the result of your hand calculation is much too high. The Comsol result is in the correct order of magnitude.
Cheers Edgar
-------------------Edgar J. Kaiser
emPhys Physical Technology
www.emphys.com
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Thanks for the quick response!
Can you explain, why that is the case?
Jonas
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Just take the textbook formula for a plate capacitor.
-------------------Edgar J. Kaiser
emPhys Physical Technology
www.emphys.com
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Whenever the NUMBER is right...but the order of magnitude is wrong...check the units.
(In fact, check the units anyway.)