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Dielectrophoresis simulations or gradient of electric field

Posted 6 feb 2012, 00:48 GMT-5 Microfluidics Version 3.5a 5 Replies

Andy Liu
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Hi,

I am doing dielectrophoresis simulations using simulations. Basically I use AC/DC module -conductive medium DC to get the electric field distribution. But I face some problems geting gradient of electric field. I tried some methods of previous threads but was not successful.

I have some questions.

1. If I want to extract gradient of electric field in x direction, I define d(Ex_dc^2,x) in global expressions. Is that right ?
2. The bias is a AC voltage but I only know how to apply a DC voltage. Anyone knowing what module should I use then. I simplify the problems by doing DC simulation.

Anyone doing this kind of simulations? We can discuss together... Thanks.
5 Replies Last Post 3 giu 2015, 22:36 GMT-4
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago 6 feb 2012, 01:26 GMT-5
Hi

in EC or electric currrent you solve for "V" the voltage, and find the electric field (Ex,Ey,Ez)=-grad(V) so you are already taking a first derivative of V. now if you want to derivative of the field Ex you are asking for the 2nd derivative of a dependent variable, this is only possible if you are using a 2nd order (or preferrably higher) shape function, and that your mesh is of sufficient quality (symmetric) to allow such high order shape functions

Whn you apply AC currents, you should consider the frquency domain solver, this does a development of the ime derivativeinto the harmonic representation with omega = 2*pi*f, you define the amplitude and the phase ans well as the frequency in latter in the solver section (or frequency range for a scan) and off you go.

Check the doc and the examples in the model library

--
Good luck
Ivar
Hi in EC or electric currrent you solve for "V" the voltage, and find the electric field (Ex,Ey,Ez)=-grad(V) so you are already taking a first derivative of V. now if you want to derivative of the field Ex you are asking for the 2nd derivative of a dependent variable, this is only possible if you are using a 2nd order (or preferrably higher) shape function, and that your mesh is of sufficient quality (symmetric) to allow such high order shape functions Whn you apply AC currents, you should consider the frquency domain solver, this does a development of the ime derivativeinto the harmonic representation with omega = 2*pi*f, you define the amplitude and the phase ans well as the frequency in latter in the solver section (or frequency range for a scan) and off you go. Check the doc and the examples in the model library -- Good luck Ivar
Andy Liu
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Posted: 1 decade ago 6 feb 2012, 01:51 GMT-5
Hi, Ivar,

Thanks for your reply.

I saw the pre-defined expression for electric field, norm: normE_dc; x component: Ex_dc; y component: Ey_dc;
Now I want to get grad(E^2) in the x direction. I write it as d(Ex_dc^2,x) but it still give zero value...

I checked some previous thread but can't figure it out...
www.comsol.com/community/forums/general/thread/4711/
www.comsol.com/community/forums/4-1/thread/17498/

For AC simulations, all I need to do is to change the solver parameter ?
Hi, Ivar, Thanks for your reply. I saw the pre-defined expression for electric field, norm: normE_dc; x component: Ex_dc; y component: Ey_dc; Now I want to get grad(E^2) in the x direction. I write it as d(Ex_dc^2,x) but it still give zero value... I checked some previous thread but can't figure it out... http://www.comsol.com/community/forums/general/thread/4711/ http://www.comsol.com/community/forums/4-1/thread/17498/ For AC simulations, all I need to do is to change the solver parameter ?
Andy Liu
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Posted: 1 decade ago 6 feb 2012, 03:13 GMT-5
I think there should be something wrong with my plots. How could I plot the global expression at each point and give a surface plots ?
I think there should be something wrong with my plots. How could I plot the global expression at each point and give a surface plots ?
Abid Iqbal
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Posted: 1 decade ago 26 nov 2012, 03:34 GMT-5
I also want to do same king of simulation but i am not able to get exact solution? can u tell me how can i start to simulate the AC Dielectrophoresis?
I also want to do same king of simulation but i am not able to get exact solution? can u tell me how can i start to simulate the AC Dielectrophoresis?
Allen Shalom
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Posted: 9 years ago 3 giu 2015, 22:36 GMT-4
Dear Sir,

I did my doctorate on dielectrophoresis in 1988 and my master's on magnetic separation.
I am not answering your request directly but I thought it could be useful to note that it's easier to plot magnetic fields using fine iron powder.

Dr. Allen Shalom
Dear Sir, I did my doctorate on dielectrophoresis in 1988 and my master's on magnetic separation. I am not answering your request directly but I thought it could be useful to note that it's easier to plot magnetic fields using fine iron powder. Dr. Allen Shalom

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