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Heating inside microwave oven

Posted Dec 23, 2010, 5:27 p.m. EST RF & Microwave Engineering Version 4.0, Version 4.2 3 Replies

Iman Hassaballa
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Dear Sir
I'm trying to model the electromagnetic field distribution inside microwave oven used to heat a small specimen inside a container. I've survyed your example of heating a potato inside the cavity of microwave oven, but I couldn't understand making the mesh vector cubic, quadratic & linear using geometric multigrid. Also, about free mesh, why setting the maximum element size to 0.049/sqrt(dielectric constant)?
Does changing the location of th waveguide have an effect on the equation of the electric field you used? and if so, how can i formulate the suitable port equation for my model.

Thanks a lot,
Awaiting your kindly reply,
Iman Hassaballa
3 Replies Last Post Sep 14, 2011, 11:48 a.m. EDT
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Dec 24, 2010, 4:28 a.m. EST
Hi

if you are in RF or ACDC you must check that you have enough mesh elements inside a wavelength to resolve correctly the field, and as the wavelength changes with the index of refraction, or the dielectric constant, one way is to impos that the maximum mesh size is related to these variables.

In the example then main reason is to have a coarse mesh to be able to solve it on a laptop, but to ensure that is adapted everywhere, hence the dependency on "1/n" wich is proportional to 1/sqrt(dielectric_constant). You could as well use 0.01/sqrt(dielectric constant) if you have enough RAM, but overdoing it just requires more time without a significant increase in correctness of the result

--
Good luck
Ivar
Hi if you are in RF or ACDC you must check that you have enough mesh elements inside a wavelength to resolve correctly the field, and as the wavelength changes with the index of refraction, or the dielectric constant, one way is to impos that the maximum mesh size is related to these variables. In the example then main reason is to have a coarse mesh to be able to solve it on a laptop, but to ensure that is adapted everywhere, hence the dependency on "1/n" wich is proportional to 1/sqrt(dielectric_constant). You could as well use 0.01/sqrt(dielectric constant) if you have enough RAM, but overdoing it just requires more time without a significant increase in correctness of the result -- Good luck Ivar
Iman Hassaballa
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Posted: 1 decade ago Dec 27, 2010, 2:13 p.m. EST
Hi,

Thanks a lot for your reply. I have another question concerning the equation of the waveguide port. As shown in the example of the microwave oven, there is a rectangular waveguide operating in TE10 mode having power of 1KW. I have two concerns: regarding the power, it is diminished to half its value in port tab to be 500W instead. Second, I can't understand the equation of the Eo having the value cos(pi*(y-13.5[cm])/7.8[cm]) in the Z direction. What does 13.5 come from? and if I changed the location of the waveguide, what parameters would change in the equation?

Awaiting your kindly reply,
Iman Hassaballa

Hi, Thanks a lot for your reply. I have another question concerning the equation of the waveguide port. As shown in the example of the microwave oven, there is a rectangular waveguide operating in TE10 mode having power of 1KW. I have two concerns: regarding the power, it is diminished to half its value in port tab to be 500W instead. Second, I can't understand the equation of the Eo having the value cos(pi*(y-13.5[cm])/7.8[cm]) in the Z direction. What does 13.5 come from? and if I changed the location of the waveguide, what parameters would change in the equation? Awaiting your kindly reply, Iman Hassaballa
SOhan
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Posted: 1 decade ago Sep 14, 2011, 11:48 a.m. EDT
The example in model library was meant for running the model on low end laptops. If you have good computer you can use whole Microwave oven and put full rectangular wave guide piece and simply assign TE10 mode on rectangular section cross section. In this case you do not need to E field expression. However, this approach is just good for understanding the interaction of microwave with the materials. For actual simulation, one has to take into account of actual wave-guide port as we see in the domestic microwave oven and use magnetron as coaxial source.

With best,
Sohan Birla,
The example in model library was meant for running the model on low end laptops. If you have good computer you can use whole Microwave oven and put full rectangular wave guide piece and simply assign TE10 mode on rectangular section cross section. In this case you do not need to E field expression. However, this approach is just good for understanding the interaction of microwave with the materials. For actual simulation, one has to take into account of actual wave-guide port as we see in the domestic microwave oven and use magnetron as coaxial source. With best, Sohan Birla,

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