Re: [Meep-discuss] Question about setting the current source
Hi Steven, Thanks a lot for helping me find out a big mistake I made - that is, I was confused by the defination of current in MEEP, which is totally different from that in driving circuit. So here comes another question. I notice that in other FDTD softwares such as XFDTD and SEMCAD, source is always defined using driving circuit, sometimes a voltage source, sometimes a current source. Is there a relation or a method to convert between these two ways of defination? I mean the ways in MEEP and other softwares. I've read some books and articles about EM emission but failed to find what I want to know. Best regards, Roy Steven G. Johnson stevenj@gmail.com wrote in message news:8afde0f6-d69c-4e60-89b9-62458b04a...@fftw.org... The current in Meep is added directly as a specified free current J in Maxwell's equations (see Maxwell's equations in the Meep intro). Meep does not simulate the driving force behind this free current, nor does the current have to be placed in a conductor. Specifying a current means that somehow you are shaking a charge at that point (by whatever means, Meep doesn't care) and you want to know the resulting fields. Also, if you are thinking in terms of lumped circuit models, resistances, voltages, capacitances, and so on, then possibly Meep is the wrong tool. Lumped-circuit models are generally only valid in the quasi-static limit where the wavelength is much larger than your circuit elements, and if you are in this limit you don't want to be solving the full Maxwell equations (which are not only overkill, but are also very expensive if your wavelength is very large because your computational cell must normally be much larger than the wavelength), you want to be solving the equations of electrostatics and magnetostatics (Poisson's equation etc.). Steven On Sep 15, 2009, at 9:40 AM, Roy Zhang wrote: I'm trying to set a current source and find there's no parameter to describe the resistance(50 ohm, normally) in the feeding point, which is frequently used in EM emission system. That's quite strange. Can you tell me why? Your earliest reply will be greatly appretiated. ___ meep-discuss mailing list meep-discuss@ab-initio.mit.edu http://ab-initio.mit.edu/cgi-bin/mailman/listinfo/meep-discuss
Re: [Meep-discuss] Question about setting the current source
(I don't see my reply posted, so I'm posting it again. I'm sorry if this mail is duplicated.) Hi Steven, Thanks a lot for helping me find out a big mistake I made - that is, I was confused by the defination of current in MEEP, which is totally different from that in driving circuit. So here comes another question. I notice that in other FDTD softwares such as XFDTD and SEMCAD, source is always defined using driving circuit, sometimes a voltage source, sometimes a current source. Is there a relation or a method to convert between these two ways of defination? I mean the ways in MEEP and other softwares. I've read some books and articles about EM emission but failed to find what I want to know. Best regards, Roy Steven G. Johnson stevenj@gmail.com wrote in message news:8afde0f6-d69c-4e60-89b9-62458b04a...@fftw.org... The current in Meep is added directly as a specified free current J in Maxwell's equations (see Maxwell's equations in the Meep intro). Meep does not simulate the driving force behind this free current, nor does the current have to be placed in a conductor. Specifying a current means that somehow you are shaking a charge at that point (by whatever means, Meep doesn't care) and you want to know the resulting fields. Also, if you are thinking in terms of lumped circuit models, resistances, voltages, capacitances, and so on, then possibly Meep is the wrong tool. Lumped-circuit models are generally only valid in the quasi-static limit where the wavelength is much larger than your circuit elements, and if you are in this limit you don't want to be solving the full Maxwell equations (which are not only overkill, but are also very expensive if your wavelength is very large because your computational cell must normally be much larger than the wavelength), you want to be solving the equations of electrostatics and magnetostatics (Poisson's equation etc.). Steven On Sep 15, 2009, at 9:40 AM, Roy Zhang wrote: I'm trying to set a current source and find there's no parameter to describe the resistance(50 ohm, normally) in the feeding point, which is frequently used in EM emission system. That's quite strange. Can you tell me why? Your earliest reply will be greatly appretiated. ___ meep-discuss mailing list meep-discuss@ab-initio.mit.edu http://ab-initio.mit.edu/cgi-bin/mailman/listinfo/meep-discuss
Re: [Meep-discuss] Question about setting the current source
The current in Meep is added directly as a specified free current J in Maxwell's equations (see Maxwell's equations in the Meep intro). Meep does not simulate the driving force behind this free current, nor does the current have to be placed in a conductor. Specifying a current means that somehow you are shaking a charge at that point (by whatever means, Meep doesn't care) and you want to know the resulting fields. Also, if you are thinking in terms of lumped circuit models, resistances, voltages, capacitances, and so on, then possibly Meep is the wrong tool. Lumped-circuit models are generally only valid in the quasi-static limit where the wavelength is much larger than your circuit elements, and if you are in this limit you don't want to be solving the full Maxwell equations (which are not only overkill, but are also very expensive if your wavelength is very large because your computational cell must normally be much larger than the wavelength), you want to be solving the equations of electrostatics and magnetostatics (Poisson's equation etc.). Steven On Sep 15, 2009, at 9:40 AM, Roy Zhang wrote: I'm trying to set a current source and find there's no parameter to describe the resistance(50 ohm, normally) in the feeding point, which is frequently used in EM emission system. That's quite strange. Can you tell me why? Your earliest reply will be greatly appretiated. ___ meep-discuss mailing list meep-discuss@ab-initio.mit.edu http://ab-initio.mit.edu/cgi-bin/mailman/listinfo/meep-discuss
[Meep-discuss] Question about setting the current source
Hello everyone, I'm trying to set a current source and find there's no parameter to describe the resistance(50 ohm, normally) in the feeding point, which is frequently used in EM emission system. That's quite strange. Can you tell me why? Your earliest reply will be greatly appretiated. Best regard, Roy ___ meep-discuss mailing list meep-discuss@ab-initio.mit.edu http://ab-initio.mit.edu/cgi-bin/mailman/listinfo/meep-discuss
