Re: [Meep-discuss] why the energy spectrum radiated by a point source doesn't match with the spectrum of source itself?
On Apr 22, 2014, at 10:01 AM, Ehsan Saei e.s...@hotmail.com wrote: I simulated a point source which is located in free-space (air ) and tried to compute the power radiated by the source and travels through a cubic that surrounds the source. After plotting the data I have noticed that the power has a frequency center different from that I have used for the source. Regardless of whether you use an exact gaussian source or not, the radiated power spectrum is never the same as the power spectrum of the source (except in 1d vacuum), because it gets multiplied by the local density of states (which in 3d goes as frequency squared). This has nothing to do with Meep, it is an intrinsic fact of wave equations. See: http://ab-initio.mit.edu/wiki/index.php/Meep_FAQ#How_does_the_current_amplitude_relate_to_the_resulting_field_amplitude.3F___ meep-discuss mailing list meep-discuss@ab-initio.mit.edu http://ab-initio.mit.edu/cgi-bin/mailman/listinfo/meep-discuss
Re: [Meep-discuss] why the energy spectrum radiated by a point source doesn't match with the spectrum of source itself?
May it be attributed to that the radiated field is a derivative of the current, so that high-frequency components are enhanced compared to the lower frequency ones? Or is it a more complicated deviation? Regards, Filip 2014-04-22 16:01 GMT+02:00, Ehsan Saei e.s...@hotmail.com: Dear Steven and MEEP users, I simulated a point source which is located in free-space (air ) and tried to compute the power radiated by the source and travels through a cubic that surrounds the source. After plotting the data I have noticed that the power has a frequency center different from that I have used for the source. Any idea about this behavior? Thanks in advance, Ehsan ___ meep-discuss mailing list meep-discuss@ab-initio.mit.edu http://ab-initio.mit.edu/cgi-bin/mailman/listinfo/meep-discuss
Re: [Meep-discuss] why the energy spectrum radiated by a point source doesn't match with the spectrum of source itself?
This appears exactly as the result of the said effect. The good point is that the gaussian source shape is reasonably preserved upon differentiation, so you may pre-compensate it by fcen=0.40. Or, if you have tighter requirements on the source, you may use the newly implemented feature of band-source (), which guarantees flat spectrum and suppressed spectral leakage. Its advantages are a tradeoff with a much longer source duration. You would also have to compile the fresh version of MEEP from github. Filip 2014-04-22 16:17 GMT+02:00, Ehsan Saei e.s...@hotmail.com: I've just used fcen=0.45 for source but the power has a frequency center at 0.5. Is there any solution for this behavior? Date: Tue, 22 Apr 2014 16:08:12 +0200 Subject: Re: [Meep-discuss] why the energy spectrum radiated by a point source doesn't match with the spectrum of source itself? From: filip.domi...@gmail.com To: e.s...@hotmail.com; meep-discuss@ab-initio.mit.edu May it be attributed to that the radiated field is a derivative of the current, so that high-frequency components are enhanced compared to the lower frequency ones? Or is it a more complicated deviation? Regards, Filip 2014-04-22 16:01 GMT+02:00, Ehsan Saei e.s...@hotmail.com: Dear Steven and MEEP users, I simulated a point source which is located in free-space (air ) and tried to compute the power radiated by the source and travels through a cubic that surrounds the source. After plotting the data I have noticed that the power has a frequency center different from that I have used for the source. Any idea about this behavior? Thanks in advance, Ehsan ___ meep-discuss mailing list meep-discuss@ab-initio.mit.edu http://ab-initio.mit.edu/cgi-bin/mailman/listinfo/meep-discuss
Re: [Meep-discuss] why the energy spectrum radiated by a point source doesn't match with the spectrum of source itself?
On 4/22/2014 4:08 PM, Filip Dominec wrote: May it be attributed to that the radiated field is a derivative of the current, so that high-frequency components are enhanced compared to the lower frequency ones? Or is it a more complicated deviation? Regards, Filip and furthermore, the radiated power is proportional to the fourth power of frequency times the square of the dipole moment, see http://en.wikipedia.org/wiki/Dipole_radiation#Dipole_radiation So it is expected that the spectrum of the radiated power will be skewed compared with the spectrum of the source. Best, Mischa 2014-04-22 16:01 GMT+02:00, Ehsan Saei e.s...@hotmail.com: Dear Steven and MEEP users, I simulated a point source which is located in free-space (air ) and tried to compute the power radiated by the source and travels through a cubic that surrounds the source. After plotting the data I have noticed that the power has a frequency center different from that I have used for the source. Any idea about this behavior? Thanks in advance, Ehsan ___ meep-discuss mailing list meep-discuss@ab-initio.mit.edu http://ab-initio.mit.edu/cgi-bin/mailman/listinfo/meep-discuss ___ meep-discuss mailing list meep-discuss@ab-initio.mit.edu http://ab-initio.mit.edu/cgi-bin/mailman/listinfo/meep-discuss
