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bandpass filter signal processing

Posted Jun 2, 2014, 5:49 p.m. EDT Version 4.3 4 Replies

Shu Wang
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Hi all,

I am very new to COMSOL, forgive me if I've asked silly questions...
Anyhow, my goal is to define some parameters (i.e. resistance, capacitance, and inductance) of a RLC bandpass filter, which would take a single short pulse (~1THz) and filter out "higher order" harmonics in frequency domain, retaining only the first harmonic, and finally convert it back to time domain.

So my question is, how do I go about obtaining some plots for time/freq domain for the signal alone? and throwing in the RLC circuit in there? PS I've done the tutorial for AC/DC module but didn't help too much.

Thanks in advance!




4 Replies Last Post Jun 3, 2014, 12:43 p.m. EDT
Edgar J. Kaiser Certified Consultant
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Posted: 1 decade ago Jun 3, 2014, 6:41 a.m. EDT
Hi,

three comments regarding your question:

- You can simulate RLC circuits in COMSOL, but

- It sounds like this is a task for a circuit simulator like SPICE, however

- Which meaning do RLC values have in the THz region? You normally don't consider lumped elements at these frequencies.

Cheers
Edgar
--
Edgar J. Kaiser
emPhys Physical Technology
www.emphys.com
Hi, three comments regarding your question: - You can simulate RLC circuits in COMSOL, but - It sounds like this is a task for a circuit simulator like SPICE, however - Which meaning do RLC values have in the THz region? You normally don't consider lumped elements at these frequencies. Cheers Edgar -- Edgar J. Kaiser emPhys Physical Technology http://www.emphys.com
Shu Wang
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Posted: 1 decade ago Jun 3, 2014, 12:13 p.m. EDT
Hi Edgar,

It makes sense what you said first two comments; I've been wondering about the same thing actually. And just a quick follow up on the third comment you made. In the scale of THz, what type of bandpass filter would be a plausible design? (I take it that you implied RLC doesn't quite work) Thank you.

Shu

Hi Edgar, It makes sense what you said first two comments; I've been wondering about the same thing actually. And just a quick follow up on the third comment you made. In the scale of THz, what type of bandpass filter would be a plausible design? (I take it that you implied RLC doesn't quite work) Thank you. Shu
Edgar J. Kaiser Certified Consultant
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Posted: 1 decade ago Jun 3, 2014, 12:31 p.m. EDT
Shu,

at THz frequencies the wavelength (in air) is sub-mm. So I can imagine that micro-machined stripline or waveguide structures might be used. Also filters that are analogous to optical filters comprising stacked layers of dielectric materials might be an option.
You can model such structures and their frequency response in COMSOL, but you have to use the RF module (maybe the Wave Optics Module), not AC/DC, because those structures need to have dimensions that are in the order of magnitude of the wavelength or larger. AC/DC only works for structures that are much smaller than the wavelength.

Cheers
Edgar

--
Edgar J. Kaiser
emPhys Physical Technology
www.emphys.com
Shu, at THz frequencies the wavelength (in air) is sub-mm. So I can imagine that micro-machined stripline or waveguide structures might be used. Also filters that are analogous to optical filters comprising stacked layers of dielectric materials might be an option. You can model such structures and their frequency response in COMSOL, but you have to use the RF module (maybe the Wave Optics Module), not AC/DC, because those structures need to have dimensions that are in the order of magnitude of the wavelength or larger. AC/DC only works for structures that are much smaller than the wavelength. Cheers Edgar -- Edgar J. Kaiser emPhys Physical Technology http://www.emphys.com
Shu Wang
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Posted: 1 decade ago Jun 3, 2014, 12:43 p.m. EDT
Hi Edgar,

Thanks alot, that really clears my confusion. And you're right, I've found this: www.laserfocusworld.com/articles/2012/10/terahertz-optics-how-to-choose-the-best-terahertz-or-infrared-bandpass-filter.html

Thanks again.

Shu
Hi Edgar, Thanks alot, that really clears my confusion. And you're right, I've found this: http://www.laserfocusworld.com/articles/2012/10/terahertz-optics-how-to-choose-the-best-terahertz-or-infrared-bandpass-filter.html Thanks again. Shu

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