getting THz into a waveguide? - Page 1
Forum section: electronics / rf-microwave

author: coppercone2
author_rank: Super Contributor
timestamp: April 28, 2020, 03:11:24 am
content: So I see you can generate THz broadband radiation with a globar source, which heats up ceramic to get it to emit as part of the blackbody spectrum, and then some how filters it.If you do this in some kind of necked down waveguide, is it possible to get a wideband THz source into a system, then possibly filter it down to a somewhat cleaned up narrowband signal with filter elements?

author: TheUnnamedNewbie
author_rank: Super Contributor
timestamp: April 28, 2020, 07:22:08 am
content: I mean, technically, yes, that is totally possible. What would you want to do with it though?And keep in mind that single-mode waveguides at THz frequencies are tiny. Like, WR-1.0 (which is 750 GHz ->1.1 THz, if memory serves me right) is 250x125 micrometers.

author: aussie_laser_dude
author_rank: Contributor
timestamp: April 28, 2020, 11:42:15 am
content: Pulsed THz (wide spectrum of abour 0.1 - 3 THz) has been channeled through a "honeycomb" like waveguide that is big at one end and really small at the other. This allows THz (either a narrow spectrum or broad spectrum depending on honeycomb design) to be funnelled to a specific point at the tip of the waveguide end. In this example, THz surface imaging of semiconductor materials could focus THz toless thanthan the diffraction limit of THz (It has a sub millimeter wavelength). This is very tight focusing considering most techniques cannot even beat the diffraction effects.Using a honeycomb structured waveguide you could make for example a microscope imaging THz spectrometer (any / all wavelengths you want) using a waveguide that starts big one end and ends small on the other. The honeycomb cross section can select out THz frequencies (such as uniform honeycomb - specific wavelengths, or non-uniform for wideband). These are made in Sydney, very advanced and expensive processes, pretty impressive what they can do in the lab there. You could 3D print your own metal / plastic versions at a lower resolution. Best ones are made from drawn heated wires encased in some kind of resin or something, but I bet there's lots of ways to do this more easily.So yes, been done, those guys are actively making and researching this stuff, very cool I think. May I ask why? Are you researching this stuff at uni or something?

author: coppercone2
author_rank: Super Contributor
timestamp: April 28, 2020, 02:48:49 pm
content: Quote from: TheUnnamedNewbie on April 28, 2020, 07:22:08 amsince its already a really bootleg source, I wonder if you can solder two pcb's together face to face to make a shady waveguide structure for thz1/4 mm end mill is too hard, but you can etch it.. but it would be really janky. Like delaminate and put between two sheets

author: coppercone2
author_rank: Super Contributor
timestamp: April 28, 2020, 02:49:31 pm
content: Quote from: aussie_laser_dude on April 28, 2020, 11:42:15 amjust another radio project

author: aussie_laser_dude
author_rank: Contributor
timestamp: April 28, 2020, 06:30:36 pm
content: Oh nice! Thz, particularly above 1 THz is kinda tricky to measure, maybe you know a fair bit about this already? Bolometers, pyroelectric detectors, ti-saphire pulsed fs lasers with crystals with lockin amplifiers etc are often used in measuring this stuff. I've linked a project where a guy made a cheap (0.1 thz) detector using a small plasma tube.Here's what the cross sections looked like in some waveguides i've seen:https://www.mdpi.com/2079-6439/6/3/43/htmHere's a link to the cheap thz detector:https://link.springer.com/article/10.1007/s10762-018-0495-1

author: coppercone2
author_rank: Super Contributor
timestamp: April 28, 2020, 06:35:05 pm
content: the detectors are interesting but you need a source and the ability to make some kind of structure for this to be worth doing (unless you wanna fork it to thorlabs).I would want to get a circuit/source feasible before I work on a detector, because there will be nothing to detect or measure. I think making the source is doable, but it needs a circuit to be interesting.. not sure what kind of engineering you could do with just a detector and emitter.If you go right to 1THz and skip the mixers/stuff for 0.1THz or so, it gets seriously weird. I always like to think about the guy who first worked with THz, in like 1895. You won't really be able to push >300GHz real equipment on ebaythis is in the fun/cool category because anything serious requires real wealthI made that mistake with my first spectrum analyzer, microwave, it sat unused for 3 years before I got a circuit to plug it into and actually see something. It practically grew mushrooms.This is interesting because its thermal and mechanical design, not hunting for mixers and hoping they work. (rational way to increase bandwidth, not very fun). I learned to try not to spend any more money on MW. Allergic to K connectors now.

author: TheUnnamedNewbie
author_rank: Super Contributor
timestamp: April 29, 2020, 06:22:09 am
content: Quote from: coppercone2 on April 28, 2020, 06:35:05 pmTHz/millimeter-wave imaging and spectroscopy is a growing field within research right now.I also imagine that with 'the guy who first worked with THz, in like 1895' you are referring to is J.C. Bose, who used tiny sparkgap transmitters to transmit at 60 GHz. While it was an amazing achievement, I wouldn't exactly call that 'THz'. I've already tolerated certain researchers calling first 300 GHz 'THz', then 100 GHz became 'THz', but I ain't gonna allow people to push THz all the way down to 60 GHz.Dielectric waveguides are a somewhat upcoming technology for use at millimeter-wave frequencies. They already have niece uses at 77 GHz in metrology/cryo applications, but lots of people working on more consumer/commercial applications of them at millimeter-wave/THz frequencies. Could be interesting to study if that is what you are into.

author: coppercone2
author_rank: Super Contributor
timestamp: April 30, 2020, 09:08:57 pm
content: so a SLA resin printed grid of converging cones coated with silver may work (the stuff with glucose or w/e that silver plates anything weakly).I wonder what the dimensions (slope) would be, I wonder if its possible to use a taper pin reamer to really make them nice. A large one could be made by gluing multiple pieces together.How does the convergence point look like? (the point at which the cone tips join into a center), what is the outlet dimension? Is it perpendicular to the focused conductor (so the top is lopped off (looks like a drain)), or is it impedance matched with complex geometry (weird bowl)?Not sure I understand the physics correctly, I assume you don't want one cone end to feed into the other cone end with its angle to reemit from the absorber) bunch of nested dimples? (i assume you don't want to emit from a round slot on a plane....)can someone sketch the outlet flare angle/geometry?can you make a broadband THz source coherent some how? (this would be the dielectric lens part).. what material is acceptable?kinda wish someone would draw this thing.. but anyway once you get it into the waveguide, playing with the 'antenna' here is just playing with power levels in the waveguide right? perhaps then you can reemit it with a parabola