Nuclear Quadrupole Resonance (NQR) spectroscopy at home - Page 1
Forum section: electronics / projects

author: radiolistener
author_rank: Super Contributor
timestamp: June 20, 2025, 11:34:17 pm
content: About ten years ago, I considered building a Nuclear Quadrupole Resonance (NQR) spectroscopy setup for substance identification using a signal generator and a spectrum analyzer. I even conducted some experiments, but unfortunately, they were unsuccessful. At the time, there was very little practical information available on the subject, so after a series of unsuccessful experiments, I eventually abandoned the project.Today, I came across a fascinating video where someone actually managed to do it. The video details how he addressed both the technical challenges and theoretical aspects of the method. Interestingly, he achieved this without using a strong magnetic field. An amazing piece of work.

author: mtwieg
author_rank: Frequent Contributor
timestamp: June 21, 2025, 12:48:03 pm
content: As someone who worked with NMR/MRI tech on a daily basis and built a couple DIY NMR setups, NQR seemed like magic. This video was really interesting and tried to address some of those "magic" aspects (neat explanation of why precession can happen without an external field, but I still don't understand how you can get a useful signal from randomly oriented spins though). He did mess up the explanation of spin echoes, mixed up T1/T2, etc, but still a very good layman's introduction. Very curious about the 107 degree flip angle thing...Very surprised he's able to see signal with such simple hardware and no averaging. Odd that he doesn't seem to share more details on the design.

author: mtwieg
author_rank: Frequent Contributor
timestamp: June 21, 2025, 01:07:57 pm
content: Quote from: radiolistener on June 20, 2025, 11:34:17 pmIMO the main reason getting a DIY NMR setup working is you have to satisfy a number of conditions to see any recognizable signal:1. Accurately knowing your static field strength (B0), which tell you what larmor frequency f0 you should be operating at (and therefore what to tune your coil to, and what frequency to transmit/receive at).2. The static field being homogeneous enough so that a decent amount of your sample is actually near f0.3. Building a decent coil and tuning/matching it properly4. Adjusting the pulse amplitude/duration to give sensible flip angles.5. Adjusting the receiver gain so you can actually detect the signal when it's there.6. Your shielding is good enough to prevent the NMR signal from being drowned out.If you screw up any of these, you will probably not see any signal (that you recognize, anyways). Without any signal, it can be very difficult to determine what is wrong and what needs improvement.I suppose NQR has the advantage that since it doesn't require any external field, issues 1 and 2 do not apply (and in my case those were the biggest problems since I was building my own magnet).

author: moffy
author_rank: Super Contributor
timestamp: June 21, 2025, 10:29:04 pm
content: Quote from: mtwieg on June 21, 2025, 12:48:03 pmHe seems to state that the spin orientations are defined by the internal E-Field of the material, and that they have a resting orientation, the quarter flip and return would generate the signal but probably not as strongly as if all the spins are oriented the same way by an external B field. It does seem like magic.

author: Leek25
author_rank: Newbie
timestamp: June 23, 2025, 10:02:39 am
content: I am currently designing FTIR NMR and some hardware implementation are questuionable for me.Quote from: mtwieg on June 21, 2025, 01:07:57 pmCan you share more details please about your project and what results/milestone you reached?Or can I contact you to discuss some details?

author: mtwieg
author_rank: Frequent Contributor
timestamp: June 23, 2025, 12:32:13 pm
content: Quote from: Leek25 on June 23, 2025, 10:02:39 amThis is basically the output of my DIY NMR project. In hindsight, as far as open source hardware projects go, I didn't document it very well. The MS thesis in the github repo is the best description of its operation.Not sure what "FTIR NMR" is though. AFAIK those are two completely separate technologies.

author: electron_plumber
author_rank: Regular Contributor
timestamp: June 23, 2025, 12:48:34 pm
content: The applied science youtube channel is amazing.

author: joeqsmith
author_rank: Super Contributor
timestamp: June 24, 2025, 01:05:23 am
content: I had a recommended YT video where he made a SEM. Home made. I thought no way. I was captivated and hooked. Watched his channel ever since.Always interesting but then he does the mass spec. Who does that that for fun!!?? Then when he shows the Quad, I was inspired to move ahead with my EPR. Physics is fun.

author: Leek25
author_rank: Newbie
timestamp: June 24, 2025, 10:39:23 am
content: Quote from: mtwieg on June 21, 2025, 01:07:57 pmI am most interested in the magnet construction.Quote from: mtwieg on June 23, 2025, 12:32:13 pm"FTIR" was my mistake, sorry. I mean "FT NMR", to process FIDs with NMR software to obtain a spectra.Where you sourced the magnet?

author: mtwieg
author_rank: Frequent Contributor
timestamp: June 24, 2025, 12:58:52 pm
content: Quote from: Leek25 on June 24, 2025, 10:39:23 amMy system used a single-sided magnet, suitable only for relaxometry and depth profiling. If doing actual spectroscopy is your goal, then you need an extremely homogeneous magnet. It is possible, and some commercial systems are available (look up Magritek and Spinsolve), but I'm not aware of any open-source designs like that. They probably are based on a halbach magnet array, combined with an active shim system.I imagine it takes years just to develop such a high performance magnet.QuoteI think I sourced mainly fromK&J magneticsandmagnets4less. Looks like there are now many more vendors available than there were 15 years ago, though.