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Author: Subject: do-it-yourself nuclear magnetic resonance spectroscopy
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[*] posted on 21-9-2011 at 10:51


Quote: Originally posted by aliced25  

Sitting here laughing about the number of blackened fingernails and blood-blisters (aside from cuts from shattered magnets) I've acquired.

Urgh. Sorry, mate. Wish it was otherwise.
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[*] posted on 23-9-2011 at 19:21


here is a bloody interesting paper - it really goes into the nitty gritty of how the researcher 'did' build a working NMR Spectrometer and then goes off into conjecture into how he'd improve it.

Given the accessibility of the TMS320 series and the McBSP channels integrated into most of them, it comes up with some interesting ideas. Reducing the number of DDS chips from 2 to 1 also makes a great deal of sense. Why this needs to work with a smart phone when any real research work would presumably have at least a laptop/etc. is beyond me. If the complex processing/mathematics were handled on the PC/Laptop/Tablet/whatever then the complexity (parts count, layers, IC's, etc) on the board (plus temperature problems) become less of an issue.

The current magnet is 1.132T with inhomogeneity in the >1,000 ppm range which would appear to be significantly better than that used in that article (and in others), with the complex & phase-shifted signals used to cancel out inhomogeneity on a much larger scale.




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[*] posted on 7-10-2011 at 22:05


Ok, playing with Mathematica and FEMM, got two designs on the boil, we'll be playing in the ~60 & ~90MHz range using small Permanent magnets.

Spin Echo pulses were first reported by Hahn (1950) (in the ref request thread), discussed by Solomon (1955) and also by Carr & Purcell (1954).

It would appear that the industry (and research) has gone off on a tangent from that point, the calculations involved in working back from T1-T2 to get a narrow linewidth spectrum are not trivial (particularly in 1950's terms), whereas Golay's invention of shim coils made work on the concept unnecessary. It was easier and probably a great deal cheaper to design and build bigger and bigger magnets than to even try and contemplate quantum computing (which of course would allow the complex algorithms to be run in next-to-real-time).





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[*] posted on 8-10-2011 at 01:41


Anbody had schematic on modern components, not from vacum tubes:) ?
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[*] posted on 10-11-2011 at 04:09


Ok, looking very seriously at this now, as stated in several articles, we aren't going to be transmitting while we are receiving, so if the output can be digitized effectively (24-Bit Sigma-Delta ADC), a bandpass filter could* "potentially" be used to block the unwanted pulse-signal (thereby significantly reducing the complexity of the signal chain - no carrier wave, no modulation/demodulation, etc.) which is significantly higher than the ppm FID signals (which would be, given that 1MHz = 1,000,000 Hz, so the 0-15ppm shifts below 1KHz). The idea being that there is no data collected until the signal coming out of the receiver coil drops below the bandpass (could we use 1KHz?)

* Anyone got any reason why it wouldn't work?




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[*] posted on 2-12-2011 at 20:13


According to FEMM if one were to utilize a certain design (using 25mm cubes as well as other components), the output in a central bore section is 125MHz. The homogeneity is 2.93794-2.93798T through that bore, which is around 13-14ppm prior to shimming.

femm.output.2.937976T.jpg - 23kB




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[*] posted on 13-3-2012 at 08:23


Quote: Originally posted by aliced25  
Ok, looking very seriously at this now, as stated in several articles, we aren't going to be transmitting while we are receiving, so if the output can be digitized effectively (24-Bit Sigma-Delta ADC), a bandpass filter could* "potentially" be used to block the unwanted pulse-signal (thereby significantly reducing the complexity of the signal chain - no carrier wave, no modulation/demodulation, etc.) which is significantly higher than the ppm FID signals (which would be, given that 1MHz = 1,000,000 Hz, so the 0-15ppm shifts below 1KHz). The idea being that there is no data collected until the signal coming out of the receiver coil drops below the bandpass (could we use 1KHz?)

* Anyone got any reason why it wouldn't work?


you are going to need to build a tuned LC circuit. The resonant frequency of this circuit will need to be match the lamor frequency as dictated by your sample / static field strength. The LC circuit is resonant whilst the pulse(s) is applied and then damped afterwards to stop the oscillation in the circuit. In the read phase the tank is resonant in order to "amplify" very small signals and tune out noise.

I am building a set-up for my doctorate. It is not a simple project!
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[*] posted on 16-12-2018 at 04:23


I'm planning on doing some DIY NMR experiments. Still awaiting a bunch of deliveries I'll need, but I have assembled a Halbach array:
image0-7.jpg - 1.9MB unknown-5.png - 158kB
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[*] posted on 16-12-2018 at 08:40


Quote: Originally posted by DavidJR  
I'm planning on doing some DIY NMR experiments. Still awaiting a bunch of deliveries I'll need, but I have assembled a Halbach array:


That was probably tricky to assemble. It looks like you used a jig to hold them then cast the plastic cylinder round them ?

How will you adjust the field strength or do you sweep the generator and receiver frequency using modern electronics?




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[*] posted on 16-12-2018 at 09:10


I will be in awe of anyone who can build a functional NMR at home.

That being said, commercial NMRs have come down in price, enough that a benchtop NMR can be had for about $30K.




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[*] posted on 16-12-2018 at 09:16


Quote: Originally posted by DraconicAcid  
I will be in awe of anyone who can build a functional NMR at home.
I second that... and if they could also make their detailed design publicly available here so that others could replicate, that would be even more amazing. I'll certainly be following this thread!



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[*] posted on 16-12-2018 at 10:26


Quote: Originally posted by DavidJR  
I'm planning on doing some DIY NMR experiments. Still awaiting a bunch of deliveries I'll need, but I have assembled a Halbach array:


shouldn't the field be as uniform as possible?





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[*] posted on 16-12-2018 at 13:54


Quote: Originally posted by wg48  

That was probably tricky to assemble. It looks like you used a jig to hold them then cast the plastic cylinder round them ?

How will you adjust the field strength or do you sweep the generator and receiver frequency using modern electronics?


It’s not cast, I 3D printed the blue thing and then inserted the magnets. It was pretty tricky to get them all in though...

No varying the field for scanning, i’ll vary the frequency as needed instead. I’d rather use a Fourier transform approach and not do old school scanning though.

Quote: Originally posted by Ubya  

shouldn't the field be as uniform as possible?

Yes, it should be, at least over the sample area.

I’m not certain this magnet design is good enough but it’s a start. I may well need to modify the design. I may also need to add some small shim coils but we’ll see how it goes.

The magnets I bought are 15x15x50mm, N48.

[Edited on 16-12-2018 by DavidJR]

[Edited on 16-12-2018 by DavidJR]
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[*] posted on 16-12-2018 at 16:55


Quote: Originally posted by DavidJR  

No varying the field for scanning, i’ll vary the frequency as needed instead. I’d rather use a Fourier transform approach and not do old school scanning though.


Yes that's the way to do it these days. Look how a modern cell phone works or a the front end of a satellite receiver or a stick TV receiver for a PC. Though i suspect for the best signal to noise it is still narrow band tuned receiver but there is probably not a significant difference unless your trying to pick up signals from one of the Voyager spacecraft.

I read a few pages of the thread. The analysis of the shimming coils is similar to the way multi axis optical pointing systems trim out pointing errors due to mechanical inaccuracies between the axes, alignments of the sensors and geometric distortion of the sensors. Its complicated maths (big equations) but in the final analysis it just a polynomial correction for each axis. I guess the trick in shimming is working out where to put the coils to generate the polynomial correction. The first colour TVs had complicated trimming to align the three electron beams and correct image distortions.

An interesting project do keep us informed of your progress.




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[*] posted on 8-2-2020 at 09:06


FYI: just stepping in to revive this 2012/2018 thread on DIY NMR. I'm just going through what's been published before on the subject, and I'm planning out some of my first initial experiments and gearing up my toolset. In the next couple of months I'll try to post more on what I find out. At the end of this it looks like I'm going to have to learn a lot of AC analog electronics I never bothered to learn just to get to first base with this project, but it looks interesting and worthwhile, and if anything, the resurgence of benchtop NMRs doing 2d pulse sequences gives me hope that I can get to a spectrum of ethanol by end of year.



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[*] posted on 9-2-2020 at 04:41


Quote: Originally posted by mattharbowy  
FYI: just stepping in to revive this 2012/2018 thread on DIY NMR. I'm just going through what's been published before on the subject, and I'm planning out some of my first initial experiments and gearing up my toolset. In the next couple of months I'll try to post more on what I find out. At the end of this it looks like I'm going to have to learn a lot of AC analog electronics I never bothered to learn just to get to first base with this project, but it looks interesting and worthwhile, and if anything, the resurgence of benchtop NMRs doing 2d pulse sequences gives me hope that I can get to a spectrum of ethanol by end of year.



i'm looking forward to it, it is a really interesting project, it is one of the many things i'd like to do. as amateurs we don't have many modern ways of checking if the compound we made is what we meant





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[*] posted on 9-2-2020 at 05:47


I was curious as to how difficult DIY NMR detection or spectroscopy would be. Apparently detecting NMR in cobalt nuclei can be done with a grid dip meter but that is a special case. A quick google reveals several DIY projects. Here is one one with a description the instrument https://www.youtube.com/watch?v=b2n1-nvo7d4. Below is a pic of the instrument,

NMR-diy.JPG - 52kB

Below is some general info on NMR

mmkhttps://www2.chemistry.msu.edu/faculty/reusch/VirtTxtJml/Spectrpy/nmr/nmr1.htm

Attachment: NMRBasics_2016.pdf (4.6MB)
This file has been downloaded 341 times




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[*] posted on 9-2-2020 at 12:41


yup i saw that when i was researching the subject. radar magnets are not something that is usually sold in italy lol, i'll have to make my own electromagnet from pure iron and a helmholtz coil. the RF part of the project is what bugs me, and i can't find an easy enough "tutorial" or at least explanation, it is all or very theoric, or too much technical, so i can't follow (i don't have an electrical engeneering background)




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[*] posted on 9-2-2020 at 14:25


Quote: Originally posted by Ubya  
yup i saw that when i was researching the subject. radar magnets are not something that is usually sold in italy lol, i'll have to make my own electromagnet from pure iron and a helmholtz coil. the RF part of the project is what bugs me, and i can't find an easy enough "tutorial" or at least explanation, it is all or very theoric, or too much technical, so i can't follow (i don't have an electrical engeneering background)


I was hoping to get a feel for the magnitude of the task in terms of the strength and homogeneity of the required magnetic field, the sample size and the signal strength and noise. But so far I have no data. From the construction of that DIY system it does not look like it has any thing exotic. i am guess that the RF part could be achieved with a digital radio receiver and perhaps a low noise pre-amp.

[Edited on 2/9/2020 by wg48temp9]




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[*] posted on 10-2-2020 at 02:39


i have no clue, but the receiver isn't the only part, you also need a transmitter that can produce a high power, very short, broadband signal with a precise and tunable timing

[Edited on 10-2-2020 by Ubya]





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[*] posted on 10-2-2020 at 04:02


i think i found a solution, probably the best as of right now
http://kuchem.kyoto-u.ac.jp/bun/indiv/takezo/opencorenmr2/in...

it is open source, he/them described the board and the software
https://opencorenmr.github.io/opencorenmr-docs/

in theory one could send the eagle files to a PCB manifacturer, ans the populate the board with the right components by hand





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[*] posted on 10-2-2020 at 05:57


Quote: Originally posted by Ubya  
i have no clue, but the receiver isn't the only part, you also need a transmitter that can produce a high power, very short, broadband signal with a precise and tunable timing

[Edited on 10-2-2020 by Ubya]


I don't know how precise or broadband the drive signal has to be but you can get an idea from the diy unit I linked to. That unit used 555 timer chips for the envelope of the drive signal which are simple RC timers probably about 5% timing accuracy. So the envelope timing is not critical.

You can buy a 50MSa/s sample rate, 14bits vertical resolution Arbitrary Waveform Generator for about £100 that will generate that signal.
https://www.ebay.co.uk/itm/FY6800-60M-DDS-Signal-Generator-2...
There are potentially problems with fine control of the rf signal.
Though a few 555 and an LC oscillator could used with at least one stage of amplification to drive and isolate power amp.

Ebay sells 70W linear power amps 3.5 to 30MHz for £24 including postage

lin70w-s-l500.jpg - 22kB

I have made some progress on the task size for the magnet and receiver. The DIY unit I linked to states the magnet is 4,500 Gauss and that in can be varied by a few hundred Guass with the 10A coils. That implies it could be replaced with an electromagnet with about 20 times the ampere turns. Ok that's a big coil at least x20 of size of the small adjustment coils and much bigger to keep the power down. However that set up does not use all the surface area of pole faces. With more focused pole face the total flux could be reduces and hence the coil size could be reduced. I think the magnet construct is big task but doable probably using transformer cores as the main material with sold soft iron poles faces or the neodymium version shown in this thread or if your lucky and find an other big magnatron magnets.

Again from the linked system the receiver uses a amp with voltage gain of 10,000 apparently driving a scope displaying signal at about 100mV implying the input signal is about 10uV. Typical short wave radios are in the 2.-3uV range so suspect a digital radio stick will be similar for example :

chipradioCapture.JPG - 49kB

cost about £20 direct digitisation up to 28MHz but only 8bit It has a built in FFT. I don't know how easy it will be interface to it. The hardware and some of the PC software to use it is open source.

This is just the initial look at the feasibility and practicality.




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