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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.




Borosilicate glass:
Good temperature resistance and good thermal shock resistance but finite.
For normal, standard service typically 200-230°C, for short-term (minutes) service max 400°C
Maximum thermal shock resistance is 160°C
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