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not_important
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Calculate the field strength the shim is going to be generating, then consider the effect of a 10%, 1%, 0,1% ripple on that field, and finally how
much ripple is the PWM going to impose on the shim field. DACs + power amps will give smoother currents, but with much higher power dissipation. You
need to determine what is allowable, ripple and heat generated, for your system in order to decide DAC vs PWM
| Quote: | | To go into the details of all this would be too lengthy and boring, but you sure see the logic behind it. Marcel Golay ended up with 13 sets of thin
coils (4 of which zonal) which were glued into grooves machined in the Golay plates. The result was a shim system capable of producing field
homogeneity of 1 part in 10^8 (without rotation; sample rotation improves the specification by another order of magnitude). That was quite sufficient
for the 30 to 100 MHz iron magnets of the 50's to 70's and permitted, for example, the measurements of long range couplings smaller than 0.1 Hz. Due
to the pretty good orthogonality it was also possible to shim the field manually by 20-turn current-source trimmers (though some empirical skill was
needed and not everybody was up to the task). |
If you wonder about that name : http://en.wikipedia.org/wiki/Marcel_Golay
note the 13 sets of coils, more or less pancake-like. High field superconductor systems take 30 to 40 shim sets as their fields are messy.
The pulse shimming is a nice trick, but both fairly new and more demanding in comprehension and equipment. Given that you've repeatedly confused
fairly basic concepts, including that bit with MRI vs NMR spectroscopy, I'd not want to bet on pulse shimming being an easy solution for your project.
Note that pulse shimmy has mostly been used with external sample systems, with a very large volume of sample being excited - in effect they are doing
MRI to isolate a small section of the sample that lies in a fairly uniform portion of field, then other tricks to further compensate.
The size of compressor needed to drive the spinner is fairly small, this isn't shop tool stuff.
As for a reference for field strength, it needs to be in the same location as the sample during the time the same is being examined, although a
guestimate could be done by doing a quick series of scans Ref,sample,Ref If the reference is present at the same time as the sample it can't
contribute proton signals that could overlap with those of the sample, thus alcohols are likely out of the running.
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aliced25
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Yeah, Golay is famous for a lot of things, sensors, algorithms (including the smoothing function) - a modified version of which is involved in that inhomogeneous NMR routine by the looks. The moving average would smooth the
results, then the inhomogeneous field 1 is compared to field 2 (slightly more homogeneous) and the constant determined (unlikely to be linear). I've
got to finish reading the articles, but it appears that by acquiring a statistically useful set of samples, they can work back from the known
inhomogeneity and the FID from the same and compare it to the FID of more homogeneous fields (same sample). I wonder how far the peaks move? Do you
reckon the peaks move as far as the bottoms, or would it be more like the FWHM diagrams?
Why bother with 13 coils? Set up 8/9 per side, then 2 more above N & S (no field until the pulse-spin is put through them) they will be separated
(given the equality of the field at the equivalent positions in the NW,SW,SE & NE Quadrants) - so 1,9,11&19 would be equal (as would 0 &
10 {N-S} and also 5 & 15 {W-E}). 2,8,12 & 18 would be equal to each other as would 3,7,13 & 17 & 4,6,14 & 16. Quite simply the
result would be better than Golay's as there are 7 additional coils (with the poles covered). The only reason for this is to allow for the pulse-spin.
0 & 10 would get a small pulse (increasing the field slightly), then the pulse would move on through 1, 11 then 2, 12, 3,13, 4,14, 5,15, 6,16,
7,17, 8,18, 9,19, 0,10 and so on... It is effectively spinning a small part of the magnet around the sample. In MRI they use that to regenerate the
FID, or something along those lines...
Personally I think DAC's would be the way to go, but I keep running into articles talking about using PWM instead...
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not_important
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You're making big assumptions about the actual field shape; you're dealing with a 3D shape with small deviations not in the simulation as a result of
actual physical artifacts in the magnets and supporting structure, plus from the electronics nearby such as tuning capacitors.
BTW Golay's setup was CW not FT and no pulses. I would like to see a rigorous analysis showing that your configuration is better than Golay's. He
was a pretty smart dude, somehow I doubt he picked the arrangement of coils because he liked the number 13.
DACs vs PWM is in part going to depend on how much current/power is needed for the electronic shims. Do a good job with PM shimming and the electronic
shims can be lower power.
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aliced25
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Golay was a genius, I doubt He did anything much for fun, or from lack of thought. That said, he didn't have the extent of the control that is
available now insofar as controlling the impulse to the magnet coils with anywhere near the accuracy we can achieve now. The Golay Cell for
IR-Measurement is another one of his, it too suffers from the fact that processing speeds were so fucking slow a child with a new calculator could
probably have kept pace with his mainframes. As the whole of MRI was developed upon sending pulses to gradient coils so that the magnetic field spun
about the patient, and there are articles about spinning permanent magnetic fields about the sample (instead of spinning the sample), the pulse-spin
routine would work, how well remains to be seen.
As far as assumptions about field shapes, yes, I am making assumptions. I'm basing these upon several articles where the author's have built "similar"
shaped magnetic fields and found the problems lay not along the z-axis but on the N-S part of the X,Y. They've got the experimental data to show it,
they also used solutions to measure the fields as Hall Effect Sensors & Reed switches, just cannot cut it. By comparing their results with the
known spectra of water, the inhomogeneity of the field they produced was made clear. But note, they did get a spectrum. If there is an issue with the
Z-axis, it can be reduced with Hemholtz pairs inside/outside the shims.
But there has to be some experimental data, I'm engaged in the search for ways to get light into and out of optical fiber at present, can we return to
this argument in a little while? We are not going to find a way to make shit work without trying out a couple of ideas and seeing if they work out.
PS What do you mean FT in terms of Golay's set up? I don't recall suggesting that it was anything but a constant wave, but like all things, if
improvements are ever to be made, they are made on the basis of the work of others (and applying new ideas & minute changes at great concepts).
Golay was into a lot of things with spectroscopy, his least squares/moving average data smoothing is the basis of statistical data manipulation. That
said, there are a lot of improvements, amongst those are the ones coming from sheer horsepower in processor output. Crunch enough numbers from the
same sample, with various fields and you'll start to see patterns emerging, you know the "true" outcome, the difference between it & your results
(statistically) must sooner or later show a range of responses that are either curved or that correlate in some way.
"10,000 monkeys at 10,000 typewriters" type of stuff, throw enough results at an anomaly, with meticulous records of field inhomogeneity/pulse
inhomogeneity corresponding to those results and all of a sudden a pattern MUST emerge. Irrespective of how broad some of the results would appear,
narrowing each of the two variables (field & pulse homogeneity) in a linear manner and we know that we get a nice narrow result-set. So the
results from narrowing one at a time were finally measured (or something) and someone found a relationship... It was improbable that they wouldn't,
the results broaden differently (presumptively) if only one of the variables is changed, compared to what they do if the other is changed. So there is
a relationship, tentative, but a relationship nonetheless. So what happens when we broaden one and keep the other narrow? and vice versa? is there a
possible complex relationship within the two matrices? Work out the relationship between keeping a narrow pulse and a broadly inhomogeneous field and
all of a sudden shimming becomes immaterial.
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aliced25
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C'mon, I'm sure everyone here has at least basic physics (well, at least who is keeping up in this thread) and advanced mathematics...
1. If a result-set is altered by the changing of a single variable, the result-set has a relationship with that variable (oversimplification perhaps,
but also I believe a technically accurate description).
2. If the alteration of the result-set increases/decreases in line with the increase or decrease in the variable, then we have a linear/semi-linear
relationship.
3. If we have a liner/semi-linear relationship between a result-set and a variable, then it should be feasible to reduce that relationship to a
mathematical formula, to solve the problem spectra(<sub>A*</sub> =Spectra(<sub>B</sub>* or / function<sub>x</sub>.
* The theoretical spectra solved for would be the one from a theoretically "perfectly" homogeneous sample.
Yes, the instrument is used in chemistry, but it belongs to physics, therefore the mathematical constructs and formulae that come from physics can and
should be applied to it, where-ever a linear/semi-linear relationship between a variable and a result occur. This isn't rocket science, it is complex
algebra, matrices and the effect of vectors on matrices. As results from various machines at each level of inhomogeneity are reproducible on other
machines at the same levels, using samples, the spectra of which are able to be reproduced on the same machines without inhomogeneity, then
inhomogeneity is not the problem. Ignorance is. Solving the riddle would remove the need for complex shimming, which in turn would make portable NMR a
realistic choice in instrumentation.
As there is published (and peer reviewed) data on the problem and the numerous groups looking to solve the riddle (NB Many of these groups seem to
struggle to present the problem in plain English, which suggests they aren't looking at the problem from the direction it may best be solved), if
homogeneity is described as each axis being at 0, then a homogeneous field would be Field (<sub>X=0, Y=0 & Z=0</sub> and the inhomogeneous field is represented as Field(<sub>X=1, Y=1,
Z=0</sub>, then the difference in results should be measurable. If the effect
on the results is measurable, then it should be theoretically possible to ascertain a relationship between the magnitude of the variables that were
changed and the magnitude of the change in the result. If one were to systematically pursue such a line of investigation, the several
possible/potential relationships would be narrowed down by the number of results (and the fact that many theories wouldn't fit most results). The
result would be an electronic/digital shimming algorithm, which could narrow the result set based upon known algorithms, with the magnitude of the
inhomogeneity (and which axes) fed in.
That would make mechanical/electromechanical shimming a thing of the past, a hangover if you will. The study groups are on the problem, so it is
likely to be solved (provided they don't get off-track). But I repeat, there is an obvious relationship between the homogeneity of the system and the
accuracy of the result-set, an obvious relationship is nothing more than a problem awaiting a solution.
[Edited on 15-11-2010 by aliced25]
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arsphenamine
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Quote: Originally posted by aliced25  | | That would make mechanical/electromechanical shimming a thing of the past, a hangover if you will. The study groups are on the problem, so it is
likely to be solved (provided they don't get off-track). But I repeat, there is an obvious relationship between the homogeneity of the system and the
accuracy of the result-set, an obvious relationship is nothing more than a problem awaiting a solution. |
In
principle, yes, but only in principle.
Proving the possibility of a solution
is not a blueprint for a solution, and
a blueprint is not an implementation.
Similarly, while quantum chemical computations have elucidated a great deal of electron cloud structure, most NMR shift prediction software is a
reasoned mixture of ab initio calculations tempered by empirical data.
While it is possible to strain shit out of the Ganges and declare it potable, the prospect of doing so can only be expensive and a last resort in the
absence of more practical methods.
It is not necessary to replicate 60 years of field shimming technology.
Given the initially high homogeneity of a Halbach or Stelter array, it should be possible to do first order correction using a smaller array of
magnets.
State-of-the-craft superconducting NMR devices may have close to 40 different shim coils. You could probably get by with much less since the
Halbach/Stelter is so good to begin with. In this case, I would look at the field homogeneity patents up to but not including Golay's original
patent.
The perfect is the enemy of the good
when you want adequately useful results in a timely fashion.
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aliced25
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I'd agree with all of that arsphenamine, the difficulty is that the studies are underway and good results are starting to come from them. We can
ignore those results, which are based upon the existence of more processing power on the average desktop/laptop (with which to implement the
line-narrowing electronic shimming of imperfect results) or we can try and play with the big boys in terms of trying to fit enough shims into a tiny
package to do enough to get us a decent spectral result. When you look at it, in order to get a decent result, we are going to have to implement
Christ only knows how many shims, plus spinning.
I honestly think that this concept, the whole idea of portable NMR based upon permanent magnets and a laptop/pc would be better suited to the
electronic shimming system. I mean, it would make the whole system a hell of a lot easier to implement, it would use nothing that wasn't already in
use (well additional algorithms in the software) and would ensure good results from minimal equipment (notice I didn't say perfect - perfect requires
ever greater superconductive magnets & coils and a mainframe).
I suspect watching & waiting might be the answer, as unpalatable as it may appear. Once there are known algorithmic approaches to effective
spectral determination via the digital/electronic shimming routine, this project becomes feasible in a big way. At the moment it is at best
borderline.
But that is not to say that the papers and the complexity of the field they are dealing with are overly complex (the mathematics looks it, but it
always does). Take a good look at this paper & especially page 4/9. The design of the pulsed spin is based upon the NMR Mouse, which is unique in that the field is above the magnet.
Here, where we are dealing with inhomogeneity of relevance only in the X,Y region of the area we are (1) going to irradiate and (2) going to get our
response signal from, the pulse signal would have to travel around the circumference of the sample bore. They rotate left, then right and then
essentially subtract anything that is one and not the other to be left with an essentially useful NMR Spectra.
Obviously for this to work, the pulsed spin induces the broadening to the left or right of the "actual" signal depending upon the direction of the
spin. I'm not suggesting for a moment it is the "WHOLE" answer, but it would be something to have a bloody good look at. It even makes sense in a
way, the central signal (the one we are after) would have to be the same in each regardless of the direction of the spin. The spin is a rotating
magnetic field which allows for the excitation of different areas by bringing them from just below the field strength to just above it as it rotates.
The RF Pulse is not rotating, it is static, so the broadening of the pulse would have to be determined by the rotating nature of the field, not the RF
pulse. The broadened pulse comes from the FID of molecules in slightly lower/higher Magnetic Fields vibrating with the slightly higher/lower ends of
the RF Pulse. I suspect that what the paper is discussing is the fact that when the rotating pulse is applied, it narrows the line, but also
introduces broadening specific to the direction of the pulsed-rotation, comparing the clockwise/anti-clockwise spin pulse FID's would therefore allow
for the manipulation of the resultant data. It would appear to be similar to the other variation of NMR where they remove the magnetic field
completely (rapidly) inducing FID.
[Edited on 16-11-2010 by aliced25]
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arsphenamine
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In software, you can remove a lot of undesirable artifacts or
emulate some hardware functionality but
that doesn't make it a good idea.
If you do more work at the front of the tranduction chain,
exponentially less work is required downstream.
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Polverone
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By chance I happened upon a company called picoSpin that claims to have developed a compact 45 MHz proton NMR spectroscopy system with 80 ppb resolution based on permanent magnets. Units
start shipping Q1 2011 at $20,000. This suggests that if you are very patient, future cheaper iterations, imitators, or second-hand units may
eventually be available to the reasonably serious hobbyist. If the company or any of its team members have filed patents relating to their work, they
may well be worth reading.
[Edited on 11-18-2010 by Polverone]
PGP Key and corresponding e-mail address
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arsphenamine
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| Quote: Originally posted by Polverone | | By chance I happened upon a company called picoSpin that claims to have developed a compact 45 MHz proton NMR spectroscopy system with 80 ppb resolution based on permanent magnets.
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Spectacular disruptive technology.
Benchtop spectroscopy is back!
Other features are ~7lb. weight in a shoebox, solenoid magnet shape, network output using JCAMP-DX format
(~version 5.x, I assume), and a 20 μl sample volume in a 300 μ diameter capillary.
The last bit tells us that they have a ~2mm long sweet spot for the field
homogeneity, suggesting that the magnet is probably quite small, perhaps
10mm height.
Elsewhere, they mention using an internally doped water sample for field strength
calibration -- something that has recurred from the very beginning starting with
Varian patents from the 50's.
I wonder if it runs embedded Linux.
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not_important
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"temperature controlled permanent magnet" also argues for a smallish magnet, that is one way to keep field drift down. It does appear to be good for
qual and quant both.
At a selling price of US$ 20K, that suggests a production cost of 1500 to 4000 dollars.
[Edited on 18-11-2010 by not_important]
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aliced25
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The permanent magnet is not the problem, why on earth it would need to be temperature controlled is beyond my comprehension. It is getting the spectra
out of the inhomogeneous (well only mildly inhomogeneous in comparison to some set ups) sample core that lies at the heart of the problem. As
inhomogeneity in the RF pulse is something we'll have to live with (and moreover, something that the researchers of a shitload of papers of note have
artificially contrived in order to hit the inhomogeneous field with a pulse that had matched inhomogeneity - the spectral width being based upon the
MHz correspondent to the Upper & Lower levels of the magnetic field (the Larmour Frequency of the upper & lower modeled field), gives a decent
spectral return - all of the protons are excited by the pulse (which hits all of the Larmour Frequencies) and by the looks the average of the spectral
returns narrows the spectral linewidth appreciably. It is nice to actually read the information on the subject, obviously there is quite a lot of
study going into it.
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arsphenamine
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| Quote: Originally posted by aliced25 | | The permanent magnet is not the problem, why on earth it would need to be temperature controlled is beyond my comprehension. |
NdFeB magnet fields have a 0.1%/degree C temperature coefficient.
That's 1000 ppm/degree field variation, or 43.5 kHz Larmor Frequency drift in a 1 Tesla field.
When you want to resolve something at 0.4 ppm, it's an important consideration.
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not_important
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Continuing on that riff, several of the journal papers you yourself referenced discuss the temperature sensitivity and the need for temperature
stabilisation. In some configurations and applications the temperature drift can create inhomogeneity in the magnetic field.
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12AX7
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Good way to handle that would be a Peltier controlled box of heavy aluminum. Two of them, one inside the other, with lots of insulation between
(aside from the Peltier). With a suitable thermistor and controller, that should keep it within a few milikelvin of nominal (give or take a few Hz
shift). Shim coils will have to go outside, since they'll add heating from odd sides. The effect of the work coil and test sample may require an
aluminum or copper housing inside the chamber to shield the temperature difference, which will affect the field noticably (dia/paramagnetism).
Tim
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not_important
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Or run at slightly elevated temperatures, say 35 C, with some but not really heavy insulation, and just use a heater outside the magnet region - put
the magnet in a "warm box". Shim coils need to be fairly close to the sample area, else they need to be strong which will introduce another set of
problems. If the basic magnet is fairly good, or shimmed to be so with permanent magnets, then the shims use little power.
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aliced25
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I was thinking that the shims would use minimal power, they aren't being used to cover massive amounts of inhomogeneity, I still don't think that
temperature would be the concern it is being rated as, but be that as it might.
The low-field or zero-field articles are of interest in terms of the spin-pulse design, the area of homogeneity in such small magnets is going to be
minute, say four or five shims high, wrapped on a core and some seriously intricate spin designs could be tested. I'd be very interested to compare
such tests, particularly with something that has a known spectra (in a homogeneous field) and keep trying out options and then comparing them to the
known spectra. If the pulses are running while the RF Pulse is run, then stopped/allowed to keep going while the FID is occurring, what happens? There
are a lot of seriously gray areas here, left by researchers with access to multi-million dollar equipment, who had no need to find out. Necessity is
the mother of invention, so I'd be interested to see what comes of the interest in the designs.
As to cooling, why go with a Peltier, generate heat at the outset and use a modified "Icy Ball" design to keep the magnets at -33C/240K for the duration of the spin-echo experiments. If temperature is going to be that big a concern,
then it would shit all over peltier cooling. Actually, would be just the thing for a lot of electronic cooling, lasers & the like, think about it,
build the heat sink (the ball that needs heating) into your heatsink (on your PC) and let that continually regenerate the NH3 (or use the Einstein variant, which I'm suspecting uses lower pressures... It would alter thinking on desktop cooling wouldn't it? Of course at that
temperature we start running into semiconductors, which would be an interesting idea...
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watson.fawkes
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That's because you haven't done the calculation yourself. Go do an estimate about what happens if one side of a permanent magnet
array is 0.1 °C cooler than the other because of, say, a draft in the room.
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arsphenamine
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It's importance was covered
in this thread around 17/10/2010.
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aliced25
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I don't expect that a draft in a room would affect a magnetic array in a Copper/Aluminium Enclosure, the sheer bulk of the housing and the insulating
effect of the same would normally be expected to ensure that the various parts thereof don't have major differences in temperature. I don't see how
you would alter the entire volume of the magnets temperature with a peltier cooler on the base anyway, the cooling would have to be through the
center, through the core, through the horizontal axis, etc. If it were such a difficulty, I'd imagine there'd be more mention of it in the journals
where they are using permanent magnets to make magnetic fields. The only sure-fire way to ensure proper cooling distribution would be to run a liquid
coolant over the surface (depending upon the substrate too, if it is too thick, surface cooling will only exacerbate the issue) and circulate that
through a cooling pump. I've yet to see anyone bother.
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not_important
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The journals are research devices, not manufacturing; they may be in a well controlled environment. As such much detail is left out. However several
of the papers you have listed do explicitly state that various enhancements would be needed for practical devices, including
temperature control. Others are for devices that have much less demanding quality requirements than analytical NMR, MRI can get away with nearly an
order of magnitude greater inhomogeneity than structural analysis, pore-filling and elastomer curing measurements are yet another order of magnitude
less demanding; several of the papers you've listed are refering to such applications.
For example, from 2 papers that I'm fairly sure you were the source of:
| Quote: |
A simple, small and low cost permanent magnet design to produce homogeneous magnetic fields
B. Manz *, M. Benecke, F. Volke
doi:10.1016/j.jmr.2008.02.011
As spectral resolution is enhanced through the measures
described above, the system will finally be susceptible to
very fine temperature gradients and fluctuations. An effi-
cient thermal insulation as well as a frequency lock will
be mandatory to commercial high resolution portable
NMR sensors. Finally, remaining field inhomogeneities
will have to be compensated by a set of shim coils, as it
is common practise for other high resolution NMR mag-
nets. However, for many NMR applications, even proton
linewidths of 50 ppm are sufficient for a quick characterisa-
tion of samples via relaxation and/or diffusion contrast,
like gels, polymers or high viscosity liquids.
Small Magnets for Portable NMR Spectrometers
Ernesto Danieli, Juan Perlo, Bernhard Bl.mich, and Federico Casanova
DOI : 10.1002/anie.201000221
Further improvements in the strength, size, homogeneity,
and temperature stability of the magnet are a matter of
technological refinement. A higher field can be achieved by
increasing the outer diameter of the magnet array. For
magnets built from SmCo, 1.5 T (corresponding to a proton
frequency of 60 MHz) can be obtained with an outer diameter
of 7.5 cm. This material has better thermal stability than
NdFeB, but remaining field drifts arising from fluctuations of
the magnet temperature must still be eliminated, for example,
by combining standard temperature control schemes with a
field-frequency lock.
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There are a number of ways of obtaining the required uniformity and stability, you picked one of the more complicated ones.
You might also consider why such functionality would be designed in, if it was not at least useful if not required. Every zloty of parts boosts the
sale price by roughly 10 zloty, so there's price pressure to keep unneeded hardware to a minimum.
[Edited on 25-11-2010 by not_important]
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aliced25
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Anyone on here with experience getting the bloody 3D models to work, Comsol, etc. would be greatly appreciated.
I've decided to go with the AD9850, it runs at 125MHz (so it is useful to what, 62.5MHz theoretically?), with a 1T field, with a median inhomogeneity of +/-0.001T, it should
be possible to work out some shim pulses to take it up to what we need. The TI ECG Front-end-type ADC, the 4-channel ADS1294 should be ample (with a
small modulating frequency). Using the DDS Chip, the ability to generate some funky-as-fuck pulses should come easy enough (according to the person I
asked who is doing the research with the bloody thing).
Quite simply, the shim-pulse, spin-echo technique(s) are probably the only way this is ever going to be suited to "home" or "portable" use, building
in the controllers for the X,Y,Z shims would suck (although I suppose a PID controller could be utilized) but that would require feedback and apart
from using a known spectra, I suppose distilled water would do, feedback would be difficult to say the least.
With regard to PCB's there is a move toward Cu/Al2O3, especially for high-temperature circuits, there are a lot less toxic requirements, particularly
if the board is machined rather than etched. Given the existence of the same and the toxic output of the alternative (plus the fucking greens being in
charge of this Cunt-tree), I'm half-expecting to be seeing the same in more widespread use.
From a Knight of the Realm: "Animated movies are not just for kids, they're also for adults who do a lot of drugs." Sir Paul McCartney
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aliced25
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Strangely enough, there is a 3D version of the Halbach/Stelter array which uses exceptionally simple magnets, which if a 0.2" gap is left in the top
and bottom pole piece, gives a fucking incredible homogeneous field, especially through a 0.2x0.2" (~5.4x5.4mm) square in the center of the unit and
allows for the sample to be put in and for the electrical connections to come in from the other end.
I've decided to purchase a small lathe & mill - with a view to setting up a CNC Conversion on both (X,Y,Z via stepper motors) and a design for a
small-ish X,Y router table, with the Z-axis being restricted to on or off. The table will be used to route copper coated alumina or plastic to make a
shitload of boards at once. With the small router I can also design the paste-overlay for the solder paste and with almost all of this using SMD's
I'll try some of the ideas suggested by sparkfun to heat the paste/units properly.
I've also decided to stop fucking around with what others have designed, if what they have designed works, the only changes will be to reduce the
parts count and simplify the setup.
From a Knight of the Realm: "Animated movies are not just for kids, they're also for adults who do a lot of drugs." Sir Paul McCartney
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aliced25
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| Quote: Originally posted by un0me2 |
...
A.Prof Takeda is currently working with a 1T magnet (with poor homogeneity reportedly, requiring X,Y,Z coils, or so I've been told) in order to try
and work out a portable, home built system.
...
[Edited on 26-9-2010 by un0me2] |
Ok, I may (or may not) have spoken to someone in a Japanese lab who is not only interested in the latest magnet design (simple as fuck, N40 & N52
Magnets with a 1" central void (which the "person" suggests would suffice for coils, shims, etc.) which is modeled at 1.184 (± 0.001) T or a N52 only
design which is modeled at 1.231 (±0.003) T (inhomogeneity of around >0.5%) through the central 0.2" sample holder. Currently working on the
design of a modified Cylinder/Cube based upon the design, if that works (based upon the strength of standard Halbach Cylinders v arrays), multiple
Tesla field strengths are possible.
The person I may or may not be dealing with is a published author, with a working spectrometer based upon open-source software and hardware
configurations. The magnets would cost less than $50 and the electronics would be less than $200 per unit (less with volume). If it works it would be
envisaged that pre-assembled kits/units could be sold online.
PS Anyone here any good with modeling 3D magnetic fields using Matlab/Mathematica/Comsol/etc.? It is starting to become vital to the cause.
[Edited on 3-9-2011 by aliced25]
From a Knight of the Realm: "Animated movies are not just for kids, they're also for adults who do a lot of drugs." Sir Paul McCartney
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aliced25
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| Quote: Originally posted by arsphenamine |
Regarding NMR magnets, I am deeply apprehensive about wrestling with
1"<sup>3</sup> magnets that exert a 75lb hold, out of fear for my fingers.
Watson.fawkes assures me that 75lb isn't so bad but I remain incompletely convinced.
When aliced25 gets to the magnet array construction stage, will his posts
decrease in number and length as a result of severe hand injury?
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Sitting here laughing about the number of blackened fingernails and blood-blisters (aside from cuts from shattered magnets) I've acquired. That isn't
the reason for the lack of recent activity, the necessary designing & machining, plus the need to complete an insane number of papers (yeah, back
at Uni) while getting fitness back to a minimum standard all take time That plus
kids now
From a Knight of the Realm: "Animated movies are not just for kids, they're also for adults who do a lot of drugs." Sir Paul McCartney
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