| Electronics > Projects, Designs, and Technical Stuff |
| Annealed cast iron as magnet pole pieces (for low-field NMR) |
| << < (3/4) > >> |
| ChristofferB:
Great! 1018/1020 mild steel, preferably hot rolled it is! I'll see what's available. I have no machining capabilities myself but facing two steel rounds on the lathe is a pretty small operation, I'm pretty sure I can find a local machine shop or engineering college shop willing to do it for cheap :) I think I will stay off of the flux return for now, I want to assess how homogenous a field I can get before I go too overboard. Tim, I think permanent magnets was disfavored over electromagnets because early nmr used a gradient magnetic field, which is pretty easy to do by just modulating the AC to the magnet with a slow ramp. Temp likely also was a factor. I agree it's a bit iffy if I get any sort of resolution out of this thing. Either way, project plan is: 1. Produce a homogenous, shimmable magnet putting the hydrogen larmor freq between 2 and 20 mhz 2. Produce a probe accommodating excitation (saddle) and pickup coils, 5mm nmr tube and maybe a shim coil. 3. Find H2O peak by rf sweep 4. Rf pulse gen for excitation 5. Lock-in amplifier 6. Adc and dsp to handle the entire mess Thanks for the interest! --chris |
| Ian.M:
A lot of late 19th century experimental electromagnetic apparatus used bundled soft iron wire for cores. If you don't have access to a machine shop, its still a viable method of building the yoke. The ends of the bundle can be cropped one wire at a time to the desired plane, bonded with epoxy then finished by grinding or filing to flatness, limited only by the amount of time you put in to the work, bluing the face and checking it against a reference surface. |
| ChunkyPastaSauce:
--- Quote from: Ian.M on June 04, 2019, 10:59:41 am ---A lot of late 19th century experimental electromagnetic apparatus used bundled soft iron wire for cores. If you don't have access to a machine shop, its still a viable method of building the yoke. The ends of the bundle can be cropped one wire at a time to the desired plane, bonded with epoxy then finished by grinding or filing to flatness, limited only by the amount of time you put in to the work, bluing the face and checking it against a reference surface. --- End quote --- 0.9T gap with wire yoke 1.2T gap box frame |
| pwlps:
--- Quote from: ChristofferB on June 04, 2019, 09:43:32 am ---2. Produce a probe accommodating excitation (saddle) and pickup coils, 5mm nmr tube and maybe a shim coil. --- End quote --- I think nobody uses separate coils for excitation and measurement for pulsed NMR, except in some double-resonance probes. A single coil setup will save a lot of space so that the probe can be thinner and magnet poles closer, the field homogeneity improving accordingly. Using the same coil it is also easier to get a more homogeneous H1. |
| RoGeorge:
--- Quote from: ChristofferB on June 04, 2019, 09:43:32 am ---3. Find H2O peak by rf sweep --- End quote --- If you are interested for the water's NMR, I've seen many DYI projects of NMR done in the Earth's magnetic field. Earth's field is pretty low (about 50uT) but the advantage is that it has a very, very good uniformity, which is crucial for postprocessing. Another big advantage of that low 50uT value is that the corresponding precession (Larmor) frequency of the H is in the audio spectrum, so very easy to amplify, then sample the echo with a soundcard. There are open source programs to process the captured sound, and prepare a 3D NMR image from the spin echoes. |
| Navigation |
| Message Index |
| Next page |
| Previous page |