Introduction to Waveguides using the LiteVNA, Part5, EPR Spectroscopy
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- Опубликовано: 10 июл 2024
- This video describes and demonstrates a homemade electron paramagnetic resonance spectrometer based on the LiteVNA. We attempt to touch on the subject of quantum mechanics.
EEVBLOG thread, Experimenting with waveguides using the LiteVNA
www.eevblog.com/forum/rf-micr...
The Zeeman Effect:
courses.physics.ucsd.edu/2016...
EPR Spectroscopy: The Basics
www.healthcare.uiowa.edu/core...
Orbitals: What they are and how they work?
www.cuyamaca.edu/student-supp...
This is not what an atom really looks like:
bigthink.com/hard-science/ato...
Practical Aspects
webhome.auburn.edu/~duinedu/e... 
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A friend caught a few mistakes and provided the following feedback:
Great video on your explorations of the EPR world!
Only two remarks:
(1) At video time point 30:00 you explain the equation E = h = gh, and you say that the last ‘h’ in the equation is planck’s constant. If that would be true, it would drop out of the equation because h is also on the left side of the equal sign. It is actually a printing error in the document that you show. It should be capital H for magnetic flux density (or in the language that I am used to: B for magnetic field). In the next page of the shown document the h is changed into H.
(2) Around video time point 1,03:00 you say that ‘It is the manganese that has the unpaired electron’. This is formally not correct. Mn(II) has five unpaired electrons and the spin therefore is S = 5/2, with sublevels mS = 5/2, 3/2, 1/2, -1/2, -3/2, -5/2. And thus with five possible EPR transitions for |mS|=1. It so happens that you only see the transition between the levels +1/2 and -1/2 because the other spectra are much broader (therefore lower in intensity) and anyway beyond your field range.
This is an excellent video Joe. This reminded me of a magnetic materials class I took in grad school 40 years ago where I had to calculate the resonance vs. field. I really don't remember more than I did it, I have never used it since.
This video is great because of your obvious joy heading down this rabbit hole. I really enjoyed watching this and heading down the hole with you. Thank you.
Very impressive setup. I love and learn from your videos. Thanks.
Fantastic video Joe, coming from a physics background I very much appreciated your effort to dive a bit into the theory and technical details.
Great, as always
A very related video by CuriousMarc: "How an Atomic Clock Really Works, Round 2: Zeeman Alignment". They go from 9GHz down to kHz range while tuning their atomic clock. Apparently atomic clocks do what you did but in reverse: they find where electrons flip in Cesium and that frequency is what drives our time standards.
Thanks. I'll have a look.
Super cool. Joe I want to be your best friend. Every thing you do is great, seriously.
One quick correction - those magnets aren't cooled in water. Water has some of thebest thermal transfer characteristics (hence it's use as a coolant in basically everything) but it only can get down to 0 degC (hence why ethylene glycol is added to coolant - so the manufacturers don't have to make one product for Florida and one for Alaska).[1]
Helium is used to cool any magnets down, since you can stay liquid down to 4.2ish deg Kelvin. You recirculate the fluid continuously out of the magnet cavities and back into your coolers in a closed loop. I think generally you have an outer casing of liquid nitrogen, a second casing of vacuum which gets roughed down then turbomolecular pump'd down. Your inner-most layer is helium, where your magnets are directly placed and constantly circulating in its own closed loop to out to the medical or research facilities cooling unit.
See description, Practical Aspects: "In this case the coils of the magnet are water cooled, with the cold water coming from the cooling unit. "
"Samples can be measured at room temperature, but in most cases lower temperatures are needed, sometimes as low as 4.2 K. To be able to do that, the spectrometer can be fitted with a cryostat. Liquid and gaseous helium will flow through this system in response to the working of the gas flow pump. The liquid helium comes from a large storage Dewar via a transfer line. The cold helium is protected from the ‘hot’ environment by a high vacuum generated by the turbomolecular pump."
Flipper done good! I appreciate every video you have made, especially the NanoVNA ones. If I'd seen them sooner I would have gotten a very good paying job at a government lab characterizing passive microwave devices. But I wanted to understand VNA work in any event. It shows us cleaarly nearly everything going on with a network, with pretty darn good precision for the price. Oh, to have had a NanoVNA when I was a kid.
BTW, I like the compass demonstration as an analogy. Great idea!
I fully understood very little of what you were talking about, but it was nonetheless interesting. It was at least useful in reminding me of the sheer magnitude of what I don't know that I don't know.
👏👏👏👏👏
Thank you Joe, that was very interesting!
I followed you thru the RF and physics, but got lost on the nano software (never used it). What peaked my curiosity is the homebrew magnet structure - would Peltier strips help linearize (and widen) your field strength ?
By field strength, I assume you are referring to the magnetic field. Please explain in more detail about your thoughts on why you feel it may improve it.
If your goal was to attempt to cool the solenoid, with this small system we are looking at about 0-15W that we would need to remove. If we used thin ceramic to try and thermally isolate the waveguide, it may help keep the sample at a more constant temperature.
@@joesmith-je3tq At about 14:50 you mention the sensitivity is inversely proportional to temperature. I don't know the BH curve of your magnet or steel; but it takes a lot of current (ie ampere/turns = heat) to force the flux density to change in a permanent magnet. I also don't know how fast you stepped through the flux density while taking each measurement. 0-15 watts seems pretty easy to compensate with a crude temperature controlled loop = string of diodes {8mv/C etc}, opamp and Peltier strips [ cheap lunch coolers ?]. Quite amazing you guys made that simple system work with shims and a 'small' coil. Just a thought, can a Peltier shim(s) be stuck next to the resonant chamber? You don't need to cool the whole magnet structure - just the chamber & sample.
...another silly thought, what's the internal surface of your RF stuff? I assume brass. Silver? Gold? Is it economical to plate it for higher Q?
Great fun! 10dB might show the other lines in that one with a little more current...
@@jim9930 I was referring to the temperature of the sample, not the magnets. We want to cool the sample in many cases. We are not trying to change the permanent magnets strength, rather add to the total field. The easiest way may be to heat the solenoid above ambient rather than trying to cool it. Again the goal is a controlled field.
Most of the waveguide parts shown are silver. I am not sure with the resonant chamber what the coating is. It could certainly be stripped and coated with silver but there are many other shortcomings I would address first.
@@joesmith-je3tq Dip the sample in ice water first?
@@jim9930 See description, Practical Aspects: "Samples can be measured at room temperature, but in most cases lower temperatures are needed, sometimes as low as 4.2 K. To be able to do that, the spectrometer can be fitted with a cryostat. Liquid and gaseous helium will flow through this system in response to the working of the gas flow pump. "