Monitor and operate the microwaves / know how to find correct frequency

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Using LabView for mmWaves

  • (David?)

Finding the correct frequency

In order to start looking for the optimum millimeter/microwave frequency, the variables below are important to know. Note that here the frequencies are given in GHz, as the frequency for 5 T fields will always be around 140 GHz.

  • Electron Gyromagnetic Ratio: <math>\frac{\gamma_e}{2\pi}=28.024~951~6~\mathrm{GHz/T}</math>
  • Proton Gyromagnetic Ratio: <math>\frac{\gamma_p}{2\pi}=0.042~577~478~92~\mathrm{GHz/T}</math>
  • Deuteron Gyromagnetic Ratio: <math>\frac{\gamma_D}{2\pi}=0.006~535~902~311~\mathrm{GHz/T}</math>

In order to find both the ideal mm-wave and NMR frequencies, some combination of the above numbers are multiplied by the magnetic field strength <math>B</math> in T. This gives the particle's Larmor frequency, <math>\nu_i = \frac{\gamma_i}{2\pi}B</math>, that is used in the descriptions below.

Proton Frequency

Proton mmwaves.png

  1. Find & measure TE using the Larmor Frequency
    • <math> \nu_p = \frac{\gamma_p}{2/pi}B</math>
      • Use the central value of the measured TE to extract the magnetic field for the calculations below
  2. To calculate the best positive enhancement frequency for mm-waves:
    • <math>f_{\uparrow}=\nu_e-\nu_p</math>
  3. To calculate the best negative enhancement frequency for mm-waves:
    • <math>f_{\downarrow}=\nu_e+\nu_p</math>

Note that the above should be considered starting points. The actual frequency will shift slightly due to the number and position of free radicals in the material (this causes <math>\nu_e</math> to shift slightly). It's good practice to:

  1. Start at the frequencies calculated above
  2. Carefully go up in frequency and note if the maximum polarization increases or decreases
    • Typically the above calculations tend to be slightly lower than the actual polarization numbers, though this may not always be the case
  3. If a point of maximum polarization is not found:
    1. Go back to the starting frequency
    2. Carefully go down in frequency to see if the maximum polarization improves
  4. Keep track of where maximum polarization occurred and use that as your frequency