Difference between revisions of "Monitor and operate the microwaves / know how to find correct frequency"
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=Finding the correct frequency= | =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. | + | 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 for finding mmwave frequency, as the frequency for 5 T fields will always be around 140 GHz, and in MHz for nuclei to aid in finding NMR signals. |
* Electron Gyromagnetic Ratio: <math>\frac{\gamma_e}{2\pi}=28.024~951~6~\mathrm{GHz/T}</math> | * 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> | + | * Proton Gyromagnetic Ratio: <math>\frac{\gamma_p}{2\pi}=0.042~577~478~92~\mathrm{GHz/T}=42.577~478~92~\mathrm{MHz/T}</math> |
− | * Deuteron Gyromagnetic Ratio: <math>\frac{\gamma_D}{2\pi}=0.006~535~902~311~\mathrm{GHz/T}</math> | + | * Deuteron Gyromagnetic Ratio: <math>\frac{\gamma_D}{2\pi}=0.006~535~902~311~\mathrm{GHz/T}=6.535~902~311~\mathrm{MHz/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. | 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. |
Revision as of 17:46, 12 June 2020
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 for finding mmwave frequency, as the frequency for 5 T fields will always be around 140 GHz, and in MHz for nuclei to aid in finding NMR signals.
- 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}=42.577~478~92~\mathrm{MHz/T}</math>
- Deuteron Gyromagnetic Ratio: <math>\frac{\gamma_D}{2\pi}=0.006~535~902~311~\mathrm{GHz/T}=6.535~902~311~\mathrm{MHz/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
- 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
- <math> \nu_p = \frac{\gamma_p}{2/pi}B</math>
- To calculate the best positive enhancement frequency for mm-waves:
- <math>f_{\uparrow}=\nu_e-\nu_p</math>
- 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:
- Start at the frequencies calculated above
- 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
- If a point of maximum polarization is not found:
- Go back to the starting frequency
- Carefully go down in frequency to see if the maximum polarization improves
- Keep track of where maximum polarization occurred and use that as your frequency