The Relationship between Pulse Widths, Power, and Field Strengths
This relationship is discussed in detail in Cavanagh, et al., page 168-169.
Rainer Haessner also has aexcellent web page for Calculating Pulse Widths and Power Levels.
PW90 = 90 degree pulse width of RF pulse
B1 = field strength of RF pulse = 1/PW360 = 1/(4*PW90)
P = power setting on Varian Inova spectrometer (units of decibels, dB; higher number = higher power)
To calculate a new PW90 and P from a known PW90 and P:
PW90(1) / PW90(2) = 1e{ [P(2) - P(1)] / 20}
OR
P(2) - P(1) = (20)(log-base-10 [PW90(1) / PW90(2) ])
Examples:
| P(2) - P(1) | PW90(2) / PW90(1) |
|---|
| 1 | 1.122 |
| 2 | 1.259 |
| 3 | 1.413 |
| 4 | 1.585 |
| 5 | 1.778 |
| 6 | 1.995 (~2) |
| 7 | 2.239 |
| 8 | 2.512 |
| 9 | 2.818 |
| 10 | 3.162 |
| 12 | 3.981 (~4) |
| 15 | 5.623 |
| 18 | 7.943 (~8) |
| 24 | 15.849 (~16) |
| 30 | 31.623 (~32) |
| 35 | 56.23 |
| 40 | 100 |
| 45 | 177.8 |
| 50 | 316.2 |
Note that:
- B1 is proportional the the actual voltage of the signal
- B1 and the voltage of the signal are proportional to the square root of the actual power fo the signal
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Last updated: April 2nd, 1998
URL: http://nmr.chem.indiana.edu/NMRguide/misc/pw_power_fieldstrength.html
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