NMR: what is the area under the curve of the radio transmitter?

[bhimberg]

Using two pernament magnets, a transmitter coil and a pickup coil, we applied a match filter to find the resonant frequency (our sample was wrapped in the pickup coil with the trasmitter stationary wrt it: the magnets are the round type, ceramic I think). Using this frequency we can map the strength of the magnetic field.

Two sets of data were taken, one was the frequency at each point, another was the area under the curve on channel 1 of the osilliscope. Channel one is the output of the pickup coil: the coil around the sample that absorbs the photons created by the nuclei when they return to their ground state.

What I don't understand is what the area under this curve represents. The magnetic field appears to be nearly uniform (with small variances that result in the resonant frequency changing from 15.52 Mhz to 15.55 Mhz), yet this area has a peak near the center of the magnets, a magnitude of around 1600, and drops off radially to the edge, a magnitude of 60.

Units on the scope are volts*seconds, though I *think* the prof may have mentioned they were volts*seconds*meters (which doesn't make sense). It may have something to do with magnetic flux, but if there were the case then it too would be unifor since the field is uniform, correct?

 

[AndyW]

Thank you for sharing your experiment and data with us. It sounds like you have conducted a very interesting study on mapping the strength of a magnetic field using two permanent magnets, a transmitter coil, and a pickup coil.

Based on your description, it seems that the area under the curve on channel 1 of the oscilloscope represents the amplitude of the signal detected by the pickup coil. This amplitude is affected by the strength of the magnetic field, as well as the resonant frequency of the system. The fact that the area has a peak near the center of the magnets and drops off radially to the edge suggests that the magnetic field is stronger at the center and weaker at the edges.

The units on the scope, volts*seconds, are likely related to the voltage induced in the pickup coil by the changing magnetic field. The mention of volts*seconds*meters by your professor may have been a mistake, as magnetic flux is typically measured in webers (Wb) or tesla-meters squared (Tm²).

It is important to note that even though the magnetic field may appear to be nearly uniform, there can still be small variations in its strength that can affect the resonant frequency and the amplitude of the signal detected by the pickup coil. These variations could be caused by imperfections in the magnets or the setup of the experiment, or even external factors such as nearby electrical currents.

Overall, your data seems to indicate that the magnetic field is strongest at the center of the magnets and decreases radially towards the edges. This could be due to the shape and orientation of the magnets, as well as the distance between them. It would be interesting to compare your results with different setups and configurations to further understand the behavior of the magnetic field.

I hope this helps to clarify the meaning of the area under the curve on channel 1 of the oscilloscope. Keep up the great work in your research!

 

[sir-pinski]

The area under the curve of the radio transmitter in an NMR experiment represents the energy absorbed by the sample from the radio frequency pulse. This energy is then released by the nuclei as they return to their ground state, which is what is detected by the pickup coil.

The resonant frequency, determined by the match filter, is used to map the strength of the magnetic field. The magnetic field strength can vary slightly due to small variances in the setup, resulting in a change in resonant frequency.

The area under the curve on channel 1 of the oscilloscope is a measure of the energy absorbed by the sample. This area may vary even in a uniform magnetic field because the strength of the magnetic field is not the only factor that determines the energy absorbed by the sample. The composition and structure of the sample also play a role in the amount of energy absorbed.

The units on the scope, volts*seconds, represent the voltage (measured in volts) multiplied by the time (measured in seconds) that the pulse is applied. This gives a measure of the energy absorbed by the sample.

In summary, the area under the curve on channel 1 of the oscilloscope represents the energy absorbed by the sample from the radio frequency pulse, and it can vary even in a uniform magnetic field due to factors such as sample composition and structure.