Hawaslsh
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Hello All,
I am working on a side project at work that I am not too familiar with so I thought I'd reach out for some advice. At the start I was told we needed to create a setup which could produce a magnetic field with a strength of 200 Gauss with 5% uniformity over a 1mm^3 volume. Initially I thought it was going to be a simple DC current to produce a static field B field. I proceeded by creating a simple MATLAB script that would add up a bunch of biot-savart approximations for a helmholtz coil setup. (I did something very similar for this group in the past which is why I assumed DC).
The above picture cheaply illustrates the setup we are using. We are interested in the strength and uniformity of the B field within the red sample. To achieve a good field uniformity a Helmholtz pair of coils is used. To create the coils we are wrapping 32 gauge transformer wire around a 3D printed bobbin. Imagine the bobbins used in sowing machines with a hollow space in the middle (picture on the right is just an example). Using the script it was easy enough to come up with a number of turns, distance between the coils, and current needed to produce the needed field. Below is plotting the field strength as a function of position from the center of the coil setup.
However, when I presented these results today i was informed we would need to drive these coils at 5 MHz. This lead to so many questions, and I was too flustered at the time to ask the right questions.
1) Putting aside impedance at the moment, are my biot-savart approximations still valid at frequencies > 0 Hz? Would the same 330 mA calculated for DC produce the same field strength at 5MHz assuming the same current?
2) The inductance of a single coil is pretty huge, and in the Helmholtz configuration I have 2 in series! The impedance of these coils at 5 MHz looks to be around 700Kohms. Clearly I would some sort of matching network to drive this?
3) Someone in the meeting suggesting created a tank circuit with a cap of similar impedance, and somehow that would increase my field strength while also lowing the required current? In my mind I thought it should be a series RC in order to resonate a short circuit at 5 MHz making it easy to push current. However, the person was pretty adamant it should be a parallel RC circuit to help? How would this help and how could i recalculate the field strength given the presence of the resonant tank circuit?
Happy to provide more context to help out,
Thanks in advance!
I am working on a side project at work that I am not too familiar with so I thought I'd reach out for some advice. At the start I was told we needed to create a setup which could produce a magnetic field with a strength of 200 Gauss with 5% uniformity over a 1mm^3 volume. Initially I thought it was going to be a simple DC current to produce a static field B field. I proceeded by creating a simple MATLAB script that would add up a bunch of biot-savart approximations for a helmholtz coil setup. (I did something very similar for this group in the past which is why I assumed DC).
The above picture cheaply illustrates the setup we are using. We are interested in the strength and uniformity of the B field within the red sample. To achieve a good field uniformity a Helmholtz pair of coils is used. To create the coils we are wrapping 32 gauge transformer wire around a 3D printed bobbin. Imagine the bobbins used in sowing machines with a hollow space in the middle (picture on the right is just an example). Using the script it was easy enough to come up with a number of turns, distance between the coils, and current needed to produce the needed field. Below is plotting the field strength as a function of position from the center of the coil setup.
However, when I presented these results today i was informed we would need to drive these coils at 5 MHz. This lead to so many questions, and I was too flustered at the time to ask the right questions.
1) Putting aside impedance at the moment, are my biot-savart approximations still valid at frequencies > 0 Hz? Would the same 330 mA calculated for DC produce the same field strength at 5MHz assuming the same current?
2) The inductance of a single coil is pretty huge, and in the Helmholtz configuration I have 2 in series! The impedance of these coils at 5 MHz looks to be around 700Kohms. Clearly I would some sort of matching network to drive this?
3) Someone in the meeting suggesting created a tank circuit with a cap of similar impedance, and somehow that would increase my field strength while also lowing the required current? In my mind I thought it should be a series RC in order to resonate a short circuit at 5 MHz making it easy to push current. However, the person was pretty adamant it should be a parallel RC circuit to help? How would this help and how could i recalculate the field strength given the presence of the resonant tank circuit?
Happy to provide more context to help out,
Thanks in advance!
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