Applications of the Helmholtz Coil: Shielding and Stabilizing Fields

In summary, the conversation discusses the use of Helmholtz coils for canceling external interference and producing a more stable and uniform field with the addition of a third coil. The main application of this setup is in magnetic resonance experiments, where the uniformity of the field is crucial for precise results. James Clerk Maxwell also showed that adding a third coil can reduce the variance of the field on the axis to zero, known as a Maxwell coil.
  • #1
CricK0es
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Homework Statement



Hi,

I've got a presentation on an experiment we did using the Helmholtz coil and I'm starting to run dry on material. As some additional applications I found that you can:

- Use the coil set up to cancel external interference (Shield other experiments? Not sure about that one.)

- Produce a more stable and uniform field when a third coil is added around the outside.

I'm struggling to find anything regarding these that may be worth talking about. Just wondering if anyone has a very brief, qualitative description of how these two effects work. It's just a small presentation so I don't want to delve into the mathematical depths; especially having gone through all the data...

Many thanks

Homework Equations

The Attempt at a Solution

 
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  • #2
One of the properties of Helmholtz coils (two coils face-to-face, separated by their own diameters, if I remember correctly) is that they produce an extremely uniform field at the midpoint of the line joining their centres. This was invaluable for people doing magnetic resonance, because it meant that a the whole of a sample placed at that point would experience the same field, and therefore the same resonance condition, to very high precision. Electromagnets for EPR, and (in the old days before superconducting magnets) NMR, were designed in that way, with Helmholtz coils wrapped around the pole pieces, and the sample and its associated EM radiation source mounted in the middle of the gap between the poles. (I'm using the past tense, but it may still be common practice.) The poles could be up to about 25 cm in diameter, though 15 cm or so was probably more common. For EPR a common field would be 0.35 T, and, judging by the sharpness of some of the resonance lines, the fields were uniform to a few ppm over as much as a couple of cm.

Not quite what you asked, but perhaps of interest.
 
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Likes CricK0es
  • #3
Yeah but you gave me something else to throw in xD So thank you
 
  • #4
Don't know about shielding. Doubt it. But - per wikipedia:
To improve the uniformity of the field in the space inside the coils, additional coils can be added around the outside. James Clerk Maxwell showed in 1873 that a third larger-diameter coil located midway between the two Helmholtz coils can reduce the variance of the field on the axis to zero up to the sixth derivative of position. This is sometimes called a Maxwell coil.
 

1. What is a Helmholtz coil and how does it work?

A Helmholtz coil is a set of two identical circular coils placed parallel to each other with a distance equal to the radius of the coils. It produces a uniform magnetic field in the space between the coils when equal and opposite currents flow through the coils in the same direction. This is achieved through the principle of superposition, where the magnetic fields created by each coil add up to create a larger and more uniform field in the center.

2. How is the Helmholtz coil used for shielding?

The Helmholtz coil is often used in experiments and research to shield sensitive equipment from external magnetic fields. By placing the equipment inside the coils, it will be surrounded by a uniform magnetic field that cancels out any external magnetic fields, reducing interference and allowing for more accurate measurements.

3. What are the applications of using the Helmholtz coil for shielding?

The Helmholtz coil is commonly used in the fields of physics, biology, and medicine to shield sensitive equipment from external magnetic fields. It is also used in geology to study the Earth's magnetic field and in engineering to test the effects of magnetic fields on materials and devices. Additionally, it is used in the production of electronic devices to reduce interference and improve performance.

4. Can the Helmholtz coil be used for stabilizing fields?

Yes, the Helmholtz coil can also be used to stabilize magnetic fields. By adjusting the currents flowing through the coils, the strength and direction of the magnetic field in the center can be controlled and kept constant. This is useful in experiments and research where a stable and uniform magnetic field is required.

5. What are the advantages of using the Helmholtz coil over other methods of shielding and stabilizing fields?

The Helmholtz coil offers several advantages over other methods of shielding and stabilizing fields. It is relatively simple and inexpensive to construct, making it accessible for use in a wide range of experiments and applications. It also produces a highly uniform magnetic field that can be easily controlled and adjusted. Additionally, it does not require any external power sources or complex equipment, making it a convenient and efficient option for shielding and stabilizing fields.

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