Measuring low Electromagnetic field

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Discussion Overview

The discussion revolves around the feasibility of generating and measuring a magnetic field using an electromagnet powered by very low currents (micro to nano amps). Participants explore the implications of solenoid geometry, magnetic permeability of materials, and measurement techniques relevant to this low-current scenario.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant questions the feasibility of generating a measurable magnetic field with very low current, suggesting that the field strength will be very small even with a high number of turns in a solenoid.
  • Another participant provides the formula for calculating the magnetic field in a solenoid and notes that the Earth's magnetic field strength serves as a benchmark for measurement.
  • A participant discusses the challenge of measuring the field at a distance from the solenoid's edge, indicating that the field strength decreases compared to the center.
  • Concerns are raised about the difficulty in finding magnetic cores with high magnetic permeability, with one participant noting that purchased materials did not meet expected permeability values.
  • Suggestions are made regarding the use of high-permeability materials to enhance field strength, with a participant proposing that these materials would multiply the calculated field strength.
  • Another participant counters that high-permeability materials would guide the magnetic field rather than multiply it, and discusses the potential benefits of shaping the core material to improve measurement accuracy.
  • One participant mentions the possibility of using a SERF magnetometer to improve measurement sensitivity, although noting potential drawbacks.

Areas of Agreement / Disagreement

Participants express differing views on the effectiveness of increasing the number of turns versus using high-permeability materials, and there is no consensus on the best approach to achieve measurable magnetic fields under the specified conditions.

Contextual Notes

Participants highlight limitations related to the assumptions about magnetic permeability and the geometry of the solenoid, as well as the impact of air gaps on field strength. There are unresolved questions about the actual performance of the materials used and the effectiveness of proposed measurement techniques.

msarker
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Hi, I am working on a project where I've to make an electromagnet and very very low amount of current (micro amp to nano amp) will be supplied to the electromagnet. And finally have to measure the magnetic filed with a sensor.

My question, is it feasible to generate measurable magnetic field with this low amount of current?
 
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Assuming you're using a solenoid shape which is longer than it is wide (and not all that wide) you can estimate the strength of the field in the center of the solenoid with B = μNI/L. As you can see you will have a very, very small field with micro or nano amps even with a high number of turns. You should be able to easily estimate the strength of the field with this equation knowing what geometry you will be using. Remember that you want your answer in Gauss and not Tesla.

The Earth's magnetic field is .3 to .6 Gauss (Source:Hyperphysics) so your field will need to be larger relatively just to be able to simply measure it. If you estimate that you will generate a field that is "close" to this value then you can calculate the strength of the field by the deflection of a compass needle or other small magnet of known magnitude.
 
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thank you so much for your reply. I've used the equation of magnetic field along the axis of the solenoid. I've to measure the field at a distance (>=2 mm) from one edge of the solenoid. at this distance the field get reduced than the center of the solenoid.
Increasing number of turns is not good for low current that also it increases the diameter of the solenoid. I've bought a DC milligaussmeter (-2000 milligauss to 2000 milligauss). this milligaussmeter can detect small deflection.
I've only one option to use magnetic core with high magnetic permeability to increase the field strength.
I've bought bunch of core but none of them has high magnetic permeability. I've even bought an expensive alloy rod from GoodFellow. Their website says that it has magnetic permeability more than 50,000 but I've got very low (around 10_based on my experiment).
Based on my calculation, If I use magnetic permeability more than 50,000 than I will have decent measurable magnetic field at a certain distance.
What I understand that, high magnetic permeability value will be multiplied with the value of magnetic field that I've calculated for without core. Am I missing something here?
And also why it is hard to find a magnetic core with high magnetic permeability?

Thank you for your time and consideration.
 
From another thread
https://www.physicsforums.com/threads/how-does-a-wheatstone-bridge-work.844848/#post-5349324

1768_big.jpg
 
msarker said:
thank you so much for your reply. I've used the equation of magnetic field along the axis of the solenoid. I've to measure the field at a distance (>=2 mm) from one edge of the solenoid. at this distance the field get reduced than the center of the solenoid.
Increasing number of turns is not good for low current that also it increases the diameter of the solenoid. I've bought a DC milligaussmeter (-2000 milligauss to 2000 milligauss). this milligaussmeter can detect small deflection.
I've only one option to use magnetic core with high magnetic permeability to increase the field strength.
I've bought bunch of core but none of them has high magnetic permeability. I've even bought an expensive alloy rod from GoodFellow. Their website says that it has magnetic permeability more than 50,000 but I've got very low (around 10_based on my experiment).
Based on my calculation, If I use magnetic permeability more than 50,000 than I will have decent measurable magnetic field at a certain distance.
What I understand that, high magnetic permeability value will be multiplied with the value of magnetic field that I've calculated for without core. Am I missing something here?
And also why it is hard to find a magnetic core with high magnetic permeability?

Thank you for your time and consideration.

If increasing your number of turns is no good, can you decrease the diameter of the air gap? That will also give you a stronger field. Materials with high magnetic permeability won't multiply your field- they will "guide" it to some extent so you can more easily measure it. Any ferromagnetic core will also roughly double your field (below saturation, which you are) to measure.

Most materials do not have a high permeability. Pure iron does (~10,000 maybe for 99.9%pure iron? Not sourced.) and then special materials such as Mu-metal or Vanadium Permedur. I know you can order small specially shaped pieces of Permedur online, but I think it has a permeability of only 20-30,000. Mu metal is higher, I think.

https://en.m.wikipedia.org/wiki/Permeability_(electromagnetism)

Turned to wikipedia. You might be ablw to get mu-metal or any of the other materials (those permeabilities are insane. I didnt think any material was over 50,000) but I'm not sure how much it will help. What WILL help you measure the magnetic field more easily is crafting the high-permeability material into a cone-shape, with the wide end at the entrance of the solenoid. The "tip" of the cone will then "output" a concentrated flux which is much easier to measure- in essence the flux lines are being forced together as they struggle to stay inside the highly permeable material instead of the surrounding air. Then by geometry the magnitude of the field you measure, times the area of the tip of the cone, divided by the area of the base of the cone is the magnetic field in the center of the solenoid (or close, not all of the flux will "travel" inside the cone, some will escape.

It would be a lot easier to increase current, or the number of turns, though, but this core geometry tip could help you measure.
 
You may do several (4) orders of magnitude better on your Gaussmeter. A SERF (spin exchange relaxation free) magnetometer may help. It has some drawbacks which may be unacceptable though.
 
msarker said:
And also why it is hard to find a magnetic core with high magnetic permeability?
Karmaslap said:
Materials with high magnetic permeability won't multiply your field- they will "guide" it to some extent so you can more easily measure it. Any ferromagnetic core will also roughly double your field (below saturation, which you are) to measure.

msarker - read up on "magnetic circuit"

Only if the entire path is high permeability, which air is not, do you reap the benefit.
 

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