Question about Field Strength of Solenoid Positioned Near a Magnet

[JayAshby]

TL;DR

Hi, I've been working on a solenoid design and was wondering if I have this configuration, how would the strength of the solenoid (specifically the south pole) be affected by the permanent magnet? Would it potentially gain strength, or would it result in a loss? Assume minimal distance between magnet and solenoid.

 

[berkeman]

Welcome to PF.

They would add linearly, unless the magnet were free to move under the influence of the magnetic field from the solenoid. In that case you would need to analyze the differential equations for the movement of the magnet and the induced EMF in the solenoid.

Can you say more about what you are trying to do or analyze?

 

[JayAshby]

Welcome to PF.

They would add linearly, unless the magnet were free to move under the influence of the magnetic field from the solenoid. In that case you would need to analyze the differential equations for the movement of the magnet and the induced EMF in the solenoid.

Can you say more about what you are trying to do or analyze?

Hi berkeman, thanks for the reply. I should have added that both the magnet and solenoid would be fixed. The purpose would be to increase the strength of the solenoid's south pole (if possible).

 

[berkeman]

Are you trying to attract a ferrous slug cylinder into the solenoid, and wanting to increase the attractive force? The more you can say about what you want to do, the more we can offer as helpful suggestions and calculations.

 

[JayAshby]

Are you trying to attract a ferrous slug cylinder into the solenoid, and wanting to increase the attractive force? The more you can say about what you want to do, the more we can offer as helpful suggestions and calculations.

I haven't finalized the design of the valve yet but yes essentially I want to increase the attraction force of the south end of the solenoid for the purpose of an on/off valve. I want the strength of the solenoid to be as much as possible, therefore giving the off position a better seal.

 

[berkeman]

Okay, are you using a spring to do the return/ON position? Can you post an updated diagram that shows your full assembly with dimensions and all 3/4/5
pieces? Thanks.

 

[JayAshby]

The valve design is in more of a conceptual state right now. I'm more concerned about the strength of the solenoid, I've tried in the past to make a water tight seal with magnets alone, but it ended up leaking ( RC submarine, not good lol). Would you say your confident that the inclusion of the permanent magnet results in a stronger magnetic field for the solenoid?

 

[berkeman]

Would you say your confident that the inclusion of the permanent magnet results in a stronger magnetic field for the solenoid?

Sure. If you are only concerned with increasing the attractive force, then adding a DC magnet to the solenoid pull-in force will increase it. But obviously that makes it harder to release the solenoid, so that's why you don't usually see a DC magnet as part of the solenoid assembly.

 

[JayAshby]

Oh true, that's a good point, I wasn't thinking about the release as much. Thanks for the candor.

 

[hutchphd]

You should examine the engineering of solenoidal relays (and water valves). The magic words are "magnetic circuit".

In addition the fluidics for most water valves (for water at pressure) use the magnet to control a small water flow which drives a diaphragm actuated valve. The engineering is very clever indeed.

Study what's been done.