Extending a magnetic flux field from the tip of a rod

[mjuin]

TL;DR

How to design an field projecting electromagnet

I could use some help to point me in a direction. I am looking to create an electromagnet roughly 1/4" square x 1-3 inches long. The flux needs arc across the tip so it can reach a device that will be ~0.25" away. So I'm thinking of wrapping the wire end over end rather than around the rod. I'm looking to control/trigger a device on a PCBA -> CT8131BV-HS3.

 

[Baluncore]

Welcome to PF.

The geometry of the magnetic core used, will determine the field projection beyond the end of the magnet. I believe you will need a 'U' shaped core with the separated ends either side of the sensor chip. That will provide a maximum field on the other side of the gap.

Have you considered what core geometry and material to use? Please attach or insert a diagram of the section through the separated magnet and sensor, to your next post.

 

[mjuin]

OK
If I use a U shaped core I have two options. A narrow one that ill fit inside a cavity or a wider one that ill fit outside the cavity. I'm thinking the outside one will be the best option given the strength of field I need to generate and the distance between the end of the EM and device.
attached are some 3D perspectives and my understanding of what you are suggesting.

 

[berkeman]

attached are some 3D perspectives and my understanding of what you are suggesting.

Be sure to draw the bobbin(s) to figure out how much volume you have for the coil windings. What material are you going to use for the U-core? What AC bandwidth do you need to get out of the electromagnet? How many turns of what gauge wire are you calculating that you will need?

 

[mjuin]

Yes those are all good questions. I've not done this before.
Is this u shape core and application of it what @Baluncore was suggesting?

You mention a bobbin as if that would be inserted in the center of the U shape. I don't think that would result in the flux path I'll need. I was thinking the wire would be wrapped around the U shape. Originally I was thinking of a bobbin with the core more of an H shape and the flux arcing across the tips of the H.= but getting the projection of the flux lines didn't seem reasonable.

I'm planning on building the EM.
I'm not sure if 30G at this distance and these geometries is a reasonable expectation.
I'll have <0.5A of current @ 5V
I planned on a DC pulse @ min duration to trigger the device.
I planned on crafting the core out of soft iron.
https://www.amazon.com/dp/B0BNNCZ4ZR?tag=pfamazon01-20

Is there a modeling tool to help verify the materials and design?

 

[mjuin]

Little more looking at it appears this would be the U-shape wrapping
I have 34AWG wire represented here
300 turns on each leg.

 

[berkeman]

it appears this would be the U-shape wrapping

It is generally easiest to wind the coils on bobbins and slide the bobbins onto the core. You can either buy an inexpensive coil winding machine or improvise with a drill setup clamped in a couple of vises. How many of these do you plan on making? How much experimenting will you be doing with different cores and different coil winds (gauge, number of turns, etc.)?

Also, what experience do you have working with magnet wire to make magnetic coils? Magnet wire comes with different insulation thickness options called "single build" (thinnest), "double build", etc. Since you are only using 5Vdc for the drive voltage, you should be able to get away with the thinnest "single build" magnet wire, which will give you the most turns per volume for your coils.

https://www.digikey.com/en/products/filter/bobbins-coil-formers-mounts-hardware/935

https://www.digikey.com/en/products/detail/epcos-tdk-electronics/B65812N1005D001/3914213

 

[mjuin]

Less than 50 Qty. 10 in the immediate term
I see about the bobbins.
0 experience :)
Presently I'm wondering if I can just use a pair of inductors or a couple of the coils that are for sale as levitation kits.