Very old shielding materials and techniques for permanent magnets and resulting possibilities Answered
Forromagnetic meterials are not just called that for no reason.
It comes from ferrous - iron.
Iron has the highest permeability at normal temperatures.
That means a magnet is attracted to it very strongly.
We utilise this for transformer cores, the stuff inside a relay and the moving latch of the relay itself.
Like current from an electrical system magnetic fields like to take the easiest route possible.
Air is a very bad medium, so any iron close by will be prefered even if it is at a slight distance.
You can check with a magnet, a steel bar and some iron shavings - please cover the are with plate first ;)
Slightly less known is the option to also guide and extend the magnetic field this way.
If you check how far the magnetic field of a magnet reaches and note that distance,
then you can add some steel bars or rods at the poles - the field will extend through the metal.
The most powerful example of this are the shielded magnets used for hooks or speakers.
Except for a tiny area the entire magnetic flux goes through the metal.
So in this lefover area the magnetic flux density will my many times greater than what the magnet alone would be able to.
What most people don't know is that magnets also interact with other magnets in terms of their fields changing and distorting.
The Halbach Array is a good example of this.
Seen as a single magnet the array would have one weak and one strong side instead of even strenght for both.
Wherever magnetic fields change a conductor can produce electricity or current.
This in return causes an electromagnetic field that opposes the one from the magnets.
Just drop a magnet through a copper or aluminium pipe ;)
Since these distortions are widely unknow to the hobby tinkerer mistakes can happen ;)
In the early days of exploring science some people already knew about shielding.
And they also knew that certain metals have certain properties.
Where it is quite hard to create a good coil from steel wire, copper works fine as it is not magnetic.
What would then a copper shielding do?
If you have two moving magnets with only a tiny gap then the resulting field distortions are quite huge.
A copper shield around the magnet like a pipe would then react to these changes and also create a megnetic field that works in relation to the enclosed magnet.
In simple terms it means the shield would let the magnet appear weaker or stronger depending on the field change.
A quite old document I found gave some hints on how people thought in different directions back then.
It was in regards to the design of a magnet motor by the way.
Here various magnets were shielded in tube made of a copper-bismuth-alumium alloy.
These tubes were then electrically connected so it created a single loop conductor.
The claim was that the resulting electromagnetic field of this ring would drive the fields of the enclosed magnets sideways out of alignment.
Like bending straight pastic tubes sideways.
This "pulsating" would always happen when the magnetic binding forces reach max and so basically drastically weaken this binding effect.
Another document talks about a "magnetised brass rod".
A holes of the rod diameter is drilled through a block magnet.
Not from north to south but through the middle where the flux is greatest.
The claim here was that if that rod rotates fast enough a very low voltage with a very high current will be generated.
Sounds easy and interesting enough that I might have to test one myself one day.
The best one however is what I consider a hoax or being as good as Starlite.
Someone back in 1908 claimed to have created a material the reflects magnetic fields.
In lame man's terms it would be like an insulator around some electrical wire.
The claim and some pics showed it, was that no magnetic field can pass the material.
Or to be correct only a tiny fraction of what would be possible through air.
A small magnet inside a longer tube of this material would create almost the same attraction to steel at the tubes ends as on the magnet itself.
Measurements showed the field strength would be almost equal to a long mangnet of the same field strength.
Imagine guiding the field of a big and powerful magnet through a tube around some corners or other magnets and then end in just a tiny hole for the entire flux...
Too bad he never shared his secret formula to anyone knows to mankind.
Imagine you have an array of changing magnetic fields and quite strong magnets.
Then you might face the problem that your focus on the "working" end neglected the other end of the magnet (stack).
Providing some iron core material will keep thes field lines contained and away from interfering with your setup ;)
But it also allows to use te otherwise unused end of your magnets more directly.
For example by guiding to another magnet to affect its field strenght ;)
Placing a sheet or steel between two magnets in a setup provides a "shared pole" so to say.
If you have a north and south pole on a rotor at a distance of 5mm then a sheet of steel between will drastically weaken the strenght and reach of this combined field.
It is like pulling the arch between the magnets down to make it more flat.
And at and an angle the resulting field will also be slightly angled ;)
When I first encounter this many years ago I couldn't really make sense of it.
If you check the magnetic field lines with iron filings or similar then you notice how they go in a rounded manner from pole to pole.
This is because the single field lines are of equal polarity and will dirve apart like opposing magnets.
By capping the ends of a magnet you provide a short.
Instead of diverting out like mad they will follow the cap and create very intersting magnetic field in return.
If both poles are capped it is like pressing the magnet flat but without having a field on top of the oles - only aorund the center part.
For this the thickness much must match what is required for the flux density.
As a rule of thumb: if the end is still very magnetic then it is not enough material tickness ;)
Interacting fields in a tube...
This one is quite old too and seemed to have found no usable inventions apart from simple magnetic spring replacement systems.
But it gave me some clues about Tesla "earthquake machine" ;)
If you place a magnet in a tube and at it's ends magnets with opposing fields to the one inside then you can fix this magnet in place.
Push one magnet deeper and the distance from the inner magnet to the other end will shrink the same amount.
In this old paper two coils were around the pipe with the inner magnet between them.
In this gap and at about the same width as the magnets length another coil was placed.
Violent shaking would then create electrical energy at much higher level then modern shaker torches.
In return an AC current on the outer coils would cause the inner magnet to move back and forth to create electricity in the center coil.
According to the paper possible uses include: core less transformer, measuring minute changes in AC voltages, providing free power from a running motor...
The last one had me stumbled for a very long time.
Until I considered a different configuration.
The whole thing is basically a linear DC motor - with correct timing of course.
And in some motors we use permanent magnets.
I am starting to wonder what would happen if we would design a rotor magnet like this?
The running motor would be subject to constant field changes that affect the rotor.
And a normal motor is always "even".
By using four magnets instead of one we can push the field really flat.
This means the area where the coil would operate (about 1/5 of the magnets area) will have a much stronger field.
The resulting torque should be higher by about 25% !!
Even a simple two coil model setup should show a significant increase in performance here.
Timing is critical here but I tried some calculations based on 8 poles and the required "on times" for the coils.
In a standard motor configuration with a single rotor magnet the coil is active for about 12° of the rotation.
With a 4 magnet configuration this "on time" can be reduced to under 8° of the rotation to get the same amount of torque.
An energy reduction of about 4% if you neglect losses and only think in time.
If you think in terms like impulse energy then we are talking of about 15% !
Shorter on time but still much higher flux density overall than for the long standard timings.
Going the long run now:
If you check how most DC motors work then you realise soon that for most one rule seems to followed.
Only use one coild pair at a time.
This is quite contradictive if you consider the geometry and options.
A dual commutator would allow to use a second coil pair with a field OPPOSING the magnets instead of being attracted to it.
After all: on you bike you pedal with both legs and not just one...
And if you do it professionally then yu do the same as I suggested for the motor - you use the up pull of your legs as well.
Doing it brushless only requires amodified h-bridge desing to drive the second coil pair at the right timing.
Some will now say that it requires twice the energy, I say that for the same motor size your get twice the torque!
Just imagine what that means in possible weight reduction for a motor - or its size to deliver the same torque at the same power levels when a normal motor is used ;)
The more poles the more complicate the precise timing but no big deal really with modern electronics.
Can it be improved even further?
I though long and hard about that one until I considered EMF.
A DC motor produces a lot of it when the elecromagnetic field collapses in the the coils.
We do not utilise this energy...
There is a tiny delay until the released energy levels are at max.
My theory is that it should be possible to divert this energy into another coil set.
If that coil is not the next active but still within a strong enough field area then the EMF would actually add to the drive of the motor.
Only downside is that according to my calculations at least 16 poles would be required to get an optimum result.
Way above of what I can create in my little garage :(
In theory it should then be possible to reach about 98% efficiency for the motor....