Magnet Myths and Misconceptions

[TinselKoala]

If you subscribe to the model of a permanent magnets being composed of tiny magnetic dipoles (domains) then it does.
According to that model, the energy stored in permanent magnets is due to the spatial orientation of these domains.
If those domains were allowed to rotate freely (e.g. by exceeding the Curie temperature or cutting up the magnet), then the net magnetic field of a magnet would disappear.

Such disappearance would induce EMF in a coil encompassing the magnet.

And would be irreversible without remagnetizing the magnet, and would require an _input_ of energy to heat the magnet. So you have a situation where energy is input to magnetize the PM, then energy is input to heat it past the Curie point to demagnetize it....  does this sound like an efficient process to you?  Don't forget that the induced voltage is proportional to the time rate of change of the change in magnetization. So to get anything much out of the solenoid you have to have all your domains flipping within a short period of time. Good luck doing that with heating past the Curie point.

Yes, of course.  That's why I asked you about the efficiency of reversibility of such process.

In the situation you describe I doubt if you could reverse the orientation of the two magnets, or half-magnets, by pulsing the external solenoid. As you said, once the magnet-halves have flipped so they are in mutual attraction, very little of their fields "leak" out, so what will the pulsed solenoid's field be acting upon?

I do not really suggest cutting a magnet up.  Two magnets rotating on a common axis are sufficient to illustrate the process.  They are also magnetic dipoles, just larger...

So you have to put energy in to "c o c  k" the system, then when you release whatever is holding it in the cocked state, the solenoid recovers the energy that you put in in the first place. This may be relatively efficient except for the inevitable electrical losses, just as the ordinary "cogging" of a rotor magnet passing a core is relatively energy-neutral except for eddy current losses and bearing wobble, etc. It also has nothing to do with storing and recovering energy by magnetizing and demagnetizing permanent magnets! Your comparison of this process to the alignment and de-alignment of domains is a real stretch, I think.

[TinselKoala]

TK will be happy to point to papers on certain EMP weapons that he has in the past that leverage the rapid demagnetization of hard magnetic material by blowing the material up.

The Curie temperature idea could be a fun experiment.  I'd have to ponder a bit on how to perform the experiment safely.  Maybe this can be done by taking an ordinary iron bar as a control and a neodymium magnet as the DUT and placing each successively inside a large diameter coil for thermal insulation and then exposing each to a propane torch.

Well, I remember posting information about explosively pumped Flux Compression Generators coupled to Vircator emitter systems used to produce EMP. That's a bit different from what you describe here, though. I don't remember talking about fragmenting permanent magnets to recover their energy of magnetization (which after all isn't very great.) In the FCG an _electromagnet_ in the form of a solenoid coil is rapidly and progressively short-circuited by an explosive charge driving a shunt which effectively forces the initial magnetic flux to concentrate into fewer and fewer turns of the electromagnet coil, eventually to be released as a very strong, fast rise-time pulse into the virtual cathode emitter/antenna system which then radiates the energy onto the target. Much of the radiated energy comes from the high-explosive charge that drives the shunt, I think.
http://en.wikipedia.org/wiki/Explosively_pumped_flux_compression_generator
This is another excellent example of how the conventional view of flux lines is used to design, control, and predict the behaviour of real devices that work as their designers intend them to.

I did find one type that uses an exploded magnet as the first "seed" stage to power the electromagnet solenoid second stage (second image below). Most systems that I am aware of use a capacitor bank for the "seed" power to the FCG solenoid stage, though. Again, it is the high-explosive's energy that is converted into electrical energy by the fragmenting magnet within the first-stage solenoid, not the magnetization energy per se.

[EMJunkie]

IMO, the most important research skills are:  1) Critical thinking, 2) The ability to search for relevant existing information, 3) The presence of mind and humility to ask questions.  Somewhere down the list is the ability to personally set-up and conduct experiments.  Many things that we want to know about will be well beyond our individual means to directly research.  Creativity is very useful but it is also down the list.  Those who master the criitical basic skills and are also creative thinkers are able to take jumps where linear thinkers must plod.  Linear thinkers who master the basic skills are equipped to make advances.  Those who do not master the basic skills but are creative can have interesting ideas but are unequipped to sift gems from dross.  Those who think linearly but who do not master the basic skills tend to regurgitate what they are taught without consideration for the fact that mostly correct is not totally correct.

Again MarkE - You have surprised me - I agree!

I don't agree with the numbering of each item but agree these are good guidelines!

1) The ability to search for relevant existing information - Research Skills
2) The presence of mind and humility to ask questions - Intuition - Looking outside the Box!
3) Ability to personally set-up and conduct experiments.
4) Keep things Simple! - Don't over complicate things!
5) Critical thinking - Believe Nothing, Assume Nothing until Experiment proves it! Even then Experiment must be repeatable every time! Check for Experiments that Contradict the first!
6) Documentation!
7) Extension of the above - More Intuition!

This list may not be ideal also but certainly the above is important! Else one will never progress!

Kind Regards

  Chris

[MarkE]

Well, I remember posting information about explosively pumped Flux Compression Generators coupled to Vircator emitter systems used to produce EMP. That's a bit different from what you describe here, though. I don't remember talking about fragmenting permanent magnets to recover their energy of magnetization (which after all isn't very great.) In the FCG an _electromagnet_ in the form of a solenoid coil is rapidly and progressively short-circuited by an explosive charge driving a shunt which effectively forces the initial magnetic flux to concentrate into fewer and fewer turns of the electromagnet coil, eventually to be released as a very strong, fast rise-time pulse into the virtual cathode emitter/antenna system which then radiates the energy onto the target. Much of the radiated energy comes from the high-explosive charge that drives the shunt, I think.
http://en.wikipedia.org/wiki/Explosively_pumped_flux_compression_generator
This is another excellent example of how the conventional view of flux lines is used to design, control, and predict the behaviour of real devices that work as their designers intend them to.

I did find one type that uses an exploded magnet as the first "seed" stage to power the electromagnet solenoid second stage (second image below). Most systems that I am aware of use a capacitor bank for the "seed" power to the FCG solenoid stage, though. Again, it is the high-explosive's energy that is converted into electrical energy by the fragmenting magnet within the first-stage solenoid, not the magnetization energy per se.

Yeah those are the sorts of machines I was thinking of.  Even a modest amount of energy when released quickly enough translates to lots of power. 

[EMJunkie]

@MarkPersonally I have found the laws almost always apply however many people have failed to consider the context in which they are applied. For instance a drop of water cannot climb up a wall against the force of Gravity, it is impossible and violates many known laws of science. Yet this is exactly what one scientist did using an engineered material (nano-material) and he did not break any laws doing it. In fact his experiment did not violate any laws but in fact proved them on that scale.

My magnetic bearing is another example and when I told some people I built a 99% passive magnetic bearing based solely on attractive forces they said it cannot be done and violates the laws of science. It doesn't violate the laws of science or Earnshaws theorem because it is 99% passive not 100% and again basically proves the laws but in a completely different context than most would expect.  Thus in my mind it was never the laws which were ever in question but a persons ability to understand the context in which the laws may be applied.
At which point we could go one step further and say the laws we know may always apply however we may never know the infinite number of ways in which the context of there application could change. Almost anything is still possible however it is not a matter of breaking a law but how we interpret and apply it from our own perspective.
The Down wind faster than the wind technology is another perfect example because I didn't see that one coming. I mean I have decades of experience researching and experimenting in aerodynamics but that one caught me completely off guard no matter how obvious it was after the fact.

AC

@AC - I completely Agree!

Millikan's Oil Drop Experiment! Law still applies but the conditions under which the prior known Laws were applied have now been changed!

I watched a Video online the other day, Earnshaw's Theorem, URL: https://www.youtube.com/watch?v=djPdEsL7EHY

Claiming to disprove Earnshaw's Theorem! However, the distance of the Charged Particles is not taken into account! As Charged Particles get closer together, the Inverse Square Law, actually Inverts relative to Quantum Distance!

So as the Particles move closer together, what was attractive actually becomes repulsive! Due to the Inverse Square Law!

So Laws are still relevant! Only under the conditions they were defined under!

Kind Regards

  Chris