Good morning, I have a theoretical project, which concerns the wireless energy transfer, therefore considering an electromagnet, which has a cylindrical or horseshoe shape (for space reasons I can not use the circular shape), which magnetic core material between powders (MPP, sendust) or amorphous metals (metglas) is the most suitable? The frequencies that I should operate are between 100 khz and 200 khz, but this is still all theoretical yet. The two materials have different characteristics as well as different saturation levels, but which of the two is the best for my purpose?

 

Over what distance? Is it a long-wave radio?

 

Over what distance? Is it a long-wave radio?

the distance should be around 20 cm, obviously with a very limited efficiency, the system is not resonant, no no I will not use radio waves, since we are talking about near field induction

 

First, at that frequency, the core magnetic properties certainly matter. Second is that the description is quite vague, in fact, seriously vague. Without more detail, what you will get is a bunch of guesses.

 

First, at that frequency, the core magnetic properties certainly matter. Second is that the description is quite vague, in fact, seriously vague. Without more detail, what you will get is a bunch of guesses.

yes yes of course, as already said this project I need to obtain a wireless energy transfer, with low efficiency. the choice between the two materials of the magnetic core is in the fact that they have different magnetic permeabilities, metglas about 35,000 and MPP about 550 (in the highest values, here having such a high magnetic permeability, doing the calculations for the metglas, it would take 2 amperes and about 6 turns to reach the saturation of the core (1.4 T), while with MPP to reach the saturation 0.7 T it would take 50 turns and 8 amperes. here in this case having so few turns for the metglas, could I generate a good electromagnetic induction? here's what I don't understand, the theory says that to obtain high levels of induction you need many amperes of power, but for the metglas a few are enough, but the field remains trapped and concentrated in the magnetic core, or can it project it outside??

 

The flux is equal to the Magnetomotive force divided by the reluctance.
magnetomotive force = current *number of turns.
The reluctance is the sum of all the reluctances in the magnetic circuit.
The reluctance of a core is the reciprocal of its Al value, and the reluctance of air is L/(μo.A) where L is the length (in metres) and A is the cross sectional area (In square metres)
In your system the magnetic path is mostly air, and that makes it more difficult to calculate as the flux doesn’t follow a neat path of constant cross sectional area, so much so that the reluctance of any core you might have used is irrelevant, except for making the flux come out of the ends.

 

The flux is equal to the Magnetomotive force divided by the reluctance.
magnetomotive force = current *number of turns.
The reluctance is the sum of all the reluctances in the magnetic circuit.
The reluctance of a core is the reciprocal of its Al value, and the reluctance of air is L/(μo.A) where L is the length (in metres) and A is the cross sectional area (In square metres)
In your system the magnetic path is mostly air, and that makes it more difficult to calculate as the flux doesn’t follow a neat path of constant cross sectional area, so much so that the reluctance of any core you might have used is irrelevant, except for making the flux come out of the ends.

yes I understand so the flux depends on the ampere - turns but since the electromagnet is cylindrical in shape, it is difficult to calculate the reluctance due to the large air section, so if I understand correctly using metglas or mpp as the magnetic core material has little importance in the induction of the voltage induced in a nearby conductor, so I could choose to use mpp because it allows me to have more ampere turns and also does not concentrate the magnetic field like metglas?

 

@Ian0 @MisterBill2 good morning guys, you haven't answered me, I don't want to be too repetitive, but let's say that I can't find the solution alone, so between the two materials of the cylindrical magnetic cores (mpp and metglas) which is the most suitable for my application and that is inductive coupling, that is inducing voltages in a nearby conductor??? I metglas having more perneability will tend to close the electromagnetic field lines more quickly??

 

@Ian0 @MisterBill2 good morning guys, you haven't answered me, I don't want to be too repetitive, but let's say that I can't find the solution alone, so between the two materials of the cylindrical magnetic cores (mpp and metglas) which is the most suitable for my application and that is inductive coupling, that is inducing voltages in a nearby conductor??? I metglas having more perneability will tend to close the electromagnetic field lines more quickly??

I would guess at Metglas, because MPP is a distributed gap material, and I would guess it has more leakage flux from the core.

 

I have a theoretical project
…
which has a cylindrical or horseshoe shape (for space reasons I can not use the circular shape)

If it is a theoretical project, why is space a concern? That sounds like a practical consideration to me.

 

I would guess at Metglas, because MPP is a distributed gap material, and I would guess it has more leakage flux from the core.

yes, that's exactly what I wanted to talk about, the mpp having a much lower permeability than the merglas will tend to disperse the electromagnetic field more, so is the mpp more suitable for inductive coupling? and then with the same dimensions the magnetic cores in metglas need fewer ampere-turns to generate the same electromagnetic field, but if all two generate 0.7 tesla (for example) will the induced emf in a nearby conductor be the same for both or does the mpp create more induced voltage in the nearby conductors??

 

If it is a theoretical project, why is space a concern? That sounds like a practical consideration to me.

yes it is a theoretical experiment, I have examined the cylindrical shape arbitrarily and for me it is easier to visualize it, in this case both magnetic nuclei have the same dimensions. yes, this is exactly what I wanted to talk about, the mpp having a much lower permeability than the metglas will tend to disperse the electromagnetic field more so the mpp is more suitable for inductive coupling? and then with the same dimensions the magnetic nuclei in metglas need fewer ampere-turns to generate the same electromagnetic field, but if all two generate 0.7 tesla (for example) the emf induced in a nearby conductor will be the same for both or the mpp creates more induced voltage in the nearby conductors??

 

By tha

the mpp having a much lower permeability than the metglas will tend to disperse the electromagnetic field more so the mpp is more suitable for inductive coupling

By that reasoning, no core is best. And that may very well be the case for long distance power transfer.

Have not researched it enough to know, but I do remember seeing a demo of long distance wireless power transfer, and, from memory:

1. Both sender and receiver were resonant, and that was a critical aspect of it.
2. Distance was about 2m.
3. Sending coil was about 1.5m in diameter with air core.

My understanding of magnetic (dipole) fields is that they fall off like a 1/r^2 at distances comparable to size of the source and 1/r^3 thereafter. So, expecting wireless power transfer over distances greater than the size of the emitter is wishful thinking. If you want to do that, use light or microwaves in a directed beam.

 

By tha

By that reasoning, no core is best. And that may very well be the case for long distance power transfer.

Have not researched it enough to know, but I do remember seeing a demo of long distance wireless power transfer, and, from memory:

1. Both sender and receiver were resonant, and that was a critical aspect of it.
2. Distance was about 2m.
3. Sending coil was about 1.5m in diameter with air core.

My understanding of magnetic (dipole) fields is that they fall off like a 1/r^2 at distances comparable to size of the source and 1/r^3 thereafter. So, expecting wireless power transfer over distances greater than the size of the emitter is wishful thinking. If you want to do that, use light or microwaves in a directed beam.

yes yes I know all those calculations, and I'm sure I'll get very little transfer, but my problem was to understand if using two magnetic nuclei of different materials in this case mpp and metglas, which of the two can create more electromotive force in a conductor 10 cm away, the literature states that the metglas having more permeability tends to close the field more towards the inside, and the mpp therefore tends (with the same field) to induce more electromotive force on the outside. is this reasoning correct?

 

Thinking about it for just a minute, when there is an air gap, very little of the flux is stored in the core - the air gap dominates before it gets very large.

For your application you just want a core material that has significantly higher permeability than air. In other words, it hardly matters.

 

Thinking about it for just a minute, when there is an air gap, very little of the flux is stored in the core - the air gap dominates before it gets very large.

For your application you just want a core material that has significantly higher permeability than air. In other words, it hardly matters.

yes indeed, my application involves wireless energy transfer with pulsed waveform, and using a cylindrical core shape, so there is a lot of air gap between the coil and the conductor to be induced. but in general, the metglas having much more permeability than the mpp, will tend to close the field lines more towards the core, and therefore less electromotive force?? and the metglas having much more permeability, very few ampere-turns are enough compared to the mpp, but can the metglas create the same electromotive force at the same distance as the mpp? I just want to know the answer to these two questions

 

@Ian0 @BobTPH @MisterBill2 @DickCappels good morning I would like to ask one last question, with your permission, so in the study of the shapes of the nucleus I have only two shapes left (cylindrical and "U") here considering one above all the magnetic nucleus in the shape of "U" how do you calculate the ampere turns necessary for the saturation of the nucleus? and also how do you calculate the electromotive force at a distance of 10 cm from the poles? so what formulas and what data do I have to use??

 

If there is a “U” only (no “I” across the end of the “U”core) the core should not saturate because the flux will be concentrated in the air gap between the ends of the top of the “U” rather than the core.

 

If there is a “U” only (no “I” across the end of the “U”core) the core should not saturate because the flux will be concentrated in the air gap between the ends of the top of the “U” rather than the core.

yes the U-shaped core would be horseshoe-shaped, therefore open at the end where the field is concentrated at the poles and therefore in the air gap, but what are the formulas to calculate the magnetic field B, and the ampere-turns?? that is, what formulas should I use to determine the magnetic field at the poles (air gap) and the ampere-turns needed?? I can't find the formula anywhere and I try to derive it from Hopkinson but I can't

 

yes the U-shaped core would be horseshoe-shaped, therefore open at the end where the field is concentrated at the poles and therefore in the air gap, but what are the formulas to calculate the magnetic field B, and the ampere-turns?? that is, what formulas should I use to determine the magnetic field at the poles (air gap) and the ampere-turns needed?? I can't find the formula anywhere and I try to derive it from Hopkinson but I can't

How good is your vector calculus? You have to integrate the flux over all possible paths to calculate it. You will a probably need some grads, divs and curls which I haven’t tackled since I graduated.