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# Function of the ferrite for wireless power transfer

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#### F-Moura

##### Junior Member level 2
Hello guys,
I´m developing a project that I want charge battery with wireless power transfer. For this I´m using a demo kit LTC4120 by Linear.
I no have experience with wireless power transfer and transformers, I always worked RFID and simple analog electronic and for this I'm having difficulty for understand how the system work.
My demo board use 25mm ferrite above receive coil, I received other ferrite of 35 mm for put above other disk for increase received power in 30%, it really happens!
I want study about ferrite disks, how dimension and geometry their can help me to increase power received and consequently increase the distance that I can transfer my power

A ferrite disc focusses the magnetic field to a certain extent, it also isolates possibly lossy conductor structures in the vicinity. Visualizing the field geometry in a simulation helps to understand the effect.

F-Moura

### F-Moura

Points: 2
generally the receiving and sending coils are bigger than the gap. If ferrite is coupled between them then the lines of force are concentrated into a smaller cross-sectional area and thus a rod can extend the gap beyond the efficient loop diameter or be used to improve the coupling factor for transformer efficiency.

F-Moura

### F-Moura

Points: 2
Well, as far as I know ferrite make the magnetic field density stronger. The magnetic field density is given by the product of the permeabilty of the material in question and the magnetic field. Usually, the permeability of ferrite is much bigger than that of the air, thus for ferrite the magnetic field density is much stronger.
The power, which is of interest, is proportional to the current and the variation of flux. The flux is proportional to the magnetic field density (it is not proportional at all times, but you get the ideia). So, the stronger the field density, the power should increase. You might think that the bigger the ferrite, the more power. However, you can only get as much power as your power input. So it might be possible that changing the ferrite once more does not get you that much energy.

What do you mean when you say that you want to charge a battery with wireless power transfer? For what I understand when someone says wireless these days, this means that you want to do it by some distance. Perhaps you want to put the battery over a desk near a charger and the battery will start charging. In this case, thing are much different.

F-Moura

### F-Moura

Points: 2
Hello,
sorry for delay, I Had to travel.
I want share with you any informations that I got with Liner:
-
generally the receiving and sending coils are bigger than the gap.
The maximum range of power transfer is half of coil diameter.
No is easy relationship geometry of ferrite and improvement range, but ferrite really improvement range with limitation previously mentioned.
I will buy other ferrites to test the best for me.
Well, as far as I know ferrite make the magnetic field density stronger. The magnetic field density is given by the product of the permeability of the material in question and the magnetic field. Usually, the permeability of ferrite is much bigger than that of the air, thus for ferrite the magnetic field density is much stronger.
The power, which is of interest, is proportional to the current and the variation of flux. The flux is proportional to the magnetic field density (it is not proportional at all times, but you get the ideia). So, the stronger the field density, the power should increase. You might think that the bigger the ferrite, the more power. However, you can only get as much power as your power input. So it might be possible that changing the ferrite once more does not get you that much energy.
I no undestand one think, I know that permeability of ferrite is much bigger than air, but the ferrite should be positioned in back coils, if I put the ferrite disk between coils the power transmission is interrupted. Why ? It work as a barrier?
If I use cylindrical ferrite, Can I have better result?
What do you mean when you say that you want to charge a battery with wireless power transfer? For what I understand when someone says wireless these days, this means that you want to do it by some distance. Perhaps you want to put the battery over a desk near a charger and the battery will start charging. In this case, thing are much different.
I will use wireless power tranfer to provide energy to my charger controler and it charge a battery.

if I put the ferrite disk between coils the power transmission is interrupted. Why ? It work as a barrier?

I think that is because the magnetic density will attenuate on the air and there will be little magnetic density for the ferrite do "concentrate".

I think a cylindrical ferrite will give you better results as long as the coils are of the same size. If the ferrite is bigger than the coils, the size won't matter much more. But I am not sure.

Can you send pictures of your set up?

F-Moura

### F-Moura

Points: 2
This is imagem of boards.

In transmister we have 40mm coil and in receiver we have 20mm pcb coil.

Well, one think I now, Ferrite will be improve best range to may system.

Now I am study other system to power transfer. We are talking about inductive couple, but exist magnetic resonance couple too, that have any benefits.

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I see what you trying to do. Well, in this case I don't think the shape matters much. I was talking about transformers, which are wireless. I'll take a look and let you know

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