Halbach array arrangement for a transformer

[coolboyshane88]

TL;DR

We know that Halbach array works well with a permanent magnet by giving a strong magnetic field in one side and weak on the other side.

Can we use Halbach array for the electromagnetic field since the magnet field change with direction? What would be the disadvantage? Imagine if we use Halbach array special arrangements for the transformer instead of an iron core. Maybe it could give us the same result? Kindly Maybe we can design a halbach array arrangement using solenoid which behave same as permanent magnet but my question what happens when we give alternative current to solenoid, the direction will change so we won't be able to get halbach array result.

I'm trying to find Halbach array designs or arrangement for electromagnets in google but didn't get any good result. This method mainly used in permanent magnets and motors.

 

[berkeman]

Welcome to the PF.

Magnets typically make bad cores for transformers. Can you maybe guess why?

https://www.kjmagnetics.com/images/blog/normalvshalbach.png

 

[coolboyshane88]

Welcome to the PF.

Magnets typically make bad cores for transformers. Can you maybe guess why?

https://www.kjmagnetics.com/images/blog/normalvshalbach.png
View attachment 252032

Thank you for answering.

I mean that I want to use Halbach configuration using coils. I'm thinking to arrange solenoid in Halbach array arrangement to give strong flux in one side and weak in the other side. We know that solenoid behave similarly to the permanent magnet. Since alternative current change current in direction, I'm thinking to give pulse DC to solenoid which will give similar result like permanent magnet. Just my idea, kindly advise.

 

[hutchphd]

You are not alone:
www.jpier.org › PIERC › pierc56 › 18.15011411.pdf

 

[coolboyshane88]

You are not alone:
www.jpier.org › PIERC › pierc56 › 18.15011411.pdf

I have read this before but it's not mentioned what supply was given, I think most probably DC current. My question is that what happens if we give pulsed DC to this concept because Pulsating DC doesn't change direction. Will, there be any eddy current problem between the coils?

 

[Baluncore]

... Imagine if we use Halbach array special arrangements for the transformer instead of an iron core. Maybe it could give us the same result? ...

The topology of the Halbach array is quite different to the topology needed for a transformer. A transformer benefits from a reduced magnetic path length with tightly coupled windings. The Halbach topology is more applicable to linear or rotating motors where the magnetic path crosses a gap to a moving armature.

Electromagnets are inefficient when arranged as a Halbach array because of the great length of wire required. The Halbach configuration is more suitable for the fabrication of permanent magnets. Permanent magnets are bad news near transformers as they cause asymmetric saturation, which generates harmonics and reduces the maximum power that can be transferred.

 

[coolboyshane88]

Can we arrange solenoid in Halbach arrangement with few numbers of turns and achieve the result that I need? We know solenoid behave similarly to the permanent magnet. Just a thought.

 

[Baluncore]

Can we arrange solenoid in Halbach arrangement with few numbers of turns and achieve the result that I need?

Yes you can, but every pole must be wound individually, with all poles wired together in series or parallel. You will also need magnetic core material arranged to control the magnetic path.

We need to know where you are going with this. What are you really trying to do?

 

[coolboyshane88]

Yes you can, but every pole must be wound individually, with all poles wired together in series or parallel. You will also need magnetic core material arranged to control the magnetic path.

We need to know where you are going with this. What are you really trying to do?

My plan is to create a wireless power transfer using halbach array configuration. Since halbach gives strong magnetic field, this mechanism may help to improve the efficiency. let me know your thoughts.

 

[Baluncore]

The magnetic cores used to form the array will need to be a material suitable for RF.
What wavelength or frequency will you use?

A Halbach array has many N and S poles near each other. The poles will cancel unless there is close aligned contact between the transmit and receive arrays.

How far must the power travel across the gap?

 

[coolboyshane88]

The magnetic cores used to form the array will need to be a material suitable for RF.
What wavelength or frequency will you use?

A Halbach array has many N and S poles near each other. The poles will cancel unless there is close aligned contact between the transmit and receive arrays.

How far must the power travel across the gap?

I want to use inductive or magnetic resonant coupling concept using a series of capacitors in the coil. The frequency is between 100-200 Khz. The distance between the tx and rx is between 5mm to 20mm distance. I want to transfer 15 watts and try charging a smartphone. Let me know your suggestion.

 

[Baluncore]

Let me know your suggestion.

What phone modifications would be needed to make it work?

Flux will not cross a gap if there is a shorter route to close the magnetic path.

With 20 mm separation you can only have a maximum of two poles on the phone, so Halbach is really not applicable, and I cannot see how Halbach could be useful.

 

[coolboyshane88]

What phone modifications would be needed to make it work?

Flux will not cross a gap if there is a shorter route to close the magnetic path.

With 20 mm separation you can only have a maximum of two poles on the phone, so Halbach is really not applicable, and I cannot see how Halbach could be useful.

But don't you think this method could improve the power transfer efficiency. Currently, wireless chargers are only 75% efficient. Maybe Halbach arrangement could improve up to 85-90% since the majority of the magnetic flux in one direction. Maybe there could be an increment inefficiency?

I want to use a regular smartphone with 3500 maH battery capacity. I want to connect a receiving coil with rectification in the phone and would like to try an experiment with short distance between tx and rx.

 

[Rive]

But don't you think this method could improve the power transfer efficiency. Currently, wireless chargers are only 75% efficient. Maybe Halbach arrangement could improve up to 85-90% since the majority of the magnetic flux in one direction. Maybe there could be an increment inefficiency?

The most important reasons of the low efficiency is the flat design, the air gap and the low voltages involved. The only issue you can address is the former, indeed. But this Halbach thing won't be a help, since the magnetic field is already quite well 'directed', with barely and leakage on the bottom: that half of the pot core does that well.

It is just flat pots are no good pots

This picture from this paper (if you can dig up the full text somewhere) might be a help: at least it can give some directions and keywords to move forward.

 

[Baluncore]

I want to connect a receiving coil with rectification in the phone and would like to try an experiment with short distance between tx and rx.

The receive coil in the phone would have to be a mirror image Halbach array with the same position and orientation as the transmitter array. More poles over the area of the phone means the poles are closer. So for the same efficiency the separation will have to be proportionally reduced.

But don't you think this method could improve the power transfer efficiency.

No I do not. You only need two poles to charge a phone, one is the inside area of a circular coil, the other is the outside of the coil. Then the orientation is irrelevant, and alignment is not critical.

 

[erh_kov]

hi everyone. I wonder if it is possible to use electromagnet Halbach array for increasing a detector coil``` s depth range...would be happy for having some helpful ideas. thx.

 

[Baluncore]

Welcome to PF.

Coils like those used in metal detectors have a depth range of approximately their diameter. Several smaller coils as a Halbach array will have significantly less penetration depth. For deeper detection you need to use greater diameter loops.

Deep geological detectors use several very large loops laid out on the Earth's surface, then they monitor loop voltage as the Earth's magnetic field varies due to solar wind and magnetic storms.

Are you working with hand held metal detectors, as used for finding gold?

If you detect deep targets you will need an excavator to extract the target. There is not so much digging with small coils, and you do not need a mining license with an environmental impact statement.

 

[zoki85]

But don't you think this method could improve the power transfer efficiency. Currently, wireless chargers are only 75% efficient. Maybe Halbach arrangement could improve up to 85-90% since the majority of the magnetic flux in one direction. Maybe there could be an increment inefficiency?

I want to use a regular smartphone with 3500 maH battery capacity. I want to connect a receiving coil with rectification in the phone and would like to try an experiment with short distance between tx and rx.

If you want to increase distance and still have a reasonable charging efficiency, you may want to try principles of resonance using magnetically coupled tuned circuits. About such principles you can read on this wiki page
Don't know if anything of that is available on the market for cell phones and other small devices though.

 

[erh_kov]

Hi Baluncore. Thanks for your answer.

yes I am thinking this for gold detector. I mean I want specifically to increase the single coin finding range of coil, perhaps in double, and that is how I stumbled on idea of using electromagnet Halbach array.

Actually I already made an experiment: built four flat file bifiliar coils and in the center of array i placed detectors coil...but detector became so sensitive that it started to detect even movement my own hands and any vibrations...I did not have means to monitor magnetic field and relate it to coils...so that is why i need more expert views and advises...

regards

 

[hutchphd]

The reason magnet pulls on a ferromagnetic object is mostly the strength of the gradient of the magnetic field. The Halbach array is a clever method to make the alternating (in space) fields more compact without sacrificing field strength. This makes the gradients bigger as well as the fields and so they are tenacious.
This is exactly what you do not want for the coin detector. I too was impressed by the elegant simplicity of the Halbach at first view but have found only a few places where they are the best solution. So it goes.

 

[erh_kov]

thanks hutchphd.

so now i am bit disappointed by Halbach after these comments...
by the way, is there any simple way to squeeze and elongate the beam of magnetic field of a detector? sorry for my persistence. thxxx

 

[zoki85]

"The beam of magnetic field" is not good way of describing it. I guess you are asking if there is some way to make magnetic field to die away more slowly with distance from it's source? I'm affraid not much you can do in that respect. Possible are little improvements with changing the geometry of detector but not much

 

[anorlunda]

by the way, is there any simple way to squeeze and elongate the beam of magnetic field of a detector?

If there was, don't you think that the metal detector manufacturers would have already tried it and already offer it if it worked well?

 

[Baluncore]

@erh_kov
I can tell you that a Halbach array is not the way to go.

You need to consider the mode of operation and pick an advanced design.
A good detector transmits a short magnetic pulse that induces an eddy current in a metal target. Once the pulse ends, the detector coil picks up the eddy field as it decays and compares that signal with the signal that followed previous pulses.

You may benefit from having a receiver coil mounted like a 'D' on edge above the flat transmit coil. That way the only coupling between Tx and Rx coils is via the conductive target moving to different positions relative to the 'D' coil mid-line. That has a phase reversal under the coil and so is good for fast sweeping large areas.

The best volume strategy is to search the surface to about 4 inches, then scrape off the top 3 inches with a bulldozer, and repeat. That technique has the best gold recovery for minimum investment. It is more efficient than detecting deep and digging deep because it finds many small targets that would otherwise be missed.

What make and model, or principle, is your detector based on?

 

[erh_kov]

Hi friends. thanks all for your informative answers to my case! I appreciate it much.

as for Baluncore s question: i bulit some diy detectors and also used a garret ace whose coil i wanted to modify.
But the best policy is i think is to try `two box` solution as suggested by you.
Anyway I like experimenting though sometimes it can end in loss of time if the search is unguarded and less informed!

i think, my last question would be like this: can i make depth range as function of detectors power? I mean, can i increase reach of depth incrementally by varying coils power differentially in a frame of time? that way I can also achieve some discrimination knowing the response coming from each level.

thanks.

 

[Baluncore]

i think, my last question would be like this: can i make depth range as function of detectors power?

If you increase transmitter power you will have to wait longer for the receiver to settle down after the transmit pulse, and you will flatten the battery faster.

Magnetic field strength is current * number of turns on transmit coil. But coil inductance is number of turns squared. So more turns increases the field but slows down the pulse.

Using a larger diameter coil will have greater depth range, but the density of the magnetic field is less with greater coil area, and the inductance is more, so it has a slower pulse. Both reduce the effectiveness of the detector.

Switching amongst several coils is difficult because of the voltage and current involved. At the same time the unused open circuit coils have resonances that interfere with the response.

Designing coils for best sensitivity and depth is a difficult tradeoff.

 

[erh_kov]

If you increase transmitter power you will have to wait longer for the receiver to settle down after the transmit pulse, and you will flatten the battery faster.

Magnetic field strength is current * number of turns on transmit coil. But coil inductance is number of turns squared. So more turns increases the field but slows down the pulse.

Using a larger diameter coil will have greater depth range, but the density of the magnetic field is less with greater coil area, and the inductance is more, so it has a slower pulse. Both reduce the effectiveness of the detector.

Switching amongst several coils is difficult because of the voltage and current involved. At the same time the unused open circuit coils have resonances that interfere with the response.

Designing coils for best sensitivity and depth is a difficult tradeoff.

Thanks Balincore.

Now I know the limitations at hand and will proceed accordingly.

wish all corona-free days.