Magnetics ZH42206TC toroid core

[ivconic]

The mumetal material is cold-rolled and any attempts to cut cause changes in physical properties, including magnetic permeability and Curie temperature - the sample becomes unstable and unpredictable; This also applies to anti-theft tags.
I've experienced this firsthand. You're left with a toroid or the use of tags in the form of straight cores, but beware - they can't be pressed.

Good info, thanks!
Although I didn't know that; I instinctively gravitated towards toroid solutions anyway.

[Krzysztof]

The mumetal material is cold-rolled and any attempts to cut cause changes in physical properties, including magnetic permeability and Curie temperature - the sample becomes unstable and unpredictable; This also applies to anti-theft tags.
I've experienced this firsthand. You're left with a toroid or the use of tags in the form of straight cores, but beware - they can't be pressed.

[pito]

contact producers directly on alibaba.com, some of them offer samples.
https://www.alibaba.com/product-detail/High-Permeability-MingDa-Ferrite-Core-Toroid_60417822195.html?spm=a2700.galleryofferlist .normal_offer.d_price.1e8feeb54dkKWG

[ivconic]

bad idea, I believed that mumetal and permalloy have similar mechanical properties, and permalloy is specially heated after mechanical processing....

Yes I experienced lot of troubles trying to cut and straighten them. Wasted many pieces like that.
It didn't occur to me to heat it with hot air soldering tool and try like that.
Anyway ; toroid core is much easier to handle and set the windings on it.
So I am still for toroid cores. Makes my life much easier.

[pito]

I saw one advertised somewhere that "can be cut with scissors." I have no experience either way, but it seems to me that mumetal would have a more consistent µ, I know that ferrites can vary 25-50%.

bad idea, I believed that mumetal and permalloy have similar mechanical properties, and permalloy is specially heated after mechanical processing....

[pito]

https://www.youtube.com/watch?v=dP84iJlQCDI

[ivconic]

Would be good to project an "instrument" with which we could be able to measure the µR of toroids.
Yes there is simple method by wounding exact humber of turns of the same wire over toroids and measure the inductance.
Then calculate. But that's lot of tedious job.
Something much "smarter", faster and easier is desirable.

[ivconic]

I saw one advertised somewhere that "can be cut with scissors." I have no experience either way, but it seems to me that mumetal would have a more consistent µ, I know that ferrites can vary 25-50%.

That's correct.
"Initial permeability µ = 15000 +/- 30%"
I was thinking to include small helmholtz coils setup.
It is further idea, to keep the sensor inside such setup and turn off helmholz coils just for a very short period of time when taking sample.
Or even better (more complicated) to have possibilty to adjust helmholz coils setup field strength and find a sweet spot where it will equalize in strentgh with surrounding Earht magnetic field (referent for the area and without present anomaly).
Similar to when you find a spot on soil without metals to perform GEB before start searching.
Why this? To keep the sensor "enclosed" in such magnetic field stong enough, to maintain the sensor readings always correct and at the same time weak enough so even the weakest "outside" anomaly can be catched by the sensor and recorded.
And there is extra treat from this; by slowly and gradually rising the strength of the Helmholz coil setup; to be able to "reject" unwanted small fluctuating outside anomalies.

[Carl-NC]

I saw one advertised somewhere that "can be cut with scissors." I have no experience either way, but it seems to me that mumetal would have a more consistent µ, I know that ferrites can vary 25-50%.

[ivconic]

Why not use mumetal instead? You can get a sheet of Ultraperm 80 for $30 USD and get 50-100 sensors out of it. µ_r = 50,000-100,000.

Yes, I thought about that. Even more; I still have a few "white" toroids that are made up of rolled mumetal tape. This was sent to me xx years ago by our dear friend ApBerg.
But what if I succeed and make a good sensor out of it? How will I always be able to replicate the same results later?
My wish is to establish standard components that I will be able to find whenever I need them, today, tomorrow... in 5 years.
Because I don't have too many of those "white" toroids, maybe one or two are left.
Another problem; I still don't know the permeability of that material. Therefore, such a sensor would be unique. Hardly repeatable later.
If I listen to you and get a "sheet" of such material; the geometry of such a sensor will not be the same as the one I would refer to.
For now, I have the basics based on other people's work. I have the geometry, the way it is wound, even the number of coils and the thickness of the wire.
Very little chance of it failing if I find said toroid.
And if I start with a "sheet" that I have to cut into pieces and make a "wafer" and then wind a wire for "sense" and a special one for "drive" over it...
that's already a "pioneering" work, I'm doing something that probably no one has done before nor didn't work like that.
I don't mind it, I even like it as a challenge.
But I have very bad experiences with the thin strip from the "white" toroid mentioned above.
It is very fragile and I tried to cut it with scissors, a scalpel... it is not easy to cut, it breaks suddenly and once it is rolled up; later, when it is unrolled,
it cracks unpredictably and can never be corrected. Namely; I tried cutting strips to make a copy of the FGM3 sensor from that strip. Never made.
Once I managed to barely cut a section of that strip to the required length, then I "sandwiched" it with pieces of paper and pressed it so that it stood,
hoping that under pressure it would straighten.
It had been standing like that for months, believe it or not.
When I checked it; it didn't "squeeze out" and stayed straight, it again began to bend itself and return to the position in which it was in the toroid.
And it started breaking again. So I gave up.
Does Ultraperm 80 cut easily without cracking?
I tried the same with "price tag" strips. At least they are straight. But they are too wide and I tried to cut them lengthwise. Same story, they breaks unpredictably.
In short; I need something "standard" that can always be bought, found and ordered.
If Ultraperm 80 can be cut without cracking; that's a good start. I'll see where I can find it.
But I need confirmation that it can be easily cut without cracking. Otherwise, everything is in vain.

[Carl-NC]

Why not use mumetal instead? You can get a sheet of Ultraperm 80 for $30 USD and get 50-100 sensors out of it. µ_r = 50,000-100,000.

[ivconic]

Products - Pro Audio Engineering

maybe AMIDON

http://www.amidon.de/contents/de/d541.html

MFG Walter

@Krzysztof & @walter
Thanks, but I can't find my way around those pages.

[ivconic]

Digikey have some Epcos toroids in stock with 15,000 initial permeability but only 10mm diameter.
They also have 22mm cores in stock but only up to 10,000 initial permeability.
Seems the combination you want is relatively tricky.

Indeed it is.
Higher the permeabilty = easier to saturate the core.
Design is planned to be lightweight battery operated, consuming low current, without "hot" parts.
That's why high permeability is needed. I could try with µR <15,000, of course it will work.
With µR <=10,000 thing will still be doable, but complete morphology of the instrument will suffer from many tradeoffs.
...
You see! Tough thing to find indeed!

[ivconic]

It looks like Magnetics Inc. may have discontinued their 'H' material cores, but their 'M' material cores have a permeability of 15,000u so the ZM42206TC may be a replacement if that's any easier for you to find. If not, then Wurth Elektronik make a good range of cores although I haven't checked for your exact spec yet.

I saw it before I started this topic.
Ordering from USA is several times more expensive and complicated for me.
I am inclined towards eastern sources. Price, speed, none custom complications... you name it.
Pity.

[Olly]

Digikey have some Epcos toroids in stock with 15,000 initial permeability but only 10mm diameter.
They also have 22mm cores in stock but only up to 10,000 initial permeability.
Seems the combination you want is relatively tricky.