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From: Bill Sloman <bill.sloman@ieee.org>
Newsgroups: sci.electronics.design
Subject: Re: Small magnetic tunable filter for 6G and beyond
Date: Wed, 29 May 2024 14:17:04 +1000
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On 28/05/2024 1:25 am, john larkin wrote:
> On Mon, 27 May 2024 12:58:08 -0000 (UTC), Phil Hobbs
> <pcdhSpamMeSenseless@electrooptical.net> wrote:
> 
>> Jeroen Belleman <jeroen@nospam.please> wrote:
>>> On 5/27/24 07:08, Jan Panteltje wrote:
>>>> To 6G and beyond: Engineers unlock the next generation of wireless communications:
>>>> https://www.sciencedaily.com/releases/2024/05/240524114938.htm
>>>> Source:
>>>> University of Pennsylvania School of Engineering and Applied Science
>>>> Summary:
>>>> Engineers have developed a new tool that could unlock 6G and the next
>>>> generation of wireless networks: an adjustable filter that can
>>>> successfully prevent interference in high-frequency bands of the electromagnetic spectrum.
>>>> partial quote:
>>>> What makes the filter adjustable is a unique material, "yttrium iron garnet" (YIG),
>>>> a blend of yttrium, a rare earth metal, along with iron and oxygen.
>>>> "What's special about YIG is that it propagates a magnetic spin wave," says Olsson,
>>>> referring to the type of wave created in magnetic materials when
>>>> electrons spin in a synchronized fashion.
>>>> When exposed to a magnetic field, the magnetic spin wave generated by
>>>> YIG changes frequency.
>>>> "By adjusting the magnetic field," says Xingyu Du, a doctoral student in
>>>> Olsson's lab and the first author of the paper,
>>>> "the YIG filter achieves continuous frequency tuning across an extremely
>>>> broad frequency band."
>>>> As a result, the new filter can be tuned to any frequency between 3.4 GHz and 11.1 GHz,
>>>> which covers much of the new territory the FCC has opened up in the FR3 band.
>>>>
>>>
>>> YIG filter and resonators have always been a bit exotic. Maybe this
>>> will make them common-place. And more compact, hopefully! The YIG
>>> was tiny, sure, but the magnet wasn't.
>>>
>>> Jeroen Belleman
>>>
>>
>> YIG-tuned VFOs are the champs for low close-in phase noise. My HP 8566B’s
>> noise floor at 1kHz is a good 30 dB better than any SDR-style analyzer.
>>
>> If they manage to get them down to Digikey-level practicality without
>> screwing that up, it would be huge.
>>
>> I wonder if you could use a mag amp sort of structure, with a rare earth
>> magnet biasing some cleverly designed bits of saturable ferrite, plus some
>> small coils changing the effective gap in the magnetic circuit.
>>
>> Fun to think about.
>>
>> Cheers
>>
>> Phil Hobbs
> 
> How can one keep a magnetic field stable to parts per billion?
> 
> Seems like ambient 60 Hz fields and temperature changes and tiny
> noises in the coil current would dominate. It's hard to regulate a
> current to parts per million.
> 
> Qs are low too.
> 
> Does your HP have a big ovenized mu-metal box inside?

Electron microscopes and magnetic deflection mass spectrometers regulate 
magnetic fields pretty precisely - the Cambridge Instruments EBMF 10.5 
that I worked on used two othogonal magnetic fields to put the electron 
beam precisely were it was wanted to 15-bit precision at 10MHz.

I got dragged in when the Johnson noise in the existing scanning 
amplifiers started making the lines it drew look a bit blobby, which I 
fixed by taking the low noise FETs out of the front end - we didn't need 
the low input impedance they offered - and relying on the low noise 
transistors with which they had been cascoded.

Admittedly we only had the 10MHz step rate inside a 12-bit sub-field, 
and stepped between those sub-fields involved 1msec of settling time - 
the 18-bit DAC that looked after that was bit slow.

It's certainly not easy to regulate magnetic fields to parts per 
million, but it can be done.

The big mass spectrometer - that I worked on for a couple of months at 
one point - used a Hall plate to regulate its magnetic field to that 
sort of precision.

I had a potentially patentable idea to make it work a bit better, but 
when we looked into it the idea had been spelled out elsewhere though 
the engineers who had put the machine together hadn't heard about it.

-- 
Bill Sloman, Sydney