Re: Small magnetic tunable filter for 6G and beyond

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