MEMM

[MeggerMan]

Hi Paul,
Latest update of parts ordered:

10 x ceramic magnets 50mm x 19mm x 10mm
4 x ceramic magnets 50mm x 19mm x 5mm

The gap in the AMC-320 core  is 35.5mm, so I will use 2 x 10mm (two outer) and 3 x 5mm (in middle).

I can have magnets cut from tiles but the machine setup cost of 38 GBP means I will test with the 19mm wide magnets first then look at fine tuning when things start to look promising.

I want to start the testing of the pulse circuit next on breadboard before I commit it to a pcb artwork.
I need to work out the timing capacitors for the 6 way switch on the pulse unit, (bit of trial and error I think), as the ranges need to overlap just slightly.
Aiming for 100Hz to 100Khz (maybe I should have ordered a 12 way switch now).

Regards

Rob

[PaulLowrance]

Rob,

Sounds good. I commend your professionalism. I wanted to add a side note for those people who do not have much money to spend that anyone can build the MEG on a shoestring. I'm the master of shoestring experiments, lol.

I'm discovering some really interesting effects with such nanocrystalline cores such as Metglas. From the BH graphs provided by Metglas we can see it requires very little transverse fields to saturate the core. A transverse field is not a longitudinal field. The toroids coil causes a longitudinal field. Although any stray field such as Earths magnetic field is considered a transverse field. Earths 0.5 Oe field is enough to saturate the Metglas core. Such transverse fields could cause undesirable effects in the MEG. Perhaps one solution is to encase the MEG core inside a relatively thick iron round enclosure. Another possible issue is radio waves. Any radio wave could cause similar problems. Unfortunately a big chunk of iron is not going to block magnetic fields above a few KHz-- a few hundred KHz more realistically.

Such problems are causing havoc on my MCE experiments. One moment I can measure strong MCE, but the next it's completely gone because the core snaps back into saturation caused by stray fields. As mentioned in my previous post, it is vitally important to completely degauss the core in order to perform the MCE experiment. Especially with cores that have high squareness such as Metglas cores.

Regards,
Paul Lowrance

[MeggerMan]

Hi MrAmos,
I have a lot of diffent pic chips and an ICE-Breaker development board and Microchips PICkit 2 Development Programmer/Debugger.
Its sorting out the program to generate the pulses using the interupt timers that will take time.
Also I worked out the steps are going to get a bit lumpy at the high end of 100Khz even using a 20MHz chip.
I may go down that route later on.

Hi Paul,
Yes I wound about 40 turns onto the AMC-320 core and hooked up to my new LCR meter, and I noticed that when I rotated the core slowly around on the worktop the Q value and inductanced changed slightly by about +/- 2%.  Very odd to see this happening.
I can do the test again and give you the actual values.
Meter uses 1Khz and 120Hz for its reading.

Regards

Rob

[PaulLowrance]

Hi Rob,

Wow, + and - 2% is lot for just changing the cores orientation relative to the external fields. And that's not even removing the stray field, just changing orientation. These nanocrystalline cores are amazing! Now if you had a large piece of iron, perhaps even silicon iron, that could _completely_ surround the Metglas core. I'm wondering how much that could help. Your Metglas core is large, so the iron core would have to be huge. Not sure how effective such a huge iron core would be at 1 KHz much less 30 KHz, but it's worth a try.

Personally I wouldn't bother with it for now. I'm thinking that if for some reason you are still unable to precisely replicate Naudin's scope shots then it might help to find a material capable of removing stray fields.

Regards,
Paul Lowrance

[PaulLowrance]

I've been using a method in an attempt to eliminate stray DC magnetic fields. I have two large toroids. One is silicon iron and the other I have no idea. These two toroids are stacked on top each other. I then place my Metglas core inside the two toroids.


The above will momentarily work, but it has problems. I took a compass and placed it inside the staked toroids. I then rotated the compass and notice it did not change. The toroids were blocked the Earths magnetic fields, which is in agreement with FEMM. This works fine if your toroids are degaussed. I then placed my toroids near a PM simply to slightly magnetize the toroids. I then removed the PM far away and repeated the experiment. This time when the compass changed to fixed direction when placed inside the toroids. This meant the toroids were applying a magnetic field on the compass.

This could momentarily block DC magnetic fields if you degauss the toroids, but any stray field could re-magnetize the toroid.

That covers DC fields. AC fields is another story. I'm thinking a small Faraday cage could block most AC fields. The Faraday cage needs to be non-magnetic wire. Any magnetic wire such as iron causes too much induction. Copper wire should work. Also the toroids need to be away from the Faraday cage walls.  Since I live in Los Angeles, CA. there's a lot of radio ways at just about any frequency. We know the Metglas cores are affected to fields in the MHz.


Regards,
Paul Lowrance