Visualizing Magnetic Signals On Tape

[MightyFrame]

This topic was discussed previously on the thread "Magnetic Developer AKA Magna-See", but I wanted to expand it a bit.

I've been using KyRead solution to see the data tracks on my QIC data tapes.




I think it works fairly well, but my largest concern is the scratches that it leaves on the surface of the tape when wiped off or accidently smeared with the optical magnifying devices I'm using.


I'm wondering if anyone can speak to the detrimental affect of surface scratches on magnatic data tape such as this.

AND, also, I looked into some interesting other methods of visualizing the magnetic signature/stream (whatever you call it) on the tape without putting the fine abrasive like KyRead particles directly onto the tape.

For example, the fascinating 3M Magnetic Tape Viewer device. Has anyone here ever owned or used one of these?






And scroll down to mwhite66's post where they say "Old news. We had those back in the '50s for directly viewing magnetic tape data. I have personally used one to visually pull data off a corrupted tape. You can see the individual magnetized domaines that made up the data."
That's EXACTLY what I am wanting to do here, and why I am going through this reserach effort.





Or this thing, called a magview?

http://www.emeindian.co.in/magnetic-field-analyzer.html


And the Magnetic Field Viewer Film:


I just ordered from eBay a 2" x 2" card doing something similar. I'll report here the results I get from that after it arrives.


It looks like a similar topic was discussed on an older newsfeed forum:
[ARSCLIST] Magnetic tape viewers...

Thanks for sharing your knowledge, everyone.
-AJ

[MightyFrame]

https://store.arnoldmagnetics.com/p-...er-b-1022.aspx

Has anyone used this?



https://youtu.be/_TxDdx60LZk



I guess it's also referred to as the Plastiform Magnetic Viewer.

RECORDING engineer/producer magazine July/August 1973, page 13

[Velktron]

Very interesting, I didn't know that such passive magnetic field viewers existed. Well...of course we all (?) saw a demonstration with (electro)magnets and iron filings at some school or college lab, but not something so compact and detailed.

My only concern with using 3M's "non invasive" viewer is that, in fact, it's not all that "non invasive": magnetizing the ferro-fluid it contains and then moving it away from the field you're trying to visualize requires some energy expenditure, and thus may result in some field weakening/slight demagnetization, though probably less than the one that a tape incurs during normal use.

All other methods I'm aware of rely on some form of polarized light, which require more "active" devices to visualize (I'm not sure if there are passive light-polarizing sheets that can visualize a magnetic field using just ambient light, though).

[MightyFrame]

Velktron,

Thanks for your feedback here. I think your point about the questionability of the viewer being truly "non-invasive" is extremely valid.

My experience so far has been only with the Kyread solution (ferrofluid), applied directly to the tape (which I think is clearly invasive). And it does seem to negatively affect the magnetic signals on the digital DC-600 QIC tapes.

In my tests, I write a test file to the tape, then read it back to verify that it is a good write. Then I apply the Kyread to the tape and visualize the magnetic signals (like I showed in my pictures at the top of this thread).

Then I wiped it off carefully with a Q-tip, and then tried to read the file from tape again. It usually produces an error, and is therefore unreadable. So it certainly seems like the ferrofluid Kyread has a negative affect.

I'm doing some more advanced research on the individual magnetic flux transitions for these tapes. I built hardware that allows me to capture and analyze the data pulses produced by each magnetic flux transition on these tapes.

Here's 2 videos showing how I built this hardware:

https://youtu.be/BfKUJmPSam0

https://youtu.be/n3Cbzv9l61E

I have not yet repeated my same test with before and after Kyread with my hardware, but at some point I will do that, and report the results here, if anyone finds it interesting.

As far as your polarized light viewing methods, I've never heard of this in the context of revealing the magnetic signals on media. Do you know of any examples online?

Thanks for the discussion. Good stuff.
-AJ

[Velktron]

Well, for starters, look up the Faraday and MO Kerr effect. Systems like the CMOS-MagView rely on those principles, implemented with high-resolution microelectronics sensors. The Magneto-optic Kerr Effect was/is also used in MiniDiscs and other MO data storage media.

Edit: with the Kyread solution, I think the problem is that the ferrofluid gets in direct contact with the magnetic tape's surface, so you have both a stronger induced magnetization, plus "trailing" of magnetized particles and mechanical abrasion when trying to remove them, which as you saw for yourself does measurable damage. At least with the 3M viewer you have a few microns of a film sheet between the ferrofluid and the tape.

[MightyFrame]

You're getting into some seriously advanced stuff. This is VERY cool...and a bit over my head for now, but I'm reading up on it...

[62vauxhall]

FWIW, I had one of those 3M Tape Viewers. Sometime in the mid 70's someone brought it over to show me and never wanted it back. I tried it on a 1/4" reel tape and it did reveal the magnetic pattern but it was quite faint. I regarded it as just a curiosity and did not investigate why such a thing would be needed. Not long ago I donated it to a local electronics museum thinking it was more up their alley than it was mine. By that point in time, the foam liner inside the wood box had pretty much disintegrated.

[MightyFrame]

Very cool, 62vauxhall, thanks for sharing that! They seem to be such a rare thing.

For me, these items are useful to see how many tracks are on a "mystery" data tape, and the alignment and spacing of those tracks. I wish there was a better way to see clearly without damaging the tape and the magnetic signals, like the Kyread solution does.