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Counterfeit pen

Matabiri said:
In the interests of "just in case", I found a dollar and waved a magnet about. No effect, as I thought. That's why no-one tries to use magnets to test currency.
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There is a magnetic strip in some dollars, larger denominations I think (the $100, probably the $50, and maybe the $20). However, it's extremely weak. It's useful when large sums of money are together, in which case (so I've heard) it makes a detectable magnetic field that can be tracked.

Now, that's all heresay, and it sounds dubious to me, but thought I'd give my info on the matter :)
 
phildonnia said:
I was unable to deflect a $20 at all with a small neodymium magnet.
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I just checked a $100 and $1 with an AC bulk eraser and bills deflect about .1" off verticle when hanging straight down.

I've had ceramic magnets that deflected more. Dangle the bill straight down and bring the magnet near. It's not the embedded strip. This worked on older bills from before the strip.

I've also had had a wad (about 30 bills) in my back pocket set off hand scanners at the airport.
 
marting said:
I just checked a $100 and $1 with an AC bulk eraser and bills deflect about .1" off verticle when hanging straight down.

I've had ceramic magnets that deflected more. Dangle the bill straight down and bring the magnet near. It's not the embedded strip. This worked on older bills from before the strip.

I've also had had a wad (about 30 bills) in my back pocket set off hand scanners at the airport.
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This thread is starting to remind me of the time I had a couple of Aussie friends running around flushing toilets and reporting back on which direction the water swirled. :D
 
Beady said:
This thread is starting to remind me of the time I had a couple of Aussie friends running around flushing toilets and reporting back on which direction the water swirled. :D
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[derail]
Down the hole.
[/derail]

FYI, we have plastic banknotes with a number of low-tech and hi-tech features which are far harder to counterfeit than US banknotes.
 
marting said:
This has info on designing money change machines.
http://www.sensorsmag.com/articles/1101/26/pf_main.shtml
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Fair enough; I didn't have a powerful enough magnet. It still ain't iron oxide, though...

System accuracy depends on using small, sensitive magnetic sensing devices—such as giant magnetoresistive sensors.
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Not exactly handy things to have at a cash desk, particularly if you want people to be able to use their credit cards nearby.
 
Matabiri said:
Fair enough; I didn't have a powerful enough magnet. It still ain't iron oxide, though...

Not exactly handy things to have at a cash desk, particularly if you want people to be able to use their credit cards nearby.
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Why do you say that? Iron oxides are basic to most magnetic inks. As to GMR (giant magneto resistive sensors) these are really quite small and require magnetic bias fields that are dimensionally tiny. They have been used in disk drive heads for years.

A large and strong enough magnet to easily deflect a bill is a hazard to credit cards though, like most any close magnet.
 
marting said:
Why do you say that? Iron oxides are basic to most magnetic inks. As to GMR (giant magneto resistive sensors) these are really quite small and require magnetic bias fields that are dimensionally tiny. They have been used in disk drive heads for years.
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Okay. Not familiar with GMR technology, and thought the "giant" meant "big and powerful". My error.

Also forgot about magnetite for a few seconds. Haemotite, the more common iron oxide, isn't magnetic.
 
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