More cool magnet info.

[Artie]

Here's some great magnet info I found. Its buried in tech info about hall-effect sensors, but still, a good read. Look in the box called "Technical Information", and click on the subject called "Hall Effect Sensing and Application Book Complete file".

http://content.honeywell.com/sensing/prodinfo/solidstate/lit.htm

Or . . . just click here. (Its about a 1.5meg PDF file.)

Particularly, look at page 87, paragraph "Time".

In the older permanent magnet materials, such as cobalt-steel, some metallurgical changes take place as a function of time. If such a magnet is magnetized before these changes have stabilized, flux changes will occur. (This effect can be reduced to a negligible factor by artificial aging.) In the magnet materials such as Alnico or Ceramic, metallurgical changes do not take place in any measurable degree at room temperature. A freshly magnetized permanent magnet will lose a minor percentage of its flux, as function of time. This loss of flux can be essentially eliminated by a partial demagnetization of the charged magnet in the amount of 7% to 15%. This is most conveniently accomplished by an AC field. The AC field should be in the same direction as the magnetizing field. It should be reduced to zero gradually, either by withdrawing the magnet with power on, or by reducing the AC voltage to zero with a variable auto-transformer.

So . . . It looks like "ageing" a magnet is simply applying an AC field to "scrub-off" about 10% of the initial magnetization. Interesting read.

Artie

 

[Faraday]

Re: More cool magnet info.

My job has a de-gausser that they will let me use. All I need is a gauss meter and I could reduce the field in magnets. If this turns out well, I could maybe offer this to others that would like it done.

 

[hamerfan]

Re: More cool magnet info.

I read at the Bill lawrence site that this happened with mags from the 50 to 60ties. But now they changed the formula (this refers to filler material they used in old days) to get a more industrial grade of qualtity mags. Industry doesnt like aging or changing specs. BL says nowadays this natural degaussing by time is less than 1% in 100 years. Too bad for us!
These artificial degaussing which Faraday is refering to is another thing.

 

[octavedoctor]

Re: More cool magnet info.

An interesting link Artie, thanks for posting that.

My colleague Steve, who's a proper engineer not a doofer like me, has toyed many times over the years with the idea of Hall effect based pickups...

 

[Artie]

Re: More cool magnet info.

My colleague Steve, who's a proper engineer not a doofer like me, has toyed many times over the years with the idea of Hall effect based pickups...

Thats something I'm playing with, myself. I haven't actually built a prototype yet though. The only real problem I see so far is, overcoming the "threshold" voltage. I don't think they can sense the lowest level string vibration. Kinda like how a diode doesn't "turn on" 'til it exceeds the voltage drop.

Artie