Body Modification: Magnetic Sensor

Our Larval Engineer reports that the current techie-thing-to-do involves having a tattoo artist or other unlicensed medical technician implant a tiny bar magnet in one’s finger, a process that adds a sixth sense to one’s built-in repertoire after the anesthetic shot of whiskey wears off. Evidently, converting magnetic field variations into mechanical force tweaks those little nerve endings wonderfully well, provided that your finger doesn’t subsequently rot off.

I point out that a magnet epoxied to a fingernail would probably get you within a few dB of the same result, minus the back-alley surgery thing. She counters that’s tacky and lacks style.

I point out that her medical insurance (for which, harumph, we are currently paying) probably doesn’t cover self-inflicted damage. She counters that most victims people have no problems at all.

I point out that a steampunk-style wristband incorporating a Hall effect sensor, LEDs, and maybe a vibrating pager motor would be at least as cool and probably marketable, to boot. She returns broadside fire by observing such a device requires power and she knows how I feel about batteries.

Game, set, and match.

In the interest of science and so as to not be rendered completely obsolete, I’ve epoxied a small neodymium magnet to my left little finger to discover what the world feels like. It’s surrounded by epoxy, which ought to prevent corrosion & deterioration until it eventually falls off or the nail grows out. It came with a white ceramic layer on one pole, which means it’s completely encapsulated:

Neodymium magnet on fingernail

Neodymium magnet on fingernail

She’s absolutely right: it’s tacky and lacks style.

I used JB KwikWeld fast-setting epoxy. The magnet attracted a tendril of uncured epoxy, so the “steel filled” part of the description seems accurate, and the magnetic field produced a nice smooth coat over the entire side of the disk.

It buzzes gently inside a Sonicare toothbrush handle, snaps firmly to steel surfaces. and is otherwise inoffensive. I must run some calibration tests to figure out what sort of magnetic field intensity a fingernail can detect. I’m certain it’s less sensitive than an implanted magnet, but I’m down with that.

Memo to Self: If you should occasionally use your little finger to ream out your ear or nose, that’s just not going to work any more…



  1. #1 by Josh on 2012-12-04 - 08:08

    I chose ring finger (apparently the most useless finger, even though I’ve just noticed how many letters I type with them), superglue and fingertip, years ago when I tried this. There definitely was SOME form of awareness, but I don’t think it stuck long enough for me to actually call it a sense.

    Me current thoughts on body/sense modifications lean towards audio input (wireless bone conduction transducers, attached or embedded in the ear), or navigation ( is the first link I found quickly via google, a product page unfortunately). Though if you report significant results with the epoxy, I may have to revisit this one.

    • #2 by Ed on 2012-12-04 - 08:59

      The Kindle Fire’s speaker magnets produce an interesting attraction / repulsion effect, but it’s (or, maybe I’m) not sensitive to the very low-level AC fields reported by those with embedded slivers. That’s not too surprising, I suppose, and might justify putting some processing power behind the sensor.

      I’ve doodled up a bunch of Arduino circuitry that will come in handy for that sensor wristband, although I’m undecided about the relative geekiness of half a dozen AA cells versus two prismatic lithium cells. The former would better fit in a weaponized Steampunk fashion statement, which may be the deciding factor.

      More on that starting tomorrow…

  2. #3 by madbodger on 2012-12-04 - 08:27

    I like your idea – a way to play with the concept without running all the risks. It seems to me that steel filled epoxy would provide a flux shortcut around the magnet, effectively reducing its strength, but since this is in the nature of an experiment anyway, I doubt it matters.

    • #4 by Ed on 2012-12-04 - 09:07

      without running all the risks

      Suffice it to say I have a low tolerance for personal medical emergencies; been there, done that, won’t do it voluntarily. [grin]

      In round numbers, the magnet snaps to steel plates with about the same enthusiasm as before, so the epoxy doesn’t short-circuit too much of the field. The fact that it’s a stubby disk, rather than a long sliver, means the dipole field doesn’t extend very far and it doesn’t generate much torque, although fingernails are surprisingly senstive to pressure and maybe the effects balance out.

      Being a techie, I’m not too surprised at finding magnetic fields & ferrous objects everywhere, so I’m probably missing a lot of the unexpected delight and mystery.

  3. #5 by Neil Hendin on 2012-12-04 - 14:23

    Please, for the love of Gauss, don’t get an MRI scan if you have this attached.

    • #6 by Ed on 2012-12-04 - 14:48


      Yet another key advantage of an external doodad: it’s fairly conspicuous. Not that that would convince anyone already set on an implant, ’cause it’s a stylin’ thing.[grin]

      If the MRI room has decent portal scanners, even an implant shouldn’t make it through the outer zone: they really care about “ferrous projectiles” around that machinery!

  4. #7 by Edward on 2012-12-05 - 23:40

    Yowza. Stay away from floppy disks and the backup tapes.

    • #8 by Ed on 2012-12-06 - 09:11

      And credit cards…

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