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I'm attempting to design a creature whose internal anatomy includes a powerful electromagnet so that it can do things like pulling guns out of people's hands at close range.

Like many electromagnets, this electromagnet will be a wire wound into a helical coil - a solenoid. However, this creature must biologically grow the wire itself, rather than have an artificial one implanted into it. As such, I need a biologically-grown electrical conductor.

I initially chose salt water, but, after seeing the electrical conductivity and resistivity of various materials, as well as a list of biometals, I chose calcium, which, at 20° Celsius, has a resistance of 3.36 × 10-8 (0.0000000336) ohm-meters and a conductivity of 2.98 × 107 (29,800,000) siemens; in comparison, annealed copper - a common electrical conductor - has a resistance of 1.72 × 10-8 (0.0000000172) ohm-meters and a conductivity of 5.8 × 107 (58,000,000) siemens at 20° Celsius. That's ~1.95 times less resistant and ~1.95 times more conductive than calcium.

While calcium isn't quite as good a conductor as copper (annealed or otherwise), it's much more readily available to an organism with Earthly biology. That, along with calcium's within-the-ballpark-of-copper performance as a conductor, made me decide to use a strand of calcium as the wire of this creature's electromagnet.

There are several caveats to this:

  • as far as I know, only pure calcium metal embodies these characteristics, and compounds of calcium don't
  • calcium metal "reacts exothermically with water and acids", and internal exothermic reactions aren't good for any creature
  • in addition to that, this wire will be carrying serious current (at least 2,000 amperes)
  • on top of that, calcium tends to be highly reactive, meaning that it likes doing chemistry with things
  • finally, since this biological calcium wire will be carrying a lot of current, it'll put out a lot of heat

As such, I - for the sake of insulating this calcium wire - require a calcium compound that is:

  • made out of calcium and (an)other material(s) that can be easily metabolized by a creature with biology similar to Earthly life; no xenon, uranium, arsenic, or such, please

  • resists electricity and heat as much as possible

  • conducts electricity and heat as little as possible

This way, the compound in question stops the calcium wire from reacting with, electrocuting, or burning the rest of the body.

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    $\begingroup$ Other constraints? Like within a particular body-part or must be flexible (it strikes me as probably easier to make the coil in a rigid structure than a bendy one)? $\endgroup$ May 28 at 9:31
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    $\begingroup$ Can't upvote this yet, I wonder if it can work. I read contrary requirements: if you put 2000A through a wire that has less than 2x the conductivity of copper, you'll waste a lot of energy and also produce lots of heat. When the shield does not conduct the heat, how to get rid of it ? Also, your design will require some isolating substance, not only between the shield and the wires, also between the calcium wires in the electromagnet. Real world transformer coil wires use an enamel coating. But enamel coating is baked in industrial processes, not inside animal bodies. $\endgroup$
    – Goodies
    May 28 at 10:42
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    $\begingroup$ Oxide? You handwaive a lot, but I keep having physics objections.. did you consider permeability of core material ? Did you calculate the force that results from the core, given the winding count, diameter and current ? sciencing.com/calculate-magnetic-force-solenoid-6310220.html You can't afford "solenoid" space between windings, if you need relevant attraction force. Even when you have 2000 amperes, a coil consisting of say 100 windings won't do much. You'll need thousands of solenoid windings to apply force that will attract and hold a metal weapon. The opponent will pull back ! $\endgroup$
    – Goodies
    May 28 at 11:36
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    $\begingroup$ @Goodies I'm currently at 1,500 windings. They need to be insulated (potentially viable, since the magnet won't be activated for long periods) or actively cooled; this question's sort of a trial balloon to see if insulation actually works. Yes, I know the relationship between amps/winding; the wires need to be thick enough to pass current without too much heat but thin enough so for plenty of them can fit. As for a core, there currently isn't one, since it encircles the creature's spine instead; I do plan on finding out whether a magnetic cylindrical shell would work as a magnetic core though. $\endgroup$
    – KEY_ABRADE
    May 28 at 11:42
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    $\begingroup$ hehe I wish you success with your design.. but I don't have an answer and I wonder what would happen if this creature would put all that energy into a combination of armour and agility... Rest my case. $\endgroup$
    – Goodies
    May 28 at 11:47

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I'm sorry, but it's not going to happen. While growing, the calcium wire has to be in intimate contact with whatever is doing the growing. For calcium metal you need serious temperatures, absolutely no water, and several other restrictions that make the "whatever" definitely non-biological.

On the other hand, paradoxically, metallic copper can be produced biologically - the phenomenon is similar to that giving rise to jarnbrak - and you can even get cold-precipitated metallic copper. Also, copper is available to organisms, to the point that we have copper-removal kelant mechanisms running (when these fails, copper accumulates in some districts of the body and you get e.g. Kayser-Fleischer copper rings in your eyes. That's not metallic copper, but if you add one of the existing copper-reducing mechanism in the mix, hey presto: metallic copper. Strand together copper fibers and that's your wire right there).

You'd need a lot of copper if compared to the ready availability of calcium, but that's doable.

The real problem, as you surmised, is the current. Heat production in a conductor follows the RI2 law, which means that with a generous 0.1 ohm resistance, a 2000A current is going to dissipate four hundred kilowatts of power. That's almost three orders of magnitude more than what a human-sized organism can dissipate safely.

On the other hand, you need magnetic field and that's proportional to the current, so the old trick of increasing the voltage to reduce the current while transferring the same power cannot be used. Actually you want to reduce the voltage to get the maximum possible current and magnetic flux.

Insulating the coil will avail little, it will actually be harmful, because the heat might be enough to increase the temperature of the coil beyond its likely fusion point.

Phase-change mechanisms could help (reservoirs of water that are flash-boiled, and boy is containing boiling water vapour another can of worms).

But as they say in my country, you've done thirty, do thirty-one (in for a penny, in for a pound): you have a whole EM coil setup in an organism, and even a significant energy source; why don't build that using an organic superconductor?

Organic superconductors rely on highly regular structures (picenes, even fullerenes) to build ceramic "channels", and specific dopings to alter the electric potential distribution and achieve superconductivity. This does not work too well in real life because doping imperfections cause "hot spots" that destroy superconductivity except at very low temperatures.

But there is a significant consensus on nanomachine-scale, atom-level assembly opening up previously unattainable superconductivity scenarios; even substances that are rigid enough at the microscale, or with wide enough "channels", that even thermal agitation doesn't disrupt their superconducting lattice, giving you a "hot organic superconductor".

You can't build such metamaterials using existing assemblage methods, but you perhaps could if you had subcellular-scale assemblers. I.e. "smart bacteria" able to operate with molecular-scale "tools", ensuring all molecular bonds are aligned optimally.

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    $\begingroup$ jarnbrak is a filmy sheen produced by metalllic iron-precipitating bacteria, and spies the presence of iron nodules in suitable bogs. It is Icelandic for "iron slick". Regarding resistance, the number you have is not resistance, it is resistivity. Resistance depends on resistivity and wire cross-section. Once you have resistivity, to get resistance you need to multiply by the length and divide by the section. So a 1mm2 copper wire (which is a lot biologically speaking: 1.5 mm2 is commercial household wire), 10 m long has R = 1.7E-8 by 10 divided by 1E-6, or 0.17 Ohm. $\endgroup$
    – LSerni
    May 28 at 11:08
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    $\begingroup$ ...for example, if I haven't made mistakes, your calcium coil would have a resistance of about 50 ohm (e.g. endmemo.com/physics/resistance.php ). Sustaining a 2000A current against that would dissipate about 200 megawatt per second [ shorturl.at/cfoHL ] $\endgroup$
    – LSerni
    May 28 at 11:12
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    $\begingroup$ The wire isn't 1 mm^2; it's 1 mm thick. That's a 0.78539816339 mm^2 cross-section...which is worse, actually, because the 2,000 amperes have to cram through a narrower wire this way. Yeah, I'm going to need to redo my incorrect math on this one...or use bigger wire. I think I'll use bigger wire, I'm feeling irrational today. Yeah, increase the width 5-fold, and therefore the cross section 25-fold, make it out of silver so that the creature has a reason to eat silver, decrease the amperage as much as I can tolerate it...it's all coming together. $\endgroup$
    – KEY_ABRADE
    May 28 at 11:17
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    $\begingroup$ Silver should also work. Didn't do the math, but reduced metallic deposition ought to be possible and not too different from copper. Then just keep it safe from oxygen, but that is easier. $\endgroup$
    – LSerni
    May 28 at 12:46
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    $\begingroup$ Silver is nice, but I've decided to nest solenoids around one another instead, as well as use a previous idea of mine - pumping blood over the entire assembly to cool it, mixing lye and sal ammoniac to cool that blood, and then pumping it back in again. $\endgroup$
    – KEY_ABRADE
    May 28 at 12:48

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