I am an average person being hunted down by a homicidal cyborg. He is about 90% metal, with his only remaining organ being a brain and all other meat on him being tissues which serve only as an anchor for cybernetics.

I have exhausted just about every method of killing or hiding from a person, but I have one final plan; The world I am on has a valley between two magnitised mountains, making the valley itself a massive uniform magnetic field which I will lure my pursuer through. I'm hoping that the eddy currents produced by a conductor moving through the magnetic field will be enough to either boil his organic components by heating the metal around them, or else for magnetic breaking to cause catastrophic interference to his mechanical systems.

I would like to ask primarily if this plan is feasible at all - would the heat generated by many small circuits be enough to have any real effect? - and if my scale is reasonable - would a human-sized conductor moving in a valley-sized field cause a big enough change of flux to make powerful circuits?

Edit: This is all assuming the cybernetics are made out of non-magnetic materials everywhere possible

  • $\begingroup$ You are going to have to have cyborgs that are made of metals that are influenced by magnets. Aluminum, certain kinds of stainless steel, won't be effected: scientificamerican.com/article/why-dont-magnets-work-on Now, the semiconductors tend to have magnetic properties, if they have processors in them...but a little magnetic shielding (present in any sensibly designed product) will make the plan really rough to pull off. But hey, maybe the evil genius cyborg designers were a bit incompetent/rushed? $\endgroup$
    – BrianH
    Commented Jan 11, 2017 at 17:02
  • $\begingroup$ That is wrong, Brian. Eddy currents require only a conductor.en.wikipedia.org/wiki/Eddy_current $\endgroup$
    – Willk
    Commented Jan 11, 2017 at 18:02
  • $\begingroup$ At best ur cyborg can rush the traffic light signals while giving chase on the road, other than that eddy current is useless here. $\endgroup$
    – user6760
    Commented Jan 12, 2017 at 3:31
  • $\begingroup$ Induced voltage is proportional to the rate at which he walks through magnetic field lines. The mountains would have to be absurdly magnetic and he would have to be so wildly fast that there would be no reasons why the protagonist could have survived long enough to have a plan. Powerful electromagnets, though, could actually give him seizures and hallucinations just by interacting with his organic brain. Of course if his brain isn't particularly well shielded, I'd be looking for a high power rifle. Just my two cents. $\endgroup$
    – user8827
    Commented Jan 31, 2017 at 8:54

4 Answers 4


It depends on the magnetic field strength.

Considering that the mountains have a static magnetic field produced by some permanent magnetic ore, it probably won't be enough.

But the induced currents can be enough to harm its low-voltage electronics, possibly permanently. Even this couldn't go in an Earth-like environment, you have something which produces a lot of strong permanent magnet.

Magnetic field strength decreases cubically with the distance, so you need two big mountains, in a short distance.

Maybe it could be some abandoned storage of neodymium magnets, left by an ancient civilization.


Most metals will carry a current: eddy currents, as you say. If you have a brain involved the bar for incapacitating the thing is even lower. The brain will not put up with much current flowing through it. The cyborg will have a seizure.

For a fixed large magnetic field, issues are magnetic density and how fast the cyborg is coming through it. That is doable. You could have it be well known that flying a small craft thru this area must be done slowly. The cyborg doesn't know and comes zooming in, seizes when the induced current hits the brain, and plows into the mountainside.

But a seizure is not the same as killing. Once it is down for a while the brain will recover. Now the cyborg is moving slow and cyborgs don't make the same mistake twice.

The protagonist should realize this too late. Fortunately his accomplice realized this too and removed the brain and housing from the cyborg while it was out. She has it in her duffelbag. It is awake now, but disconnected from the robot components. You never know when a cyborg brain might come in handy. Electroconvulsive therapy might have made it a little less homicidal.

  • $\begingroup$ Really, killing and incapacitation are both ideal, but I wasn't hoping to directly electrocute the brain (If that could happen the escaping protagonist isn't going to fair too great herself, eh?) I just thought increasing the temperature of its surroundings would be enough to do serious damage. That being said, do you really think the circumstances would allow the brain to carry a current? $\endgroup$
    – user32063
    Commented Jan 11, 2017 at 19:42
  • $\begingroup$ Our brains already carry and generate electrical current, at very low voltage our nerves carry chemically induced current. So if you get a few Watts extra generated in the machine-brain circuits, it could feed into the brain. $\endgroup$ Commented Jan 14, 2017 at 1:53
  • $\begingroup$ For one we do not have heads made of metal. Most of us. The other thing is how fast the conductor traverses the magnetic field. Your protagonist is probably slower than the cyborg. No question the brain can carry a current; it is bathed in electrolyte solution. I am a little concerned that a metal cranium might act as a faraday cage and protect the cyborg's brain. $\endgroup$
    – Willk
    Commented Jan 14, 2017 at 18:14

Why not? If I were creating cyborgs, I would be very careful using metal. I do not want my being to worry about corrosion or probably anything that could interfere easily like magnets. I'd also be worried about weight -- why make my cyborg any heavier than necessary? I would suggest that plastics or other manufactured material would be a better building choice. If I had to use metal, I'd choose one that was not magnetic.


Some metals are attracted to a magnet and some are not. The magnet is a good aid, though not a definitive test, in identifying metals. Metals are usually magnetic because they contain iron, though nickel is magnetic despite having no iron.

Magnetic metals include iron, nickel, cobalt and most of their alloys. Some forms of steel are magnetic, while others are not.

Non magnetic metals include aluminium, copper, lead, tin, titanium and zinc, and alloys such as brass and bronze. Precious metals such as gold, silver and platinum are also not magnetic." LINK

  • 1
    $\begingroup$ My question is assuming that the metal is non-magnetic and all damage would be done by eddy currents. I shall add that in! If the poor guy could be thrown around by magnets I doubt we'd have reached this stage of the problem. $\endgroup$
    – user32063
    Commented Jan 11, 2017 at 17:52

No, you are going to have to go big.

Much of the metallic structure of the cyborg will either not create a current or only create a random current based on the position of the part relative to the magnetic field. Some of the structure will actually act as a Faraday cage and shield other components from the effects of the magnetic field, and of course, any halfway competent evil genius isn't going to create an unshielded cyborg to begin with.

The other issue is current strength would be proportional to how fast the metal is moving through the magnetic field. A walking or even running cyborg isn't really going to go fast enough to generate an appreciable amount of current even if it was made out of copper (you would have to be running the cyborg at the speeds of cars or faster, alternatively the mountain has the sort of magnetic field an MRI generates, which has a few issues of its own).

The only way to do what you want is to overload it with a massive EMP pulse. Detonating a nuclear device high up in the atmosphere is one way, the x-ray pulse interacts with the electrons in the upper atmosphere, stripping them from the molecules of the air and releasing energetic free electrons into the Earth's magnetic field. This is useful if you don't really know where the cyborg is and you are stuck in the middle of ISIS held territory so are less concerned with the effects on the local electrical grid.

Non nuclear EMP pulse devices are also possible, and many are designed as bombs, using the chemical energy of the explosive to power an explosively pumped flux compression generator, although at this point it might be simpler to drop an actual bomb on the cyborg. The highly directional EMP should be sufficient to fry the electronic circuitry of the cyborg, rendering it harmless or outright destroying the non organic electronic components, and presumably causing massive burn damage to connection pants between the electronics and the organic nervous system.

Getting the cyborg in a valley between the mountains simply narrows your arcs of fire and makes it somewhat easier to aim and fire the device.


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