I have an inductive stove, and some very large pots that don't work on the stove. It seems that the material is invisible to the induction coil, and if I were to place a steel disk inside the pot, then that steel disk would act as a heating element. Would this work?
This would be for liquids, boiling large amounts of mostly water (bone broths, beer, etc.), so the cooking surface isn't really a factor.
edit: The stainless pots I'm using are quite thin. I have tried placing them on a cast iron skillet similar to the adapter idea, but that doesn't work well at all. I am hoping the disk would heat, and being inside the pot, would be much more efficient. I could also test with some generic bits of steel I can find. I thought I'd ask first.
Best Answer
It would not work
As Benjamin Kuykendall stated, you may place magnetic iron or steel under the pan. I will tell you why placing it in the pan won't work.
Induction
As the name states, induction cooking works through induction: The stove runs an alternating current through a coil, producing a changing magnetic field. This changing magnetic field then induces a current in anything conductive placed in it.
Conduction
What happens when you place an aluminium or copper pan on top of the stove? A current will be induced in them, but they are very good conductors, and pans are much thicker than the copper in the coils, so not a whole lot would happen. The stove would likely notice that little energy is being absorbed from the magnetic field, complain and turn the stove off.
Impedance
So what is the difference with iron? Well, iron is not as good a conductor as copper or aluminium, but it's not that bad. The thing is though, iron is magnetic, and resists the magnetic field from the stove. This means that all the current is confined to the very surface of the iron, greatly increasing the current density, and therefore the power dissipated.
You can tell that this is the reason by finding a non-magnetic stainless steel pan and trying it. It won't work. (it's the nickel in the alloy that changes the crystal structure, making it non-ferromagnetic)
So what happens?
When you place the steel under the pan, the steel acts as usual, confining the current and heating up.
When you place the steel in the pan, the entire pan between the steel and the coil will happily conduct the current, and heat up less than the coil under the stovetop.
Other tricks
So, the reason that iron works is that the current is confined to a small thickness of the metal. Can we use this in other ways?
Foil
Aluminium foil is very thin, so it doesn't matter whether the material conducts well. A strategically placed piece of aluminium foil can absorb all that energy, melt, and totally ruin your induction stove. Don't do that.
Possibly you may be able to improvise a pan with glass cookware containing aluminium foil and water, but I wouldn't recommend it
High frequencies
There's another trick that engineers can use. At high frequencies, alternating currents will confine themselves to increasingly thinner thicknesses of metals. This means that if you use a high enough frequency, any conductive metal will work. There are stoves that use this principle, but they are rare and new.