An induction stove uses induction heating for cooking. An induction stove transfers electrical energy by induction from a coil of wire in the stove into a utensil made of a material which must be electrically conductive and ferromagnetic.
Induction stove may be a built-in hob, part of a range, or a standalone unit. Built-in units usually have multiple elements, similar to separate burners on a LPG cooking range. Stand-alone induction modules too exist with a single-element, or sometimes have two elements. The design of all such heating elements is similar. An electromagnet is sealed beneath a heat-resisting glass-ceramic sheet. This glass sheet can be easily cleaned. When the stove is turned on the utensil is placed on the ceramic glass surface and begins to heat up, along with its contents.
In this type of stove a coil of wire is mounted under the cooking surface, and a large alternating current is passed through it. This current creates a changing magnetic field. When an electrically conductive utensil is brought close to the cooking surface, the magnetic field induces an electrical current, called an "eddy current", in the utensil. The eddy current, flowing through the electrical resistance, causes electrical power to be dissipated as heat; the utensil gets hot and heats its contents by heat conduction.
The cooking utensil is typically made from stainless steel or iron, which is much less conductive and is ferromagnetic. The copper coil, present under the cooking surface on the other hand, is made from wire known as litz wire, which is a bundle of many tiny wires in parallel. This coil has many turns, and the bottom of the utensil effectively forms a single shorted turn. This arrangement forms a transformer that steps down the voltage and steps up the current. The resistance of the utensil, as viewed from the primary coil, appears larger. That, in turn, means that most of the energy becomes heat in the high-resistance steel utensil, while the driving coil remains cool.
Inside view of an induction stove. The large copper coil forms the magnetic field, a cooling fan is visible below it, and main and auxiliary power supplies surround the coil.
Since heat is being generated by an induced electric current, the unit can detect whether cookware is present (or whether its contents have boiled dry) by monitoring how much power is being absorbed. That allows such functions as keeping a utensil at minimal boil or automatically turning an element off when the utensil is removed from it.
Materials used for the cooking surface and the utensils/cookware
The cooking surface is made of a material which is a poor heat conductor, so only minimal heat is transferred from the utensil to the cooking surface . In a normal operation the cooking surface stays cool enough to touch without injury even after the cooking utensil is removed.
Induction hobs (cook tops) work well with any pans with a high ferrous metal content at the base. Cast iron pans and any black metal or iron pans will work on an induction hob.
The reason why iron or steel cookware works on an induction stove and aluminium or copper cookware do not is because of the permeability and resistivity of the material. Aluminium or copper cookware is more conductive and nonmagnetic. That means that the effective resistance of such utensils is much lower, and so the induction stove will not work efficiently with such utensils. The heat that can be produced in a utensil is a function of the surface resistance. A higher surface resistance produces more heat for similar currents. This is a "figure of merit" that is used to rank the suitability of a material to be used for manufacturing induction heating cookware.
Induction stoves are safer to use than conventional stoves because there are no open flames and the element itself reaches only the temperature of the cooking vessel and only the utensil generates heat. Induction stoves are easy to clean because the cooking surface is flat and smooth, even though it may have several heating zones. Since the cooking surface is not directly heated, spilled food does not burn on the surface.
They have a definite advantage over conventional gas flame and electric stoves, as they provide rapid heating, improved thermal efficiency, and greater heat consistency, yet with precise control. The usage of these stoves is ideal in situations where a hotplate would be dangerous, as an induction stove, itself creates no heat.
A far greater advantage is that these stoves are almost flush with any cooking platform, and they can be easily accessed and used by disabled people in wheel chairs unlike other types of stoves.