A magneto coil is an electrical conductor, such as a coil, helix, or helix. Magneto coils are used in electrical engineering. In application, current interacts with magnetic field. The current generates a magnetic field through the wire of the magneto coil, and vice versa. The electromotive force is generated in the conductor through the external time-varying magnetic field inside the coil.

Because of Ampere's law, the current flowing through any conductor will generate a circular magnetic field around the conductor. The advantage of using the coil shape of magneto is that it can increase the magnetic field strength at a given current. The magnetic field generated by the separated turns passes through the center of the coil and is added (superimposed) at the center to generate a strong magnetic field. The more wire turns of magneto coil, the stronger magnetic field will be generated. On the contrary, due to Faraday's law of induction, changing the external magnetic flux will induce a voltage in a conductor (such as a wire). Since the magnetic lines of force intersect the circuit many times, the induced voltage can be increased by winding the wires into coils.

The direction of the magnetic field generated by the magneto coil can be determined by the right hand grip rule. If the finger of the right hand wraps around the core of the coil in the direction that the normal current passes through the wire, the thumb will point to the direction that the magnetic field wire passes through the coil. The core end of the magnetic field line is defined as the North Pole.

Many magneto coils have a magnetic core with an iron sheet similar to ferromagnetic material in the center, thus increasing the magnetic field. The current through the coil increases the magnetic field of iron magnetization and magnetized material to the magnetic field generated by the conductor. This is called a ferromagnetic core or core coil. Compared with the case without magnetic core, ferromagnetic core can increase the magnetic field and inductance of magneto coil hundreds or thousands of times. Ferrite core coil is a kind of magneto coil with ferrite core. Ferrite is a kind of ferrite ceramic compound. Ferrite coil has low iron loss at high frequency. The iron core constitutes a closed-loop coil, in which there may be some narrow air gaps, which is called a closed-loop coil. By providing a closed path for the field lines, this geometry can reduce the magnetoresistance and generate a strong magnetic field.

A magneto coil without a ferromagnetic core is called a hollow core coil. This includes coils wound in plastic or other non-magnetic form, and magneto coils that actually have cavities in their windings.