The search coil magnetometer or induction magnetometer, based on an inductive sensor (also known as inductive loop and inductive coil), is a magnetometer which measures the varying magnetic flux. An inductive sensor connected to a conditioning electronic circuit constitutes a search coil magnetometer. It is a vector magnetometer which can measure one or more components of the magnetic field. A classical configuration uses three orthogonal inductive sensors. The search-coil magnetometer can measure magnetic field from mHz up to hundreds of MHz.

The inductive sensor is based on Faraday's law of induction. The temporal variation of the magnetic flux ${\displaystyle \Phi }$ through a N turns circuit will induce a voltage ${\displaystyle e}$ which follows

which can be expressed in a simpler way

by assuming that the induced magnetic field B is homogeneous over a surface S (the magnetic flux will be expressed ${\displaystyle \Phi =B\times S}$).

The induced voltage (${\displaystyle e}$) may be increased several ways:

When a coil is wound around a ferromagnetic core, that increases the sensitivity of the sensor thanks to the apparent permeability of the ferromagnetic core.

The magnetic amplification, known as apparent permeability ${\displaystyle \mu _{app}}$, is the result of the magnetization of the ferromagnetic core response to an external magnetic field. The magnetization is reduced by the demagnetizing field.

where ${\displaystyle \mu _{r}}$ is the relative permeability, ${\displaystyle N_{z}}$ is the demagnetizing coefficient in the z direction.