This articleneeds additional citations forverification. Please helpimprove this article byadding citations to reliable sources. Unsourced material may be challenged and removed. Find sources: "Search coil magnetometer" – news ·newspapers ·books ·scholar ·JSTOR(June 2016) (Learn how and when to remove this message)

Thesearch coil magnetometer orinduction magnetometer, based on aninductive sensor (also known asinductive loop and inductive coil), is amagnetometer which measures the varyingmagnetic flux. An inductive sensor connected to a conditioningelectronic circuit constitutes a search coil magnetometer. It is avector 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 onFaraday's law of induction. The temporal variation of themagnetic flux${\displaystyle \mathrm{\Phi }}$ through aN turns circuit will induce a voltage${\displaystyle e}$ which follows

${\displaystyle e=-N\frac{\mathrm{d}\mathrm{\Phi }}{\mathrm{d}t}}$

which can be expressed in a simpler way

${\displaystyle e=-NS\frac{\mathrm{d}B}{\mathrm{d}t}}$

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

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

• increase the surface (S),
• increase the turn number (N),
• use a ferromagnetic core.

When a coil is wound around aferromagnetic 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 themagnetization of the ferromagnetic core response to an external magnetic field. The magnetization is reduced by the demagnetizing field.

${\displaystyle {\mu }_{app}=\frac{{\mu }_r}{1+N_z({\mu }_r-1)}}$

where${\displaystyle {\mu }_r}$ is therelative permeability,${\displaystyle N_z}$ is the demagnetizing coefficient in thez direction.

The induced voltage will be written

${\displaystyle -Ne=NS{\mu }_{app}\frac{N\mathrm{d}B}{\mathrm{d}t}}$

The demagnetizing coefficient can easily be computed in the case of simple shapes (spheres and ellipsoids).

• Eye tracker: a search coil is used to measureeye movement using coils that are embedded into a contact lens.
• Education
• Non-destructive testing
• Magnetotellurics
• Space research
• Natural electromagnetic waves observations on Earth.

• Pavel Ripka,Magnetic Sensors and Magnetometers, Artech House Publishers
• S. Tumanski,Induction Coil Sensors - a Review
• [1]

• Waves (Juno) (Uses a magnetic search coil)

• Vision
• Magnetometers

• Articles with short description
• Short description matches Wikidata
• Articles needing additional references from June 2016
• All articles needing additional references