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 through a N turns circuit will induce a voltage which follows
which can be expressed in a simpler way
by assuming that the induced magnetic field B is homogeneous over a section S (the Magnetic flux will be expressed ).
Figure 1: Induction sensor made up of a winding (orange) surrounding a ferromagnetic core (grey)
The induced voltage () may be increased several ways:
increase the surface (S),
increase the turn number (N),
use a ferromagnetic core.
Search coil using a ferromagnetic core
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.
Apparent permeability
The magnetic amplification, known as apparent permeability , 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 is the relative permeability, is the demagnetizing coefficient in the z direction.
The induced voltage will be written
The demagnetizing coefficient can easily be computed in the case of simple shapes (spheres and ellipsoids).
Applications
Eye tracker: a search coil is used to measure eye movement using coils that are embedded into a contact lens.
search, coil, magnetometer, this, article, needs, additional, citations, verification, please, help, improve, this, article, adding, citations, reliable, sources, unsourced, material, challenged, removed, find, sources, news, newspapers, books, scholar, jstor,. This article needs additional citations for verification Please help improve this article by adding 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 template message 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 Contents 1 Principle 2 Search coil using a ferromagnetic core 2 1 Apparent permeability 3 Applications 4 References 5 See alsoPrinciple EditThe inductive sensor is based on Faraday s law of induction The temporal variation of the Magnetic Flux F displaystyle Phi through a N turns circuit will induce a voltage e displaystyle e which follows e N d F d t displaystyle e N frac mathrm d Phi mathrm d t which can be expressed in a simpler way e N S d B d t displaystyle e N times S frac mathrm d B mathrm d t by assuming that the induced magnetic field B is homogeneous over a section S the Magnetic flux will be expressed F B S displaystyle Phi B times S Figure 1 Induction sensor made up of a winding orange surrounding a ferromagnetic core grey The induced voltage e displaystyle e may be increased several ways increase the surface S increase the turn number N use a ferromagnetic core Search coil using a ferromagnetic core EditWhen a coil is wound around a ferromagnetic core that increases the sensitivity of the sensor thanks to the apparent permeability of the ferromagnetic core Apparent permeability Edit The magnetic amplification known as apparent permeability m a p p 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 m a p p m r 1 N z m r 1 displaystyle mu app frac mathrm mu r mathrm 1 N z times mu r 1 where m r displaystyle mu r is the relative permeability N z displaystyle N z is the demagnetizing coefficient in the z direction The induced voltage will be written N e N S m a p p N d B d t 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 Applications EditEye tracker a search coil is used to measure eye movement using coils that are embedded into a contact lens Education Non Destructive Testing Magnetotellurics Space research Natural electromagnetic waves observations on Earth References EditPavel Ripka Magnetic Sensors and Magnetometers Artech House Publishers S Tumanski Induction Coil Sensors a Review 1 See also EditWaves Juno Uses a magnetic search coil Retrieved from https en wikipedia org w index php title Search coil magnetometer amp oldid 1117471239, wikipedia, wiki, book, books, library,