Magnetometer

A magnetometer or a compass is a navigation device that measures the strength of the magnetic field or magnetic dipole moment. A magnetometer is an instrument with a sensor that measures the magnetic flux density.

Magnetometers determine the direction, strength, or relative variation in the magnetic field at a certain location.

We also use magnetometers to calibrate electromagnets and permanent magnets and to determine the magnetization of the material.

The first magnetometer was invented by Carl Friedrich Gauss in1833 that was capable of measuring absolute magnetic intensity.

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Types of Magnetometers

There are two types of magnetometers; these are:

• Vector magnetometers

• Scalar magnetometers

Vector Magnetometers

Vector magnetometers measure the flux density value in a specific direction in three-dimensional space. One such type is a fluxgate magnetometer. It measures the strength of the component of the earth’s field by positioning the sensor in the direction of the desired component.

Types of Vetor Magnetometers

A fluxgate magnetometer is also called the saturation magnetic circuit. It has two parallel bars wrapped with a coil placed close to each other. The magnetic field in the fluxgate magnetometer is caused by applying an alternating current through it.

A fluxgate magnetometer consists of a magnetically susceptible core wound by two coils of wire, where one coil is supplied an AC and the changing field produces an induced current in the other coil. Thus the alternating magnetic field and the induced output current is produced.

Squid Magnetometer

Squid magnetometers contain two superconductors set apart by two thin insulating layers to form two junctions.

These magnetometers are highly sensitive to the low range intensity fields and most are commonly used in measuring the magnetic field generated by the brain and heart.

Search-Coil Magnetometers

Search-coil magnetometers function on the phenomenon of Faraday’s law of induction. It contains copper coils that are wrapped around the magnetic core. When the core gets magnetized by the magnetic field lines produced inside the coil, the fluctuations in the field lines result in the flow of electric current.

The changes in this current due to changing voltage is measured and recorded by the magnetic field.

Scalar Magnetometers

Scalar magnetometers measure the scalar value of the magnetic field with accuracy. It is divided into the following types:

Types of Scalar Magnetometers

• Proton Precession Magnetometers

This magnetometer uses nuclear magnetic resonance to determine the resonance frequency of the protons in a magnetic field.

When a polarizing DC is passed via a solenoid, a magnetic flux generates around the hydrogen-rich fuel, viz: kerosene, because of which a few protons align with the flux.

When the polarizing flux is released, the frequency of the precession of protons to the usual rearrangement is used to measure the magnetic field.

These magnetometers measure the magnitude of the vector passing through the sensor irrespective of the direction. A quantum magnetometer is an example of such a type.

• Overhauser Effect Magnetometer

The working of the overhauled effect magnetometer is similar to the proton precession magnetometer; however, the difference lies in the type of radiofrequency employed. An overhauled magnetometer uses low power radio frequency signals to align the protons.

When an electron-rich liquid combines with hydrogen, it is subjected to an RF signal, under the overhauled effect, protons couple to the nuclei of the liquid. As soon as the precession frequency becomes linear with the magnetic flux density, we can measure the magnetic flux density.

The best part of such types of magnetometers is, these devices consume less power and have low sampling rates.

• Ionized Gas Magnetometers

These magnetometers are more precise than the proton precession magnetometers. They comprise a photon emitter light and a vapor chamber filled with vapors of cesium, helium, and rubidium.

When the atom of the cesium (Cs) hits the photon of the lamp, the energy levels of the electrons vary corresponding to the external magnetic field. This frequency variation helps measure the magnetic field strength.

Uses of Magnetometers

We find the applications of magnetometers in the following fields:

• In doing geographical and archaeological surveys.

• As a metal detector.

• To detect mineralization and geographical structures.

• In the oil and gas industry for the directional drilling process.

Applications of Magnetometers

In Archaeology

Magnetometers serve as an aid in archaeological study. It helps to detect the archaeological sites viz: buried and submerged objects.

In Coal Exploration

For locating the sills and other obstructions that can result in an explosion.

In Military Applications, Defense, and Aerospace

Magnetometers are used in defense and navy to perform submarine activities.

In Oil and Gas Exploration

For drilling the discovered wells. 

Health Care Monitoring

Used to perform cardiac operations viz: a diagnostic system for a non-invasive measure of the heart rate.

Pipeline Monitoring

Underground systems have higher chances of getting corroded; therefore, to detect this issue, we use magnetometers.

We find the application of magnetometers in the following field of geological Physics:

• Compasses.

• Applications in space.

• Image processing of the magnetic data.