Magnetometer

A magnetometer is a device that measures magnetic fields or the magnetic properties of materials. It can show the direction, strength, or changes in magnetic fields in a specific place. A simple example of a magnetometer is a compass, which points toward the Earth's magnetic field. Other magnetometers can measure how materials like ferromagnets affect electric currents.

The invention of the magnetometer is often credited to Carl Friedrich Gauss in 1832, although earlier versions were made by Christopher Hansteen in 1819 and William Scoresby by 1823. Today, magnetometers are used in many important ways. They help scientists study the Earth's magnetic field during geophysical surveys and can find hidden magnetic anomalies. In airplanes, they help determine the aircraft's direction as part of the attitude and heading reference system.

In recent years, magnetometers have become very small and cheap to make. They can now be built into tiny electronic chips and are used as small compasses in many modern devices, known as MEMS magnetic field sensors.

Introduction

Magnetic fields

Magnetic fields have strength and direction. We measure their strength in units called tesla or gauss. The Earth's magnetic field is usually measured in smaller units called nanotesla. Some special tools, called gaussmeters and teslameters, can measure these fields.

Types of magnetometer

There are different kinds of magnetometers. Some measure the direction of a magnetic field, like a compass. Others measure how strong the field is. Magnetometers can be fixed in one place or carried around. They help scientists study the Earth's magnetic field and find things like metal deposits.

Performance and capabilities

Magnetometers have different abilities. They can take many readings quickly, track fast changes in magnetic fields, and detect very small changes. They also have limits, like how much their readings can change over time or with temperature.

Early magnetometers

The compass is an early type of magnetometer. It uses a magnetized needle that points in the direction of the magnetic field. In the 1800s, scientists invented new ways to measure magnetic fields more accurately. One scientist, Carl Friedrich Gauss, created a tool using a magnet suspended on a thin fibre. Another scientist, Francis Ronalds, used photography to record magnetic movements continuously.

Laboratory magnetometers

Laboratory magnetometers measure how strong a material's magnetic pull is, also called its magnetic moment. Unlike tools used outside, these need the material to be placed inside the device. Often, the temperature and magnetic field around the material can be changed to learn more.

These tools help scientists understand how materials act with magnetic fields. They look at how tiny parts inside atoms line up and affect the material's magnetic pull. This is important for studying physics, chemistry, and Earth sciences.

Main article: SQUID

SQUID magnetometers are very sensitive tools used in labs and outside. They work by using special loops that can spot very small changes in magnetic fields. However, they need to be kept very cold, which can make them tricky to use in some places.

Main article: Inductive sensor

Inductive pickup coils measure a material's magnetic pull by watching the electric current made when the magnetic pull changes. This helps tell the difference between the material's own magnetic pull and the outside field.

Vibrating-sample magnetometers (VSMs) measure a material's magnetic pull by shaking the material inside a special coil. This shaking makes a small electric current that can be measured. VSMs are good for many uses but can be tricky for delicate materials.

Pulsed-field magnetometry is another way to measure magnetic pull. Instead of shaking the material, the magnetic field around it is changed very fast. Special tools are then used to find the material's own magnetic pull.

Magnetic torque magnetometry can be very sensitive. It measures the twist on a material in a magnetic field. This twist can tell scientists about the material's magnetic properties.

Faraday force magnetometry uses the push or pull on a material in a changing magnetic field. This push or pull can be measured in different ways. It is good for many places but can be tricky because it needs both a magnetic field and a changing field.

Optical magnetometry uses light to measure magnetic pull. One way is by watching how light changes when it hits a magnetic material. Another way uses special films to see how the light's direction changes. This can help map out magnetic properties on a material's surface.

Susceptometry is a related technique that measures how a material's magnetic pull changes with an outside field. It is useful for studying how materials behave in changing magnetic fields.

A dipole in a changing magnetic field feels a push or pull. By measuring this force and using special tools, very small changes can be found.

Survey magnetometers

Survey magnetometers are tools that measure magnetic fields. There are two main types: scalar and vector magnetometers.

Scalar magnetometers measure how strong a magnetic field is, but not which way it points. Vector magnetometers can measure both how strong a magnetic field is and which way it points. For example, a magnetic compass shows direction, while a vector magnetometer can show both direction and strength.

These devices are used in many areas, such as archaeology and geology, to find hidden structures or measure changes in the Earth's magnetic field. Some types work quickly, while others give more detailed measurements.

Calibration of magnetometers

To check how well a magnetometer works, special coils are used. These coils make a magnetic field when electricity flows through them. This helps to see how sensitive the magnetometer is. Helmholtz coils are often used because they create a steady magnetic field. For harder tasks, other coils or the Earth's natural magnetic field can be used to test the magnetometer.

Uses

Magnetometers are tools that measure magnetic fields. They help find things like sunken ships, hidden dangers under the ground, and even track heartbeats.

People use them in many ways, such as finding minerals and helping guide airplanes and spacecraft.

These devices can be put on planes, boats, backpacks, or even inside smartphones. They help scientists study Earth’s magnetic field, explore space, and search for ancient archaeological sites.