Overall description: Principle and Application of Helmholtz Coil

The origin of the Helmholtz coil

A Helmholtz coil is a device consisting of two coils of the same size and the same orientation, which is commonly used to generate a uniform magnetic field. The device was invented by German physicist Hermann von Helmholtz, hence the name.

How Helmholtz Coils Work

A Helmholtz coil usually consists of two parallel circular coils of exactly the same radius and number of turns, which are fixed on a common axis and whose radius is equal to the distance between them. The distance between them is often referred to as the "width" of the Helmholtz coil.
When two coils are passed current in the same direction, they generate a magnetic field. This magnetic field can be described by Maxwell's equations. Since a Helmholtz coil is symmetrical, the magnetic field it produces is uniform along its axis.
When the two coils are supplied with reverse current, the superposition weakens the magnetic field, so that a region where the magnetic field is zero appears.

Features of Helmholtz Coils
 

Open space, easy to use;
Helmholtz coils can generate extremely weak magnetic fields, and can also generate magnetic fields of hundreds of Gs;
Can realize one-dimensional, two-dimensional, three-dimensional combined magnetic field;
It can provide AC and DC magnetic fields, and the current has a good linear relationship with the magnetic field.

Applications of Helmholtz Coils

Generate a standard magnetic field;
Calibration of Hall probes and various magnetometers;
Compensation for the Earth's magnetic field;
Judgment of magnetic shielding effect;
Measurement and elimination of space radiation magnetic field;
The study of the magnetic properties of matter;
Research on biomagnetism.

For example, in the laboratory, Helmholtz coils can be used to measure the properties of magnetic materials such as magnetization and hysteresis loops. In medical devices, Helmholtz coils can be used to generate magnetic fields to help treat diseases such as cancer and neurological disorders. In geophysics and astronomy, Helmholtz coils are used to measure the magnetic fields of the Earth and planets. In engineering, Helmholtz coils are also used to manufacture high-precision sensors. These sensors can accurately measure the magnetic flux in the ambient magnetic field, and through this quantitative level of magnetic field data, various other physical quantities can be analyzed in a variable manner. Helmholtz coils are therefore an integral part of the engineering world.

Precautions

  
The design of a Helmholtz coil requires consideration of the size and current of the coil, as well as the distance of the circular coil. According to the empirical formula, two coils with a radius of R and a distance of 2R, if their current is I, the magnetic field strength generated is B=0.9μ0I/R, where μ0 is the vacuum permeability.

The frame and support system of the coil must be non-metallic and the radius of the coil should be at least 2.5 times the largest specimen to be tested. This confinement allows all samples to be within the homogeneous area of the coil, making measurements mindful of distant electromagnetic interference. Such as other magnets, transformers or fluorescent sources, etc.

Summarize

Helmholtz coils can generate static DC or AC magnetic fields, and they are widely used in various fields such as materials, electronics, biology, medical treatment, aerospace, chemistry, and applied physics.

Related recommendation

User's Manual of Dexinmag Series Helmholtz Coils.pdf