Our helmholtz coil facility comprises three pairs of parallel electromagnetic coils, mounted in orthogonal directions (X, Y, Z), which can be used to create a nearly uniform magnetic field at the centre of an experimental control volume.
Each pair comprises of two identical parallel electromagnet coils wound in a series, and mounted distance “R” apart, where R is the radius of the coil. A variable electric current is passed through each coil of the pair, and this arrangement enables a uniform magnetic field to be set up between them.
By mounting three coils orthogonally, a magnetic field of the desired strength and direction may be synthesized, enabling, for example, the cancelation of internal or external magnetic fields, such as the magnetic field generated by electronic devices, or that due to the earth. This enables the magnetic “cleanliness” of a test item to be evaluated and also allows us to calibrate the navigation magnetometers carried by a small spacecraft.
The control volume is large enough to accommodate a 27U CubeSat, and the magnetic field strength can be controlled from a few nanotesla to more than 100 microtesla – which exceeds the field due to the earth. The field generated is measured by a precision, 3-axis magnetometer. Honeywell HMC1053 and HMR2300 three-axis magnetometers are used in this facility. They are magnetoresistive sensors designed for low level magnetic field sensing. They have low power consumption, can be used over a wide temperature range, and they are already used on-board many Nano-Satellites.