What Is a Flux Meter?
A flux meter is an instrument that measures the magnetic flux passing through and changing within a coil. It’s different from a magnetometer, which is a general term for devices measuring the magnetization of materials, and the strength and direction of magnetic fields.
Flux meters can measure even minute magnetic forces, especially when the number of coils is increased. A more sensitive type is the SQUID flux meter, using superconductors. SQUID magnetometers include a Josephson junction in a superconducting ring and measure magnetic flux based on changes in tunnel current at extremely low temperatures.
Principle of Flux Meters
Flux meters measure the amount of magnetic flux through a coil and its changes. They are often used alongside gauss meters, which measure magnetic flux density. When magnetic flux through the coil changes, an electromotive force is generated in the coil.
Magnetometers, like vibrating sample magnetometers, vibrate a sample in a DC magnetic field to measure the magnetic moment of the sample based on changes in the magnetic force and electromotive force in the attached coil.
Flux Meters and Search Coils
Search coils are crucial in flux meters for detecting magnetic fields. Flux meters display the measurement as the product of coil turns and magnetic flux, enabling the measurement of minute forces or small samples by increasing coil turns. The accuracy of the coil winding is essential for sensor performance.
Principle of SQUID Flux Meters
The SQUID flux meter, or “Superconducting Quantum Interference Device,” is a highly sensitive detector for small magnetic flux changes. It consists of one or two Josephson junctions in a superconducting ring. When cooled to cryogenic temperatures, the tunneling current through these junctions changes, making SQUID flux meters highly sensitive.
Medical Applications
SQUID flux meters have wide-ranging R&D applications, from new material magnetic properties to superconductor research and trace impurity studies. In medicine, they are used to measure biomagnetic fields, like detecting weak magnetic fields from neural activity in the brain or heart. However, the minute magnetism from the heart requires a magnetic shield room during measurement to reduce external magnetic noise.