Search Coil Vector Magnetometer 2024-10-31 07:00:00.0 0.1 Search coil magnetometers (sometimes called induction coil magnetometers) are passive observing instruments sensitive to magnetic field variations along the coil axis. They consist of a long and slim permalloy or mumetal rod surrounded by a coil with up to several million turns of copper wire. A varying magnetic field induces a circular electric field around the coil core which is measured as an electric potential difference (voltage) between the two ends of the coil wire. It is often used to measure magnetic field variations in the ULF-VLF range, but a sensibility to higher frequencies is also of interest for the investigation of plasma waves. Because of their large size two search coils are often placed flat on the ground in orthogonal directions and measure horizontal components of magnetic field variations. But three-axis search coil magnetometers were also constructed and successfully employed for full vector measurements of geomagnetic field variations.