Detecting ULF waves
There are two common instruments used to detect the signatures of ULF waves. These are induction and fluxgate magnetometers.
A time varying magnetic flux through a coil of wire generates a voltage. We have designed induction magnetometer systems that are used in Antarctica, South Africa, China, and Australia.
The sensor has 190,000 turns of cooper wire wound onto a PVC bobbin, which is then threaded with mu-metal strips. The resulting inductance is about 10,000 Henries. A specially designed, chopper type, pre-amp boosts the signal which is then fed to an A/D board, designed by Peter McNabb.
These are very good for the low end of the ULF wave spectrum, measuring the ambient (steady) field up to variations of about 1 Hz. Hysteresis of the ring core material produces harmonics that depend on the applied magnetic field (Earth's field). Our systems were designed and built by Narod Geophysics, Vancouver, Canada.