Long-term outdoor observation of geomagnetic fields using tunneling magnetoresistance-based magnetometer and detection of long-period oscillations of geomagnetic pulsations: prospects for earthquake disaster prevention

Abstract

We investigated the appropriateness of a tunneling magnetoresistance (TMR)-based magnetometer for detecting geomagnetic fields with long-period oscillations through observation of the geomagnetic pulsation (Pi). Pi was not sufficiently observed in the raw outputs due to thermal noise; a bandwidth-limitation treatment helped extract Pi without data stacking. The detectable intensity was reduced to 1 nT with a period of 30 s, but detection was impossible for 100 s. The frequency characteristics revealed that reducing the cutoff frequency of a TMR magnetometer is a promising approach for detecting field oscillations occurring over long periods, such as 100 s.