AC biased sub nano tesla magnetic field sensor for low frequency applications utilising magneto impedance in multilayer films

In this paper we propose a new technique to improve substantially the sensitivity of low-frequency field detection with the use of ac biased thin-film MI and return loss directional coupling methods. The techniques presented in this paper are able to reach a field resolution that is limited by thermal noise a high frequency and through AC biasing a one order improvement in field resolution and magnitude detection and lower frequencies. The measurements are limited by the 3 Hz resolution and noise performance of the spectrum analyzer, phase noise of the oscillator and background magnetic noise.