The diameter of the induction coil was 0.8 m with 40 turns, and the distance between the induction coil and the MR sensor was maintained at 0.5 m. The induction coil was driven by sinusoidal currents. The frequencies of the driven currents were 50 Hz to 1 kHz, with peak-to-peak amplitude of 1 A. The amplitude of the induced magnetic field was 4.0 mT at the sample surface measured along the induction coil center axis.