High-Performance Amorphous Wire Magneto-Impedance Sensor for Biomagnetic Field Detection

We have developed a gradiometer based on the magneto-impedance (MI) sensor, which can operate at room temperature. The gradiometer is composed of a pair of MI elements with 1 cm length each. The developed MI gradiometer has a good linearity and a high sensitivity of 1.2 × 105 V/T even for no amplification by semiconductor device. The precise magneto-impedance (MI) gradiometer was tested as biomagnetic field detectors. We can obviously identify a sharp magnetic peak with amplitude of about 100 pT, corresponding to the QRS complex of ECG. Meanwhile, there is a gentle magnetic peak, which corresponds well to the T wave of ECG, following the R wave of MCG. The spontaneous brain activity (alpha rhythm) measurements were also carried out on a male subject. As expected, the alpha rhythm signals measured by MI gradiometer were significantly attenuated when the subject opens eyes and then intensified with eyes close. The subject’s α wave MEG signal had a main frequency component of 10–11 Hz and the maximum amplitude was about 10 pT (effective value) for a male subject. In addition, the measurement of evoked magnetic field N100 were carried out in the unshielded environment.