Development of pico tesla resolution amorphous wire magneto-impedance sensor for bio-magnetic field measurements

Abstract

For achieving the room temperature magnetoencephalography (MEG) and magnetocardiography (MCG) measurements in an unshielded environment, we have developed a high performance, pico-tesla resolution magnetoimpedance (MI) sensor system with the peak-to-peak voltage detector, by synchronized switching. We have achieved a high field detection sensitivity with good linearity, and a noise level lower than 1 pT/Hz1/2, by utilizing the time-differential measurement in each MI element for suppressing the low frequency noise components and increasing the stability of sensor system. We have successfully developed a Pk–pk VD-type MI sensor system aiming to measure the room-temperature real-time alpha rhythm signals, and demonstrated a clear sensitivity for spontaneous brain activity with SNR of about 8. The considerable enhancement of alpha rhythm measured by new MI sensor system in each eyes-closed condition is further evidence that these recorded signals are emanating from spontaneous brain activity. Meanwhile, we have also achieved the real time MCG measurements via pk-pk VD-type MI sensor system, with a high real time SNR of about 14 dB, and successfully measured the T wave and R wave of MCG signals, in averaging over 10 cycles, with a high SNR of more than 20 dB.