A thin film magnetic field sensor of sub-pT resolution and magnetocardiogram (MCG) measurement at room temperature

We developed a very sensitive high-frequency carrier-type thin film sensor with a sub-pT resolution using a transmission line. The sensor element consists of Cuconductor with a meander pattern (20mm in length, 0.8mm in width, and 18 mm in thickness), a ground plane, and amorphous CoNbZr film (4 mm in thickness). The amplitude modulation technique was employed to enhance the magnetic field resolution for measurement of the high-frequency field (499 kHz), a resolution of 7.10 x 10(-13) T/Hz(1/2) being achieved, when we applied an AC magnetic field at 499 kHz. The phase detection technique was applied for measurement of the low frequency field (around 1 Hz). A small phase change was detected using a dual mixer time difference method. A high phase change of 130 degrees/Oe was observed. A magnetic field resolution of 1.35 x 10(-12) T/Hz(1/2) was obtained when a small AC field at 1Hz was applied. We applied the sensor for magnetocardiogram (MCG) measurement using the phase detection technique. We succeeded in measuring the MCG signal including typical QRS and T waves, and compared the MCG with a simultaneously obtained conventional electrocardiogram (ECG) signal. (C) 2008 Elsevier B. V. All rights reserved.