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Magnetoresistive Sensors Based on Magnetic Tunneling Junctions
Published in Evgeny Y. Tsymbal, Igor Žutić, Spintronics Handbook: Spin Transport and Magnetism, Second Edition, 2019
Nearly every physical object generates magnetic fields, some strong and some extremely weak. A human heart generates picotesla-scale (10−12 T) magnetic pulses, revealing critical cardiac information. A spinning disk inside a hard drive emits magnetic signals with frequency approaching 1 GHz, making the information age possible. The Earth’s magnetic field can be a useful navigation tool, particularly where global positioning systems (GPS) are not accessible (e.g., underground and deep sea). Magnetic sensors have been used pervasively in industrial and consumer products [3]. Ultrasensitive magnetic sensors find increasing utility in a number of emerging applications [3]. Magnetocardiography (MCG) [4] uses magnetic sensors to measure the weak electrical signals from the beating heart, allowing the diagnostics of cardiac functions. Magnetoencephalography (MEG) [5], on the other hand, is the magnetic measurement of the electrical activities in the brain. The information obtained from MEG can be used to pinpoint problem regions in the brain of a patient to minimize the invasiveness of brain surgery. Ultrasensitive magnetic sensors used in MCG and MEG are expensive superconducting quantum interference devices (SQUIDs), which require low-temperature operation.
Application in Superconducting Quantum Interference Devices SQUIDs
Published in Edward Wolf, Gerald Arnold, Michael Gurvitch, John Zasadzinski, Josephson Junctions, 2017
Since the heart generates the strongest magnetic signal among the human organs, biomagnetic research started with magnetocardiography (MCG). About five years after the invention of the SQUID, a first magnetocardiogram was measured with a point-contact rf SQUID to which a second-order wire-wound pickup coil was coupled [102,103]. Since then, SQUIDs were applied to record the magnetic field of numerous other body organs, for example from the brain (magnetoencephalography, MEG), the fetal heart (fMCG) and brain (fMEG), the eye (magnetooculogram, MOG), the peripheral nerves (magnetoneurogram, MNG), the liver (liver susceptometry), the stomach (magnetogastrogram, MGG), the small intestine (magnetoenterogram, MENG), the skeletal muscles (magnetomyogram, MMG), and the lungs.
Measurement of Electrical Potentials and Magnetic Fields from the Body Surface
Published in Robert B. Northrop, Non-Invasive Instrumentation and Measurement in Medical Diagnosis, 2017
The currents associated with cardiac muscles active in the beating of a heart also produce time-varying magnetic fields that can be sensed with SQUID magnetocardiography (MCG) arrays. A question that must be asked is: Can SQUID-based MCG outperform conventional multielectrode ECG arrays in terms of providing diagnostic information?
Solving Inverse Problem in Magnetocardiography by Pattern Search Method
Published in IETE Journal of Research, 2021
Pragyna Parimita Swain, S. Sengottuvel, Rajesh Patel, Awadhesh Mani, Raja J. Selvaraj, Santhosh Satheesh
Magnetocardiography (MCG) is a non-invasive and non-contact technique to measure the magnetic fields generated by the heart. The diagnostic information provided by MCG is complementary to that offered by the electrocardiography (ECG). MCG measurements are mostly performed using a highly sensitive magnetic field detector, namely the Superconducting QUantum Interference Devices (SQUID) inside magnetically shielded rooms (MSR) [1].