ABSTRACT
Nearly every physical object generates magnetic ¢elds, 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. že Earth’s magnetic ¢eld 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 ¢nd 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. že information obtained from MEG can be used to pinpoint problem regions in the brain of a patient to minimize the invasiveness of a brain surgery. Ultrasensitive magnetic sensors used in MCG and MEG are expensive superconducting quantum interference devices (SQUIDs), which require low-temperature operation.
