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1 November 1990 Instrumentation and techniques for high-resolution magnetic imaging
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Recently-developed, high-resolution Superconducting QUantum Interference Device (SQUID) magnetometers can provide magnetic images of small objects with a signal-to-noise ratio and spatial resolution that are an order of magnitude better than is achievable with conventional SQUID magnetometers. The MicroSQUIDtm magnetometer has 4 channels, each of which is a differential magnetometer with a 3 mm diameter pick-up coil located less than 1.5 mm from the room-temperature region outside the Dewar. The system noise is approximately 100 fT/Hz1/2. We present magnetic field data recorded from several two-dimensional current distributions, and from the remanent magnetization in rocks, photocopier images, and magnetic contamination in metallic tubes. The system is capable of locating to better than 10 µm a straight wire carrying a 20 µA peak-to-peak sine wave current. The system can detect growth currents in a fertile chicken egg, and signals from a voluntarily-activated single motor unit in the human thumb. Magnetic fields produced by two-dimensional current distributions can be converted into current density images using Fourier-transform spatial filtering algorithms. This approach allows us to examine the difference between the imaging and localizing resolution of a magnetometer, and allows us to devise apodized pick-up coils with increased spatial resolution.
© (1990) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
John P. Wikswo Jr., Jan van Egeraat, Yu Pei Ma, Nestor G. Sepulveda, Daniel J. Staton, Shaofen Tan, and Ranjith S. Wijesinghe "Instrumentation and techniques for high-resolution magnetic imaging", Proc. SPIE 1351, Digital Image Synthesis and Inverse Optics, (1 November 1990);

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