A numerical and experimental investigation of planar asymmetric SQUID gradiometer characteristics

Klein, U., Walker, M.E., Cochran, A. , Hutson, D., Lang, G., Weston, R.G. and Pegrum, C.M. (1996) A numerical and experimental investigation of planar asymmetric SQUID gradiometer characteristics. Superconductor Science and Technology, 9(4A), A124-A128. (doi:10.1088/0953-2048/9/4A/032)

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A low-cost, high-performance magnetic field sensor for applications such as biomagnetism and nondestructive evaluation can be fabricated by integrating a superconducting quantum interference device (SQUID) and a gradiometer on a single chip. Conventionally, the gradiometric pick-up loop would have a rectangular outline divided symmetrically about the midpoint of its length so that its spatial response was also symmetrical. However, it is also possible to divide the same outline asymmetrically, maintaining the field rejection order of the gradiometer by adding an extra crossover. The spatial response of this arrangement will also be asymmetric, which may be exploited to reduce the effects of the nearby SQUID as a magnetic anomaly or to enhance the sensitivity of the device to magnetic sources at a particular distance. The techniques to calculate the crossover positions are well established. Here we outline how different designs may be evaluated theoretically and report on first experimental results for three simple designs. Several devices have been fabricated using a well established Nb/Al–Al2O3/Nb trilayer process with high yields. The measurement of the spatial response of an asymmetric first-order gradiometer shows the expected magnetometer characteristics for a magnetic dipole source in the near field and first-order gradiometric characteristics for a far-field source. The balance of the integrated gradiometer appears to be better than one part in 104, and the magnetic field gradient sensitivity has been measured to be 100 fT cm−1 Hz−1/2.

Item Type:Articles
Glasgow Author(s) Enlighten ID:Cochran, Professor Sandy
Authors: Klein, U., Walker, M.E., Cochran, A., Hutson, D., Lang, G., Weston, R.G., and Pegrum, C.M.
College/School:College of Science and Engineering > School of Engineering > Systems Power and Energy
Journal Name:Superconductor Science and Technology
Publisher:Institute of Physics
ISSN (Online):1361-6668

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