Berkeley Laboratory researchers have demonstrated a novel superconducting gradiometer that helps to reduce ambient magnetic field noise generated by relatively distant sources in favor of tiny magnetic signals generated by a local source. This is another step toward the operation of SQUID-based instruments in an unshielded environment: for example, for the detection of magnetic signals produced by the human heart or brain.
The asymmetric gradiometer consists of a thin film of YBa2Cu3O7-x (YBCO) patterned to form two interconnected loops, one much bigger than the other. The smaller loop is inductively coupled to a high-transition-temperature (high-TC) magnetometer. The dimensions of the gradiometer are carefully chosen so that a uniform magnetic field induces no response from the magnetometer. On the other hand, application of a magnetic field that varies spatially along the length of the gradiometer produces a response that is proportional to the gradient. Tests show that uniform magnetic fields in any direction are reduced by at least a factor of 1000. The device involves a single layer of YBCO, and should be relatively inexpensive to manufacture, even with baselines sufficiently long for medical applications.
The most likely applications are in biomagnetism: for example, magnetocardiology and magnetoencephalography. Other potential applications are in nondestructive evaluation of materials.