Development of planar thin film HTSC-SQUID gradiometers for different applications

We investigated the main dependencies of the gradient resolution of planar galvanometer superconducting quantum interference device (SQUID) gradiomete rs made of YBa2Cu3O7-x (YBCO). We focussed especially on the influence of a ntenna layout and the parameters of the galvanometer SQUID such as effectiv e and parasitic areas on the performance of the gradiometer and the behavio r in an unshielded environment. The efficiency (that is, the quotient of ef fective area to inductance) of different geometries of antennas will be com pared. Some aspects of the layout of the galvanometer SQUIDs are discussed in terms of parasitic area and best current resolution. Special problems du e to the use of bicrystal Josephson junctions in gradiometers for operation in highly disturbed environment are shown. Step-edge Josephson junctions c an offer alternative concepts. Reached gradient sensitivity values in the w hite noise region are 0.46 pT/(cm/root Hz) in the case of bicrystal junctio ns and 0.69 pT/(cm/root Hz) for step-edge junctions. (C) 1999 Elsevier Scie nce Ltd. All rights reserved.