DEVELOPMENT OF INTEGRATED DIRECT-CURRENT SUPERCONDUCTING QUANTUM INTERFERENCE DEVICE GRADIOMETER FOR NONDESTRUCTIVE EVALUATION

Direct Current Superconducting Quantum Interference Device (DC-SQUID) gradiometer for nondestructive evaluation was developed. A pick-up coi l and a DC-SQUID were integrated on a 3 x 3 mm(2) Si chip. In order to raise the spatial resolution of the gradiometer, a coplanar concentri c second-order derivative coil was adopted as a pick-up coil. The pick -up coil consisted of a one-turn outer coil and a four-turn inner coil connected in series and counterclockwise to each other. The diameters of the outer coil and the inner coil were 2 mm and 1 mm, respectively . The size of the pick-up coil was determined by calculating the spati al resolution in relation to the bottom thickness of the cryostat. The high spatial resolution of the DC-SQUID gradiometer was experimentall y confirmed.