A single-channel high-Tc dc-SQUID magnetometer and gradiometer have been developed to record the magnetic field component perpendicular to the human chest generated by heart-beat. Magnetocardiogram (MCG) measurements have been carried out inside a magnetically shielded room. By sequentially adjusting a non-magnetic patient table with 5 cm pitch in X and Y directions, the field signals on a rectangle grid 5×5 over the chest area were registered in real time trace point by point with a typical dwell time over 30 cardiocycles each. Utilizing standard electrocardiogram (ECG) recordings as timing reference measured simultaneously with the MCG signals, the MCG data were then averaged and combined to form magnetic field patterns every 10 ms or so. Both the current dipole, which is parallel to MCG measuring plane and produces the vertical magnetic field, and its depth were determined as a function of time in a standard way. We have compared the MCG of healthy hearts with that of a heart with right bundle
A frequency mixing system including microwave coupling and intermediate frequency (IF) measurement arrangements is designed. In lieu of liquid nitrogen, a pulse tube cryocooler is used to cool the whole system. With YBa2Cu3O7/Yttrium stabilized zirconia (YBCO/YSZ) bicry-stal Josephson junction as the mixing element, 36th harmonic frequency mixing at the 8 mm waveband is obtained.
Mesa-structured intrinsic Josephson junctionsare fabricated in Bi2Sr2CaCu2O8+x single crystals. Typicalcurrent-voltage characteristics of intrinsic Josephson junc-tions are observed, which include multiple quasi-particle branches, surface junction with critical current lower than those of inner junctions, and subgap structures on quasi-particle branches. The corresponding physical explanationsare also given. The energy gap voltage of the intrinsicJosephson junctions at 30 K is about 20 mV. Besides, themeasured Ic-T relationship agrees quite well with thetheoretical computations based on -22-wavexyd supercon-ductor. Our measured dI/dV-V relationship shows theV-shaped gap structure, obviously differing from theU-shaped gap structure of the s-wave superconductor.
