Superconducting quantum interference device: The most sensitive detector of magnetic flux

SQUIDs are the most sensitive devices in detecting the magnetic flux. The devices have been used to detect small magnetic field, current, voltage, inductance and magnetic susceptibility etc. In this work, we reported studies and applications of high-T_c YBa₂Cu₃O _y SQUIDs. Two main techniques of depositing YBCO thin films are described; the characteristic of thin film and high-T_c SQUID are addressed. In magnetocardiography (MCG) application, we set up an electronic SQUID gradiometer system to optimize the environmental noises. The MCG measurements are performed in magnetically unshielded environments. In the SQUID NDE with the SQUID magnetometer and gradiometer were used to detect the buried flaws. The phase-depth relation of the buried flaw shows linear dependence. It was found that the phase-depth relation is useful to evaluate the depth of the buried flaws. In the scanning SQUID microscopy, the SQUID probe is used to detect the circuits using the lock-in detection technique. We successfully demonstrate that we can image the electrical circuits with the SQUID probe with samples at room temperature.