SQUID probe microscope with through-hole SQUID

We have developed a high T_C SQUID probe microscope for investigation of samples at room temperature in air. A high permeability probe needle was used as a flux guide to improve the spatial resolution. A directly coupled DC SQUID with a through-hole in the pickup loop was prepared to improve the coupling of magnetic flux between the probe and the SQUID. By adjusting the position of the SQUID head, the probe could be made to penetrate through the hole in the pickup loop. We observed the magnetic fields emanating from a Japanese thousand yen bill and a current carrying meander line. We also investigated the coupling efficiency of the magnetic flux for various depths of penetration of the probe through the pickup loop of the SQUID by both experiment and numerical simulation.