Due to the potential of SQUID (superconducting quantum interference device) to detect small defects in material and structure and changes in magnetic properties caused by degradation of materials, the use of SQUIDs for non-destructive evaluation (NDE) using SQUID has attracted interest. Recently several SQUID systems for NDE have been developed including high Tc SQUID systems. Some preliminary experiments were carried out using these systems to explore the ability of SQUID for NDE. In this paper, the sensitivity and spatial resolution of a SQUID system are described in association with the liftoff distance and the size and configuration of the pick-up coil. SQUID systems and scanning SQUID microscopes are reviewed. Some preliminary experimental results are presented.
The possibility of utilizing MRI for the non-destructive quality evaluation of watermelons is described. MRI is a unique, non-destructive and non-invasive detection technique. Today it has become an important medical diagnostic modality. Recently several attempts have been made to utilize MRI for agricultural or industrial application. We have tried to apply MRI method to the detection of internal voids in watermelons. Our experimental apparatus consisted of a 0.5T superconducting magnet with a bore 68cm in diameter, an actively shielded gradient coil with highpower amplifiers and a PC-based spectrometer. From a practical point of view, it is not practical for the inspection of watermelons to take cross sectional images with two-dimensions, because it takes quite a long time. In order to increase measurement rate, we adopted a 1-D MRI. We have carried out void detection on 30 watermelons by this method and obtained convincing results.
This paper describes a suspension technique using high-Tc superconductors and soft magnetic materials. For a field-cooled superconductor and adjacent magnetic material, it was found that restoring force generated due to flux gathering effect in case of small gap length. In two separate experiments using this technique, both stable contact-less suspension of a 0.18kg steel weight under a superconductor and of a 1.4kg superconductor vehicle under a steel rail has already been reported. In this paper, for magnification of the stable gap length and for exclusion of mass regulation of the floator, modification of the levitation mechanism was carried out. The tangential force between the superconductor and the magnetic material was used for levitation, and the flux gathering effect was used for horizontal stabilization. A Maglev model was manufactured and stable levitaion was achieved using this construction.
The Bean model was introduced to a 3-D simulation code so that the electromagnetic phenomena in superconductors can be analyzed. The AC loss of a cylindrical superconductor which was obtained by the simulation with this code under a forced AC current was compared with the analytical result based on the Bean model. According to the results, the value of AC loss of the simulation coincided with that of the theoretical analysis if the initial electric conductivity was appropriately selected according to the mesh size. The current and magnetic field distribution as well as AC loss of the multi-filamentary superconducting wires were analyzed by the code under an external longitudinal magnetic field. The current distribution profile indicated the existence of current flow, with a density an order of magnitude larger than that of a typical eddy current, which seemed to link the adjacent superconducting filaments. This current component, thereby, gives rise to the AC loss of the silver region in addition to the eddy current. A reasonable agreement was found in terms of AC loss between the simulation and the experiment.