In order to use superconductors as nonresistive conducting wires, there must exist some mechanisms by which vortices are pinned against the Lorentz force due to a current. Since flux pinning phenomena occur on a microscopic scale, they have been difficult to observe directly, and therefore we can only presume what happens from macroscopic measurements. A new way was revealed to observe the dynamics of vortices in real time together with material defects by using both coherent field emission electrons and detecting the phase of the electrons, thus making it possible to microscopically observe the flux pinning phenomena.
The contact stiffness of a glass fiber-reinforced plastic, EL-850, has been measured at room temperature and in liquid nitrogen. Dimensions of the specimens were 20×20mm2 with three different thicknesses of 2.7, 4 or 8mm. Contact pressures up to 80MPa were applied to the specimens. Results showed how the contact stiffness increased with the applied contact pressure. It seemed that roughness and waviness on the surfaces of the EL-850 were factors which reduced contact stiffness. A computer simulation of contact stiffness, which took account of only the waviness, and measurements of the real contact areas using thin PET films, indicated that the waviness considerably affected contact stiffness. Contact stiffness measured in liquid nitrogen was less than that measured at room temperature when the contact pressure was low. This result was presumably caused by greater waviness of the specimen because of thermal distortion caused by liquid nitrogen.
Ag-sheathed superconductor tape is going to be used widely for many practical applications. However, this type of conductor may suffer damage to its superconducting filaments through production lines or degradation through the winding process, such as coil winding. So we propose a new method for non-destructive inspection at room temperature using ultrasonic waves. This method is a kind of ultrasonic transfer function method using a couple of piezoelectric sensors. One is the driver and the other is the receiver. This time, the authors report the relation between the acoustic characteristic for ultrasonic waves at room temperature and the electrical characteristics at 77K using sample tapes which experienced a bending strain up to 1.0%.