The temperature is one of the important parameters, both in experiments and analysis, in cryogenic research and development. Recently the definition of the unit of temperature, Kelvin, which is one of the seven basic units in the International System of Units (SI) was redefined along with three other basic SI units. An outline of the redefinition of the Kelvin and its background are presented. Despite the historic redefinition of the Kelvin, practical cryogenic thermometry is not, and will not be, affected at least for a while. Practical cryogenic thermometry is based on the International Temperature Scales (ITSs). The definitions of the ITSs were not changed after the redefinition of the Kelvin. The relationship between the ITSs and the Kelvin definition, and the characteristics of thermodynamic thermometry are also presented.
In the new SI, the unit of thermodynamic temperature, Kelvin (K), was defined based on the Boltzmann constant k determined through various thermodynamic temperature measurements. This paper describes a Johnson noise thermometer that uses a quantum voltage noise source, which is a type of precise thermodynamic temperature measurement method.
Since May 20, 2019, new definitions for four of the seven base units of the International System of Units (SI) have been implemented worldwide. In the new definitions, the unit of electric current, ampere, is defined as the number of electrons flowing in unit time, whereas the value of elementary charge is defined as a constant without uncertainty. This paper focuses on the SI units of electrical quantities and reviews the realization of the unit of voltage, volt, based on the Josephson voltage standard system that uses a cryocooler. Furthermore, this paper reviews the influences of the revised SI units on precise electrical measurements.
Thermophysical properties are widely used in thermal design for saving energy and safety and security. In order to secure reliability in these areas, the National Metrology Institute of Japan (NMIJ) has developed some precision measurement techniques. This paper describes details of the guarded hot-plate method for thermal conductivity, the flash method for thermal diffusivity, the adiabatic calorimetric method for specific heat capacity and the optical heterodyne interferometric method for thermal expansion coefficient. These methods give SI traceable thermophysical property values and well evaluated uncertainties.
A high Q value for resonant circuits is necessary for wireless power transfer. The resistance in the circuit degrades the Q factor; thus, it is important to use elements with a low internal resistance such as superconductors. In this study, we focused on reducing the internal resistance in capacitors by using superconducting electrodes. We fabricated a multilayered structure with epitaxially grown BaTiO3 films on biaxially oriented YBa2Cu3Oy films and measured the superconducting and dielectric properties. As a result, the multilayered film showed superconducting transition at 86.1 K and a large reduction in ESR at temperatures below 90 K. The temperature dependence of the capacitance density peaks at 265 K and coincides with the structural phase transition of BaTiO3. The relative permittivity εr of the multilayered structure was 1.9-23.3, possibly due to a lower crystalline orientation.