BS EN IEC 61788-7:2020 pdf download – Superconductivity Part 7: Electronic characteristic measurements — Surface resistance of high-temperature superconductors at microwave frequencies.
2 Normative references The following documents are referred to in the text in such a way that some or all of their content constitutes requirements of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. IEC 60050-81 5, International Electrotechnical Vocabulary (IEV) – Part 815: Superconductivity 3 Terms and definitions For the purposes of this document, the terms and definitions given in IEC 60050-81 5 apply. ISO and IEC maintain terminological databases for use in standardization at the following addresses: • IEC Electropedia: available at http://www.electropedia.org/ • ISO Online browsing platform: available at http://www.iso.org/obp 4 Requirements The R s of a superconductor film shall be measured by applying a microwave signal to a dielectric resonator with the superconductor film specimen and then measuring the attenuation of the resonator at each frequency. The frequency shall be swept around the resonant frequency as the centre, and the attenuation–frequency characteristics shall be recorded to obtain the Q- value, which corresponds to the loss. The target relative combined standard uncertainty of this method is less than 20 % for the measurement temperature range from 20 K to 80 K.
It is the responsibility of the user of this document to establish appropriate safety and health practices and to determine the applicability of regulatory limitations prior to use. Hazards exist in this type of measurement. The use of a cryogenic system is essential to cool the superconductors to allow transition into the superconducting state. Direct contact of skin with cold apparatus components can cause immediate freezing, as can direct contact with a spilled cryogen. The use of an RF generator is also essential to measure high-frequency properties of materials. If its power is too high, direct contact to human bodies can cause an immediate burn. 5 Apparatus 5.1 Measurement system Figure 1 shows a schematic diagram of the system required for the microwave measurement. The system consists of a network analyzer system for transmission measurement, a measurement apparatus, and a thermometer for monitoring the measuring temperature. An incident power generated from a suitable microwave source such as a synthesized sweeper is applied to the dielectric resonator fixed in the measurement apparatus. The transmission characteristics are shown on the display of the network analyzer. The measurement apparatus is fixed in a temperature-controlled cryocooler.
5.2 Measurement apparatus for R s Figure 2 shows a schematic of a typical measurement apparatus (closed type resonator) for the R s of HTS films deposited on a substrate with a flat surface. The upper HTS film is pressed down by a spring, which is made of phosphor bronze. The plate type spring should be used for the improvement of measurement uncertainty. This type of spring reduces the friction between the spring and the other part of the apparatus, and allows the smooth movement of superconductor films due to the thermal expansion of the dielectric rod. In order to minimize the measurement uncertainty, the sapphire rod and the copper ring shall be arranged coaxially. Two semi-rigid cables for measuring transmission characteristics of the resonator shall be attached on both sides of the resonator in an axial symmetrical position ( φ = 0 and π, where φ is the rotational angle around the central axis of the sapphire rod). Each of the two semi-rigid cables shall have a small loop at the ends. The plane of the loop shall be set parallel to that of the superconductor films in order to suppress the unwanted Transverse Magnetic Wave Modes (TM mn0 modes). The coupling loops shall be carefully checked for cracks in the spot weld joint that may have developed upon repeated thermal cycling. These cables can move right and left to adjust the insertion attenuation (IA). In this adjustment, coupling of unwanted cavity modes to the interested dielectric resonance mode shall be suppressed. Unwanted, parasitic coupling to the other modes reduces the high Q-value of the Transverse Electro-Magnetic Mode (TE mode) resonator. For suppressing the parasitic coupling, special attention shall be paid to designing high-Q resonators. Two other types of resonators along with the closed type shown in Figure 2 can be used. They are explained in A.4.