Showing papers by "Keiji Enpuku published in 1988"
TL;DR: In this article, the power emission from a flux-flow-type Josephson oscillator with a thin-film coupling method is studied experimentally, where the thickness of one electrode of the oscillator is made thin enough to allow electromagnetic fields generated by the oscillators to be emitted through the thinfilm electrode.
Abstract: Power emission from a flux‐flow‐type Josephson oscillator with a thin‐film coupling method is studied experimentally. The thickness of one electrode of the oscillator is made thin enough to allow electromagnetic fields generated by the oscillator to be emitted through the thin‐film electrode. Radiation power from the oscillator is detected with superconductor‐insulator‐superconductor detectors, which are fabricated on top of the oscillator. Experimental results show that sufficient power can be obtained from the oscillator by using the thin‐film coupling method when the thickness of the electrode is comparable to the London penetration depth. The results obtained are in reasonable agreement with theoretical predictions. The thin‐film coupling method will be useful when the oscillator is connected to external circuits, such as an impedance matching circuit.
58 citations
TL;DR: In this article, the noise characteristics of dc SQUIDs in large β regimes have been studied experimentally in the case when a SQUID inductance is resistively shunted, and it is shown experimentally that the performance of the dc SQUID does not degrade significantly even for large β values; for example, the minimum energy resolution of the SQUID is as small as e=25h and the flux region where e<50h is as wide as 0.1Φ0, even for the case β=12, where h is the Planck constant.
Abstract: Noise characteristics of dc SQUIDs in large β regimes have been studied experimentally in the case when a SQUID inductance is resistively shunted. Here, β=2LI0/Φ0 is the modulation parameter, L is the SQUID inductance, I0 is the critical current of the Josephson junction and Φ0 is the flux quantum. It is shown experimentally that the performance of the SQUID does not degrade significantly even for large β values; for example, the minimum energy resolution of the SQUID is as small as e=25h and the flux region where e<50h is as wide as 0.1Φ0, even for the case β=12, where h is the Planck constant. The experimental results agree quantitatively with the theoretical ones.
8 citations
TL;DR: In this article, the spatial distribution of trapped magnetic flux density B in polycrystalline YBaCuO superconductors was measured and it was shown that B is similar to that predicted from the critical state model of the type II superconductor.
Abstract: We measured spatial distributions of the trapped magnetic flux density B in polycrystalline YBaCuO superconductors. It is shown that the spatial distribution of B for external magnetic fields is similar to that predicted from the critical state model of the type II superconductor. Furthermore, the spatial gradient of B becomes steep in proportion to the coupling strength among superconducting grains. It is also shown that the spatial distribution of B changes when the grain-coupling strength is degraded by postannealing around 200°C.
7 citations
TL;DR: In this article, a large-β dc dc SQUID with a modulation parameter β larger than unity has been studied theoretically and it has been shown that an order-of-magnitude increase in the output power can be achieved without a degradation of noise characteristics, compared with the case of β=1.
Abstract: The conversion efficiency between a signal magnetic flux and the output power of a large-β dc SQUID, i.e., a SQUID with a modulation parameter β larger than unity, have been studied theoretically. In our investigation the inductance of the SQUID was shunted by using a damping resistor. The dependence of the output power on such SQUID parameters as β, the McCumber parameter βc and the damping parameter γ=Rs/Rd(Rs and Rd are the shunt and the damping resistances, respectively) was investigated in detail. It has been shown that an order-of-magnitude increase in the output power can be realized with a large-β SQUID without a degradation of noise characteristics, compared with the case of β=1. It has also been shown that the values of βc=0.4 and γ=1 are optimum with regard to a large output power and a low-noise operation of the SQUID.
6 citations