• Progress in Superconductivity
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• v.9 no.2
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• pp.162-166
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• 2008

We are developing a sensitive gamma ray spectrometer based on superconducting transition edge sensors. The detector consists of a small piece of high purity Sn as an absorber and a Ti/Au bilayer as a temperature sensor. It is designed to measure the thermal signal caused by absorption of gamma rays. The mechanical support and the thermal contact between the absorber and the thermometer were made with Stycast epoxy. The bilayer was formed by e-beam evaporation and patterned by wet etching on top of a $SiN_X$ membrane. A sharp superconducting transition of the film was measured near 100 mK. When the film was biased to the edge of the transition, signals were observed due to single photon absorption emitted from an $^{241}Am$ source. The measured spectrum showed several characteristic peaks of the source including 59.5 keV gamma line. The full with at half maximum was about 900 eV for the 59.5 keV gamma line. The background was low enough to resolve low energy lines. Considerations to improve the energy resolution of the gamma ray spectrometer are also discussed.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.65 no.1
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• pp.13-17
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• 2016

EMC (Electro Magnetic Compatibility) of the electrical railway must be ensured for safety of passenger. Maglev trains has not friction between the wheels and the rails because levitation by an permanent magnets, electromagnets and superconducting magnets etc. So, it is advantageous to maintain a high speed without noise and vibrations. In this paper, we investigated that the magnetic field of the before and after installation electromagnetic waves absorber in order to analyze the effects of electromagnetic waves. The theoretical analysis of the electromagnetic wave absorber was simulated using finite element method. The magnetic field properties of electromagnetic waves absorber were measured by EMI (Electro Magnetic Interference) test receiver.

• Current Optics and Photonics
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• v.5 no.4
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• pp.375-383
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• 2021

We present a simulation method to design antireflection coating (ARCs) for fiber-coupled superconducting nanowire single-photon detectors. Using a finite-element method, the absorptance of the nanowire is calculated for a defined unit-cell structure consisting of a fiber, ARC layer, nanowire absorber, distributed Bragg reflector (DBR) mirror, and air gap. We develop a method to evaluate the uncertainty in absorptance due to the uncontrollable parameter of air-gap distance. The validity of the simulation method is tested by comparison to an experimental realization for a case of single-layer ARC, which results in good agreement. We show finally a double-layer ARC design optimized for a system detection efficiency of higher than 95%, with a reduced uncertainty due to the air-gap distance.

• Progress in Superconductivity
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• v.12 no.1
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• pp.41-45
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• 2010

Low temperature micro-calorimeters have been employed in the field of high resolution alpha spectrometers. These alpha detectors typically consist of a superconducting or metal absorber and a temperature sensor. The temperature sensor can be a transition edge sensor (TES), a metallic magnetic calorimeter (MMC) or other low temperature detectors for an accurate measurement of temperature change due to an alpha particle absorption. We report a recent study of the heat flow between a replaceable absorber and a temperature sensor. A piece of gold foil in $2.4{\times}2.7{\times}0.03\;mm^3$ is used as an absorber. A $40\;{\mu}m$ diameter Au:Er paramagnetic sensor is attached to another small piece of gold foil in $400{\times}200{\times}30\;{\mu}m^3$ to serve as the temperature sensor. This sensor assembly, Au:Er and gold foil, is placed on a miniature SQUID susceptometer in a gradiometric configuration. The thermal connection between the absorber and the sensor was made with three gold bonding wires. The measured thermal conductance shows a linear dependence to the temperature. The values are in a good agreement with Wiedemann-Franz type thermal conductance of the gold wires.