Keisuke Yamamoto

Active endoscope with SMA (Shape Memory Alloy) coil springs

This paper describes the development of an active endoscope which allows a large bending angle for practical application and has a simple structure for miniaturization. An active endoscope (image fiber with 4200 pixels and light guide fiber) 2 mm in outer diameter with a shape memory alloy (SMA) actuator was designed and fabricated. The practical specifications of the SMA coil spring were determined based on a design chart and equation. The active endoscope consists of a bending part, the SMA actuator, and an endoscope. The mechanical properties of the bending part were investigated. The shear modulus of the SMA at room temperature and in the parent phase were determined in designing the actuators.

Multi-link active catheter snake-like motion

A prototype of a catheter which can move like a snake, incorporating distributed shape memory alloy actuators, is described. Since this active catheter has an instrumental navigation ability, minimally invasive diagnosis and interventional therapy will be possible. The outer diameter of the active catheter is 2.8 mm and it has many links fabricated by 3-dimensional silicon micromachining. The silicon batch process was used for the fabrication of the link to minimize assembly work. A new heating method (indirect heating) is suggested which is necessary when the JC chip is mounted on the link.

Nonstoichiometry Effects and Their Additivity on Anomalous Photovoltaic Efficiency in Lead Lanthanum Zirconate Titanate Ceramics

(Pb 0.97 , La 0.03 )(Zr 0.52 , Ti 0.48 ) 1-0.03/4 O 3 ceramics doped with various amounts of Ta were sintered at 1200°C for 2 h and then heat-treated in nitrogen at 900°C for 1 h to investigate the nonstoichiometric effects on the anomalous photovoltaic effect (APE). In the samples pretreated in nitrogen, both the photovoltaic current and the photovoltage were increased by the doping of Ta, and showed maxima around 1.5 mol% of doped Ta. Similar photovoitaic change with various amounts of Ta was observed in the nitrogen-treated samples. They, however, showed markedly higher values of the photovoltaic current and voltage than those in the doped samples pretreated in nitrogen. From this result, additivity is confirmed to hold for the effect of Ta doping and that of nitrogen treatment on the APE, indicating the coexistence of two types of contributions to the APE through different mechanisms. The spectral responses showed peak shifts and curve extension of the photovoltaic current to different directions according to the two effects. The mechanisms of those effects were discussed.

Electromagnetic Properties and Detailed Preparation Methods of Ag-sheathed Bi-Pb-Sr-Ca-Cu-O Superconducting Tapes

We conducted researches on Bi-Pb-Sr-Ca-Cu-O powders, for preparing Ag-sheathed superconducting tapes with high critical current density (Jc) at 77.3 K. Three different powder compositions (Bi8Pb2Sr10Ca10Cu15Ox, Bi9Pb2Sr10Ca11Cu15Ox, and Bi10Pb2Sr10Ca10Cu15Ox) were investigated. With these powders, superconducting tapes about 0.2 mm in thickness were prepared by powder-in-tube method and the process combining sintering and intermediate uniaxial pressing. The highest Jc was 19,500 A/cm2(77.3 K,0 T) on the specimen using Bi9Pb2Sr10Ca11Cu15Ox. Influence of powder compositions on electromagnetic properties such as Jc and A.C. susceptibility in various magnetic fields are also reported.

A.C. susceptibility and critical current density of Bi-based oxide superconductors

Abstract Polycrystalline oxide superconductors exhibit a complex magnetic susceptibility which is dependent on temperature. For a given applied magnetic field, the imaginary component of the observed susceptibility can be maximized at T ci , the peak temperature. We have investigated the relationship between the dependence of J c on applied D.C. magnetic field H dc and the dependence of T ci on the magnitude of applied A.C. field H ac for samples of silver-sheathed Bi 1−x Pb 0.2 Sr 1 Ca 1+y Cu 1.5 O z superconducting tapes. From the investigation, it was found that T ci was, in all cases, inversely related to the applied A.C. field. However, the degree to which T ci was sensitive to H ac correlated with the degree to which J c decreased with increasing H dc .

Preparation and Properties of Ag-Sheathed Bi2Sr2CaCu2O8+δ Superconducting Tapes

Ag-sheathed Bi2Sr2CaCu2O8+δ (2212) superconducting tapes have been developed by growing the 2212 phase through a partially melted state. In this paper, the Bi2Sr2Ca1−XCu2−XO8+δ (X=0,0.18 and 0.36) powder were investigated. With these powders, superconducting tapes about 0.18mm in thickness were prepared by powder-in-tube method and heat-treated under the maximum heating temperature of 890°C to achieve partial melt. The samples were then kept at 860°C for 40 hours. When X was 0.36, the highest critical current density Jc at 4.2K were 1.67×105 A/cm2 and 1.06×105 A/cm2 at 0T and 3T, respectively. Influence of powder compositions on electromagnetic properties such as Jc and A.C. susceptibility in various magnetic fields will be also discussed.