Structural investigation and mechanical properties of a representative of a new class of materials: nanograined metallic glasses

A new class of materials: Au-based nanograined metallic glasses (NGMGs) were synthesized using magnetron sputtering with powder targets. A detailed study by x-ray diffraction and high-resolution transmission electron microscopy (TEM) documents the unique nanoscale granular structure of the Au-based NGMG. This material inherited the good mechanical properties of metallic glasses, showing a high hardness of ∼5.3 GPa and a low elastic modulus of ∼79 GPa. In addition, in contrast to most MGs the nanoglassy particles can deform along the loading direction, exhibiting unique tensile elongation up to 100%. During thermal crystallization of NGMG material, even smaller sized Au solid solution nanocrystals are formed within the glassy nanograins, offering a new way for production of the nanocomposites with tailored structural length scales.

Maximum accuracy evaluation scheme for wireless saw delay-line sensors

This paper describes an evaluation scheme that prevents phase ambiguity of surface acoustic wave (SAW) delay-line sensors. Although it is well-known that phase evaluation yields accuracies of 150~1500 times higher than time-delay evaluation, the problem of phase ambiguity has prevented phase evaluation of sensors operating over a range larger than 2 pi. This paper addresses this unsolved problem with a complete strategy. Furthermore, the existence of an optimum choice of the relative reflector positions on the sensor is shown. The presented relations enable the design of maximum accuracy SAW delay-line sensors.

Development of active catheter, active guide wire and micro sensor systems

SUMMARY

Active catheters and active guide wires which move like a snake have been developed for catheter-based minimally invasive diagnosis and therapy. Communication and control IC chips in the active catheter reduce the number of lead wires for control. The active catheter can be not only bent but also torsioned and extended. An ultra minature fiber-optic pressure sensor, a forward-looking ultrasonic probe and a magnetic position and orientation sensor have been developed for catheters and guide wires. These moving mechanisms and several sensors which are fitted near the tip of the catheter and the guide wire will provide detailed information near the tip and enable delicate and effective catheter intervention.

Near-field optical apertured tip and modified structures for local field enhancement

We present experimental measurements and simulation of the spatial distribution of near-field light at the aperture of a Si micromachined near-field scanning optical microscopy (NSOM) probe. A miniature aperture at the apex of a SiO(2) tip on a Si cantilever was fabricated with the low temperature oxidation and selective etching technique. An optical transmission efficiency (optical throughput) of the fabricated probe was determined to be approximately 10(-2) when the aperture size was approximately 100 nm, which is several orders of magnitude higher than that for conventional optical fibers. A three-dimensional finite difference time domain (FDTD) simulation shows that the near-field light is well confined within the aperture area with a throughput of 1% for a 100-nm aperture, which is in good agreement with the measurement. The spatial distribution of the near-field light at an aperture of 300-nm diameter shows a full width at half-maximum of 250 nm with a sharp peak that is nearly 60 nm wide. The 2.4% throughput for a 300-nm aperture was estimated based on the measured spatial distribution of the near-field light that is almost the same as the experimental result. We also present the initial results of the fabrication of high throughput coaxial and surface plasmon enhancement NSOM probes.

Spatial distribution and polarization dependence of the optical near-field in a silicon microfabricated probe

This paper reports on the spatial distribution and polarization behaviour of the optical near-field at the aperture of a Si micromachined probe. A sub-100 nm aperture at the apex of a SiO2 tip on a Si cantilever was successfully fabricated by selective etching of the SiO2 tip in a buffered-HF solution using a thin Cr film as a mask. The aperture, 10-100 nm in size, can be reproducibly fabricated by optimizing the etching time. The optical throughput of several apertures was measured. For a 100 nm aperture, a throughput of 1% was approved. The probe shows a very high optical throughput owing to the geometrical structure of the tip. The spatial distribution of the near-field light is measured and simulated using a finite difference-time domain method. The polarization behaviour of apertures with different shapes was analysed using a photon counting camera system.

Microfabrication and microsensors

In order to fabricate microsensors, a micromachining, microfabrication technique based on LSI technologies has been used. In this paper, useful micromachining techniques are described. Examples of integrated microsensors, such as a pressure sensor including a readout circuit and a multisensor cell for blood gas analysis, are introduced. Microflow control devices, such as microvalve and a micropump for integrated chemical analysis systems, are also described.

Micro-pressure sensor for continuous monitoring of a ventricular assist device

We have been involved in the development of a clinical ventricular assist device (VAD) system. Here, we report our investigation of in vitro and in vivo stability and sensibility of pressure microsensors. The sensors were mounted in the in-flow and out-flow cannulae wall to measure the left atrial and aortic pressures during VAD pumping. The pressure sensitive surface of the piezoresistive effect absolute pressure sensor was coated with a thrombo-resistant polymer, as was the inner surface of the cannulae of the VAD. In the in vitro and chronic animal experiments which were of more than a month duration, reliable stability and sensitivity, without any thrombus formation on the blood contacting surface of the sensors, and high sensitivity were observed. After chronic experiments, the sensitivity of sensors was reevaluated in the mock circulatory system as compared to reference values. The relationship between the output of the micro-sensors and the reference value was linear and correlated well.

Solid-state micro sensors

Recent research activities on solid state micro sensors in Japan are reviewed. Many kinds of micro sensors for chemical and physical quantitative analysis have been developed for biomedical instrumentation. Many of these sensors are fabricated with the advanced art of semiconductor technology, which is called micromachining. This technology enables fabrication of sensors so small that they can be used in catheter tubes etc. Moreover, it has brought out integrated sensing systems or multi sensors. In the field of chemical sensors, the development of ISFETs, i.e. ion sensitive field effect transistors, has been much advanced. These have been applied not only as ion sensors but also as biosensors or dissolved gas sensors. On the other hand, the major research activities on micro sensors for physical quantities have been on pressure sensors for measurements in blood vessels etc.

Characterization of human dental plaque formed on hydrogen-ion-sensitive field-effect transistor electrodes

The purpose of this study was to evaluate (with scanning electron microscopy and microbiological characterization) the bacterial deposits which accumulate on hydrogen-ion-sensitive field-effect transistor electrodes (pH-ISFET) under conditions normally employed for telemetric monitoring of changes in human dental plaque pH. Electrodes were mounted in a carrier appliance which was worn for two, four, and six days. The plaque pH response to a sucrose solution increased with the age of the plaque, as expected from previous studies. After two days, the electrode was shown to be almost completely covered with cocci. At days 4 and 6 there was a dramatic increase in the number of rods present in the plaque. Adjacent enamel surfaces showed similar accumulations of bacteria. The total number of bacteria which had accumulated per unit area by day 4 was very similar for the electrode and enamel surfaces. On both surfaces the plaque contained approximately 25% streptococci, and the dominant species was Streptococcus sanguis (approximately 75%). The plaque which accumulated on pH-ISFET electrodes could not be distinguished visually or microbiologically from that which formed on control enamel surfaces.