Kenichi Morimoto

Carbon atoms in ethanol do not contribute equally to formation of single-walled carbon nanotubes

We propose a unique experimental technique in which isotopically labeled ethanol, e.g., 12CH3-13CH2-OH, is used to trace the carbon atoms during the formation of single-walled carbon nanotubes (SWNTs) by chemical vapor deposition (CVD). The proportion of 13C is determined from Raman spectra of the obtained SWNTs, yielding the respective contribution of ethanols two different carbon atoms to SWNT formation. Surprisingly, the carbon away from the hydroxyl group is preferably incorporated into the SWNT structure, and this preference is significantly affected by growth temperature, presence of secondary catalyst metal species such as Mo, and even by the substrate material. These experiments provide solid evidence confirming that the active carbon source is not limited to products of gas-phase decomposition such as ethylene and acetylene, but ethanol itself is arriving at and reacting with the metal catalyst particles. Furthermore, even the substrate or other catalytically inactive species directly influences the formation of SWNTs, possibly by changing the local environment around the catalyst or even the reaction pathway of SWNT formation. These unexpected effects, which are inaccessible by conventional techniques, paint a clearer picture regarding the decomposition and bond breaking process of the ethanol precursor during the entire CVD process and how this might influence the quality of the obtained SWNTs.

High Performance Recuperator With Oblique Wavy Walls

A series of numerical simulation of the flow and heat transfer in modeled counterflow heat exchangers with oblique wavy walls has been made toward optimal shape design of recuperators. The effects of oblique angles and amplitudes of the wavy walls are systematically evaluated, and the heat transfer and pressure loss characteristics are investigated. It is found that counter-rotating streamwise vortices are induced by the wavy walls, and the flow field has been drastically modified due to the intense secondary flow. By using the optimum set of oblique angle and wave amplitude, significant heat transfer enhancement has been achieved at the cost of relatively small pressure loss, and the j/f factor becomes much larger than that of straight square duct or conventional compact recuperators. When thermal coupling of hot and cold fluid passages is considered, the heat transfer is found to be strongly dependent on the arrangement of counterflow passages. The total heat transfer surface area required for a given pumping power and heat transfer rate can be reduced by more than 60% if compared to the straight square duct.

Design and characterization of high-performance contactless gripper using spiral air flows

We present a MEMS-based contactless gripper with arrayed spiral air flows, aimed at the mitigation of the flow-induced vibration of the levitated object. For non-contact levitation as applied to the robot end-effector, the air flow-based handling system has attracted increasing attention due to the simplicity of the structure and its control. Our design is based on the concept of distributed forcing by arrayed spiral-flow chambers. In each chamber, a spiral flow is generated, which effectively induces the attraction force by negative pressure. Our device has extremely thin structure, compatible with MEMS-based fabrication. In the present study, we fabricate proof-of-concept devices, and examine the basic characteristics. We demonstrate the promising performance of the present gripper through force-measurement experiments. Design considerations by CFD analysis and a simplified analytical model of the attraction force are also presented. The present results support the effectiveness of our strategy, and it is suggested that the arrayed structure with spiral-flow chambers and suction hole is much effective for obtaining desired attraction force while enhancing the holding stability.

A design of longitudinally-divided balloon structure in PDMS pneumatic balloon actuator based on fem simulations

Toward optimum design of micro devices using pneumatic balloon actuators (PBAs), we propose a design concept with longitudinally-divided balloon structure. We have performed FEM-based simulation and demonstrated its applicability to compute and characterize the bending motion of PBAs fabricated from PDMS (polydimethylsiloxane) material. In the present study, it is shown through the simulation that the bending characteristics can be significantly altered dependent on the number of balloon divisions. Moreover, it is experimentally indicated that, with the present design, the magnitude of the balloon inflation can be reduced so as to achieve a desired bending motion in more compact space than required with a single-balloon structure of the equivalent size of the balloon.

Liquid-tolerant electret using super-lyophobic pillar surface

For the first time, we have realized electret that can be used in the liquid environment toward better performance of electret-based generators and actuators. By using super-lyophobic overhanging pillar surface, stable Cassie-Baxter (C-B) state is sustained even with low-surface-tension hexadecane liquid and with high surface potential. Pillar surface with a SiO2 electret layer has been successfully charged with soft X-ray photoionization we previously developed. The pillar surface significantly suppressed the charge decay, and surface potential as high as 160 V has been maintained after 5-day contact with hexadecane droplet.

Modeling and characterization of the transient performance of a gas detector based on fringe-field capacitance

This paper presents the first comprehensive assessment of the transient performance of a gas detector (chemicapacitor) based on fringe-field capacitance using detailed computational modeling and experimental validation. Intended for use with a micro-gas chromatograph (μGC), this 1 mm2 detector is comprised of interdigitated thin-film metal electrodes that are patterned on a glass substrate and covered with 0.5-4 μm thick polymer. The model couples gas flow, vapor diffusion with partitioning, and capacitance response. The computational results illustrate the dynamic process of vapor peaks passing through the detector. The existing design provides ≈ 0.06 fF/ng sensitivity for n-pentane, and fast response with ≈ 0.1 s peak broadening, which are appropriate for the μGC applications under consideration. The performance is experimentally validated.

MEMS wireless temperature sensor for combustion studies

A MEMS wireless wall temperature sensor for combustion studies is proposed. Electrical resistance change in a LCR circuit is used to measure the temperature through inductive coupling the sensor coil and the read-out coil. Equivalent circuit model and 3-D electromagnetic simulation are employed to design sensor configuration. The resonant frequency is increased with increasing the resistance due to the temperature increase. The prototype sensor was successfully fabricated with MEMS technologies. The impedance phase angle shows a sharp dip at the resonant frequency, which is in good accordance with the equivalent circuit model. The measured temperature sensitivity is found to be as high as 6 kHz/K, when the distance between the read-out and the sensor coils is 0.71 mm.

Electrostatic Thermal Energy Harvester Using Unsteady Temperature Change

A model electrostatic thermal generator using unsteady temperature change is proposed. The device consists of a capacitor based on high-permittivity ceramics, and an electret layer serving as a permanent voltage source. Connecting them in series, permittivity change by temporal temperature change alters the amount of induced charges on the electrode thereby produces electric current in the external circuit. Optimum design parameters of the system have been obtained using a simplified circuit model. An early prototype using BaTiO3 ceramic as the dielectric and SiO2 as the electret is microfabricated, and its response is compared with the model prediction.

Flexible Wireless Wall Temperature Sensor for Unsteady Thermal Field

We present a novel flexible wireless wall temperature sensor with high spatio- temporal resolution and its performance evaluation in an unsteady thermal field. A base part of the sensor is made of thermally-stable polyimide and the copper films. Using a Si hard mask fabricated by standard lithography and DRIE process, 1 mm-sized sensing resistor is sputtered on the copper coil. We enhance the time response for each measurement by reducing the frequency sweeping points. It is shown that the accuracy of the present temperature measurement is in acceptable range for most combustion studies, based on a series of error- estimation analyses. The temperature measurement uncertainty of ± 6.4 °C has been achieved with the measurement time interval as small as 2.48 ms.

Adaptive Blood Cell Separation using Cooperation of Serially Connected Membrane Filters

This paper proposes a cooperative operation of serially connected membrane filters toward adaptive blood cell separation system in order to overcome a restriction of a single membrane filter. A cooperation of serially connected membrane filters allows that downstream filters extract blood plasma from residual blood at upstream filters. Consequently, it becomes possible to adapt filtering characteristics to changing properties of blood. We focus on trans-membrane pressure (TMP) in order to prevent hemolysis. Our strategy can be realized as a miniaturized PDMS fluidic chip. Our laboratory experiment using a prototype shows that plasma extraction efficiency is improved from 34% to 75%. Toward an integrated system, this paper successfully demonstrates multiple filters integrated into a PDMS fluidic chip.