Masaki Esashi

Medical and welfare applications of shape memory alloy microcoil actuators

We have successfully developed several mechanisms using Ti–Ni shape memory alloy (SMA) microcoil actuators, for example, a bending mechanism, an extension/contraction mechanism, a torsional mechanism and a stiffness control mechanism. The principles involved in these mechanisms and the structure of each mechanism are detailed, and medical and welfare applications are presented. One of the devices which has been developed is an active bending soft tube using an SMA microcoil actuator. Doctors can control the bending motion of the tip of the tube from outside the body. One application of this tube is the treatment of intestinal obstruction. The tube consists of a bending tip (external diameter, 6 mm; length, 40 mm) and a 3 m long silicone rubber tube. It enables easier and more reliable passage at the lower end of the stomach (pylorus). The maximum bending angle is 110°. Another device we have developed using SMA microcoil actuators is a dynamic tactile pin display which displays Braille characters and graphic information by dynamic up-and-down movement of an array of pins. SMA microcoil actuators enable up-and-down movement of the pins and a magnetic latch mechanism keeps the pins in an up or down state. This two-dimensional pin display consists of 100 (10 × 10) pins with a pin pitch of 2.5 mm, the actuation length of each pin being 2 mm. The tactile information can be displayed sequentially every 0.3 s.

High power electrostatic motor and generator using electrets

For application to a micro-machined gas turbine, we first designed the motor/generator using electrets. Theoretical calculation confirmed that the motor/generator generates 30.4 W at a rotational speed of 1 Mrpm after its electrode design is optimized. Next, we proposed a novel circuit using LC resonance for the generator, which can avoid the charging-discharging loss of the parasitic capacitance. And we confirmed that the circuit could generate over 80% output of the theoretical maximum. Lastly, we developed an electret-charging equipment using Corona discharge. Using it, an electret was charged, showing the average surface voltage of 354 V and the standard deviation of 16 V.

P1I-9 Passive 2.45 GHz TDMA based Multi-Sensor Wireless Temperature Monitoring System: Results and Design Considerations

This paper presents a TDMA (time division multiple access) based wireless temperature monitoring system using 2.45 GHz passive surface acoustic wave (SAW) delay line sensors. A three-step resolution refinement scheme using a combined delay and phase evaluation is proposed. Using a transmission power of 2 dBm (1.59 mW) a temperature accuracy of 0.19 K and 0.1 K(6sigma), were achieved for an interrogation distance of 1.4 m, and 1.3 m, respectively. The sensor design is discussed using experimental results concerning the relationship between the SNR (signal to noise ratio) of the sensors and the accuracy in time delay or phase measurement. Also, the direct electron beam writing on chemically-reduced (black) LiNbO3 is described

High power electrostatic motor with micropatterned electret on shrouded turbine

The paper describes the fabrication process of a shrouded turbine and surface modification using fluorinated silane coupling agents to stabilize the charges of a silicon-dioxide electret. The shrouded turbine was fabricated by cavity-through etching, which is deep reactive ion etching (DRIE) through a wafer having cavities made by DRIE and fusion bonding. By using this process, a shrouded turbine with little eccentricity was obtained without damaging the inner structures such as blades and flow ways. Charge stability of electrets was deteriorated by miniaturizing the size. The charge deterioration was caused by leakage current through the surface. To decrease the surface conduction, the surface was terminated by fluorine with silane coupling agents. As a result, the charge stability of a silicon-dioxide electret was improved 100 times compared with HMDS (hexamethyldisilazane) treatment.

Debris-free in-air laser dicing for multi-layer MEMS by perforated internal transformation and thermally-induced crack propagation

We have developed a novel debris-free in-air laser dicing technology, which gives more design freedoms in the structure, process and materials of MEMS as well as improves yields. Our technology combines two processes: dicing guide fabrication and wafer separation process. The first process is the internal transformation using a fundamental wavelength of a Ti: Sapphire laser or a Nd:YAG laser. The second process is non-contact separation by thermally-induced crack propagation using a CO2 laser or mechanical separation by bending stress. The internal transformation fabricated in the first process worked well as the guide of separation, and the processed wafer was diced with low stress. The diced lines completely followed the internal transformation.

Vacuum sealed ultra miniature fiber-optic pressure sensor using white light interferometry

We have developed a fiber-optic Fabry-Perot interferometer pressure sensor of 125 /spl mu/m in diameter of which cavity is sealed in vacuum. White light interferometry is used to avoid noise caused by bending of the optical fiber and a fluctuation of the light source. The reflection light is measured by high-speed spectrometer. A Fabry-Perot cavity is formed at the optical fiber end. A deformation of the diaphragm induced by pressure varies the cavity length. To avoid influence of temperature change to the sensor output, the cavity is sealed in vacuum. The sensing element is bonded to the optical fiber end by soldering in vacuum. Sn layer is formed on the metal spacer of the sensing element and is bonded to the Cr/Cu/Au layer patterned at the optical fiber end. Cr half-mirror is also patterned at the core of the fiber end for making interferometer. Pressure is successfully monitored in real-time using the sensor system.

An SOI 3-axis accelerometer with a zigzag-shaped Z-electrode for differential detection

We have developed a fully-differential 3-axis accelerometer with a novel zigzag-shaped Z-electrode, which is used for motion controls of automobiles and robots.

Normally-Closed Electrostatic Micro Valve with Pressure Balance Mechanism for Portable Fuel Cell Application

This paper describes an electrostatic micro valve which controls fuel in a portable direct methanol fuel cell (DMFC) system under development. A novel pressure balance mechanism is adopted to achieve both normally-closed operation against pressurized fuel and low voltage operation. The fabricated micro valve was tested using air as a working fluid in terms of leak pressure and driving voltage. The micro valve kept close state at input pressure from 0 kPa to 20 kPa. The driving voltage to fully open the micro valve was from 30 V to 60 V. These results well agree with the theoretical estimation.

Fabrication Techniques for Multilayer Metalization and Patterning, and Surface Mounting of Components on Cylindrical Substrates for Tube-Shaped Micro-Tools

This paper reports fabrication techniques for multilayer microstructures and surface mounting of small components on cylindrical substrates for tube-shaped high-performance micro-tools. A cylindrical shape is an ideal shape for micro medical tools inserted temporarily or implanted in the human body. Miniaturization, multifunctional capabilities, and high-performance are required for these tools. Tubular lumens, which are useful for the insertion of medical tools and for the injection of drugs, are necessary for endoscopes and catheters. Micro-fabrication on cylindrical substrates meets these demands. Multilayer metallization and patterning, as well as three-dimensional resist patterning have been performed using maskless lithography techniques on glass tubes with 2 and 3 mm outer diameters. Using laser soldering techniques, a high-speed OP amp has been mounted on a multilayer circuit formed on a glass tube to amplify small signals from micro medical sensors. These techniques will realize multifunctional and high-performance tube-shaped micro medical tools with small diameters

Magnetic torque driving 2D micro scanner with a non-resonant large scan angle

In this paper, a non-resonant 2D optical scanner with extremely large optical scan angle has been reported. A mirror, which is supported with a double-gimbal structure, is inclined by a rotational magnetic torque. Two of four permanent magnets are mounted on the mirror and the gimbal, respectively. The scanning angle of two axis can be controlled independently using external electromagnets. A static drive with maximum optical scan-angle of 118 degree has been achieved.