Yuichiro Hamate

High Ram Acceleration Using Open-Base Projectile

High-acceleration operation has been realized in a 25-mm-bore ram accelerator by employing an open-base projectile. The projectile comprises a centerbody and four e ns like a conventional ram accelerator projectile, but is manufactured as a single piece. The base of the centerbody is perforated so that pressures inside and outside are almost balanced, thereby reducing the required thickness of the centerbody wall and the total mass. Reliable ram acceleration could be started only when the entrance velocity was increased by 0.1 km/s from that set for the conventional projectile. Although the propellant e ll pressure was as modest as 3.5 MPa, an average acceleration of 4:4£ £10 4 g and a velocity increment of 1.0 km/s have been achieved through a 4.1-m-long, three-stage ram acceleration section.

Aging characteristics of electret used in a vibration-based electrostatic induction energy harvester

In this paper, we investigated charge stability of electrets made of 10 dielectric materials to examine what material properties are important factor for the stability. Since long lifetime is preferable for electrets energy harvester, charge stability of electret is one of the most important issue in performance optimization. Stability test revealed that water absorption of the dielectrics seems to affect charge stability. Effect of charge stability on output power of energy harvester was also investigated using rotational energy harvester. Using two dielectric materials as electret, output power measured at 0 hour and 44 hours later from charging confirmed that charge stability of electret significantly affect lifetime of energy harvester.

Thermally choked operation in a 25-mm-bore ram accelerator

The system of a 25-mm-bore ram accelerator (RAMAC25) was installed at Shock Wave Research Center, Institute of Fluid Science, Tohoku University. The total length of the ram acceleration tube is 6 m. It uses a powder gun as a pre-accelerator. The propellant mixture is supplied through a system composed of mass flow controllers and backpressure regulators. Pressure signals are recorded through multiplexer systems, thereby saving the number of channels of the data storage device. Experimental study was conducted, changing the amount of the smokeless powder in the pre-accelerator, the component and pressure of the mixture, the initial pressure in the launch tube of the pre-accelerator, the design of the sabot and disk, and the thickness of the diaphragm etc. Ram acceleration was realized using a methane-based mixture. Results of the operation experiments are presented here.

Optimal geometry of a parallelized electret-based vibration energy harvester

Electret-based vibration energy harvesters often contain electrets forming a pattern of periodically repeated strips with period L to increase the output power by parallelization. Given a gap length g between the stationary electrets and the movable electrodes facing them, the natural question is how to choose L to maximize the output power. Our analysis, based on conformal mapping, shows that the optimal ratio L/g is represented by a rapidly convergent series starting with the dominant term π = 3.14, followed by terms amounting to a correction of less than 0.3%. We establish the practical relevance of this finding through an experiment involving a voltage-biased energy harvester.

Micro blender and separator using inner-vortex of droplet induced by surface acoustic wave

We report on a micro vortex in a droplet induced by surface acoustic wave acoustic streaming (SAW-AS), which is applicable as a stirrer in micro fluidic devices. Fine controllability of the flow rate in a micro vortex was revealed using two flow-tracking methods with colored aqueous fluids, or scattering laser beams by distributed particles. We performed two practical tasks of a micro stirrer as an on-chip blender and as a separator. Demonstrations results with a small concentrated blood specimen are also shown.

Significance of unsteadiness in operation of the small bore ram accelerator

Starting conditions are explored on the 25-mm-bore ram accelerator with a conventional fin-guided centerbody projectile, in which the standard condition in the 38-rnm-bore ram accelerator of University of Washington resulted in starting failure. It was found that the perforation ratio of the sabot (obturator) was a key parameter for the starting. With the perforation ratio of 0.46 or higher, ram acceleration operation was realized with reproducible thrust performance. The relevant mixture, 2.8 CH4+2O2+6.6N2, has a relatively low energy, its dimensionless heat release equaling 4.2. These results are discussed based on unsteady wave dynamics associated with the sabot motion. Once ram acceleration was realized, the thrust performance was not affected by the starting process, reaching a level of the Chapman-Jouguet detonation speed.

A novel narrow mist spray device using surface acoustic wave with a channel

This paper presents a novel device which can atomize a droplet into narrow mist spray using surface acoustic wave (SAW). A channel was cut into piezoelectric substrate between two IDT electrodes which drives SAWs in opposing directions. Then, SAW streaming in opposing directions are isolated in both sides of the channel, which converged atomized mist into narrow mist spray, whose width is nearly 1/4 compared with that of no-channel device.

OPEN-BASE PROJECTILE PERFORMANCE IN RAM ACCELERATOR

Experimental investigations were conducted in the 25-mm-bore ram accelerator using open-base projectiles, which were designed to obtain higher acceleration by reducing the mass. Single stage operations were conducted in a starting mixture, 2.8CH4+2O2+5.7N2. With a low entrance velocity, ram acceleration initiation delayed. The reliable start was obtained with an entrance velocity higher than 1.3 km/s. A maximum velocity of 2.3km/s was achieved through a 4-m-long ram acceleration section, where a ballistic efficiency higher than 0.1 was kept.

Observation of breakdown induced by CO2 laser focusing in an in-tube laser propulsion configuration

Time-resolved spectroscopy using a combination of a monochromator, streak camera, image intensifier and CCD camera is conducted to investigate the radiative flow field generated in the in-tube laser propulsion configuration. A 5-J CO2 TEA laser beam is focused through a specially-designed, double- reflection optical system in atmospheric air. Radiation emission in the wavelength range of 320 to 850 nm is observed during a typical period of 10 microseconds.

5.4.5 A Hydrogen Sulfide Sensor Based on a Surface Acoustic Wave Resonator Combined with Ionic Liquid

This paper describes a hydrogen sulfide (H2S) gas sensor using ionic liquid (IL). In this sensor, a reservoir for the IL was integrated above a surface acoustic wave (SAW) resonator. The IL serves as an absorber for H2S gas. Mass change due to this absorption is detected as a frequency-shift of the resonance. In this study, we fabricated and demonstrated the sensor using the LiNbO3 SAW resonator with the resonant frequency of 38 MHz. The integrated reservoir was filled by the IL 1-butyl-3methlimidazlium tetrafluoroborate ([BMIM]-[BF4]). As experimental results, we could observe the linear correlation between the amount of the frequency-shift and the exposure time of the sensor to the H2S gas.