Yoshiyuki Kawamura

Effective deep ultraviolet photoetching of polymethyl methacrylate by an excimer laser

Photoetching of polymethyl methacrylate (PMMA) for pulsed high power UV light is demonstrated. As a high power UV light source, a KrF excimer laser was used. Etching depth obtained by deep UV light irradiation has not only energy dependence, but also power dependence. It increased abruptly by increasing the exposed power density for the same exposed energy density.These experimental results show that high power excimer lasers are the effective light source for UV photoetching of PMMA.

Generation of relativistic photoelectrons induced by excimer laser irradiation

For the first time, photoelectrons from a metal surface irradiated by a pulsed excimer laser were accelerated to relativistic energy. The energy, the current density, and the pulse duration of the accelerated photoelectrons were 0.41 MeV, 0.5 A/cm2, and 20 ns, respectively.

Clapping-wing Micro Air Vehicle of Insect Size

The efficiencies for generating the axial thrust and the lift of a flapping wing micro air vehicle (MAV) were increased by clapping the wings together, using the “Weis Fogh clap and fling mechanism” from studies on the aerodynamics of the insect flight. Making use of this effect, we have succeeded in the development and the flight of an insect-size clapping wing MAV. The span and the weight were 10cm and 2.3g, respectively, which are very close to those of the hawkmoth (Manduca sexta), and amongst the smallest and the lightest ever built. The flight characteristics of the clapping MAV were similar to those of the hawkmoth. These results are the first step towards MAVs that mimic insects at lower Reynolds numbers.

Fabrication of Multilayers with Growth Controlled by Sequential Surface Chemical Reactions

A multilayer of aluminum oxide and titanium oxide was fabricated with growth controlled by sequential surface chemical reactions of trimethylaluminum/hydrogen peroxide for the aluminum oxide layer, and tetrachlorotitanium/hydrogen peroxide for the titanium oxide layer. Evaluation of the multilayer using a transmission electron microscope and an X-ray diffractometer indicated that the 1.6 nm thickness of each layer equaled the design value, and the ratio (Δ2θ/2θ0) of the full width of the first peak to the center angle of the peak was close to the theoretical minimum.

The strange flight behaviour of slowly spinning soccer balls

The strange three-dimensional flight behaviour of slowly spinning soccer balls is one of the most interesting and unknown phenomenon associated with the trajectories of sports balls. Many spectators have experienced numerous exciting and emotional instances while observing the curious flight behaviour of these balls. We examine the aerodynamic mechanisms of erratic ball behaviours through real flight observations, unsteady force measurements and flow pattern visualisations. The strange behaviour is elucidated by the relationship between the unsteady forces on the ball and the wake flow. The irregular changes in position for twin longitudinal vortices have already been discovered in the supercritical Reynolds number region of a sphere with a smooth surface. This finding is applicable to the strange behaviour of the flight of soccer balls with this supercritical flow. The players, spectators, and television viewers will gain greater insight into the effects of soccer ball flights.

Angular velocity spread of relativistic photoelectrons induced by excimer laser irradiation

The angular velocity spread of relativistic photoelectrons induced by a pulsed excimer laser was measured. The energy, the current density, and the pulse duration of the accelerated photoelectron were 0.34 MeV, 0.5 A/cm2, and 20 ns, respectively. (The method of measurement is based on measuring Larmor radius which corresponds to the transverse component of the electron velocity.) The angular velocity spread β⊥/β∥ was found to be less than 8×10−3, which means that the energy component due to β⊥ was as small as ≲17 eV.

Observation of periodical short pulse trains in free-electron laser oscillations

Periodical short pulse trains were observed in a long pulse, low current, low voltage waveguide mode free‐electron laser. The pulse width and the pulse train intervals of the periodical short pulse trains were about a few ns and about 23 ns, respectively. These pulse trains can be explained as self‐mode‐locked oscillations of a free‐electron laser.

Measurement of the Energy Spread of the Cold Relativistic Electron Beam Using Thomson Backscattering of a High Power CO2 Laser

The energy spread of the cold relativistic electron beam was measured by the Thomson backscattering of a high power CO2 laser. The energy spread was about 1.2% of the total energy. The wavelength and the power of the scattered light were in good agreement with the theoretically calculated values.

Direct Measurement of the Energy Distribution of an Intense Relativistic Electron Beam

The energy distribution of an intense relativistic electron beam (IREB) having a voltage of ≈0.75 MV, a current of 23 kA, and a duration of 30 ns was investigated using a magnetic-deflection-type energy analyzer. The IREB was found to have an exponential distribution with a sharp discontinuity at the maximum energy and a gradual decay toward lower energy. The energy spread was 6% of the maximum energy.

System Identification and Controller Design of a Micro Air Vehicle using Magnetic Suspension and Balance System

Magnetic Suspension and Balance Systems (MSBSs) allow for non-contact balance and actuation. During wind tunnel tests, these systems can eliminate support interference to allow for more accurate measurements of aerodynamic forces and moments acting on an experimental model. MSBSs also make it easy to change the position and attitude of the model. Furthermore, MSBSs can adjust the Degree of Freedom (DOF) of the experimental model so that system identification and controller design can be effectively achieved during wind tunnel tests. In this paper, an MSBS is used during wind tunnel tests to measure the aerodynamic coefficients of a Micro Air Vehicle (MAV) model for various angles of attack and elevator deflection angles. The results are used to design a height hold controller for a MAV model. The height hold controller is implemented into the model and the MSBS is again employed during wind tunnel tests to measure the performance of the controller.