Harumichi Sato

High-speed optical microscanner driven with resonation of Lam Waves using Pb(Zr.Ti)O3 thick films formed by aerosol deposition

A high-performance optical microscanner with a resonance frequency over 20 kHz and a scan angle (peak-to-peak value) over 30° in atmospheric ambient, was successfully fabricated by deposit piezoelectric materials at a high rate by the AD method onto a metal scanner structure, which was fabricated by mechanical machining. The scanner is applicable to SVGA high-resolution display of 800×600 or more. This method is a powerful tool for realizing ceramic integration with metal components.

Surface acoustic wave velocity and attenuation dispersion measurement by phase velocity scanning of laser interference fringes

We developed a noncontact, nondestructive surface acoustic waves (SAW) velocity and attenuation measurement method in the frequency range of 30-110 MHz. This method is based on the phase velocity scanning method previously proposed by the authors that uses laser interference fringes scanned at the phase velocity of SAW to generate single-mode SAW with high intensity and directivity. In order to verify the validity and accuracy of the method, we measured SAW velocity and attenuation in Al and AISI 304 steel. The error in SAW velocity measurement was less than 1% in Al. Also, the attenuation was obtained with high precision in the AISI 304 steel. Then, we applied this method to porous silicon (PS) films on Si wafers as an example of a layered medium. The SAW velocity in PS films decreased with increasing porosity. By fitting the calculated dispersion curve to the measured one, the elastic stiffness of PS films was determined with a relative accuracy of 0.2%, which is thought to be the highest using laser ultrasonic methods. The attenuation of PS films was found to be 6-80 dB/cm in the frequency range of 30-70 MHz. The frequency dependence of attenuation was obtained with high precisely.

Theoretical and Experimental Investigation of Propagation of Guide Waves in Cylindrical Pipe Filled with Fluid

Cylindrical pipes are widely used in industries such as nuclear power plants and micro total analysis systems (µTAS). The nondestructive evaluation (NDE) of such pipes is therefore crucial. NDE and ultrasonic flowmeters can be used to characterize pipes filled with fluid. Lafleur and Shields [J. Acoust. Soc. Am. 97 (1995) 1435] and Pan et al. [J. Acoust. Soc. Am. 113 (2003) 3209] theoretically and experimentally investigated a pipe filled with fluid, but they only considered the axi-symmetrical mode. Commonly used ultrasonic transducer or laser ultrasonic methods, however, also generate non-axi-symmetrical mode guide waves. Here, guide waves propagating in a cylindrical pipe filled with fluid were theoretically investigated. The results were used to develop a computer program for calculating the phase velocity of guide waves. The calculation results were then compared with experimental results.

Finite Element Method Analysis of Evaluation of Surface Micro Cracks Using Laser Ultrasound Generated by Phase Velocity Scanning Method

Nondestructive evaluation of defects that reduce material strength is critical to maintain the reliability of micro electro mechanical system (MEMS) components. We developed a new laser ultrasonic method, the phase velocity scanning (PVS) method, for this purpose. In a feasibility study, 200-µm-long micro standard defects (slits) on a Si wafer were fabricated with various depths (6.8 to 28.7 µm) and widths (2 to 5 µm), and scattered waves from a 6.8-µm-deep slit were successfully detected using 60 MHz surface acoustic waves. To analyze the directivity of acoustic waves generated by the PVS method and scattered waves from the slits, we developed 2D and 3D finite element method (FEM) programs. Using these programs, we confirmed that scattered waves are generated from a slit of 200 µm length, 10 µm depth, and 5 µm width. A comparison with the simulation of a conventional laser ultrasonic method showed that the PVS method has better directivity to suppress disturbing echoes generated in small objects.

Room-temperature fast deposition and characterization of nanocrystalline Bi0.4Sb1.6Te3 thick films by aerosol deposition

P-type nanocrystalline Bi0.4Sb1.6Te3 thick films were directly deposited on copper substrates by aerosol deposition (AD) involving shock compaction of the starting powder at room temperature. The film deposition rate was over 700 μm/min. The relative density of the films was above 95%. Films with a thickness of over 2 mm were obtained. They consisted of nanocrystals with grain sizes of several tens of nanometers. The crystal structure of the films was the same as the bulk materials prepared by spark plasma sintering (SPS) using the same starting powder. We measured the electrical conductivity, carrier concentration, Hall mobility, and thermal conductivity of the films and compared them with those of the bulk materials. The thermal conductivity of the AD film was 20-30% lower than that of the bulk materials, which is attributed to the increased number of grain boundaries and some defects in the AD films.

Evaluation of Surface Defects Using Surface Acoustic Waves Generated by Phase Velocity Scanning of Laser Interference Fringes

In order to maintain the reliability of structural materials such as ceramics, it is important to nondestructively detect surface defects that reduce the strength of materials. Therefore, we have developed the phase velocity scanning (PVS) method. The PVS method does not involve the use of coupler (noncontact) and has excellent directivity. We report that the sensitivity for detecting surface acoustic waves (SAW) was improved using a video signal. The video signal S/N ratio, which is defined as the ratio of generated SAW to background noise, is 46.5 dB. Back propagation waves were not detected within the limit of the S/N ratio. Utilizing this excellent directivity we succeeded in B-mode imaging to detect indentation cracks (Knoop indentation cracks). Scattered waves were detected on the indentations of above 100 gf but could not be detected for those of below 50 gf. This result implies that this method can be used to evaluate the critical load of initiating median cracks which is difficult using conventional methods.

Advanced micromachine fabrication using ion implantation

Abstract Ion-implantation followed by etching was used to fabricate micromachine components from bulk silicon. The size of the ion-modified region was sufficiently small to make microdevices (e.g. devices with submicrometer dimensions). Ion implantation/etching techniques have the advantages of high controllability, high selectivity and non-thermal processing. For 3.1 MeV gold ions implanted into silicon to a dose of 1×10 17 cm −2 , microcantilever beams were fabricated with a Young’s modulus of 60 GPa and a surface resistance of 36 kΩ. The elastic property was lower than conventional materials used for making microdevices, and the electrical resistance was sufficiently low that such components can be used as electrical conductors.

Estimation of Elastic Constants from Surface Acoustic Wave Velocity by Inverse Analysis using the Downhill Simplex Method

The measurement of surface acoustic wave (SAW) velocity is used to estimate the surface properties because the velocity depends on the elastic properties near the surface. To estimate the elastic constants, we developed a new inverse method combining the Monte Carlo method and the downhill simplex method. The initial values are determined using many random numbers, instead of an arbitrarily chosen several sets of values, in order to reduce the risk of trapping by the local pseudo minima. We confirm that the estimated elastic constants agree well with the reported elastic constants of Si and the experimental SAW velocity is quite well reproduced. We estimate the elastic constants of quartz for application purposes.

Nondestructive evaluation of elastic properties in porous silicon film on Si(100) by the phase velocity scanning of laser interference fringes

Investigating an attractive application of a porous silicon (PS) film as a micromachine jointing layer, we evaluated elastic properties of the PS film by the analysis of velocity dispersion of surface acoustic waves (SAW). We developed a novel laser ultrasonic method which utilized the laser interference fringes scanned at the phase velocity of the SAW and measured, for the first time, SAW velocity dispersion of the PS film in a dry condition. The phase velocity of the SAW of the PS film was found to decrease with an increase of the porosity. Curve fitting of the measured dispersion to the computed one gave extremely small elastic stiffness of the PS film compared to that of Si wafer. Morphology of pores in the PS film, estimated from a relationship between the porosity and elastic stiffness C/sub 44/, was found to be an ordered and less open structure.

Theoretical and Simulated Analysis of Guided Waves Propagating in Fluid-Filled Pipes

To keep the safety of nuclear power plants, nondestructive evaluation (NDE) of cylindrical pipes, which carry hot water, is an issue of a great interest. Ultrasonic methods using bulk wave are commonly used for NDE of such pipes, however still having problems that the methods consume a long time to inspect large areas. On the other hand, NDE methods using guided wave should overcome this problem because the guided wave has a characteristic of long propagation range. Nevertheless, there have been few investigations to clarify the behavior of the guided wave in the fluid-filled cylindrical pipes. We therefore developed an analytical method to calculate particle displacement, and we compared the dispersion curves, cut-off frequencies, and particle displacements of guided waves propagating in the hollow pipe and the fluid-filled pipe.