A Novel Method and an Equipment for Generating the Standard Moisture in Gas Flowing through a Pipe.

When inert gas containing water molecules flows into a metal pipe, the water molecules cannot exit instantaneously from the outlet of the pipe but are captured at adsorption sites on the inner surface of the pipe until most of the sites are occupied. A theoretical model and a subsequent experiment in this article show that the delay time depends on the amount of moisture level; the higher the moisture-level, the shorter the delay time. Based on the result, we propose a new method and its implementation to the validation of a standard moisture generation to be used in the field measurement such as in factories and pipe lines.

Development of ball surface acoustic wave trace moisture analyzer using burst waveform undersampling circuit.

The measurement and control of trace moisture, where the water concentration is lower than 1 ppmv [-76.2 °C for the frost point (°CFP)], are essential for improving the yield rate of semiconductor devices and for ensuring their reliability. A ball surface acoustic wave (SAW) sensor with a sol-gel silica coating exhibited useful characteristics for a trace moisture analyzer (TMA) when the temperature drift of the delay time output was precisely compensated using two-frequency measurement (TFM), where the temperature-compensated relative delay time change (RDTC) was obtained by subtracting the RDTC at the fundamental frequency from that at the third harmonic frequency on an identical propagation path. However, the cost of the measurement circuit was a problem. In this study, a burst waveform undersampling (BUS) circuit based on the theory of undersampling measurement was developed as a practical means. The BUS circuit was useful for precise temperature compensation of the RDTC, and the ball SAW TMA was prototyped by calibrating the RDTC using a TMA based on cavity ring-down spectroscopy (CRDS), which is the most reliable method for trace moisture measurement. The ball SAW TMA outputted a similar concentration to that obtained by the CRDS TMA, and its response time at a set concentration in N2 with a flow rate of 1 l/min was about half that of the CRDS TMA, suggesting that moisture of -80 °CFP was measured within only 1 min. The detection limit at a signal-to-noise ratio of 3 was estimated to be 0.05 ppbv, comparable with that of the CRDS TMA. From these results, it was demonstrated that a practical ball SAW TMA can be realized using the developed BUS circuit.

Nonlinear ultrasonic imaging method for closed cracks using subtraction of responses at different external loads.

To improve the selectivity of closed cracks for objects other than cracks in ultrasonic imaging, we propose an extension of a novel imaging method, namely, subharmonic phased array for crack evaluation (SPACE) as well as another approach using the subtraction of responses at different external loads. By applying external static or dynamic loads to closed cracks, the contact state in the cracks varies, resulting in an intensity change of responses at cracks. In contrast, objects other than cracks are independent of external load. Therefore, only cracks can be extracted by subtracting responses at different loads. In this study, we performed fundamental experiments on a closed fatigue crack formed in an aluminum alloy compact tension (CT) specimen using the proposed method. We examined the static load dependence of SPACE images and the dynamic load dependence of linear phased array (PA) images by simulating the external loads with a servohydraulic fatigue testing machine. By subtracting the images at different external loads, we show that this method is useful in extracting only the intensity change of responses related to closed cracks, while canceling the responses of objects other than cracks.

Suppression of spurious vibration of cantilever in atomic force microscopy by enhancement of bending rigidity of cantilever chip substrate.

To improve the precision of dynamic atomic force microscopy (AFM) using cantilever vibration spectra, a simple but effective method for suppressing spurious response (SR) was developed. The dominant origin of SR was identified to be the bending vibration of the cantilever substrate, by the analysis of the frequency of SR. Although a rigid cover pressing the whole surface of the substrate suppressed SR, the utility was insufficient. Then, a method of enhancing the bending rigidity of the substrate by gluing a rigid plate (clamping plate, CP) to the substrate was developed. This chip can be used with an ordinary cantilever holder, so that the reproducibility of SR suppression when attaching and detaching the cantilever chip to the holder was improved. To verify its utility, the evaluation of a microdevice electrode was performed by ultrasonic atomic force microscopy. The delamination at a submicron depth was visualized and the detailed variation of the delamination was evaluated for the first time using clear resonance spectra. The CP method will particularly contribute to improving dynamic-mode AFM, in which resonance spectra with a low quality factor are used, such as noncontact mode AFM in liquid or contact resonance mode AFM. The effect of the CP can be achieved by fabricating a substrate with a thick plate beforehand.

Ultramultiple roundtrips of surface acoustic wave on sphere realizing innovation of gas sensors.

A thin beam of wave usually diverges due to diffraction, which is a limitation of any device using such waves. However, a surface acoustic wave (SAW) on a sphere with an appropriate aperture does not diverge but is naturally collimated, realizing ultramultiple roundtrips along an equator of the sphere. This effect is caused by the balance between diffraction and focusing on a spherical surface, and it enables realization of high-performance ball SAW sensors. The advantage of ball SAW is most fully appreciated when applied to a very thin sensitive film for which the multiple-roundtrip enhances the sensitivity, but the attenuation loss is not very large. It is exemplified in a hydrogen gas sensor that realizes a wide sensing range of 10 ppm to 100% for the first time, and realizes relatively fast response time of 20 s without heating the sensitive film.

Effect of adhesion force between crack planes on subharmonic and DC responses in nonlinear ultrasound.

Subharmonic and DC responses in nonlinear ultrasound have been expected as a possible means of detecting closed cracks. Recently, it has been reported that subharmonics in a closed crack markedly increases above a certain input wave amplitude. Such a phenomenon is called "threshold behavior". However, the mechanism of threshold behavior has yet to be elucidated. To clarify this, we introduced adhesion force as a short-range force into the previous analytical model, which expresses the nonlinear contact vibrations of crack planes with intense ultrasound and provides a DC displacement as an approximation of the subharmonic response. Consequently, upward convex curves of displacement against input wave amplitude above the threshold were reproduced for the first time. The validity of the derived analytical solution is discussed by comparison with experimentally observed subharmonics.

Removal of PCDDs/DFs and dl-PCBs in MWI fly ash by heating under vacuum.

Temperature dependence of PCDD/DF and dioxin-like polychlorinated biphenyl (dl-PCB) concentrations in fly ash from a municipal waste incinerator (MWI) heated under vacuum has been investigated as a function of sample temperature ranging from T(s)=425 to 800 K to find out if PCDDs/DFs in fly ash evaporate and are trapped in a liquid nitrogen-cooled trap. The results show that more than 99.98% of PCDDs/DFs in TEQ is removed from fly ash by vacuum heat treatment at T(s)>650 K for 4 h. Almost no PCDDs/DFs were detected in the liquid nitrogen-cooled trap. Homologue distributions indicate that dechlorination/hydrogenation (DCH) reactions proceed in fly ash at T(s)>450 K. Arrhenius rate parameters for the DCH reactions have been determined for each homologue assuming that only DCH reactions occur. The fly ash heated under vacuum at 650 or 800 K was reheated at 573 K (300 degrees C) in a stream of dry or humid air to see how much PCDDs/DFs and dl-PCBs are regenerated. We have found that (1) PCDDs/DFs are regenerated in both 650 K and 800 K treated fly ash, whereas dl-PCBs are regenerated in 650 K treated fly ash, (2) formation of PCDFs predominates over that of PCDDs or dl-PCBs, and (3) less chlorinated homologues are abundant for PCDDs/DFs and dl-PCBs.

Analysis of spurious bulk waves in ball surface wave device.

We analyzed the acoustic waves propagating in a sphere to establish a useful guideline for the design of NDE apparatus and ball surface acoustic wave (SAW) device exploiting the diffraction-free propagation of SAW on a sphere. First, we calculated the laser-generated acoustic displacements both under ablation condition and under thermoelastic condition and verified experimentally the validity of the calculation. Next, the acoustic waves excited by out-of-plane stress and those excited by in-plane stress were compared. The results showed that when the out-of-plane stress was applied, the relative amplitudes of the bulk waves to that of the SAW were larger and the number of bulk waves was larger than that when the in-plane stress was applied, while the SAW had similar waveforms in each case. The ratio of the relative amplitude of the bulk waves for the out-of-plane stress and the in-plane stress was 3.1:1 at phi(1)=90 degrees and 1.67:1 at phi(1)=0 degrees. The large amplitude for the out-of-plane stress can be explained by wide directivities of bulk waves. Consequently, we found that it is necessary for ball SAW device to select a piezoelectric material and form of interdigital transducer so that the in-plane stress becomes dominant.