Development of a time‐synchronized wireless sensor network

Network‐based wireless sensing has become an important area of research and various new applications for remote sensing are expected to emerge. One of the promising applications is structural health monitoring of buildings or civil engineering structures, which often requires vibration measurement. For vibration measurement via a wireless network, time synchronization is indispensable. In this paper we introduce a newly developed time‐synchronized wireless sensor network system. The system employs an IEEE 802.11 standard‐based TSF counter and sends the measured data with the counter value. It makes possible consistency on a common clock among different wireless nodes. We describe the accuracy evaluation by simulation studies as the size of the nodes is increased. The hardware and software specifications of the developed wireless system are presented. The experiments were conducted in a three‐story reinforced concrete building and the results showed that the system performance significantly exceeds requirements. © 2010 Wiley Periodicals, Inc. Electr Eng Jpn, 173(4): 46–53, 2010; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.21020     

Influence of External Stress on Discontinuous Precipitation Behavior in a Cu-Ag Alloy

The influence of an applied stress on discontinuous precipitation (DP) has been investigated for a Cu-5 wt pct Ag alloy aged at 573 K. A tensile stress enhances the growth of DP cells in both the loading direction (LD) and transverse direction (TD), but the cell growth rate in the TD, v _CT , is faster than that in the LD, v _CL . A compressive stress suppresses the cell growth in the TD, but does not significantly influence it in the LD. The tensile or compressive stress tends to produce discontinuous silver precipitates elongated in a á 110 ñ_a \left\langle {110} \right\rangle_{\alpha } direction of the copper matrix in a DP cell, nearly perpendicular to or parallel to the LD. This result, along with the dependence of the cell growth rate on the sense of the applied stress, can be understood through the interaction energy between the external stress and the misfit strains of silver precipitates. An analysis of length-change measurement results has enabled estimation of the ratio of the growth rate of silver precipitates in the TD, v _PT , to that in the LD, v _PL , under tension or compression. The estimated values of v _PT /v _PL are in good agreement with the values of v _CT /v _CL , experimentally obtained, indicating that the anisotropy of the cell growth rate is determined by the growth behavior of silver precipitates.     

Novel integrated photodetector on Si LSI circuits. Opticallycontrolled MOSFET

We have demonstrated a novel integrated photo-detector on Si large-scale integration circuits. This device integrated the light absorption region on the gate of metal-oxide-semiconductor field-effect transistor (MOSFET), and the long wavelength light controls the current of MOSFET. The GaInAs-InP multiple-quantum-well absorption region and SiO₂ of the MOSFET were directly bonded. From the experimental results, we confirmed that the light-controlled current was increased by shortening the gate length of the MOSFET, and that an 1850 A/W responsivity was obtained in a 3.5-μm gate length device using an irradiation of 1.5-μm wavelength light     

Joining of SiC Fiber‐Bonded Ceramics using Silver,Copper, Nickel,Palladium, and Silicon‐Based Alloy Interlayers

SiC fiber‐bonded ceramics, SA‐Tyrannohex^®, (SA‐THX) with perpendicular and parallel fiber orientations were brazed using Ag‐, Ni‐ and Pd‐base brazes, and four Si–X (X: Ti, Cr, Y, Ta) eutectics. Outcomes were variable, ranging from bonded joints through partially bonded to un‐bonded joints. Prominent Ti‐ and Si‐rich interfaces developed with Cusil‐ABA, Ticusil, and Copper‐ABA and Ni‐ and Si‐rich layers with MBF‐20. Stress rupture tests at 650 and 750°C on Cusil‐ABA‐bonded joints revealed a temperature‐dependent behavior for the perpendicular joints but not for the parallel joints with failure occurring at brazed interface. Higher‐use temperatures can be targeted with eutectic Si–Ti and Si–Cr alloys.     

Combinatorial synthesis of phosphors using arc-imaging furnace

We have applied a novel ‘melt synthesis technique’ rather than a conventional solid-state reaction to rapidly synthesize phosphor materials. During a synthesis, the mixture of oxides or their precursors is melted by light pulses (10–60 s) in an arc-imaging furnace on a water-cooled copper hearth to form a globule of 1–5 mm diameter, which is then rapidly cooled by turning off the light. Using this method, we synthesized several phosphor compounds including Y₃Al₅O₁₂:Ce(YAG) and SrAl₂O₄:Eu,Dy. Complex phosphor oxides are difficult to produce by conventional solid-state reaction techniques because of the slow reaction rates among solid oxides; as a result, the oxides form homogeneous compounds or solid solutions. On the other hand, melt reactions are very fast (10–60 s) and result in homogeneous compounds owing to rapid diffusion and mixing in the liquid phase. Therefore, melt synthesis techniques are suitable for preparing multi component homogeneous compounds and solid solutions.     

Estimation of the current peak value distribution of all lightning to the ground by electro‐geometric model

When we examine the lightning frequency and the lightning shielding e?ect of the electro‐geometric model (EGM), we need the current distribution of all lightning to the ground. The distribution of lightning current to structures is di?erent from this distribution, but it has been used in EGM conventionally. We assumed the lightning striking distance coe?cient related to the height of structures in order to obtain a result which corresponds to the observed frequency of lightning to structures, and estimated the current distribution of all lightning to the ground from data listed in the IEC 62305 series of EGM. The estimated distribution adjusted by the LLS detection e?ciency agreed well with the distribution observed by LLS. © 2013 Wiley Periodicals, Inc. Electr Eng Jpn, 184(3): 14–26, 2013; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.22356