Sensitivity enhancement for H2 gas detection using a SnO2–Ag2O–PdOx nanocrystalline system

Thick film H₂ sensors were fabricated using SnO₂ loaded with Ag₂O and PdO_x. The composition that gave highest sensitivity for H₂ was in the wt.% ratio of SnO₂:Ag₂O:PdO_x as 93:5:2. The nano-crystalline powders of SnO₂–Ag₂O–PdO_x composites synthesized by sol–gel method were screen printed on alumina substrates. Fabricated sensors were tested against gases like H₂, CH₄, C₃H₈, C₂H₅OH and SO₂. The composite material was found sensitive against H₂ at the working temperature 125 °C, with minor interference of other gases. H₂ gas as low as 100 ppm can be detected by the present fabricated sensors. It was found that the sensors based on SnO₂–Ag₂O–PdO_x nanocrystalline system exhibited high performance, high selectivity and very short response time to H₂ at ppm level. These characteristics make the sensor to be a promising candidate for detecting low concentrations of H₂.     

Controlled density of vertically aligned carbon nanotubes in a triode plasma chemical vapor deposition system

We report on the growth mechanism and density control of vertically aligned carbon nanotubes using a triode plasma enhanced chemical vapor deposition system. The deposition reactor was designed in order to allow the intermediate mesh electrode to be biased independently from the ground and power electrodes. The CNTs grown with a mesh bias of + 300 V show a density of ∼ 1.5 μm^− 2 and a height of ∼ 5 μm. However, CNTs do not grow when the mesh electrode is biased to − 300 V. The growth of CNTs can be controlled by the mesh electrode bias which in turn controls the plasma density and ion flux on the sample.     

Resonance properties and mass sensitivity of monolithic microcantilever sensors actuated by piezoelectric PZT thick film

The PZT thick film cantilever devices fabricated via MEMS process have much attraction because they are appropriate for biological transducer or sensor, resulting from their large actuating force and relatively high sensitivity especially in liquid. By means of resonance behavior, theoretical calculation and experimental verification of the PZT thick film cantilever devices have not been studied before. Accordingly, we focused on the sensitivity analysis and interpretation of the PZT thick film cantilevers in this study. Especially, the investigation for mass sensitivity of the PZT thick film cantilever is of importance for physical, chemical and biological sensing application. The PZT thick film cantilever devices were constructed on Pt/TiO₂/SiN _X /Si substrates using screen printing method and MEMS process. The harmonic oscillation response (resonance frequency) was measured using an optical laser interferometric vibrometer. The effect of cantilever geometry on the resonance frequency change was investigated. Compared with the theoretical resonant frequency change by mass loading, the experimental resonant frequency change of the PZT micromechanical thick film cantilever shows a variation of less than 2%. Mass sensitivities are estimated to be 30.7, 57.1 and 152.0 pg/Hz for the 400 × 380 μm, 400 × 480 μm and 400 × 580 μm cantilever, respectively.     

CuO formation control as a function of mixed ratio of Cu-free powders in the synthesis of YBCO superconductors on Cu substrates

YBa₂Cu₃O_x (Y123) superconducting films were fabricated on Cu substrates using a simple screen-printing method, from Cu-free powders (Y₂O₃ and BaCO₃). In the process, CuO, which causes superconducting properties of Y123 films to deteriorate, was formed on the film surface. By varying the atomic ratio of Y to Ba (Y:Ba = 1:1∼1:4), the ratio needed to prevent CuO formation was found for the film surface that had been heat-treated at 980^∘C for 17 s. The film, with the ratio of Y to Ba (Y:Ba = 1:1), is reheat-treated at 930^∘C for 9 min 30 s to form a superconducting Y123 phase. It was possible to prevent CuO formation by controlling the ratio of Cu-free powders in the mixture and to fabricate YBCO superconductors on Cu substrates using a two-step heat-treatment.     

A novel way to improve the dispersion-limited transmission distance of electroabsorption modulated lasers

We propose and demonstrate a way to improve the dispersion-limited reach of electroabsorption modulated lasers (EMLs). We generate continuous-phase frequency-shift keying/amplitude-shift keying (ASK) signals with the EML by applying a small current modulation to the laser diode (LD) on top of electroabsorption-modulated ASK signals. The amount of frequency deviation induced by the current modulation is adjusted to have the EML output signals experience /spl pi/ phase shift at every space. The experimental demonstration shows that with the proposed scheme we can increase the dispersion-limited transmission distance of the EML-based transmitter by 25%-75%, and it can be further improved by employing an LD with flat frequency-modulation response.     

A 60-GHz point-to-multipoint millimeter-wave fiber-radio communication system

A 60-GHz point-to-multipoint wireless access link with data rate of 156 Mb/s incorporating 60-GHz transceiver modules and full-duplex fiber-optic millimeter-wave transmission is developed for short-range applications such as indoor wireless local area networks and intelligent transport systems. For compact system configuration, a small-size millimeter-wave transceiver module with planar antennas is developed. The transceiver module is based on broadband planar integration and packaging of millimeter-wave circuits. The RF output power is +10 dBm and the measured 3-dB antenna beamwidth is 30/spl deg/. The total size of the developed 60-GHz transceiver module, except input and output connectors, is 50 mm /spl times/ 75 mm /spl times/ 35 mm. A point-to-point full duplex fiber-optic configuration is extended to the scheme with multiple access points (APs) by using a tree coupler and a dense wavelength division multiplexing multiplexer. The AP has a simple configuration without frequency conversion. The bit error rate and packet error rate performances of the 60-GHz fiber-radio access link are evaluated. Furthermore, the effect of the extension to the scheme with multiple APs is investigated.     

Parallel optical transmitter module using angled fibers and a V-grooved silicon optical bench for VCSEL array

We propose an advanced structure of optical subassembly (OSA) for packaging of the vertical-cavity surface-emitting laser (VCSEL) array, using (111) facet mirror of the V-groove ends formed in a silicon optical bench (SiOB) and angled fiber apertures. The feature of our OSA can provide a low optical crosstalk between neighboring channels, a low feedback reflection, and a large misalignment tolerance along the V-groove. We describe the optimized design of fiber angle, VCSEL position, and fiber position. The fabricated OSA structure consists of 12 channels of angled fiber array, 54.7/spl deg/ V-grooves, Au-coated mirrors on (111) end facet of the V-grooves, and flip-chip-bonded VCSEL array on a SiOB. In this structure, the beam emitted from the VCSEL is deflected at the 54.7/spl deg/ mirror of (111) end facet and propagated into the angled fiber. The angled fiber array was polished by 57/spl deg/. Fabricated OSAs showed a coupling efficiency of 30%-50% that is 25 times larger than that obtained from an OSA with a vertically flat fiber array. Our OSA showed large misalignment tolerance of about 90 /spl mu/m along the longitudinal direction in the V-groove. We fabricated a parallel optical transmitter module using the OSA and demonstrated 12 channels /spl times/2.5 Gb/s data transmission with a clear eye diagram.     

High-performance 94-GHz single balanced mixer using 70-nm MHEMTs and surface micromachined technology

We reported 94-GHz, low conversion loss, and high isolation single balanced active gate mixer based on 70-nm gate length InGaAs/InAlAs metamorphic high-electron mobility transistors (MHEMTs). This mixer showed that the conversion loss and isolation characteristics were 2.5/spl sim/3.5 dB and under -29 dB in the range of 92.95/spl sim/94.5 GHz, respectively. The low conversion loss of the mixer is mainly attributed to the high-performance of the MHEMTs exhibiting a maximum drain current density of 607 mA/mm, an extrinsic transconductance of 1015 mS/mm, a current gain cutoff frequency (f/sub t/) of 330 GHz, and a maximum oscillation frequency (f/sub max/) of 425 GHz. High isolation characteristics are due to hybrid ring coupler which adopted dielectric-supported air-gapped microstrip line structure using surface micromachined technology. To our knowledge, these results are the best performance demonstrated from 94 GHz single balanced mixer utilizing GaAs-based HEMTs in terms of conversion loss as well as isolation characteristics.     

Time-accurate Navier-Stokes simulation of vortex convection using an unstructured dynamic mesh procedure

A two-dimensional Navier-Stokes flow solver is developed for the simulation of unsteady flows on unstructured adaptive meshes. The solver is based on a second-order accurate implicit time integration using a point Gauss-Seidel relaxation scheme and a dual time-step subiteration. A vertex-centered, finite-volume discretization is used in conjunction with Roe’s flux-difference splitting. The Spalart-Allmaras one equation model is employed for the simulation of turbulence. An unsteady solution-adaptive dynamic mesh scheme is used by adding and deleting mesh points to take account of spatial and temporal variations of the flowfield. Unsteady viscous flow for a traveling vortex in a free stream is simulated to validate the accuracy of the dynamic mesh adaptation procedure. Flow around a circular cylinder and two blade-vortex interaction problems are investigated for demonstration of the present method. Computed results show good agreement with existing experimental and computational results. It was found that unsteady time-accurate viscous flows can be accurately simulated using the present unstructured dynamic mesh adaptation procedure.     

Fuzzy Web ad selector based on Web usage mining

Internet and Web technologies are widely available, making it easier for companies to conduct business and transfer information to customers. Moreover, they speed up financial transactions efficiently, reducing the transaction costs of commercial activities that businesses would normally incur. So, Internet business has created a competitive environment, a successful company wanting to survive and gain a competitive advantage must provide an acceptable bundle of customized services that satisfy customers' needs. Despite the Internet's obvious benefits as a new communication medium its advertising gives the same advertising messages to all customers and so has suffered from poor responses. To raise a Web ad's effectiveness, we propose a Web ad selector that personalizes advertising messages for customers based on their preferences and interests. The Web ad selection system divides Web site customers with similar preferences into several segments through Web usage mining. It uses fuzzy rules that express customer segments' surfing patterns on the basis of expert advice, and recommends appropriate ads by fuzzy inference.