Characterization of Piezoelectric Ceramic Transducer for Accurate Speed-of-Sound Measurement

Piezoelectric ceramics mounted on the endplates of a cylindrical resonator were used as the source and detector for speed-of-sound measurements. The perturbations of the longitudinal gas modes of the cavity due to the compliance of the diaphragms (10 mm diameter, 0.3 mm thick) and the attached transducers were estimated from first-order perturbation theory. The fractional shift of the resonance frequencies in argon caused by the source and detector was 0.03 × 10⁻⁶ at 0.1 MPa and 273.16 K. The high signal-to-noise ratio (up to 1 × 10⁴ with a 6 s integration time) that was obtained with these transducers makes them suitable for acoustic thermometry. The heat dissipation in the source transducer was measured to be only 0.7 μW at the working voltage (7 V) and frequency (1 kHz).     

Effect of temperature and frequency on the dielectric properties of cellulose nanofibers from cotton

The present work has been carried out to evaluate the dielectric properties and ac-electrical conductivity of cellulose nanofibers. The cellulose nanofibers (CNF) described in this work are the ones extracted from cotton via a simple acid hydrolysis method and are characterized with X-ray diffraction analysis (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), and UV–Visible diffuse reflectance spectroscopy. The optical band gap of CNF found out using the Kubelka–Munk plot is 3.30 eV. The dielectric constant, dielectric loss, and ac-electrical conductivity of the prepared CNF have been investigated in the temperature range from 30 °C to 300 °C and in the frequency range from 50 Hz to 5 MHz. The synthesized system exhibits a higher dielectric constant value for all temperatures in the low-frequency (0.1 kHz) region and a frequency-independent behavior above 10 kHz. In the high-frequency region, the dielectric constant is independent of temperature. Also, the study shows that the conductivity increases with increasing frequency and temperature. The maximum values of ac-conductivity at room temperature (30 °C) and high temperature (300 °C) are found to be 4.58?×?10^–5 S/cm and 2.26?×?10^–4 S/cm, respectively. In brief, the studies point to the application potential of CNF for future flexible electronics.

     

自由端盖四梁凹形宽带弯张换能器设计

针对凹形弯张换能器改善低频宽带工作特性的技术需求,提出了一种自由端盖四梁凹形弯张换能器新结构。结构中将纵向振子的端部设计成弹性辅助梁,与主弯曲梁连接构成复合弯曲梁。同时为了克服弹性辅助梁对振动辐射带来的不利影响,引入了由纵向振子驱动的方形自由端盖并以此构成新的辐射端面。利用有限元软件分析了这种新结构弯张换能器的多模振动特性,模态分析表明换能器的前五阶模态是可利用的主要工作模态,频率间隔可以通过敏感结构参数进行调控。通过优化给出了一种设计方案,换能器整体几何尺寸为 140 mm×140 mm×396 mm,仿真分析了换能器在水中的导纳特性和发射电压响应曲线,结果表明：换能器最大发射电压响应大于 145 dB,发射电压响应起伏小于 6 dB的工作频带为 1.5~4.3 kHz,发射电压响应起伏小于 10 dB的工作频带为 1.5~8 kHz,具有低频宽带大功率工作特性。     

Bottom up fabrication of a nickel-lead zirconate titanate piezoelectric microcantilevers

Proof of concept for the novel bottom up manufacture of a piezoelectric microelectromechanical system cantilever demonstrator is presented. Cantilever structures, consisting of 10 µm lead zirconate titanate (PZT) and 21 µm nickel, were fabricated by electroforming Ni structures on top of PZT films, subsequently patterning the PZT and removing the temporary sacrificial silicon support structure. Following release the cantilevers exhibited minimal bending indicating low levels of internal stress. The resonant frequency was calculated to be 33.2 +/− 2 kHz, which is in agreement with that of 33.8 kHz measured using an impedance analyzer and 33.9 kHz measured using the mechanical vibration method.     

Charge integrating type position-sensitive proportional chamber for time-resolved measurements using intense X-ray sources

A position-sensitive detecting system for time-resolved diffraction measurements with very intensive X-ray sources has been developed. It consists of a charge integrating type gas-filled detector, multichannel analog multiplexers, a signal processor and a memory (120 ch.×128 phases×24 bits). The detector is 120 mm long in effective length by 10 mm×10 mm in cross section with a single anode of 20 μm diameter. One of the cathode planes consists of 120 cathode strips with a pitch of 1 mm. The spatial resolution is equal to the pitch under a certain detector current limit. The gas gain is adjustable to an appropriate value according to the X-ray intensity range of interest. For experiments with 8 keV X-ray sources, maximum absorption rates of 9×10⁷ photons/s·mm with low applied voltage and minimum absorption rates of about 3 photons/s·mm with high applied voltage can be achieved. This system was applied to a time-resolved X-ray diffraction study on frog muscle using a synchrotron radiation source at the Photon Factory and we could collect diffraction patterns with a time resolution of 10 ms and only 10 stimulations.     

Multifilament Nb3Sn superconductors produced by the E.C.N. technique

Multifilament Nb3Sn conductors are produced by reduction of composites containing bundles of niobium tubes filled with NbSn2-powder and surrounded by pure copper. Heat treatment at temperatures between 575 and 675°C after final reduction causes the tin from the NbSn2-powder to diffuse into the niobium tubes, which results in a final Nb3Sn-layer at the inner side of the tube. Two types of experimental wire are produced, the first type consisting of 4 bundles of 9 tubular filaments, the powder cores having diameters of about 35 micron, the outer size of the wire being 1 mm square. The second type consists of 4 bundles of 45 tubular filaments. This type is fabricated in 3 sizes: round φ 2.3 and square 1.4 and 1.0 mm, corresponding with powder core diameters of 26,18 and 13 microns respectively. Critical current densities in the Nb3Sn-layers reach values of about 4 - 6 × 10⁹A/m²at 8 Tesla and 1,6 - 2,4 × 10⁹A/m²at 12 Tesla. Maximum critical temperatures are about 18.1 K with a ΔTcof 0.3 K.     

Spring type conducting polymer actuator working in air

Although major advances in actuator performances have been obtained in the last few years, the actuation of conducting polymer (CP) actuator is still limited to bending movement in liquid electrolyte. It restricts the various application fields of CP actuator. So in this study, spring type CP actuator which can produce linear movement and work in air is prepared. It is composed of two polypyrrole (PPy) films having different actuation mechanism and polyurethane (PU) based solid polymer electrolyte (SPE). Even though the ionic conductivity of PU based SPE is low, the actuation behavior of CP actuator especially working in air is much influenced by the flexibility rather than the ionic conductivity of SPE. Then PU based SPE with high flexibility is used in a spring type CP actuator. The morphology of PPy films, ion conductivity of SPE, actuation movements according to its length and applied voltage and loading ability of actuator were investigated. SPE had a maximum conductivity of 2.20 × 10^?6 S/cm at room temperature for 15 wt% of Mg(ClO₄)₂ salts and the actuator which was fabricated in 21 mm length showed maximum displacement at 12 V. Also it was confirmed that spring type CP actuator could Exhibit 10 MPa of loading ability through the tensile strength test. As a result, solid-state spring type CP actuator having both linear movement and loading ability was demonstrated.     

A piezoelectric motor using two orthogonal bending modes of a hollow cylinder

This paper proposes a compact ultrasonic motor with low manufacturing costs, a simpler driving circuit, and scalability. The stator of the motor presented in this paper consists of a hollow metal cylinder, whose outside surface was flattened on two sides at 90 degrees to each other, on which two rectangular piezoelectric plates were bonded. Because the cylinder has a partially square/partially circular outside surface, the stator has two degenerated bending modes that are orthogonal to each other. A wobbling motion is generated on the cylinder when only one piezoelectric plate is excited at a frequency between the two orthogonal bending modes. A rod through a pair of ferrules was used as the rotor of this motor. The prototype motor, whose stator was 2.4 mm in diameter and 10 mm in length, operated at 69.5 kHz, was experimentally characterized, and a maximum torque of 1.8 mNm was obtained.     

Advanced Optical Techniques

The development of a digital electro-optic light beam deflector (DLD) is described. Each deflection stage consists of a DKDP polarization switch with a coating of transparent electrodes (longitudinal electro-optic effect) and a calcite prism for angular deflection. Effects which limit the switching frequency and the capacity speed product (i.e. product of the number of resolvable beam directions and the switching frequency) are theoretically investigated. A four-stage solid-state DLD has been realized which operates at switching frequencies up to 10 kHz and at a random access time of 30 μ s. The system is going to be expanded to 8 × 8 stages for the addressing of 256 × 256 beam directions.     

Effect of gas Mach number on the flow field of close-coupled gas atomization,particle size and cooling rate of as-atomized powder: Simulation and experiment

Gas velocity is a key parameter regulating the particle size and the cooling rate of the gas atomized powder applied in additive manufacturing, metal injection molding, thermal spraying, and soft magnetic composites. In this paper, on basis of the well-designed close-coupled nozzles with different gas Mach numbers at the outlet, the gas field structure was simulated by Computational Fluid Dynamics (CFD) software, and the process of cooling and solidification of Fe-6.5 wt% Si metal droplets was calculated by finite difference method. The results show that with the increase of Mach number, both the gas velocity downstream and the pressure at the base of melt delivery tube tip rise, whereas the mass flow rate of the melt decreases. The nozzles with high Mach number can produce finer powder with higher cooling rate. The median diameter of the powder prepared by the nozzle with Mach numbers of 1.0, 1.5, 2.0, and 2.5 is 44.9, 39.0, 32.5, and 29.1 μm, respectively, and the corresponding cooling rate of the metal droplet with a diameter of 80 μm is 2.85 × 10⁴, 2.98 × 10⁴, 3.32 × 10⁴, and 3.50 × 10⁴ K/s, respectively. This work provides new ideas and suggestions for the preparation of metal powder with small particle size at high cooling rate.     

Study of the structural and dielectric properties of Bi<Subscript>2</Subscript>O<Subscript>3</Subscript> and PbO addition on BiNbO<Subscript>4</Subscript> ceramic matrix for RF applications

In this paper, the structural and dielectric properties of BNO (BiNbO₄) was investigated as a function of the external RF frequency and temperature. The BNO Ceramics, prepared by the conventional mixed oxide method and doped with 3, 5 and 10 wt. % Bi₂O₃–PbO were sintered at 1,025 °C for 3 h. The X-ray diffraction patterns of the samples sintered, shown the presence of the triclinic phase (β-BNO). In the measurements obtained at room temperature (25 °C) was observed that the largest values of dielectric permittivity (ε′ _r ) at frequency 100 kHz, were for the samples: BNO5Bi (5 wt. % Bi₂O₃) and BNO5Pb (5 wt. % PbO) with values ε′ _r ~ 59.54 and ε′ _r ~ 78.44, respectively. The smaller values of loss tangent (tan δ) were for the samples: BNO5Bi and BNO3Pb (3 wt. % PbO) with values tan δ ~ 5.71 × 10⁻⁴ and tan δ ~ 2.19 × 10⁻⁴, respectively at frequency 33.69 MHz. The analysis as a function of temperature of the dielectric properties of the samples, obtained at frequency 100 kHz, showed that the larger value of the relative dielectric permittivity was about ε′ _r ~ 76.4 at temperature 200 °C for BNO5Pb sample, and the value smaller observed of dielectric loss was for BNO3Bi sample at temperature 80 °C, with about tan δ ~ 5.4 × 10⁻³. The Temperature Coefficient of Capacitance (TCC) values at 1 MHz frequency, present a change of the signal from BNO (−55.06 ppm/°C) to the sample doped of Bi: BNO3Bi (+86.74 ppm/°C) and to the sample doped of Pb: BNO3Pb (+208.87 ppm/°C). One can conclude that starting from the BNO one can increase the doping level of Bi or Pb and find a concentration where one have TCC = 0 ppm/°C, which is important for temperature stable materials applications like high frequency capacitors. The activation energy (H) obtained in the process is approximately 0.55 eV for BNO sample and increase with the doping level. These samples will be studied seeking the development ceramic capacitors for applications in radio frequency devices.     

Corrosion resistance evaluation of a Ca- and P-based bioceramic thin coating in Ti-6Al-4V

The objective of this study was to physico/chemically characterize and determine the corrosion resistance of a Calcium–Phosphate (Ca–P) based bioceramic thin coating processed by a sputtering process on titanium alloy (Ti-6Al-4V). The samples utilized in this study were uncoated and coated disks of 10 mm diameter by 3 mm thickness. The coating was characterized by SEM, XPS + ion beam milling (IBM), thin-film mode XRD, and atomic force microscope (AFM) (n = 3). Coated and uncoated Ti-6Al-4V disk surfaces were tested in Phosphate Buffered Saline (PBS) at 25°C through an area of 0.79 cm². A three-electrode cell set-up was used with a saturated calomel electrode (SCE) and a platinum wire as reference and counter electrodes. After 3, 17, and 25 days of immersion, electrochemical impedance spectroscopy (EIS) experiments were performed (n = 3). The EIS tests were carried out in potentiostatic mode at the open circuit potential (OCP). The frequency range considered was from 100 kHz to 10 mHz, using 10 mV root mean square as the amplitude of the perturbation signal. A potentiodynamic polarization scan using a frequency response analyzer potentiostat, was acquired following 3 days of immersion in PBS. The potentiodynamic polarization scans (n = 3) were carried out with a scan rate of 1 mV/s ranging from −0.8V(SCE) to 3.0V(SCE). Results: The physico/chemical characterization showed an amorphous Ca- and P-based coating of ~400–700 nm thickness with Ca–P nanometer size particles embedded in a Ca–P matrix. The Bode phase angle diagrams showed highly capacitive results at low and medium frequencies for both surfaces tested. The polarization curves showed low current densities at the corrosion potential (E _corr), in the order of 10⁻⁸A/cm², typical of passive materials with protective surface films. Coated sample current densities were comparable to the uncoated samples. Conclusion: Coated and uncoated samples were stable in the test solution with a protective film maintained throughout the 25 day immersion test period.     

Development of Electron Tracking Compton Camera using micro pixel gas chamber for medical imaging

We have developed the Electron Tracking Compton Camera (ETCC) with reconstructing the 3-D tracks of the scattered electron in Compton process for both sub-MeV and MeV gamma rays. By measuring both the directions and energies of not only the recoil gamma ray but also the scattered electron, the direction of the incident gamma ray is determined for each individual photon. Furthermore, a residual measured angle between the recoil electron and scattered gamma ray is quite powerful for the kinematical background rejection. For the 3-D tracking of the electrons, the Micro Time Projection Chamber (μ-TPC) was developed using a new type of the micro pattern gas detector. The ETCC consists of this μ-TPC (10×10×8 cm³) and the 6×6×13 mm³ GSO crystal pixel arrays with a flat panel photo-multiplier surrounding the μ-TPC for detecting recoil gamma rays. The ETCC provided the angular resolution of 6.6° (FWHM) at 364 keV of ¹³¹I. A mobile ETCC for medical imaging, which is fabricated in a 1 m cubic box, has been operated since October 2005. Here, we present the imaging results for the line sources and the phantom of human thyroid gland using 364 keV gamma rays of ¹³¹I.     

Load and resistance factor design of fiber reinforced polymer composite bridge deck

The majority of our bridges were constructed with conventional civil engineering materials of steel and concrete in a typical slab on girder or truss construction. Reinforced concrete bridge decks have approximately 40% life of the steel girders that support these structures. In order to support the use of alternative materials to replace deteriorating concrete decks, this paper outlines the Load and Resistance Factor Design (LRFD) of Fiber Reinforced Polymer composite (FRP) panel highway bridge deck. The deck would be of a sandwich construction where 152.4 mm × 152.4 mm × 9.5 mm square pultruded glass FRP (GFRP) tubes are joined and sandwiched between two 9.5 mm GFRP plates. The deck would be designed by Allowable Stress Design (ASD) and LRFD to support AASHTO design truckload HL-93. There are currently no US standards and specifications for the design of FRP pultruded shapes including a deck panel therefore international codes and references related to FRP profiles will be examined and AASHTO-LRFD specifications will be used as the basis for the final design. Overall, years of research and laboratory and field tests have proven FRP decks to be a viable alternative to conventional concrete deck. Therefore, conceptualizing the design of FRP bridge decks using basic structural analysis and mechanics would increase awareness and engineering confidence in the use of this innovative material.     

Concave cymbal transducers

 A new type of cymbal transducer, called the concave cymbal, has been developed to increase the pressure tolerance and reliability of the transducer under high hydrostatic pressure. The main feature of the new design is a lead zirconate titanate ceramic ring sandwiched between two concave metal endcaps. It shows much improved pressure performance and can withstand a pressure of up to 6 MPa while maintaining high effective hydrostatic piezoelectric coefficients. When incorporated into a planar array with a radiating area of 5.5 cm×5.5 cm and weight of only 30 g, a transmitting voltage response of around 125 dB re 1 μPa/V @ 1 m was obtained over a frequency range between 20 and 50 kHz. Received: 14 October 1998 / Reviewed and accepted: 15 October 1998     

Nanomaterial-based ionic polymer metal composite insect scale flapping wing actuators

Small size actuators (8 mm × 1 mm), IPMNC (RuO₂/Nafion) and IPMNC (LbL/CNC) are studied for flapping at the frequency of insects and compared to Platinum IPMC-Pt. Flapping wing actuators based on IPMNC (RuO₂/Nafion) are modeled with the size of three dragonfly species. To achieve maximum actuation performance with Sympetrum Frequens scale actuator with optimized Young's modulus, the effect of variation of thickness of electrode and Nafion region of Sympetrum Frequens scale actuator is studied. A trade-off in the electrode thickness and Young's modulus for dragonfly size IPMNC-RuO₂/Nafion actuator is essential to achieve the desirable flapping performance.     

Structural,optical and electrical characteristics of transparent bismuth vanadate films deposited on indium tin oxide coated glass substrates

Bismuth vanadate (BVO) thin films were fabricated on indium tin oxide (ITO) coated glass substrates using pulsed laser ablation technique and investigated their structural, optical and electrical properties. The use of the indium tin oxide coated glass substrate resulted in reducing the leakage current characteristics of crystalline BVO thin films. The X-ray diffraction (XRD) studies confirmed the monophasic nature of the post annealed (500 °C/1 h) films. The atomic force microscopy indicated the homogeneous distribution of crystallites in the as-deposited films. The as-deposited and the post annealed films were almost 90% transparent (380–900 nm) as confirmed by optical transmission studies. Dielectric constant of around 52 was attained accompanied by the low dielectric loss of 0.002 at 10 kHz for post annealed films. The leakage current of the post annealed BVO films on ITO coated glass substrates measured at room temperature was 8.1 × 10⁻⁸ A at an applied electric field of 33 kV/cm, which was lower than that of the films with platinum and SrRuO₃ as the bottom electrodes.     

Correlation between electrical conductivity and manufacturing processes of nanofilled carbon fiber reinforced composites

This paper describes the difference on the electrical performance of carbon fiber reinforced composites (CFRCs) when two different Resin Film Infusion (RFI) manufacturing techniques are used. For the panel obtained by bulk infusion the measured in plane and out of plane electrical conductivities were 2.0 × 10⁴ S/m and 3.9 S/m respectively and for the panel prepared using the traditional resin film infusion the values were 1.1 × 10⁴ S/m and 1.7 S/m respectively. Morphological investigations on the sections of etched panels have highlighted that this difference in the electrical conductivity was strictly related to the different distribution of multiwall carbon nanotubes (MWCNTs) between the carbon fibers (CFs) of the plies.     

Determination of critical load for flange buckling in concentrically loaded pultruded columns

Physical testing and theoretical methods to determine the critical local flange buckling load in concentric pultruded columns are presented. Knowledge of this critical load for wide flange profiles is required in a new universal column design procedure. Because there are too few test results for other profile sizes only the standard 203×203×9.53 mm (8×8×3/8 in.) profile is considered. Reasons are given to explain why the 14 data points give buckling loads between 307 and 406 kN. To obtain a test result corresponding to the true physical situation the minimum column length should be four half-wavelengths of the local instability. The true critical load is about 360 kN. Presented are nine closed form equations that can be used to predict the critical load for the local instability. To use these equations effectively, it is shown that the elastic constants of the flange material must be those of the profile being analysed. Numerical methods, and their closed form equations, that include the rotational stiffness at the web–flange connection are shown to be reasonably accurate. However, without direct access to the software they are difficult to apply, and these equations are therefore unsuitable for application in the preparation of universal design guidance. A simpler equation that predicts the buckling load to within 4% of 360 kN is therefore recommended.     

Use of the small punch test to determine the ductile‐to‐brittle transition temperature of structural steels

The small punch test (SPT) consists in punching very small square specimens, measuring 10 × 10 mm² and 0.5‐mm thickness, until fracture using a 2.5‐mm‐diameter hemispherical punch. Different specimens of a structural steel were tested from room temperature to cryogenic temperatures in order to determine its ductile‐to‐brittle transition temperature (DBTT). The DBTT obtained in SPT (DBTT_STP) is much lower than the DBTT obtained by means of Charpy specimens (DBTT_CVN). The variation of the mechanical parameters calculated from the SPTs with temperature was also calculated and the operative fracture micromechanisms defined using a scanning electron microscope.