Thick Film Patterned Ceramics Using UV-Curable Pastes

Screen-printed layers of Al₂O₃, BaTiO₃, 0.90Pb(Mg_1/3Nb_2/3)-0₃–0.10PbTiO₃, Pb(Zr,Ti)O₃, ZnO, and glass alumina pastes have been patterned using photoprinting techniques. Curability of each paste by ultraviolet light and formation of holes with various diameters were studied for application as a production method for very small-sized vias. The dependence of hole diameters on various experimental parameters is presented and discussed. Wall slopes were found to depend on the transmission of the powders used in the pastes.     

Computational analysis on cymbal transducer

Finite Element Analysis in collaboration with experimental studies was conducted to investigate the effects of dimensional parameters on the performance of the cymbal transducer. ANSYS 5.5 FEM code was used for computational analysis. Cymbal transducers were fabricated with steel and brass endcap materials and piezoelectric ceramic, PZT-5A, as driving elements. Admittance spectrum was measured by using HP4194A Impedance/Gain phase analyzer. Displacement and generative force characteristics of the transducers were tested by using a LVDT sensor. Experimental and calculated results matched quite well. Device diameter and cavity diameter has strong effect on cymbal transducer characteristic. Adjusting the dimensional parameters can extend potential application areas of cymbal transducer.     

High Temperature Millimeter Wave Radiometric and Interferometric Measurements of Slag-Refractory Interaction for Application to Coal Gasifiers

Millimeter wave (MMW) radiometry can be used for simultaneous measurement of emissivity and temperature of materials under extreme environments such as in slagging coal gasifiers, where sensors have been identified as a key enabling technology need for process optimization. We present a dual-channel MMW heterodyne radiometer with active interferometric capability that allows simultaneous measurements of sample temperature, emissivity, and flow dynamics. Interferometric capability at 137 GHz is supplied via a probe signal originating from a local oscillator allowing monitoring of sample dynamics such as volume expansion and thickness change. This capability has been used to monitor characteristic behavior between refractories and slag such as slag infiltration, slag melting, viscous flow, foaming, and crucible corrosion by the molten slag. These results show the promise of the MMW system for extracting process parameters from operating slagging coal gasifiers, providing valuable information for process efficiency, control, and increased productivity.     

Barrier Layer Capacitor Using Barium Bismuth Plumbate and Barium Plumbate

A new type of barrier layer capacitor is described utilizing thin glass layers on highly conducting ceramics of barium plumbate and barium bismuth plumbate. The frequency dispersion of the apparent dielectric constant has been explained using a modified version of the Maxwell–Wagner model. These capacitors have a low temperature coefficient of capacitance and a high dispersion frequency in the megahertz range. Simple processing conditions together with low firing temperature make it possible to produce the barrier layer capacitors inexpensively.     

Electrical Resistivity of Composites

Percolation and Bruggeman's effective media theories, as they apply to the electrical conductivity of composites, are reviewed, and a general effective media (GEM) equation, which combines most aspects of both percolation and effective media theories, is introduced. It is then shown that the GEM equation quantitatively fits electrical resistivity (conductivity) as a function of the volume fraction data for binary composites. The parameters used to fit the experimental data are the electrical resistivities of the two phases, the percolation threshold for the lower resistivity phase (ô _c ), and an exponent t. Preliminary work, showing how the GEM equation can be used to model the piezoresistivity of composites by postulating that ô _c is a function of the independent variable, is also presented.     

Finite element modeling of perforated PZT-polymer compositest

Perforated PZT-polymer composites with 3-1 connectivity patterns have been fabricated by drilling square holes perpendicular to the poling direction in prepoled PZT blocks and filling the holes with epoxy polymer. The influence of the separation between the holes on the dielectric and piezoelectric properties of the composite was studied. The finite element method has been used to calculate the stress distributions in this composite. The hydrostatic d_h and g_h coefficients have been calculated by summing the individual element polarization. The calculated values are compared with experimental results.     

Cymbal and BB underwater transducers and arrays

The cymbal is a miniaturized class V flextensional transducer that was developed for use as a shallow water sound projector and receiver. Single elements are characterized by high Q, low efficiency, and medium power output capability. Its low cost and thin profile allow the transducer to be assembled into large flexible arrays. Efforts were made to model both single elements and arrays using the ATILA code and the integral equation formulation (EQI). Millimeter size microprobe hydrophones (BBs) have been designed and fabricated from miniature piezoelectric hollow ceramic spheres for underwater applications such as mapping acoustic fields of projectors, and flow noise sensors for complex underwater structures. Green spheres are prepared from soft lead zirconate titanate powders using a coaxial nozzle slurry process. A compact hydrophone with a radially-poled sphere is investigated using inside and outside electrodes. Characterization of these hydrophones is done through measurement of hydrostatic piezoelectric charge coefficients, free field voltage sensitivities and directivity beam patterns. Electronic Publication     

Factors influencing the selection of analgesia in spontaneously labouring nulliparous women at term

It is the purpose of this study to compare the prognostic value of the Herring classification (lateral pillar) with that of the Catterall classification. The material is constituted by 45 patients affected with Perthes' disease and reviewed an average of 24 years after onset. At follow-up the hips were divided into three classes based on joint congruency as suggested by Stulberg. The Catterall classification demonstrated overall a better predictive value for the Herring system. Instead, the most satisfactory reproducibility seems to be that of Herring: 80% as compared to 42% for the Catterall classification.     

Symmetry of secondary ferroics. I

Although at present there are only a few well documented examples, secondary ferroic phenomena may prove to be rather common, since the symmetry requirements are not especially stringent. In this paper, the conditions for ferrobielectricity, ferrobimagnetism, ferromagnetoelasticity and ferromagnetoelectricity are discussed. It is shown that ferrobielectricity can be expected in antiferroelectric ferroelastic classes with substantial dielectric anisotropy. Nickel oxide and other antiferromagnetic ferroelastics with anisotropic magnetic susceptibility show ferrobimagnetism. Evidence for ferromagnetoelastic domains is found in CoF₂ and FeCO₃, while Cr₂O₃ shows ferromagnetoelectric switching. Of the 90 magnetic point groups, 35 are potentially ferromagnetoelastic and 40 potentially ferromagnetoelectric. In a companion paper (Part II) to be published, symmetry restrictions for ferrobielasticity and ferroelastoelectricity will be considered, and the conditions which determine the orientation of domain walls in secondary ferroics examined.     

Dielectric properties of (Ba0.95Ca0.05)(Ti1-yCay)O3-y ceramics

Calcium doped barium titanate ceramics with composition (Ba_0.95Ca_{0. 05}) (Ti_1-yCa_y)O_3-y prepared by a liquid mixing technique were used to measure the dielectric properties. The pure barium titanate and lightly-Ca-doped materials obey a Curie Weiss law when the temperature is above the Curie temperature. It has been found that the average cubic-tetragonal phase transition temperature moves downward when the octahedrally-coordinated Ca concentration increases, and heavily-Ca-doped barium titanate ceramics show relaxor behavior with a diffuse phase transition characteristic (DPT). Above the average transition temperature T_av the dielectric properties for heavily doped materials do not obey the Curie Weiss law, but can be described by a quadratic relation over a wide range of temperature. Experiments have shown that there exists an extra K(T) peak attributable to the existence of separate microregions of Ba_0.95Ca_0.05TiO₃ in a matrix of (Ba_0.95Ca_0.05) (Ti_1-yCa_y)O_3-y (where y ≤ 2%).