Stephen R. Winzer

Calculation of quasi-static electromechanical coupling coefficients for electrostrictive ceramic materials

The quasi-static coupling coefficients, k/sub 13/ and k/sub 33/, for electrostrictive ceramics are computed analytically. The calculation is based on a three-dimensional constitutive relation that models both electrostriction and nonlinear dielectric behaviors. The results show that the coupling factors depend on the amplitudes of the applied ac field and the dc bias, as well as the mechanical prestress. For an actuator without bias voltage or prestress, the coupling coefficients approach an asymptotic value with increasing electric field. The primary coefficients, k/sub 13/ and k/sub 33/, for a lead magnesium niobate, Pb(Mg/sub 1/3/Nb/sub 2/3/)O/sub 3/-PbTiO/sub 3/BaTiO/sub 3/(PMN-PT-BT), based relaxor ferroelectric are computed as an example. The results show that the coupling coefficients for PMN-PT-BT materials are roughly comparable with those of existing piezoelectrics. These coefficients are important parameters for material section and power source design for transducer devices.<<ETX>>

Stress in thick diamond films deposited on silicon

20‐μm‐thick diamond films deposited on Si single‐crystal substrates by microwave plasma‐enhanced chemical vapor deposition showed significant curvature. The internal stress distribution was estimated using the model of an elastic bimetallic strip. The results indicate that the films are under a mean tensile stress of 1.1 GPa, and are discussed using information from x‐ray diffraction and Raman spectra.

Rb, Sr and strontium isotopic composition, K/Ar age and large ion lithophile trace element abundances in rocks and glasses from the Wanapitei Lake impact structure

Abstract Shock metamorphosed rocks and shock-produced melt glasses from the Wanapitei Lake impact structure have been examined petrographically and by electron microprobe. Eleven clasts exhibiting varying degrees of shock metamorphism and eight impact-produced glasses have been analyzed for Rb, Sr and Sr isotopic composition. Five clasts and one glass have also been analyzed for large ion lithophile (LIL) trace element abundances including Li, Rb, Sr, and Ba and the REEs. The impact event forming the Wanapitei Lake structure occurred 37 m.y. ago based on K/Ar dating of glass and glassy whole-rock samples. Rb/Sr isotopic dating failed to provide a meaningful whole-rock or internal isochron. The isotopic composition of the glasses can be explained by impact-produced mixing and melting of metasediments. Large ion lithophile trace element abundance patterns confirm the origin of the glasses by total shock melting of metasediments.

The Apollo 17 'melt sheet' - Chemistry, age and Rb/Sr systematics

Major, minor and trace element compositions, age data and Rb/Sr systematics of Apollo 17 boulders have been compiled, and additional analyses performed on a norite breccia clast (77215) included in the Apollo 17, Station 7 boulder. The Apollo 17 boulders are found to be identical or nearly so in major, minor and trace element composition, suggesting that they all originated as an impact melt analogous to melt sheets found in larger terrestrial craters. The matrix dates ( 40 Ar/ 39 Ar) and Rb/Sr systematics available suggest that this impact melt formed by a single impact about 4 b.y. ago. This impact excavated, shocked, brecciated and melted norites, norite cumulates and possibly anorthositic gabbros and dunites about 4.4 b.y. old. The impact was likely a major one, possibly the Serenitatis basin-forming event.

Modeling electrostrictive deformable mirrors in adaptive optics systems

Adaptive optics correct light wavefront distortion caused by atmospheric turbulence or internal heating of optical components. This distortion often limits performance in ground-based astronomy, space-based earth observation and high energy laser applications. The heart of the adaptive optics system is the deformable mirror. In this study, an electromechanical model of a deformable mirror was developed as a design tool. The model consisted of a continuous, mirrored face sheet driven with multilayered, electrostrictive actuators. A fully coupled constitutive law simulated the nonlinear, electromechanical behavior of the actuators, while finite element computations determined the mirrors mechanical stiffness observed by the array. Static analysis of the mirror/actuator system related different electrical inputs to the array with the deformation of the mirrored surface. The model also examined the nonlinear influence of internal stresses on the active arrays electromechanical performance and quantified crosstalk between neighboring elements. The numerical predictions of the static version of the model agreed well with experimental measurements made on an actual mirror system. The model was also used to simulate the systems level performance of a deformable mirror correcting a thermally bloomed laser beam. The nonlinear analysis determined the commanded actuator voltages required for the phase compensation and the resulting wavefront error.

High-force cofired multilayer actuators

Various structural control applications (e.g., high-precision machining) require high-force actuation. Actuators made by stacking and gluing plates are not suitable for many of these applications because, unless the plates are very thin (< 1 mm), the glued stack requires high voltages (> 1 kV) and stacks of very thin plates require extreme care in fabrication to avoid compliance due to the joints. This paper describes an effort to fabricate high-force, co- fired multilayer actuators. The actuator modules were designed to be approximately 50 mm X 50 mm X 20 mm (height), with 20 1-mm thick layers and a 12.7-mm diameter hole in the center for a prestress bolt. The modules were to be stacked together to form an actuator capable of delivering > 50 micrometers stroke at 5 degree(s)C under a load of approximately 10,000 lb. The major challenge in this task is fabricating the co-fired modules because of their size. It is exceptionally difficult to burnout and sinter such a large multilayer device without introducing flaws such as delaminations and, to the best of our knowledge, this had never been done successfully before. Three co-fired, high force actuator modules were fabricated and electrically and mechanically characterized. The capacitance of the actuator modules ranged from 1.5 to 9.4 (mu) F. Co-fired actuators gave modulus values of 12.2 X 106 psi (at E equals 1 MV/m) which was close to the modulus of the material. The peak-peak strain of an actuator module at 0 prestress was 600 ppm (at a field of E equals 1 MV/m). At 2000 psi prestress, the strain measured was about 450 ppm (p-p).

Synthesis and Characterization of PZN-PT Materials

Compositions near the morphotropic boundary in the Pb(Zn1/3Nb2/3)03-PbTiO3 system were synthesized from the melt and analyzed. Up to four mol% variation in the PbTi03 component was found in meltsynthesized crystals, and both rhombohedral and tetragonal phases coexist in the region n ear the morphotropic boundary defined by earlier researchers. Powders made from the melt-synthesized crystals were used to make ceramics. Compositions of individual grains in the ceramics are the same as those of the starting powders, and up to 85% of the perovskite phase remains after firing. Individual grains of ZnO appear at grain boundaries, w ith or without a lead-rich phase, depending on the synthesis conditions. A pyrochlore phase forms that is not generally a ssociated with PbO or ZnO phases and is more concentrated n ear the outer surfaces of the ceramic pellets. Electrical properties are presented and possible approaches to increasing the amount of perovskite are discussed. INTRODUCT ION

Use of smart materials in medical diagnostics

Medical diagnostic capabilities have seen explosive growth over the past decade, as new techniques, such as MRI, have been taken from the laboratory setting into the clinical environment, with considerable benefit to the population at large. In this paper, we address another area of medical diagnostics which, we believe, stands on the verge of explosive growth, driven more by the emerging requirements for cost-effective diagnostic tools, and by the evolving needs of the defense medical community, with spinoff of those into the strongly related emergency care area of the civilian market. One of the factors that will drive this area of medical diagnostics is the development of smart materials and the sensors and sensor systems developed from them. In this paper we discuss some of the developments in the field of smart materials as they apply to development of new, low cost acoustic sensors for patient monitoring and medical imaging.

High-resolution medical ultrasound arrays using smart materials technology

Current ultrasound images have relatively low contrast (high levels of clutter) and resolution. Image quality could be dramatically improved if 2D ultrasound transducer arrays were available to perform the scans. These improvements would come from reducing clutter by eliminating target echoes that the beam width of a 1D array causes to be superimposed on a scan plane, and enhancing resolution by enabling the use of algorithms which correct the wavefront distortion introduced by propagation through tissue. The advent of 2D arrays would also enable 3D images to be displayed--eventually in real time. The fabrication of 2D ultrasound arrays is, however, very difficult. This stems from the acoustic requirements of the array (aperture, pitch and element size) which combine together to dictate large numbers (> 1000) of very-low capacitance (< 10 pF) elements. The technology problems revolve around interconnecting the elements and reducing signal losses due to stray capacitance and impedance mismatch. This paper will show how the development of composite smart materials involving the integration of electromechanical elements with electronics is being extended to the development of relatively-inexpensive high-sensitivity 2D ultrasound arrays.

Lead magnesium niobate dielectrics for high-field applications

The authors present some preliminary results aimed at exploring the potential of lead magnesium niobate (PMN) as an energy storage dielectric. In particular, relative permittivity and resistivity were studied as a function of electric field. The PMN dielectrics were evaluated as capacitor materials for pulse discharge applications. A series of compositions were prepared and compared to pure and commercial strontium titanate dielectrics. The comparison results are discussed.<<ETX>>