The multimillion dollar markets for multilayer capacitors, piezoelectric transducers, and PTC thermistors are based on ferroelectric ceramics made from oxide perovskites. Atomistic and electronic phenomena crucial to an understanding of these components are reviewed in this paper, together with a brief description of their electrical properties. All three devices make use of ferroelectric phase transformations and chemical dopants to optimize performance.

The near-interface structure of diamond films grown from a methane and hydrogen gas mixture by microwave plasma enhanced chemical vapor deposition has been studied. Freestanding diamond films grown on both silica and silicon at two different methane concentrations were analyzed by scanning and transmission electron microscopies, electron diffraction, Raman spectroscopy, and secondary ion mass spectroscopy. It was found that the substrate chemistry greatly influenced the nature of the carbon initially deposited on the substrate surface. Diamond formed large flat contact areas on silicon, whereas on silica a particulate type of intermediate layer formed first because of the chemical reactions occurring on and/or with the surface. It was found that the phase content of the films was greatly affected by the methane concentration in hydrogen. At the low (1.0% or less) methane concentrations in hydrogen, phase pure diamond formed; while at the high (5.0%) methane concentration in hydrogen, graphite and disordered carbon were codeposited along with diamond during the early growth stages. Silicon carbide was detected at the diamond interfaces which appeared in discrete areas on silica as opposed to a rather continuous layer as is believed to form on silicon.

Ceramic-polymer composites with a 1–3 connectivity can be created via a novel process called dielectrophoretic assembly. The process involves an electric field which is applied to a suspension of ceramic particles in an uncured thermoset polymer matrix. Under appropriate conditions, the applied electric field acts to induce a spatial redistribution of the particles into a chained or fibril structure. It was shown previously that the electrorheological response and fibril microstructure are dependent on both the frequency and magnitude of the applied alternating electric field.3 This paper will show that the frequency dependence of the uncured thermoset polymer suspensions results from the complex electrical phenomena specific to each thermoset system. Specifically, it will be shown through low field dielectric measurements and high field current-voltage analysis that the dielectrophoretic effect can be limited by electrode polarization, ionic conductivity, and space charge relaxation. It is the frequency dependence of these limiting phenomena that gives rise to the observed frequency dependence in the dielectrophoretic force of attraction being utilized to drive particulate assembly.

The dielectrophoretic effect is a phenomenon in which dipole-dipole interactions are induced between particles in a suspension by an electric field.1−5 This dipole interaction leads to the formation of chains or fibrils parallel to the applied electric field. Recently, the dielectrophoretic effect has been shown to be a possible composite assembly technique permitting property changes to be induced with the appropriate electric fields.6,7 The results presented in this paper show that the dielectrophoretic assembly process can be used to engineer anisotropy into composite materials. Various filler materials are aligned in a thermoset polyurethane matrix and the dielectric properties are measured. Comparisons are drawn between the dielectrophoretically assembled composites and those processed conventionally in the absence of an electric field. Dielectric properties are modeled with modified mixing laws and discussed in relation to the composite microstructure and the alpha relaxations of the polymer phase.

Abstract : As trends towards miniaturized components and systems continue in many fields, there has been a rapid development in similarly scaled-down composites. In the electronics industry, these nanocomposites (and especially active nanocomposites based on ferroic elements) form a basis for many of the recent advances in both information and charge storage. While the overall properties of some of these composites can be explained as straightforward extrapolations from the bulk properties, in other instances the small size of the ferroic phase has important consequences on the macroscopic behavior of the composite. This paper reviews some of the recent developments in small-scale ferroic nanocomposites and details the relation between component size and the resultant properties.

Applicability of the finite element method to optimize high frequency transducers is reported. Two recent studies on piezoelectric transducers or systems are presented, in which the FEM algorithm is used for the optimization of transducers performance. They provide resonance frequencies from greater than 1 MHz to below 10 kHz. First, miniature multimode monolithic flextensional transducers, with active shells, are described. They combine the advantages of small size and low-cost manufacturing with control of the shape of the acoustic radiation/receive pattern. Then, linear arrays are studied and a technique is developed to reduce cross-coupling in acoustical arrays. In each case, numerical results are compared to experiments and show how the finite element tool is used to improve the understanding of the physical behavior of the system.

This article highlights the major role Arthur von Hippel and the Laboratory for Insulation Research at the Massachusetts Institute of Technology played in the early development of the field of ferroelectricity in mixed oxides with the perovskite structure and, in particular, in the identification of ferroelectricity in barium titanate following its discovery in industrial laboratories in the United States during World War II. Very early optical and x-ray studies highlighted the characteristics of the ferroelectric domain structures in both ceramic and single-crystal BaTiO 3 , the elimination of domains at the Curie temperature T C , and the salient characteristics of the two low-temperature phase transitions. Perhaps the culmination of this work was the detailed studies of lamella 90° domains by Peter Forsbergh and the gorgeous patterns these could generate. This article also traces the manner in which the early studies contributed to whole industries based on perovskite ferroelectrics. The ceramic capacitor industry is now fabricating sophisticated, cofired multilayer capacitors (MLCs) with up to a thousand 1-μm-thick dielectric layers interleaved with base metal electrodes, addressing a market for some 10 13 capacitors per year. Manufacturers of large piezoelectric transducers depend almost exclusively on perovskite-structure oxide ceramics. Navy sonar systems are major customers, but spinoff has occurred into a wide range of commercial and medical ultrasound systems. The capability of current materials has improved more than tenfold over the original BaTiO 3 ceramics as a result of the effective application of molecular engineering, a strong testament to the insight of the founder of this area of study.

A portable transdermal drug delivery system using a composite transducer array has been designed to promote insulin transmission through the skin using ultrasound. Previous investigators used large, heavy sonicators in this type of research. The aim of this study is to demonstrate ultrasound‐mediated transdermal insulin delivery using small cymbal arrays. The cymbal transducer design was chosen because of its light, compact structure and low resonance frequency in water. To increase the spatial ultrasound field for drug delivery through the skin, 2 × 2 and 3 × 3 cymbal arrays were constructed. The performance of these arrays was tested under similar conditions. An ultrasound‐enhanced noninvasive glucose measurement system is also under development, and a comparison with conventional glucose meters was performed. The goal is to develop a noninvasive sensor–actuator array for the treatment of disease.