Magnetoacoustic properties of self-biased Terfenol-D 2-2 composites

Self-biased Terfenol-D 2-2 composites exhibit high frequency of actuation and good magnetomechanical properties; however, their potential usefulness is highly dependent on their magnetoacoustic properties, particularly for ultrasonic applications. The speed of sound, c, and its variation with an externally applied magnetic field have been measured for the above composites using a 10 MHz longitudinal pulse. When the sound propagates parallel to the layers, the acoustic impedance was found to be independent of the external applied field, and lower than that for bulk Terfenol-D. The magnetomechanical coupling coefficient was found to be generally low (up to 0.35) and dependent on the volume ratio of materials, being higher for the specimens with greater content of Terfenol-D. The low attenuation, low acoustic impedance, and high frequency of actuation make this structure an interesting alternative for use in underwatersound navigation and ranging and other ultrasonic applications. When the pulse propagates orthogonal to the layers, c was found to vary by up to 3% with the application of an external field, but the acoustic attenuation was found to be very high due to the multiple reflections produced at the interfaces between the layers. This latter phenomenon has been calculated theoretically. © 2007 American Institute of Physics.

Enhancement of magnetostriction in internally-biased Terfenol-D 2-2 composites

A key issue in the fabrication of Terfenol-D 2-2 composites with internal magnetic field biasing is the selection of appropriate constituent materials to obtain high magnetostriction while keeping optimum magnetomechanical properties. The fabrication process is costly and time consuming and, therefore, numerical methods to predict their properties are useful. In this paper, finite element analysis (FEA) of the magnetostriction of such composites has been carried out using the commercial package ABAQUS. It has been shown that composites fabricated using Nd2Fe14B for the permanent magnetic material layers possess the highest internal fields within the Terfenol-D layers, although the overall strain of these composites is limited to approximately 800 × 10-6 due to the high elastic modulus of Nd2Fe14B. Simulations showed that the strain can be enhanced by choosing a different material with a lower elastic modulus for the permanent magnetic layer even though the internal field is lower. The simulations showed that the strain can increase by 12% if the Nd 2Fe14B layer is substituted by SmCo5; by 23% if it is substituted by Sm2Co17; and by 35% if it is substituted by Alnico. © 2008 IEEE.

Efficient Implementation of Spatially-Varying 3-D Ultrasound Deconvolution

Abstract—There are sometimes occasions when ultrasound beamforming is performed with only a subset of the total data that will eventually be available. The most obvious example is a mechanically-swept (wobbler) probe in which the three-dimensional data block is formed from a set of individual B-scans. In these circumstances, non-blind deconvolution can be used to improve the resolution of the data. Unfortunately, most of these situations involve large blocks of three-dimensional data. Furthermore, the ultrasound blur function varies spatially with distance from the transducer. These two facts make the deconvolution process time-consuming to implement. This paper is about ways to address this problem and produce spatially-varying deconvolution of large blocks of three-dimensional data in a matter of seconds. We present two approaches, one based on hardware and the other based on software. We compare the time they each take to achieve similar results and discuss the computational resources and form of blur model that each requires.

Efficient registration of nonrigid 3-D bodies

We present a novel method to perform an accurate registration of 3-D nonrigid bodies by using phase-shift properties of the dual-tree complex wavelet transform (DT-CWT). Since the phases of DT-\BBCWT coefficients change approximately linearly with the amount of feature displacement in the spatial domain, motion can be estimated using the phase information from these coefficients. The motion estimation is performed iteratively: first by using coarser level complex coefficients to determine large motion components and then by employing finer level coefficients to refine the motion field. We use a parametric affine model to describe the motion, where the affine parameters are found locally by substituting into an optical flow model and by solving the resulting overdetermined set of equations. From the estimated affine parameters, the motion field between the sensed and the reference data sets can be generated, and the sensed data set then can be shifted and interpolated spatially to align with the reference data set. © 2011 IEEE.

Innovative fabrication of PZT pillar arrays by a colloidal approach

An innovative approach for fabricating pillar arrays for ultrasonic transducer applications is disclosed. It involves the preparation of concentrated piezoelectric lead zirconate titanate (PZT) suspensions in aqueous solutions of epoxy resin and its polymerization upon adding a polyamine based hardener. Zeta potential and rheological measurements revealed that 1wt.% dispersant, 20wt.% of epoxy resin and a hardener/epoxy resin ratio of 0.275mLg -1, were the optimized contents to obtain strong PZT samples with high green strength (35.21±0.39MPa). Excellent ellipsoidal and semi-circle shaped pillar arrays presenting lateral dimensions lower than 10μm and 100μm height were successfully achieved. The organics burning off was conducted at 500°C for 2h at a heating rate of 1°Cmin -1. Sintering was then carried out in the same heating cycle at 1200°C for 1h. The microstructures of the green and sintered ceramics were homogeneous and no large defects could be detected. © 2011 Elsevier Ltd.

Investigation of DyBa2Cu3O7-d superconducting domains grown by the infiltration technique starting with small size Dy-211 particles

An infiltration and growth process is here used as an alternative to the classical top-seeded melt-textured growth process for the production of Dy-123 single-domains with finely dispersed small size Dy-211 particles. The starting materials are the 211-particles and a barium and copper rich liquid phase precursor. The infiltration and growth process allows for controlling both the spatial and size distribution of the 211-particles in the final superconducting 123-single-domain. The main parameters (set-ups, maximum processing temperature with respect to the peritectic temperature, nature of reactant, porosity of the 211-preform) of the infiltration and growth process are discussed. Moreover, different processes of chimie douce are shown in order to produce Dy-211 particles with controlled shape and size, particles that can be used as precursors for the infiltration and growth process. © 2005 IOP Publishing Ltd.