Biomedical subjects

W Jack Hughes

Publications and source records attributed to W Jack Hughes.

3 recordsLinked to original sources

PubMed2005

Fabrication and characterization of micromachined high-frequency tonpilz transducers derived by PZT thick films.

Miniaturized tonpilz transducers are potentially useful for ultrasonic imaging in the 10 to 100 MHz frequency range due to their higher efficiency and output capabilities. In this work, 4 to 10-microm thick piezoelectric thin films were used as the active element in the construction of miniaturized tonpilz structures. The tonpilz stack consisted of silver/lead zirconate titanate (PZT)/lanthanum nickelate (LaNiO3)/silicon on insulator (SOI) substrates. First, conductive LaNiO3 thin films, approximately 300 nm in thickness, were grown on SOI substrates by a metalorganic decomposition (MOD) method. The room temperature resistivity of the LaNiO3 was 6.5 x 10(-6) omega x m. Randomly oriented PZT (52/48) films up to 7-microm thick were then deposited using a sol-gel process on the LaNiO3-coated SOI substrates. The PZT films with LaNiO3 bottom electrodes showed good dielectric and ferroelectric properties. The relative dielectric permittivity (at 1 kHz) was about 1030. The remanent polarization of PZT films was larger than 26 microC/cm2. The effective transverse piezoelectric e31,f coefficient of PZT thick films was about -6.5 C/m2 when poled at -75 kV/cm for 15 minutes at room temperature. Enhanced piezoelectric properties were obtained on poling the PZT films at higher temperatures. A silver layer about 40-microm thick was prepared by silver powder dispersed in epoxy and deposited onto the PZT film to form the tail mass of the tonpilz structure. The top layers of this wafer were subsequently diced with a saw, and the structure was bonded to a second wafer. The original silicon carrier wafer was polished and etched using a Xenon difluoride (XeF2) etching system. The resulting structures showed good piezoelectric activity. This process flow should enable integration of the piezoelectric elements with drive/receive electronics.

Journal Article↗

PubMed2002

Volumetric imaging with an amplitude-steered array.

Volumetric acoustic imaging is desirable for the visualization of underwater objects and structures; however, the implementation of a volumetric imaging system is difficult due to the high channel count of a fully populated two-dimensional array. Recently, a linear amplitude-steered array with a reduced electronics requirement was presented, which is capable of collecting a two-dimensional set of data with a single transmit pulse. In this study, we demonstrate the use of the linear amplitude-steered array and associated image formation algorithms for collecting and displaying volumetric data; that is, proof of principle of the amplitude-steering concept and the associated image formation algorithms is demonstrated. Range and vertical position are obtained by taking advantage of the frequency separation of a vertical linear amplitude-steered array. The third dimension of data is obtained by rotating the array such that the mainlobe is mechanically steered in azimuth. Data are collected in a water tank at the Pennsylvania State University Applied Research Laboratory for two targets: a ladder and three pipes. These data are the first experimental data collected with an amplitude-steered array for the purposes of imaging. The array is 10 cm in diameter and is operated in the frequency range of 80 to 304 kHz. Although the array is small for high-resolution imaging at these frequencies, the rungs of the ladder are recognizable in the images. The three pipes are difficult to discern in two of the projection images; however, the pipes separated in range are clear in the image showing vertical position versus range. The imaging concept is demonstrated on measured data, and the simulations agree well with the experimental results.

Journal Article↗

PubMed2002

A high frequency amplitude-steered array for real-time volumetric imaging.

Real-time three-dimensional acoustic imaging is difficult in water or tissue because of the slow speed of sound in these media. Conventional pulse-echo data collection, which uses at least one transmit pulse per line in the image, does not allow for the real-time update of a volume of data at practical ranges. Recently, a linear amplitude-steered array was presented that allows the collection of a plane of data with a single transmit pulse by spatially separating frequencies in the lateral direction. Later, by using a linear array with frequency separation in the vertical direction and rotating the array in the horizontal direction, volumetric data were collected with a small number of transmit pulses. By expanding the linear array to a two-dimensional array, data can now be collected for volumetric imaging in real time. In this study, the amplitude-steered array at the heart of a real-time volumetric sonar imaging system is described, giving the design of the array and describing how data are collected and processed to form images. An analysis of lateral resolution in the vertical and horizontal directions shows that resolution is improved in the direction of frequency separation over systems that use a broad transmit beam. Images from simulated data are presented.

Journal Article↗