Biomedical subjects

Thomas R Shrout

Publications and source records attributed to Thomas R Shrout.

5 recordsLinked to original sources

PubMed2006

High-frequency ultrasound annular-array imaging. Part I: array design and fabrication.

This is Part I of a series of two papers describing the development of a digital high-frequency, annular-array, ultrasonic imaging system. In this paper, the design and fabrication of a high-frequency annular array as well as its performance will be reported. A six-element, 50 MHz array, which incorporated an acoustic lens to provide an initial focal point, was designed and fabricated. A submicron size grain lead titanate piezoelectric ceramic was used to both reduce lateral coupling and keep the electrical impedance matched close to the 50 ohm receive electronics. The array elements were isolated using laser micromachining to fully separate the annuli, and electrical interconnection was achieved by directly soldering thin wires to the elements. The resulting array attained an average impulse response that exhibited a 43 MHz center frequency, 30% relative bandwidth, and an average insertion loss of 31 dB at 45 MHz. Maximum next-element crosstalk was -27 dB in water.

Computer-Aided Design↗

PubMed2005

Recent developments in high curie temperature perovskite single crystals.

The temperature behavior of various relaxor-PT piezoelectric single crystals was investigated. Owing to a strongly curved morphotropic phase boundary, the usage temperature of these perovskite single crystals is limited by TR-T--the rhombohedral to tetragonal phase transformation temperature--which occurs a significantly lower temperatures than the Curie temperature Tc. Attempts to modify the temperature usage range of Pb(Zn1/3Nb2/3)O3--PbTiO3 (PZNT) and Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMNT) rhombohedral crystals (Tx to approximately 150-170 degrees C, TR-T to approximately 60-120 degrees C) using minor dopant modifications were limited, with little success. Of significant potential are crystals near the mor photropic phase boundary in the Pb(Yb1/2Nb1/2)O3-PbTiO3 (PYNT) system, with a Tc > 330 degrees C, even thoug TR-T was found to be only half that value at approximately 160 degrees C. Single crystals in the novel BiScO3-PbTiO3 system offer significantly higher Tcs > 400 degrees C, while exhibiting electromechanical coupling coefficients k33 > 90% being nearly constant till the TR-T temperature around 350 degrees C, which greatly increases the temperature range for transducer applications.

Journal Article↗

PubMed2005

Elastic, piezoelectric, and dielectric characterization of modified BiScO3-PbTiO3 ceramics.

The perovskite solid solution system (1-x)BiScO3-(x)PbTiO3 represents an interesting new family of high-temperature piezoelectric materials. Compositions near the morphotropic phase boundary (x approximately 0.64) have been reported to have high Curie temperatures (Tc > 450 degrees C) and good piezoelectric coefficients (d33 approximately 460 pC/N). In this work, manganese additions were used to improve the high-temperature electrical resistivity and RC time constant of compositions near the morphotropic phase boundary. The addition of manganese was found to shift Tc to slightly lower temperatures (442 degrees C and 456 degrees C for x = 0.64 and x = 0.66, respectively). The piezoelectric activities of the modified materials were found to be reduced slightly due to the hardening effect of manganese; however, the temperature stability and resistivity of the modified materials were significantly enhanced. In this paper we present, for the first time, a complete set of materials constants, including the elastic (sij, cij), piezoelectric (dij, eij, gij, hij), dielectric (epsilonij, betaij), and electromechanical (kij) coefficients and compare them to both unmodified 0.36BiScO3-0.64PbTiO3 and PZT5A ceramics.

Ceramics↗

PubMed2004

Electromechanical properties of fine-grain, 0.7 Pb(Mg(1/3)Nb(2/3))O3-0.3PbTiO3 ceramics.

A fine grain, relaxor-based piezoelectric ceramic 0.7 Pb(Mg(1/3)Nb(2/3))O3-0.3PbTiO3 (PMN-30% PT) has been investigated, which was fabricated using the columbite precursor method. The complete set of electromechanical properties of the piezoceramic at room temperature is determined using a combination of ultrasonic and resonance techniques. This fine-grain ceramic (grain size < or = 2.5 microm) exhibits ultra-high dielectric permittivity (epsilon33(T)/epsilon0 approximately 7000) and a high coupling coefficient k(33) (= 0.78). Ultrasonic spectroscopy was used to measure the dispersion of the phase velocity and attenuation for the longitudinal wave propagating in the poling direction. Lower attenuation and smaller velocity dispersion were observed compared to modified Pb(Zr(x)Ti(1-x)O3 (PZT-5H) ceramics. The measurement results show that this fine-grain PMN-30% PT ceramic is a very good material for making ultrasonic array transducers.

Journal Article↗

PubMed2002

A 30-MHz piezo-composite ultrasound array for medical imaging applications.

Ultrasound imaging at frequencies above 20 MHz is capable of achieving improved resolution in clinical applications requiring limited penetration depth. High frequency arrays that allow real-time imaging are desired for these applications but are not yet currently available. In this work, a method for fabricating fine-scale 2-2 composites suitable for 30-MHz linear array transducers was successfully demonstrated. High thickness coupling, low mechanical loss, and moderate electrical loss were achieved. This piezo-composite was incorporated into a 30-MHz array that included acoustic matching, an elevation focusing lens, electrical matching, and an air-filled kerf between elements. Bandwidths near 60%, 15-dB insertion loss, and crosstalk less than -30 dB were measured. Images of both a phantom and an ex vivo human eye were acquired using a synthetic aperture reconstruction method, resulting in measured lateral and axial resolutions of approximately 100 microm.

Artifacts↗