Improved Performance of d₃₁-Mode Needle-actuating Transducer with PMN-PT Piezocrystal

Prototypes of a PZT-based ultrasound needle-actuating device have shown the ability to reduce needle penetration force and enhance needle visibility with color Doppler imaging during needle insertion for tissue biopsy and regional anesthesia. However, the demand for smaller, lighter devices and the need for high performance transducers have motivated investigation of a different configuration of needle-actuation transducer, utilizing the d 31 -mode of PZT4 piezoceramic, and exploration of further improvement in its performance using relaxor-type piezocrystal. This paper outlines the development of the d 31 -mode needle actuation transducer design from simulation to fabrication and demonstration. Full characterization was performed on transducers for performance comparison. The performance of the proposed smaller, lighter d 31 -mode transducer is comparable with that of previous d 33 -mode transducers. Furthermore, it has been found to be much more efficient when using PMN-PT piezocrystal rather than piezoceramic

Functional piezocrystal characterisation under varying conditions

Piezocrystals, especially the relaxor-based ferroelectric crystals, have been subject to intense investigation and development within the past three decades, motivated by the performance advantages offered by their ultrahigh piezoelectric coefficients and higher electromechanical coupling coefficients than piezoceramics. Structural anisotropy of piezocrystals also provides opportunities for devices to operate in novel vibration modes, such as the d36 face shear mode, with domain engineering and special crystal cuts. These piezocrystal characteristics contribute to their potential usage in a wide range of low- and high-power ultrasound applications. In such applications, conventional piezoelectric materials are presently subject to varying mechanical stress/pressure, temperature and electric field conditions. However, as observed previously, piezocrystal properties are significantly affected by a single such condition or a combination of conditions. Laboratory characterisation of the piezocrystal properties under these conditions is therefore essential to fully understand these materials and to allow electroacoustic transducer design in realistic scenarios. This will help to establish the extent to which these high performance piezocrystals can replace conventional piezoceramics in demanding applications. However, such characterisation requires specific experimental arrangements, examples of which are reported here, along with relevant results. The measurements include high frequency-resolution impedance spectroscopy with the piezocrystal material under mechanical stress 0–60 MPa, temperature 20–200 °C, high electric AC drive and DC bias. A laser Doppler vibrometer and infrared thermal camera are also integrated into the measurement system for vibration mode shape scanning and thermal conditioning with high AC drive. Three generations of piezocrystal have been tested: (I) binary, PMN-PT; (II) ternary, PIN-PMN-PT; and (III) doped ternary, Mn:PIN-PMN-PT. Utilising resonant mode analysis, variations in elastic, dielectric and piezoelectric constants and coupling coefficients have been analysed, and tests with thermal conditioning have been carried out to assess the stability of the piezocrystals under high power conditions

Localization Accuracy of Ultrasound-Actuated Needle with Color Doppler Imaging

An ultrasonic needle-actuating device for tissue biopsy and regional anaesthesia offers enhanced needle visibility with color Doppler imaging. However, its specific performance is not yet fully determined. This work investigated the influence on needle visibility of the insertion angle and drive voltage, as well as determined the accuracy and agreement of needle tip localization by comparing color Doppler measurements with paired photographic and B-mode ultrasound measurements. Needle tip accuracy measurements in a gelatin phantom gave a regression trend, where the slope of trend is 0.8808; coefficient of determination (R2) is 0.8877; bias is −0.50 mm; and the 95% limits of agreement are from −1.31 to 0.31 mm when comparing color Doppler with photographic measurements. When comparing the color Doppler with B-mode ultrasound measurements, the slope of the regression trend is 1.0179; R2 is 0.9651; bias is −0.16 mm; and the 95% limits of agreement are from −1.935 to 1.605 mm. The results demonstrate the accuracy of this technique and its potential for application to biopsy and ultrasound guided regional anaesthesia

Loss characterisation of piezocrystals under elevated environmental conditions

Relaxor-based piezoelectric single crystals have experienced three generations of development, from binary (e.g. PMN-PT) through ternary (e.g. PIN-PMN-PT) to doped ternary (e.g. Mn:PIN-PMN-PT). With improved composition and other relevant factors, these materials exhibit an extraordinary degree of piezoelectricity and ultrahigh electromechanical coupling coefficients, making them suitable for applications requiring high sensitivity and high bandwidth. With further increases in rhombohedral-to-tetragonal phase transition temperature (TRT), coercive field (EC) and mechanical quality factor (Qm), these piezocrystals can now be expected to work at elevated temperature, T, and pressure, P, and with high electric field drive. However, in operation, material properties can vary and performance can degrade significantly because of these elevated conditions, and the situation can be exacerbated by losses in the materials, necessitating proper characterisation of loss factors. In this paper, we report an investigation of three different loss characterisation methods then propose one combined method, demonstrating its use on TE-mode plates of PIN-PMN-PT and Mn:PIN-PMN-PT. Characterisation was performed using impedance spectroscopy for 20°C ≤ T ≤ 100°C and 0 MPa ≤ P ≤ 60 MPa. Results relating to dielectric, elastic and piezoelectric losses are reported, with detailed analysis and comparisons

Functional characterization of piezocrystals monitored under high power driving conditions

Relaxor-based ferroelectric single crystals such as PMN-PT are known to exhibit high piezoelectric properties compared with conventional piezoelectric ceramic materials, such as PZT-8. With advances in piezoelectric material development, including compositional engineering, single crystals with higher rhombohedral-to-tetragonal phase transition temperature (TRT), higher coercive field (EC) and higher mechanical quality factor (QM) have emerged, the principal example being Mn:PIN-PMN-PT. The improvements have opened up a wider application range, including more demanding high power applications where the performance of conventional materials may deteriorate at elevated temperatures resulting from intrinsic loss mechanisms. Characterization of these piezocrystals under practical and active conditions is therefore important, improving understanding of material behavior and facilitating transducer design in finite element analysis for demanding applications. In this paper, we report an active piezoelectric material characterization system that allows high resolution impedance spectroscopy under conditions similar to those experienced by piezoelectric materials in high power ultrasonic applications. The temperature consequent on the drive voltage is adaptively stabilized using a control algorithm. System function has been verified by testing with a Mn:PIN-PMN-PT thicknessextensional plate and functional characterization has been conducted on Generation I, II and III piezocrystals, with detailed analyses and comparisons of performance stability and material property variation with temperature