Jay Shieh

The selection of sensors

Abstract A systematic method is developed to select the most appropriate sensor for a particular application. A wide range of candidate sensors exist, and many are based on coupled electrical and mechanical phenomena, such as the piezoelectric, magnetostrictive and the pyro-electric effects. Performance charts for sensors are constructed from suppliers data for commercially available devices. The selection of an appropriate sensor is based on matching the operating characteristics of sensors to the requirements of an application. The final selection is aided by additional considerations such as cost, and impedance matching. Case studies illustrate the selection procedure.

An evaluation of switching criteria for ferroelectrics under stress and electric field

Abstract The multi-axial responses of barium titanate (BaTiO3) and hard lead zirconate titanate (PZT-4D) are measured for stress and electric field loadings, and are compared to the response of soft lead zirconate titanate (PZT-5H) taken from a previous study. First, poled ferroelectric specimens are subjected to an electric field at an angle to the original poling direction. Second, unpoled ferroelectric specimens are loaded by a uniaxial compressive stress and a parallel, proportional electric field. The switching surfaces of BaTiO3 and PZT-4D are constructed from the experimental measurements, and compared with existing data for PZT-5H. The measured responses are then used to evaluate the accuracy of existing micromechanical and phenomenological models of ferroelectric switching.

Effect of depolarization and coercivity on actuation strains due to domain switching in barium titanate

Large electrostrictive actuation in ferroelectric single crystals can be achieved through non-180° domain switching using various biasing fields and loads. The theoretical maximum actuation strain such as 1.1% for barium titanate crystals, however, has not been observed yet. In this letter, the authors propose a possible mechanism accounting for the depolarization effect to explain the significant strain reduction observed in their recent experiment. They find that a low-energy path requires the switching of 90° domains together with that of in-plane alternating layers of 180° domains formed to reduce the depolarization energy. Therefore, reduction in strain is significant for crystals with large 180° coercivities. The result is consistent with their recent experimental observations.

Operation of multiple 90° switching systems in barium titanate single crystals under electromechanical loading

Hysteresis evolution of a 5×5×2mm3 barium titanate single crystal during a combined electromechanical loading sequence reveals incomplete switching characteristics and a considerable disproportion of slope gradients at zero electric field for the measured polarization and strain hysteresis curves. A likely cause for the disproportion of gradients is the cooperative operation of multiple 90° switching systems by which “polarization-free” strain changes are induced. In addition, a theoretical study indicates that the presence of depolarization fields generated from the unshielded boundaries and/or incompatible domains within the crystal can have a substantial influence on the polarization measurement in the loading direction.

Reusable tissue-mimicking hydrogel phantoms for focused ultrasound ablation.

The ability of N-isopropylacrylamide (NIPAM)-based hydrogel phantoms to mimic tissues with different acoustic and thermal properties under high-intensity focused ultrasound (HIFU) ablation was investigated. These phantoms were designed to model the formation of thermal lesions in tissues above the threshold temperature of protein denaturation. By adjusting the concentration of acrylic acid (AAc) in the NIPAM-based hydrogel phantoms, the cloud point (i.e., lower critical solution temperature) of the phantoms could be tailored to produce HIFU thermal lesions similar to those formed in different swine tissues in terms of size and shape. Additionally, energy thresholds for inducing transient or permanent bubbles in the phantoms during HIFU ablation were also identified to shed light on the onset of cavitation or material damage. The NIPAM-based hydrogel phantoms developed in this study possess major advantages such as transparent, reusable and tailorable properties, and are practical tools for characterizing an ablative device (or treatment) to determine its efficacy and safety.

Multiaxial response of hard and soft ferroelectrics under stress and electric field

Samples of soft PZT-5H, hard PZT-4D and Barium Titanate were subjected to multi-axial loading in stress and electric field space. The loading paths were: (1) Poling with electric field, followed by repolarizing with electric field at an angle to the original poling direction. (2) Proportional loading with electric field and coaxial compressive stress, the proportions of stress and electric field being varied between tests. In case (1) the poled material was cut to produce faces angled to the original poling direction. The measured material responses are reported and initial switching surfaces are calculated based on an offset from linear response in electric displacement. The measurements are used to assess the features required in micromechanical or phenomenological models of switching.

Phase-transformation-induced microstructure in lead-free ferroelectric ceramics based on (Bi0.5Na0.5)TiO3–BaTiO3–(Bi0.5K0.5)TiO3

Lead-free ferroelectric ceramics with a morphotropic phase boundary (MPB) composition 85.4% (Bi0.5Na0.5)TiO3–2.6%BaTiO3–12.0% (Bi0.5K0.5)TiO3 (BNT-BT-BKT at a molar ratio of 85.4: 2.6: 12.0) doped with 0.8 mol% Nb2O5 were studied for their crystalline phases and microstructure. The crystalline phases were identified using X-ray diffractometry (XRD) with the contents determined using the Rietveld refinement technique. The phase-transformation-induced microstructure was analyzed using transmission electron microscopy (TEM) and the crystal symmetries were determined using the convergent-beam electron diffraction (CBED) technique. Samples sintered at 1200°C contain a mixture of cubic (C-), tetragonal (T-) and rhombohedral (R-) phases at a ratio of C/T/R = 56.6: 28.4: 15.0 wt%. Two types of grains are produced: one characterized by a featureless contrast consisting of nano-scale T-domains dispersed in a C-phase matrix; the other a core-shell structure with a shell containing twin and anti-phase-boundary (APB) domains coexisting with a (C + T)-phase mixture core. The T- and R-twin boundaries are determined to {111}T and {110}R, respectively, and the fault vector for T-APB to R = 1/2⟨110]T. The characteristic microstructure is discussed in terms of the reduction in the point group symmetry and changes in the unit cell volume or the Bravais lattice upon phase transformation among the C-, T- and R-phases. The twin and the APB domains are induced and explained.

Simulation of thermal ablation by high-intensity focused ultrasound with temperature-dependent properties.

An integrated computational framework was developed in this study for modeling high-intensity focused ultrasound (HIFU) thermal ablation. The temperature field was obtained by solving the bioheat transfer equation (BHTE) through the finite element method; while, the thermal lesion was considered as a denatured material experiencing phase transformation and modeled with the latent heat. An equivalent attenuation coefficient, which considers the temperature-dependent properties of the target material and the ultrasound diffraction due to bubbles, was proposed in the nonlinear thermal transient analysis. Finally, a modified thermal dose formulation was proposed to predict the lesion size, shape and location. In-vitro thermal ablation experiments on transparent tissue phantoms at different energy levels were carried out to validate this computational framework. The temperature histories and lesion areas from the proposed model show good correlation with those from the in-vitro experiments.

Enhancement of light emission from silicon by precisely tuning coupled localized surface plasmon resonance of a nanostructured platinum layer prepared by atomic layer deposition.

Plasmonic enhancement of photoluminescence from bulk silicon was achieved by spectrally tailoring coupled localized surface plasmon resonance (LSPR) in the Al2O3 cover/nanostructured platinum (nano-Pt)/Al2O3 spacer/silicon multilayer structures prepared by atomic layer deposition (ALD). Agreement between the simulation and experimental data indicates that the plasmonic activity originates from absorption enhancement due to coupled LSPR. Because of the optimized dielectric environment deposited by ALD around the nano-Pt layer, absorption of the multilayer structure was enhanced by the precise tuning of coupled LSPR to coincide with the excitation wavelength. This accurate plasmonic multilayer structure grown by ALD with high precision, tunability, uniformity, and reproducibility can be further applied in efficient light-emitting devices.

Ultrasound thermal mapping based on a hybrid method combining cross-correlation and zero-crossing tracking

A hybrid method for estimating temperature with spatial mapping using diagnostic ultrasound, based on detection of echo shifts from tissue undergoing thermal treatment, is proposed. Cross-correlation and zero-crossing tracking are two conventional algorithms used for detecting echo shifts, but their practical applications are limited. The proposed hybrid method combines the advantages of both algorithms with improved accuracy in temperature estimation. In vitro experiments were performed on porcine muscle for preliminary validation and temperature calibration. In addition, thermal mapping of rabbit thigh muscle in vivo during high-intensity focused ultrasound heating was conducted. Results from the in vitro experiments indicated that the difference between the estimated temperature change by the proposed hybrid method and the actual temperature change measured by the thermocouple was generally less than 1 °C when the increase in temperature due to heating was less than 10 °C. For the in vivo study, the area predicted to experience the highest temperature coincided well with the focal point of the high-intensity focused ultrasound transducer. The computational efficiency of the hybrid algorithm was similar to that of the fast cross-correlation algorithm, but with an improved accuracy. The proposed hybrid method could provide an alternative means for non-invasive monitoring of limited temperature changes during hyperthermia therapy.