Wei-Yi Chang

Candle soot nanoparticles-polydimethylsiloxane composites for laser ultrasound transducers

Generation of high power laser ultrasound strongly demands the advanced materials with efficient laser energy absorption, fast thermal diffusion, and large thermoelastic expansion capabilities. In this study, candle soot nanoparticles-polydimethylsiloxane (CSNPs-PDMS) composite was investigated as the functional layer for an optoacoustic transducer with high-energy conversion efficiency. The mean diameter of the collected candle soot carbon nanoparticles is about 45 nm, and the light absorption ratio at 532 nm wavelength is up to 96.24%. The prototyped CSNPs-PDMS nano-composite laser ultrasound transducer was characterized and compared with transducers using Cr-PDMS, carbon black (CB)-PDMS, and carbon nano-fiber (CNFs)-PDMS composites, respectively. Energy conversion coefficient and −6 dB frequency bandwidth of the CSNPs-PDMS composite laser ultrasound transducer were measured to be 4.41 × 10−3 and 21 MHz, respectively. The unprecedented laser ultrasound transduction performance using CSNPs-PDMS nano-comp...

A Novel Laser Ultrasound Transducer Using Candle Soot Carbon Nanoparticles

As a novel composite material for laser ultrasound transducer, candle soot nanoparticles polydimethylsiloxane (CSPs-PDMS) has been demonstrated to generate high frequency, broadband, and high-amplitude ultrasound waves. In this study, we investigated the mechanism of the high-optoacoustic conversion efficiency exhibited by the composite. A thermal-acoustic coupling model was proposed for analyzing the performance of the composite. The theoretical result matches well with the experimental observation. The acoustic beam profile was compared with Field II simulation results. The 4.41 × 10-3 energy conversion coefficient and 21 MHz--6 dB frequency bandwidth of the composite suggest that CSPs-PDMS composites is promising for a broad range of ultrasound therapy and non-destructive testing applications.

Study on dielectric and piezoelectric properties of 0.7 Pb(Mg1/3Nb2/3)O3-0.3 PbTiO3 single crystal with nano-patterned composite electrode

Effect of nano-patterned composite electrode and backswitching poling technique on dielectric and piezoelectric properties of 0.7 Pb(Mg1/3Nb2/3)O3-0.3 PbTiO3 was studied in this paper. Composite electrode consists of Mn nano-patterns with pitch size of 200 nm, and a blanket layer of Ti/Au was fabricated using a nanolithography based lift-off process, heat treatment, and metal film sputtering. Composite electrode and backswitching poling resulted in 27% increase of d33 and 25% increase of dielectric constant, and we believe that this is attributed to regularly defined nano-domains and irreversible rhombohedral to monoclinic phase transition in crystal. The results indicate that nano-patterned composite electrode and backswitching poling has a great potential in domain engineering of relaxor single crystals for advanced devices.

40-MHz Micromachined PMN-PT Composite Ultrasound Array for Medical Imaging

Ultrasonography is well known as a relatively low cost and non-invasive modality for real-time imaging. In recent years, various high frequency array transducers have been developed and used for ophthalmology, dermatology, and small animal studies. This paper reports the development of a 48-element 40-MHz ultrasonic array using micromachined lead magnesium niobate-lead titanate (PMN-PT) single crystal 1–3 composite material. Array elements with a pitch of 100-micron were interconnected via a customized flexible circuit. Pulse-echo test showed an average center frequency of 40 MHz and a −6 dB fractional bandwidth of 52%. The −20 dB pulse length was evaluated as 120 ns. The electrical and acoustical separation showed the crosstalk less than - 24 dB. An image of a steel wire target phantom was acquired by stacking multiple A-lines. The results demonstrate resolutions exceeding 70 μm axially and 800 μm laterally. Those results imply the great potential of the developed array transducer for the high frequency medical imaging.Copyright

Dielectric and piezoelectric properties of 0.7 Pb(Mg1/3Nb2/3)O3-0.3 PbTiO3 single crystal poled using alternating current

ABSTRACT In this paper, 0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 (PMN-30%PT) single crystal samples were poled using an alternating current (electric field) poling (ACP) method. Compared to the traditional poling method, the piezoelectric coefficient, free and clamped dielectric constants were improved more than 21%. X-ray diffraction result suggests the existence of monoclinic phase (MA) in ACP samples and piezoresponse force microscopy (PFM) result further depicts the finer engineered domain structures. The ACP sample also showed the unique phase transition sequences during the depoling process. Our work could provide a novel domain engineered method to enhance piezoelectric properties of PMN-PT single crystal. GRAPHICAL ABSTRACT IMPACT STATEMENT Piezoelectric and dielectric properties of relaxor-PT single crystals can be significantly enhanced by employing the new alternating current poling method, attributing to the unique heterogenous domain structure containing unprecedented domain wall density.

Domain engineering and full matrix material constants of the [111]c-poled 0.63Pb(Mg1/3Nb2/3)-0.37PbTiO3 single crystal

Domain engineering was performed on the [111]c-oriented tetragonal ferroelectric 0.63Pb(Mg1/3Nb2/3)-0.37PbTiO3 (PMN-0.37PT) single crystal in order to achieve better piezoelectric properties. Influences of the poling electric field (EP), poling temperature, and poling time on piezoelectric and electromechanical properties were investigated. The piezoelectric and dielectric constants increase with increasing the EP. In addition, the piezoelectric response increases with increasing the poling time but the crystal saturates after 10 min of poling at 30 °C or 20 min at 150 °C under EP = 2 kV mm−1. The piezoelectric strain coefficient d33 can be improved from 407 pC N−1 poled at 30 °C to 706 pC N−1 after poling at 150 °C near TC, which is 27.9% higher than the highest value reported before (d33 = 551.9 pC N−1). The enhancement of piezoelectric response results from the domain structure redistribution occurring near the ferroelectric to paraelectric phase transition temperature because the potential barrier is substantially lowered so that polarization switching becomes easier. Therefore, more domain walls appear to be beneficial for the enhancement of the piezoelectric response. Under the optimized poling conditions, a complete set of dielectric, elastic, and piezoelectric constants was measured for [111]c-poled PMN-0.37PT single crystal using a combined resonance and ultrasonic method (CRUM). Both the longitudinal (d33 = 706 pC N−1) and shear (d15 = 875 pC N−1) piezoelectric properties are outstanding for the [111]c-poled PMN-0.37PT single crystal due to domain wall motions.

Photoacoustic transduction efficiency evaluation of candle soot nanoparticles/PDMS composites

Carbon-based materials have been considered as an efficient light-absorption component of film-type laser ultrasound transducers. Our previously designed laser ultrasound patch composed of candle soot nanoparticles and polydimethylsiloxane (CS/PDMS) composites showed high photoacoustic transducer efficiency than other carbon-based composites. In this study, we demonstrate that the carbon volume fraction and the thickness of clustered carbon nanoparticles of CS/PDMS composites are highly related to the photoacoustic transduction efficiency. This study builds upon our previous study to characterize optical properties of the CS/PDMS composites in both experimental measurements and finite difference time domain (FDTD) analysis in the visible wavelength range.

Optical fiber laser-generated-focused-ultrasound transducers for intravascular therapies

In this paper, we report the development of optical fiber laser-generated-focused-ultrasound (LGFU) transducers for intravascular therapies. By combining advantages of fiber optics and photoacoustics, high frequency (>10 MHz), high pressure (> 10 MPa), short pulse (<10 ns) shock waves can be generated from a small aperture (<1 mm in diameter), which is immune to electromagnetic noise. In this work, candle soot nanoparticle (CSNP)-polydimethylsiloxane (PDMS) composite film was used as a photoacoustic layer owing to its high photoacoustic energy conversion efficiency (∼0.004) and simple fabrication procedure. A 2 mm-diameter transparent concave lens was developed by using optical adhesive and capillary-rise technique, and the CSNP-PDMS composite film was coated on it by dip-coating method. The fabricated transducer was integrated with an optical fiber (diameter of 0.6 mm), followed by acoustic characterizations to evaluate the wave form, center frequency, and pressure output. We confirmed that the optical fiber CSNP-PDMS LGFU transducer can generate 12 MHz, high pressure shock wave (peak pressure of 16 MPa) at approximately 1.3 mm away from the transducer surface by low laser energy excitation (1.5 mJ/cm2). The corresponding mechanical index of the achieved pressure output is 1.7, which is sufficient to induce inertial cavitation in microbubble-mediated therapies.

Development of forward-looking ultrasound transducers for microbubble-aided intravascular ultrasound-enhanced thrombolysis

In this paper, we report the development of miniaturized forward-looking transducers for microbubble-mediated intravascular ultrasound-enhanced thrombolysis (UET). UET has shown its efficacy for thrombo-occlusive disease by enhancing penetration of thrombolytic drugs into clots, reducing the required dose. In this study, we adopted a previously-developed forward-looking, stacked type transducer for thrombolysis treatment with low dose (approximately 0.4 μg/ml)-recombinant tissue-plasminogen activator (rt-PA). The 650 kHz-prototype transducer with a concave lens enabled a confined ultrasound beam despite the small aperture (diameter <1.5 mm) with respect to the wavelength (2.2 mm), and peak-negative-pressure of 1.35 MPa with a corresponding mechanical index of 1.67 was achieved. In vitro thrombolysis tests using the developed transducer with microbubble infusion showed that local administration of low dose-recombinant tissue-plasminogen activator (rt-PA) results in a two-fold increase in average thrombolytic rate versus without rt-PA.

Piezoelectric d36 in-plane shear-mode of lead-free BZT-BCT single crystals for torsion actuation

We report the study of piezoelectric direct torsion actuation mechanism using lead-free piezoelectric d36 in-plane shear-mode BZT-BCT single crystals. The generated angle of twist of the piezoelectric torsion actuator was obtained from the transverse deflection measurement using a laser vibrometer. The bi-morph torsional actuator, consisting of two lead-free piezoelectric BZT-BCT in-plane shear-mode single crystals with a giant piezoelectric d36 shear strain coefficient of 1590 pC/N, provided a rate of twist of 34.12 mm/m under a quasi-static 15 V drive. The experimental benchmark was further modelled and verified by the ANSYS software using three dimensional (3D) piezoelectric finite elements. The experimental results revealed that lead-free piezoelectric BZT-BCT d36-mode single crystal is a superior candidate for piezoelectric torsion actuation. This lead-free piezoelectric BZT-BCT d36-mode torsion actuator can be effectively applied in torsional deformation control by taking into account the environmen...