Publications by authors named "Chunlong Fei"

24 Publications

  • Page 1 of 1

Effects of Composition Segregation in PMN-PT Crystals on Ultrasound Transducer Performance.

IEEE Trans Ultrason Ferroelectr Freq Control 2021 Nov 30;PP. Epub 2021 Nov 30.

This study investigates the relationship between the composition segregation in lead magnesium niobate-lead titanate (PMN-29%PT, PMN-29.5%PT, PMN-30%PT, PMN-30.5%PT, and PMN-31%PT) single crystals within morphotropic phase boundary (MPB) and the corresponding ultrasonic transducer performance through PiezoCAD modeling and real transducer testing. For five crystals with compositions distributed across the main body of a crystal ingot, the piezoelectric coefficient and free relative permittivity values were measured to vary by over 30%, whereas the transducer bandwidth and center frequency values were modeled to change by less than 10%. For the single element ultrasonic transducers fabricated using those crystals without matching layers, the variations of -6dB bandwidth, insertion loss, receiver free field voltage response and center frequency were measured to be 9.61%, -15.23%, 9.76% and 1.41%, respectively, confirming the modeling results. Using the Mason and KLM Models, it is found that the relatively stable transducer performance can be attributed to the relatively consistent electromechanical coupling coefficient, acoustic impedance and clamped relative permittivity originated from the stable elastic compliance properties among the crystals of various compositions. It is expected that the relatively stable performance could be extended to multi-element transducers with matching layers, for the same contributing mechanisms. Our results suggest that it is possible to use crystal plates of different compositions within the MPB region, obtained from one and the same ingot, to fabricate a batch of ultrasonic transducers which will exhibit similar performance, significantly reducing the cost of materials.
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http://dx.doi.org/10.1109/TUFFC.2021.3131204DOI Listing
November 2021

Evolvable Acoustic Field Generated by a Transducer with 3D-Printed Fresnel Lens.

Micromachines (Basel) 2021 Oct 26;12(11). Epub 2021 Oct 26.

Interdisciplinary Division of Biomedical Engineering, The Hong Kong Ploytechnic University, Hong Kong 999077, China.

Evolvable acoustic fields are considered an effective method for solving technical problems related to fields such as biological imaging, particle manipulation, drug therapy and intervention. However, because of technical difficulties and the limited technology available for realizing flexible adjustments of sound fields, few studies have reported on this aspect in recent years. Herein, we propose a novel solution, using a Fresnel lens-focused ultrasonic transducer for generating excited-signal-dependent acoustic pressure patterns. Finite element analysis (FEA) is used to predict the performance of a transducer with a Fresnel lens. The Fresnel lens is printed using 3D additive manufacturing. Normalized intensity maps of the acoustic pressure fields are characterized from the Fresnel lens-focused transducer under various numbers of excited-signal cycles. The results demonstrate that under different cycle excitations, a temporal evolution acoustic intensity can be generated and regulated by an ultrasound transducer with a 3D Fresnel lens. This acoustical pattern control method is not only simple to realize but also has considerable application prospects.
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http://dx.doi.org/10.3390/mi12111315DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8617849PMC
October 2021

High Frequency 0.36BiScO3-0.64PbTiO3 Ultrasonic Transducer for High Temperature Imaging Application.

IEEE Trans Ultrason Ferroelectr Freq Control 2021 Oct 27;PP. Epub 2021 Oct 27.

(1-x)BiScO3-xPbTiO3 (BS-PT) ceramics have excellent piezoelectricity and high Curie temperature at its morphotropic phase boundary (x=0.64), so it is a promising piezoelectric material for fabricating high temperature ultrasonic transducer (HTUT). Electric properties of 0.36BS-0.64PT ceramics were characterized at different temperature, and a HTUT with the center frequency of about 15 MHz was designed by PiezoCAD based on the measuring results. The prepared HTUT was tested in a silicone oil bath at different temperature systematically. The test results show that the HTUT can maintain a stable electrical resonance until 290 °C, and get a clear echo response until 250 °C with slight changes of the center frequency. Then a stepped metal block submerged in silicone oil was imaged by the HTUT until 250 °C. Velocity of silicone oil and axial resolution of the HTUT at different temperature were calculated. The results verify the capability of 0.36BS-0.64PT based HTUT for high temperature ultrasonic imaging applications.
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http://dx.doi.org/10.1109/TUFFC.2021.3123331DOI Listing
October 2021

Gas-filled protein nanostructures as cavitation nuclei for molecule-specific sonodynamic therapy.

Acta Biomater 2021 Dec 13;136:533-545. Epub 2021 Sep 13.

Department of Biomedical Engineering, The Hong Kong Polytechnic University, Hung Hom Room ST409, Hong Kong SAR, PR China. Electronic address:

Sonodynamic therapy (SDT) is a promising alternative for cancer therapy, understood to exert cytotoxicity through cavitation and subsequent production of large amounts of reactive oxygen species (ROS). Gas-filled protein nanostructures (gas vesicles or GVs) produced by cyanobacteria have a hollow structure similar to microbubbles and have demonstrated comparable enhancement of ultrasound imaging contrast. We thus hypothesized that GVs may act as stable nuclei for inertial cavitation to enhance SDT with improved enhanced permeability and retention (EPR) effects due to their nanometer scale. The function of GVs to mediate cavitation, ROS production, and cell-targeted toxicity under SDT was determined. In solution, we found that GVs successfully increased cavitation and enhanced ROS production in a dose- and time-dependent manner. Then, GV surfaces were modified (FGVs) to specifically target CD44 cells and accumulate preferentially at the tumor site. In vitro sonodynamic therapy (SDT) showed ROS production and tumor cell toxicity substantially elevated in the presence of FGVs, and the addition of FGVs was found to enhance cavitation and subsequently inhibit tumor growth and exert greater damage to tumors under SDT in vivo. Our results thus demonstrate that FGVs can function as stable, nanosized, nuclei for spatially accurate and cell-targeted SDT. STATEMENT OF SIGNIFICANCE: The initiation of inertial cavitation is critical for ROS generation and subsequent cellular toxicity in SDT. Thus, precise control of the occurrence of cavitation is a key factor in increasing SDT's therapeutic efficacy. We explored nanometer-sized gas vesicles (GVs) as a new class of cavitation nuclei for molecule-specific sonodynamic therapy. Our results showed that GV-mediated SDT treatment enabled targeted disruption of specific cells expressing a known surface marker within the area of insonation, providing a spatially specific and targeted SDT treatment.
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http://dx.doi.org/10.1016/j.actbio.2021.09.010DOI Listing
December 2021

Adjustable acoustic field controlled by "ultrasonic projector" on ultrasound application.

IEEE Trans Ultrason Ferroelectr Freq Control 2021 Sep 1;PP. Epub 2021 Sep 1.

The controlling of acoustic field has great potential in many applications such as medical treatment, neuro-modulation, and bio-imaging. Recently, acoustic lenses and phased arrays have become common ways of controlling acoustic fields. However, the shortcomings of the two ways are obvious. Acoustic lenses are lack of flexibility after design, phased arrays have complicated structures and need to adjust the parameters of each array element. In this work, we propose an alternative for sound field control by using a flexible and adjustable "acoustic projector", two symmetric mirrors are used to change the direction of propagation of an acoustic wave produced by a piezoelectric element and realize acoustic focusing in the target region. The 2D "acoustic projector" model was built in finite element simulation, and the feasibility was verified with an actual prototype. The sound intensity produced by the piezoelectric element at different horizontal and vertical positions along the target area can be accurately controlled by two adjustable mirrors. When the angle of the mirror ranging from 30° to 40°, the focal depth can change from 39 mm to 140 mm. Furthermore, the focus can be controlled in a sector with an angle of 60°. The "acoustic projector" demonstrates simple but precise control of acoustic fields and may broaden their applicability. In order to show its imaging ability, the three groups of target balls at different positions were imaged and given their position information by scanning the mirrors in simulation.
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http://dx.doi.org/10.1109/TUFFC.2021.3106712DOI Listing
September 2021

Optimized Backing Layers Design for High Frequency Broad Bandwidth Ultrasonic Transducer.

IEEE Trans Biomed Eng 2021 Jul 21;PP. Epub 2021 Jul 21.

Ultrasonic transducers with broad bandwidth are considered to have high axial resolution and good ultrasound scanning flexibility for the clinical applications. The limitations of spatial resolution due to bandwidth are of great concern in ultrasound medical imaging. The method of acoustic impedance matching between the piezoelectric element and medium is commonly used to obtain broad bandwidth and high resolution. In this study, an optimized backing layer design was proposed to broaden the bandwidth by adding a tunable acoustic impedance matching layer of backing (AIMLB) between the backing layer and the piezoelectric ceramic element. The Mason equivalent circuit method was used to analyze the effect of the backing material composition and its structure on the bandwidth of the transducer. The optimized transducer was simulated using the finite-element method with the PZFlex software. Based on the PZFlex simulations, a 20-MHz ultrasonic transducer using the AIMLB with a bandwidth of approximately 92.29% was fabricated. The experimental results were in good agreement with the simulations. The ultrasonic imaging indicated that the designed ultrasonic transducer with an additional AIMLB had high performance with good imaging capability.
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http://dx.doi.org/10.1109/TBME.2021.3098567DOI Listing
July 2021

Recent Development and Perspectives of Optimization Design Methods for Piezoelectric Ultrasonic Transducers.

Micromachines (Basel) 2021 Jun 30;12(7). Epub 2021 Jun 30.

School of Microelectronics, Xidian University, Xi'an 710071, China.

Apiezoelectric ultrasonic transducer (PUT) is widely used in nondestructive testing, medical imaging, and particle manipulation, etc., and the performance of the PUT determines its functional performance and effectiveness in these applications. The optimization design method of a PUT is very important for the fabrication of a high-performance PUT. In this paper, traditional and efficient optimization design methods for a PUT are presented. The traditional optimization design methods are mainly based on an analytical model, an equivalent circuit model, or a finite element model and the design parameters are adjusted by a trial-and-error method, which relies on the experience of experts and has a relatively low efficiency. Recently, by combining intelligent optimization algorithms, efficient optimization design methods for a PUT have been developed based on a traditional model or a data-driven model, which can effectively improve the design efficiency of a PUT and reduce its development cycle and cost. The advantages and disadvantages of the presented methods are compared and discussed. Finally, the optimization design methods for PUT are concluded, and their future perspectives are discussed.
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http://dx.doi.org/10.3390/mi12070779DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8304036PMC
June 2021

Optimization Design of Ultrasonic Transducer With Multimatching Layer.

IEEE Trans Ultrason Ferroelectr Freq Control 2021 06 25;68(6):2202-2211. Epub 2021 May 25.

An optimization design strategy is developed for ultrasonic transducer (UT) with multimatching layer to improve its performance. The piezoelectric equivalent circuit model is used to determine the optimization interval of matching layer, and the PiezoCAD software is used to simulate the performance of UT with multimatching layer. The neural network (NN) models are trained by the simulation data to characterize the relationship between the thickness of matching layer and performance of UT. Then, the multiobjective optimality criteria for UT is established based on its performance parameters, including center frequency (CF), -6 dB bandwidth (BW) and pulsewidth (PW). The thickness of matching layer is optimized by particle swarm optimization (PSO) algorithm. According to the designed performance, the optimized copper thickness and parylene thickness are about 17.76 and [Formula: see text], respectively. The simulation results of UT with the optimized multimatching layer well agree with the designed targets. Also, CF, -6 dB BW, and PW of the fabricated UT with the optimized multimatching layer are 5.672 MHz, 50.08%, and [Formula: see text], respectively, which nearly achieve the designed performance. In addition, the performance of UT with the optimized multimatching layer is much better than that of UT without matching layer. Moreover, compared with UT with single or double matching layers determined by the quarter wavelength theory, the UT with the optimized multimatching layer has better comprehensive performance. Finally, the fabricated UT with the optimized multimatching layer is used to measure the thickness of testing block, and the relative errors are all less than 1.0%, which implies that the optimized UT has excellent performance.
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http://dx.doi.org/10.1109/TUFFC.2021.3059671DOI Listing
June 2021

The forbidden band and size selectivity of acoustic radiation force trapping.

iScience 2021 Jan 26;24(1):101988. Epub 2020 Dec 26.

School of Microelectronics, Xidian University, Xi'an, China.

Acoustic micro-beams produced by highly focused ultrasound transducer have been investigated for micro-particle and cell manipulation. Here we report the selective trapping of microspheres via the acoustic force using the single acoustical beam. The forbidden band theory of acoustic radiation force trapping is proposed, which indicates that the trapping of particles via the acoustic beam is directly related to the particle diameter-to-beam wavelength ratio as well as excitation frequency of the ultrasonic acoustic tweezers. Three tightly focused LiNbO transducers with different center frequencies were fabricated for use as selective single beam acoustic tweezers (SBATs). These SBATs were capable of selectively manipulating microspheres of sizes 5-45 μm by adjusting the wavelength of acoustic beam. Our observations could introduce new avenues for research in biology and biophysics by promoting the development of a tool for selectively manipulating microspheres or cells of certain selected sizes, by carefully setting the acoustic beam shape and wavelength.
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http://dx.doi.org/10.1016/j.isci.2020.101988DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7809519PMC
January 2021

Lead-Free KNN-Based Textured Ceramics for High-Frequency Ultrasonic Transducer Application.

IEEE Trans Ultrason Ferroelectr Freq Control 2021 May 26;68(5):1979-1987. Epub 2021 Apr 26.

Environment-friendly lead-free piezoelectric materials with excellent piezoelectric properties are needed for high-frequency ultrasonic transducer applications. Recently, lead-free 0.915(KNaLi)NbO-0.075BaZrO 3-0.01(BiNa)TiO (KNLN-BZ-BNT) textured piezo- electric ceramics have high piezoelectric response, superior thermal stability, and excellent fatigue resistance, which are promising for devices applications. In this work, the KNLN-BZ-BNT textured ceramics were prepared by the tape-casting method. Microstructural morphology, phase transition, and electrical properties of KNLN-BZ-BNT textured ceramics were investigated. High-frequency needle-type ultrasonic transducers were designed and fabricated with these textured ceramics. The tightly focused transducers have a center frequency higher than 80 MHz and a -6-dB fractional bandwidth of 52%. Such transducers were built for an f -number close to 1, and the desired focal depth was achieved by press-focusing technology associated with a set of customer design fixture. Its lateral resolution was better than [Formula: see text] by scanning a 15- [Formula: see text] tungsten wire target. These promising results demonstrate that the lead-free KNLN-BZ-BNT textured ceramic is a good candidate for high-frequency ultrasonic transducer applications.
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http://dx.doi.org/10.1109/TUFFC.2020.3039120DOI Listing
May 2021

An Efficient Optimization Design of Liquid Lens for Acoustic Pattern Control.

IEEE Trans Ultrason Ferroelectr Freq Control 2021 05 26;68(5):1546-1554. Epub 2021 Apr 26.

In order to effectively and flexibly control acoustic pattern, an efficient optimization design method of acoustic liquid lens (ALL) is developed by the frame of particle swarm optimization (PSO) algorithm. The ALL is composed of ethanol and dimethicone, and its parameters include ethanol concentration (EC), volume fraction of dimethicone (VFD), and total volume (TV). Based on the established finite element model and orthogonal design method, the data of acoustic pattern and ALL can be obtained by using COMSOL Multiphysics. Based on the simulation data, the neural network models are constructed to characterize the relationship between the parameters of ALL and the performance of acoustic pattern. The optimization design criteria of ALL are constructed based on the performance parameters of acoustic pattern, including focal distance (FD), transverse resolution (TR), and longitudinal resolution (LR). Based on the optimization criteria, the modified PSO algorithm is utilized to optimize the design parameters of ALL in the developed method. According to the desired FD, TR, and LR of acoustic pattern (20, 1, and 17 mm), the optimized EC, VFD, and TV of ALL are about 0.838, 0.165, and 164.4 [Formula: see text]. The performance parameters of acoustic pattern verified by simulation and experiments agree with the desired ones. In addition, using 6 MHz ultrasonic transducer with the optimized ALL, the ultrasonic imaging of tungsten wires and porcine eyeball further demonstrates the effectiveness and feasibility of the developed method.
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http://dx.doi.org/10.1109/TUFFC.2020.3040174DOI Listing
May 2021

Particle Swarm Optimization Algorithm-Based Design Method for Ultrasonic Transducers.

Micromachines (Basel) 2020 Jul 23;11(8). Epub 2020 Jul 23.

School of Microelectronics, Xidian University, Xi'an 710071, China.

In order to improve the fabrication efficiency and performance of an ultrasonic transducer (UT), a particle swarm optimization (PSO) algorithm-based design method was established and combined with an electrically equivalent circuit model. The relationship between the design and performance parameters of the UT is described by an electrically equivalent circuit model. Optimality criteria were established according to the desired performance; then, the design parameters were iteratively optimized using a PSO algorithm. The Pb(ZrTi)O (PZT) ceramic UT was designed by the proposed method to verify its effectiveness. A center frequency of 6 MHz and a bandwidth of -6 dB (70%) were the desired performance characteristics. The optimized thicknesses of the piezoelectric and matching layers were 255 μm and 102 μm. The experimental results agree with those determined by the equivalent circuit model, and the center frequency and -6 dB bandwidth of the fabricated UT were 6.3 MHz and 68.25%, respectively, which verifies the effectiveness of the developed optimization design method.
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http://dx.doi.org/10.3390/mi11080715DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7465307PMC
July 2020

High Resolution ADC for Ultrasound Color Doppler Imaging Based On MASH Sigma-Delta Modulator.

IEEE Trans Biomed Eng 2019 Aug 29. Epub 2019 Aug 29.

Objective: A high precision quantization ultrasound imaging system, capable of capturing small variances of the echo signal with a wide dynamic range, is important for producing accurate diagnostic outputs. Commercial ultrasound systems, typically utilizing 12 or 14 bits analog-to-digital converters (ADCs), lack the ability to measure blood flow deep inside the tissue and may be affected by surrounding tissue noise.

Methods: In this study, we propose a newly designed ADC with over 20-bit resolution. The superior performance was achieved by shaping the quantization noise with a [Formula: see text] sigma-delta modulator (SDM), and filtering the shaped noise at high frequencies by a digital decimation filter.

Results: Designed in a mature 0.35 μm CMOS technology and powered by a 3.3 V voltage supply, the proposed SDM integrated circuits (IC) model achieved a signal to noise and distortion ratio (SNDR) of 109.5 dB, and an effective number of bits (ENOB) of 17.9-bit in an 8 MHz bandwidth. Eight identical SDMs were integrated onto one chip, and the entire layout occupied an area of 4.8 mm × 5 mm. A total of sixteen 8-channel SDM IC models were connected to all elements of the array transducer.

Conclusion: Simulated performance with blood flow evaluation datasets using 12-bit and 20-bit ADCs demonstrates that the proposed 20-bit ADC provides superior overall performance on image contrast and estimation accuracy of the blood speed.

Significance: Owing to these advantages, the 20-bit ADC shows promise for future development of ultrasound imaging systems, especially for color Doppler imaging.
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http://dx.doi.org/10.1109/TBME.2019.2938275DOI Listing
August 2019

Ultrahigh Frequency Ultrasonic Transducers Design with Low Noise Amplifier Integrated Circuit.

Micromachines (Basel) 2018 Oct 12;9(10). Epub 2018 Oct 12.

Department of Ophthalmology and Biomedical Engineering, University of Southern California, Los Angeles, CA 90089-1111, USA.

This paper describes the design of an ultrahigh frequency ultrasound system combined with tightly focused 500 MHz ultrasonic transducers and high frequency wideband low noise amplifier (LNA) integrated circuit (IC) model design. The ultrasonic transducers are designed using Aluminum nitride (AlN) piezoelectric thin film as the piezoelectric element and using silicon lens for focusing. The fabrication and characterization of silicon lens was presented in detail. Finite element simulation was used for transducer design and evaluation. A custom designed LNA circuit is presented for amplifying the ultrasound echo signal with low noise. A Common-source and Common-gate (CS-CG) combination structure with active feedback is adopted for the LNA design so that high gain and wideband performances can be achieved simultaneously. Noise and distortion cancelation mechanisms are also employed in this work to improve the noise figure () and linearity. Designed by using a 0.35 μm complementary metal oxide semiconductor (CMOS) technology, the simulated power gain of the echo signal wideband amplifier is 22.5 dB at 500 MHz with a capacitance load of 1.0 pF. The simulated at 500 MHz is 3.62 dB.
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http://dx.doi.org/10.3390/mi9100515DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6215185PMC
October 2018

High Frequency Needle Ultrasonic Transducers Based on Lead-Free Co Doped NaBiTi₄O Piezo-Ceramics.

Micromachines (Basel) 2018 Jun 10;9(6). Epub 2018 Jun 10.

Department of Ophthalmology and Biomedical Engineeing, University of Southern California, Los Angeles, CA 90089-1111, USA.

This paper describes the design, fabrication, and characterization of tightly focused (ƒ-number close to 1) high frequency needle-type transducers based on lead-free NaBiTiCoO (NBT-Co) piezo-ceramics. The NBT-Co ceramics, are fabricated through solid-state reactions, have a piezoelectric coefficient of 32 pC/N, and an electromechanical coupling factor of 35.3%. The high Curie temperature (670 °C) indicates a wide working temperature range. Characterization results show a center frequency of 70.4 MHz and a -6 dB bandwidth of 52.7%. Lateral resolution of 29.8 μm was achieved by scanning a 10 μm tungsten wire target, and axial resolution of 20.8 μm was calculated from the full width at half maximum (FWHM) of the pulse length of the echo. This lead-free ultrasonic transducer has potential applications in high resolution biological imaging.
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http://dx.doi.org/10.3390/mi9060291DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6187828PMC
June 2018

Fabrication and Characterization of High-Frequency Ultrasound Transducers Based on Lead-Free BNT-BT Tape-Casting Thick Film.

Sensors (Basel) 2018 Sep 19;18(9). Epub 2018 Sep 19.

Department of Ophthalmology and Biomedical Engineering, National Institutes of Health (NIH) Transducer Resource Center, University of Southern California, Los Angeles, CA 90089, USA.

A lead-free 0.94(NaBi) TiO₃-0.06 BaTiO₃ (BNT-BT) thick film, with a thickness of 60 μm, has been fabricated using a tape-casting method. The longitudinal piezoelectric constant, clamped dielectric permittivity constant, remnant polarization and coercive field of the BNT-BT thick film were measured to be 150 pC/N, 1928, 13.6 μC/cm², and 33.6 kV/cm, respectively. The electromechanical coupling coefficient was calculated to be 0.55 according to the measured electrical impedance spectrum. A high-frequency plane ultrasound transducer was successfully fabricated using a BNT-BT thick film. The performance of the transducer was characterized and evaluated by the pulse-echo testing and wire phantom imaging operations. The BNT-BT thick film transducer exhibits a center frequency of 34 MHz, a -6 dB bandwidth of 26%, an axial resolution of 77 μm and a lateral resolution of 484 μm. The results suggest that lead-free BNT-BT thick film fabricated by tape-casting method is a promising lead-free candidate for high-frequency ultrasonic transducer applications.
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http://dx.doi.org/10.3390/s18093166DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6165567PMC
September 2018

PMN-PT Single Crystal Ultrasonic Transducer With Half-Concave Geometric Design for IVUS Imaging.

IEEE Trans Biomed Eng 2018 09 18;65(9):2087-2092. Epub 2017 Dec 18.

As the key component of intravascular ultrasound (IVUS) imaging systems, traditional commercial side-looking IVUS transducers are flat and unfocused, which limits their lateral resolution. We propose a PMN-PT single crystal IVUS transducer with a half-concave geometry. This unique configuration makes it possible to conduct geometric focusing at a desired depth. To compare performances, the proposed and the traditional flat transducer with similar dimensions were fabricated. We determined that the half-concave transducer has a slightly higher center frequency (35 MHz), significantly broader -6 dB bandwidth (54%) but a higher insertion loss (-22.4 dB) compared to the flat transducer (32 MHz, 28%, and -19.3 dB, respectively). A significant enhancement of the lateral resolution was also confirmed. The experimental results are in agreement with the finite element simulation results. This preliminary investigation suggests that the half-concave geometry design is a promising approach in the development of focused IVUS transducers with broad bandwidth and high lateral resolution.
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http://dx.doi.org/10.1109/TBME.2017.2784437DOI Listing
September 2018

Self-Focused AlScN Film Ultrasound Transducer for Individual Cell Manipulation.

ACS Sens 2017 Jan 11;2(1):172-177. Epub 2017 Jan 11.

Department of Biomedical Engineering and NIH Transducer Resource Center, University of Southern California , Los Angeles, California 90089-1111, United States.

Precise cell positioning is indispensable in the fields of biophysics and cellular biology. Acoustic microbeam produced by a highly focused ultrasound transducer has recently been investigated for a particle or cell manipulation. By virtue of the relatively good piezoelectric property, Sc doped AlN film was introduced for a highly focused ultrasound transducer application. Using a sputtering approach, a self-focused AlScN film based device has been designed, fabricated, and characterized at a frequency of ∼230 MHz. It had a narrow lateral beam width (∼8.2 μm). The AlScN ultrasound transducer was not only shown to be capable of remote controlling a single 10 μm polystyrene microsphere in distilled water, but also demonstrated to possess the capability to manipulate without contact individual 10 μm epidermoid carcinoma cell in two dimensions within a range of hundreds of micrometers in phosphate buffered saline. Most importantly, the cell manipulation was realized in continuous mode and no switch-on and -off operation was needed. These results suggest that self-focused AlScN film ultrasound transducer is a promising candidate for biomedical and molecular biology applications.
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http://dx.doi.org/10.1021/acssensors.6b00713DOI Listing
January 2017

Contactless microparticle control via ultrahigh frequency needle type single beam acoustic tweezers.

Appl Phys Lett 2016 10 27;109(17):173509. Epub 2016 Oct 27.

NIH Resource Center for Medical Ultrasonic Transducer Technology and Department of Biomedical Engineering, University of Southern California , Los Angeles, California 90089, USA.

This paper reports on contactless microparticle manipulation including single-particle controlled trapping, transportation, and patterning via single beam acoustic radiation forces. As the core component of single beam acoustic tweezers, a needle type ultrasonic transducer was designed and fabricated with center frequency higher than 300 MHz and -6 dB fractional bandwidth as large as 64%. The transducer was built for an -number close to 1.0, and the desired focal depth was achieved by press-focusing technology. Its lateral resolution was measured to be better than 6.7 m by scanning a 4 m tungsten wire target. Tightly focused acoustic beam produced by the transducer was shown to be capable of manipulating individual microspheres as small as 3 m. "USC" patterning with 15 m microspheres was demonstrated without affecting nearby microspheres. These promising results may expand the applications in biomedical and biophysical research of single beam acoustic tweezers.
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http://dx.doi.org/10.1063/1.4966285DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5085970PMC
October 2016

Ultrahigh Frequency (100 MHz-300 MHz) Ultrasonic Transducers for Optical Resolution Medical Imagining.

Sci Rep 2016 06 22;6:28360. Epub 2016 Jun 22.

School of Microelectronics, Xidian University, Xi'an 710071, China.

High resolution ultrasonic imaging requires high frequency wide band ultrasonic transducers, which produce short pulses and highly focused beam. However, currently the frequency of ultrasonic transducers is limited to below 100 MHz, mainly because of the challenge in precise control of fabrication parameters. This paper reports the design, fabrication, and characterization of sensitive broadband lithium niobate (LiNbO3) single element ultrasonic transducers in the range of 100-300 MHz, as well as their applications in high resolution imaging. All transducers were built for an f-number close to 1.0, which was achieved by press-focusing the piezoelectric layer into a spherical curvature. Characterization results demonstrated their high sensitivity and a -6 dB bandwidth greater than 40%. Resolutions better than 6.4 μm in the lateral direction and 6.2 μm in the axial direction were achieved by scanning a 4 μm tungsten wire target. Ultrasonic biomicroscopy images of zebrafish eyes were obtained with these transducers which demonstrate the feasibility of high resolution imaging with a performance comparable to optical resolution.
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http://dx.doi.org/10.1038/srep28360DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4916450PMC
June 2016

Design of matching layers for high-frequency ultrasonic transducers.

Appl Phys Lett 2015 Sep 24;107(12):123505. Epub 2015 Sep 24.

NIH Resource Center for Medical Ultrasonic Transducer Technology and Department of Biomedical Engineering, University of Southern California , Los Angeles, California 90089, USA.

Matching the acoustic impedance of high-frequency (≥100 MHz) ultrasound transducers to an aqueous loading medium remains a challenge for fabricating high-frequency transducers. The traditional matching layer design has been problematic to establish high matching performance given requirements on both specific acoustic impedance and precise thickness. Based on both mass-spring scheme and microwave matching network analysis, we interfaced metal-polymer layers for the matching effects. Both methods hold promises for guiding the metal-polymer matching layer design. A 100 MHz LiNbO transducer was fabricated to validate the performance of the both matching layer designs. In the pulse-echo experiment, the transducer echo amplitude increased by 84.4% and its -6dB bandwidth increased from 30.2% to 58.3% comparing to the non-matched condition, demonstrating that the matching layer design method is effective for developing high-frequency ultrasonic transducers.
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http://dx.doi.org/10.1063/1.4931703DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4583513PMC
September 2015

Multi-frequency intravascular ultrasound (IVUS) imaging.

IEEE Trans Ultrason Ferroelectr Freq Control 2015 Jan;62(1):97-107

Acute coronary syndrome (ACS) is frequently associated with the sudden rupture of a vulnerable atherosclerotic plaque within the coronary artery. Several unique physiological features, including a thin fibrous cap accompanied by a necrotic lipid core, are the targeted indicators for identifying the vulnerable plaques. Intravascular ultrasound (IVUS), a catheter-based imaging technology, has been routinely performed in clinics for more than 20 years to describe the morphology of the coronary artery and guide percutaneous coronary interventions. However, conventional IVUS cannot facilitate the risk assessment of ACS because of its intrinsic limitations, such as insufficient resolution. Renovation of the IVUS technology is essentially needed to overcome the limitations and enhance the coronary artery characterization. In this paper, a multi-frequency intravascular ultrasound (IVUS) imaging system was developed by incorporating a higher frequency IVUS transducer (80 to 150 MHz) with the conventional IVUS (30-50 MHz) system. The newly developed system maintains the advantage of deeply penetrating imaging with the conventional IVUS, while offering an improved higher resolution image with IVUS at a higher frequency. The prototyped multifrequency catheter has a clinically compatible size of 0.95 mm and a favorable capability of automated image co-registration. In vitro human coronary artery imaging has demonstrated the feasibility and superiority of the multi-frequency IVUS imaging system to deliver a more comprehensive visualization of the coronary artery. This ultrasonic-only intravascular imaging technique, based on a moderate refinement of the conventional IVUS system, is not only cost-effective from the perspective of manufacturing and clinical practice, but also holds the promise of future translation into clinical benefits.
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http://dx.doi.org/10.1109/TUFFC.2014.006679DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4522164PMC
January 2015

The effect of surface modification on the magnetic properties of CoFe2O4 nano-particles synthesized by the hydrothermal method.

J Nanosci Nanotechnol 2010 Oct;10(10):6395-9

Department of Physics and Key Laboratory of Acoustic and Photonic Materials and Devices of Ministry of Education, Wuhan University, Wuhan 430072, PR China.

Cobalt ferrite (CoFe2O4) nano-particles were synthesized by the hydrothermal method with the addition of a surfactant sodium bis(2-ethylhexyl) sulphosuccinate (AOT). Characterization measurements including X-ray diffraction, transmission electron microscopy and Fourier transform infrared spectroscopy showed that all the final products were single-phase CoFe2O4 nano-crystals with AOT molecules bonding to the surfaces, the average crystallite sizes were all near 25 nm, and the lattice constant increased with the increasing mass of AOT. The magnetic hysteresis loops measured at room temperature indicated that the bonding of the AOT to the surfaces led to an increase of the saturation magnetization (Ms), the coercivity (Hc) and the remanence ratio (Mr/Ms). Furthermore, as the concentration of AOT reached the critical micelle concentration (CMC), turning points were observed in the the curves of Hc, Mr/Ms and K(eff) (effective magnetic anisotropy constants) versus. the mass of AOT due to the formation of the AOT micelles.
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http://dx.doi.org/10.1166/jnn.2010.2518DOI Listing
October 2010
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