Piezoelectric ceramics are currently of considerable interest for their capabilities of converting compressive/tensile stresses to an electric charge, or vice versa. Because ceramics cannot be cast and machined easily, additive manufacturing (AM) processes (3D printing technology) open an effective pathway in geometrical flexibility. However, the piezoelectric properties limit the application of printed ceramics. This work demonstrates that a piezoelectric-composite slurry with BaTiO 3 nanoparticles (100nm) can be 3D printed using Mask-Image-Projection-based Stereolithography (MIP-SL) technology. After a post-process, the density of 5.64g/cm 3 was obtained, which corresponds to 93.7% of the density of bulk BaTiO 3 (6.02 g/cm 3 ). The printed 1 Zeyu Chen and Xuan Song contribute equally to this paper 2 ceramic exhibits a piezoelectric constant and relative permittivity of 160 pCN -1 and 1350respectively. An ultrasonic transducer with printing focused piezoelectric element was fabricated to realize the energy focusing and ultrasonic sensing. A 6.28MHz ultrasonic scan was achieved by the transducer and successfully visualized the structure of a porcine eyeball.

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.

A high frequency ultrasonic phased array is shown to be capable of trapping and translating microparticles precisely and efficiently, made possible due to the fact that the acoustic beam produced by a phased array can be both focused and steered. Acoustic manipulation of microparticles by a phased array is advantageous over a single element transducer since there is no mechanical movement required for the array. Experimental results show that 45 lm diameter polystyrene microspheres can be easily and accurately trapped and moved to desired positions by a 64-element 26 MHz phased array. Similar to the trapping mechanism of optical tweezers, 1,2 when acoustic gradient force (from refraction) exceeds scattering force (from reflection), an object can be attracted and trapped by a tightly focused ultrasound beam. 3,4 The direct exposure of cells to the optical trapping laser beam may induce photodamage, 5 however, it was demonstrated that the thermal and mechanical effects in acoustic trapping are negligible when the energy is maintained in the diagnostic range. 6 Recently, high frequency single element ultrasonic transducers have been used to carry out single beam acoustic trapping. In these approaches, in order to move a trapped microparticle, a mechanical scanning stage has to be utilized to move the transducer and its focus. [7][8][9] In this paper, we present results showing that it is possible to trap and move microparticles with a high frequency ultrasonic linear phased array without mechanical movement of the transducer.An ultrasonic linear phased array transducer (or simply called phased array) is a transducer consisting of multiple small transducer elements, which usually are rectangular in shape and arranged on a straight line. Ultrasonic phased arrays have been widely used in biomedical imaging 10 and industrial nondestructive testing. 11 The advantages of phased array transducers over conventional single element transducers are their capabilities of steering the ultrasound beam into different directions and/or changing the focus at different depths, not by mechanically moving transducers but by applying electronic phase shift/time delays on the transmitting pulses to the elements of the phased array. Eliminating the mechanical movement of the transducer increases the system reliability and the speed of the experiment.A customized lead zirconate titanate (PZT-5 H) 2-2 composite linear phased array transducer was fabricated with traditional array technology. 12 The center frequency of the phased array is 26.3 MHz. The array has 64 small elements arranged on a straight line in the azimuthal direction. The elevation length and lateral width of one element are 2 mm and 24 lm, respectively. The kerf between two adjacent elements is 6 lm. The F-number of the phased array is 2.6.A field programmable gate array (FPGA) based 64-channel transmit beamformer and a 64-channel pulser were also developed to drive the phased array. The transmit beamformer could send out 128 (64 pairs) delayed trigger signals, 13 with whic...

Controlling cell functions for research and therapeutic purposes may open new strategies for the treatment of many diseases. An efficient and safe introduction of membrane impermeable molecules into target cells will provide versatile means to modulate cell fate. We introduce a new transfection technique that utilizes high frequency ultrasound without any contrast agents such as microbubbles, bringing a single-cell level targeting and size-dependent intracellular delivery of macromolecules. The transfection apparatus consists of an ultrasonic transducer with the center frequency of over 150 MHz and an epi-fluorescence microscope, entitled acoustic-transfection system. Acoustic pulses, emitted from an ultrasonic transducer, perturb the lipid bilayer of the cell membrane of a targeted single-cell to induce intracellular delivery of exogenous molecules. Simultaneous live cell imaging using HeLa cells to investigate the intracellular concentration of Ca2+ and propidium iodide (PI) and the delivery of 3 kDa dextran labeled with Alexa 488 were demonstrated. Cytosolic delivery of 3 kDa dextran induced via acoustic-transfection was manifested by diffused fluorescence throughout whole cells. Short-term (6 hr) cell viability test and long-term (40 hr) cell tracking confirmed that the proposed approach has low cell cytotoxicity.

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.