Acoustic trapping with a high frequency linear phased array

Abstract

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...

A feasibility study of in vivo applications of single beam acoustic tweezers

“…The trapping performance of both types of SBAT was demonstrated previously. 11,12 Needle type transducers may be positioned closer to the particles to be trapped or cells inside of blood vessels transcutaneously after piercing through skin and tissues. The acoustic beam generated by phased array transducers could be dynamically focused at different depths and angles; therefore, no mechanical movement of transducer is required.…”

Screen-printed ultrasonic 2-D matrix array transducers for microparticle manipulation

“…More recently, independent trapping and manipulation of multiple individual microparticles were demonstrated with an electronically controlled 64-element circular transducer array [37]. The use of a one-dimensional (1-D) ultrasound array to manipulate particle agglomerates perpendicular to the direction of wave propagation was also studied [38][39][40]. Although implementation of two-dimensional (2-D) arrays could increase dexterity [10,12], this is still relatively rare in the literature, partly because of the challenges in fabrication, electrical interconnection and system integration of reliable, miniature 2-D arrays based on traditional machining and packaging methods.…”

Acoustic tweezers for studying intracellular calcium signaling in SKBR-3 human breast cancer cells

“…It was experimentally realized that individual lipid droplets and leukemia cells were trapped with a single element focused transducer at 30 MHz and 200 MHz, respectively [15,16]. A 26 MHz linear phased array was also exploited for directing a polystyrene microbead to a targeted position via electronic scanning of the array elements [17]. More recently, a 193 MHz lithium niobate (LiNbO 3 ) focused transducer was applied to studying the elastic property of breast cancer cells (MCF-7).…”