Generation of a 25-MHz high-frequency ultrasound beam for acoustic particle trapping

Abstract

In microfluidic particle manipulation using an acoustic force, two main issues should be resolved, The intensity of the focused ultrasound beam must be high enough to penetrate deep into the channel device and thus results in a higher trapping force compared to the drag force arising from the surrounding fluidic flow. At the same time, the temperature change in the focal zone should be minimized for protection of the trapped particles. In order to address the aforementioned issues, in this research, an especially-designed high-frequency ultrasound transducer (HFUT) was developed. Lead zirconate tinanate-4 (PZT-4) was chosen as piezoelectric material to improve the durability of the transducer when the transducer was activated by a long pulse. The center frequency was 25 MHz, and the 1–3 piezoelectric composite structure was employed in order to achieve a very low f-number (focal depth/aperture size = 1), resulting in a highly-focused ultrasound beam. The developed transducer was successfully driven by using pulsed and continuous chirp signals with duty factors of 50% and 100%, respectively. The temperature change was measured using a bulk sample of polydimethylsiloxane (PDMS) and was found to be less than 1.6 °C. Hence, these results show that the proposed transducer is promising for acoustic particle and cell manipulation in microfluidic channel devices.