Bessel beam generation and characterization by surface acoustic waves in microfluidic systems

In this study, the surface acoustic wave (SAW) and surface acoustic wave Bessel beams were generated by using the inter digital transducers (IDT) fabricated on the lithium niobate (LiNbO3) piezoelectric substrate. And then SAWs were examined as optically and electrically. Simulations were carried out with Comsol 5.3a program by using finite element method (Finite Element Method, FEM) in order to examine the surface behavior of Rayleigh SAWs and SAW Bessel beams. The samples were fabricated by using standard photolithography method. Firstly in this study, standing SAWs on the substrate were generated by using IDT pairs with constant finger widths. In the light of the simulation and experimental results obtained from this sample, it was foreseen that the SAW Bessel beams can be obtained with positioned IDTs have a certain tilt angle with the acoustic axis on the LiNbO3 substrate. And the SAW Bessel beam IDT pairs with constant finger width were designed and fabricated as have 15o and 20o tilt angles with acoustic axis. Also, in order to obtain SAW Bessel beam with a wide frequency range, SAW Bessel beam IDT pairs were designed and fabricated as variable finger width. Electrical characterization of SAWS have been obtained frequency spectrums in the spectrum analyzer by using as an sensing element the other and as SAW exciting one of the opposite IDTS. For the visualization of SAWS were experienced different methods such as nano-sized smoke particles, Schlieren optic, interference method, thin liquid film application and interference of thin liquid films. The resonance frequency of the generated IDT pairs in this study was calculated as 13.3 MHz with simulations. As a result of the electrical measurement, the resonance frequency was determined as 13.52 MHz in good agreement with simulations. SAW Bessel beams were generated for the first time. Since SAW Bessel beams were generated with a simple system using only two transducers, this simple system is expected to contribute to the development of simple particle manipulation approaches, which can be used in microfluidic systems.