Mems Ultrasonic Separation Of The Two-dimensional Normal Modes And Experimental Analysis

It shows special advantages to remove suspended particles from a liquid with acoustic radiation forces in MEMS. Many attempts in China and abroad have been reported in this field, and the ultrasonic micro-separator mainly depends on multi-layer resonance structure based on the model with plane standing wave and laminar flow. There are also some researches invlove MEMS devices based on two-dimensional ultrasonic standing wave field. But there hasn't been a complete theoretical acoustic model of two-dimensional ultrasonic normal mode for MEMS separator until today, and the clean stream and streams collecting particles from the outlets haven't shown up in the separation tests based on the two-dimensional normal mode.Two-dimensional normal mode of the MEMS ultrasonic separator is investigated in this paper and a theoretical acoustic model of the fluid cavity in the separator has been established. Two- dimensional normal modes in the fluid cavity of the MEMS ultrasonic separator show up in the separation tests, and the clarified stream and the streams collecting a bunch of particles are coming from the outlets. The main tasks are shown as follows:1. The two-dimensional vibration system formed with rectangular section in the fluid cavity of MEMS ultrasonic separator is investigated according to the theory of sound and electricity analogy. A set of analytic solutions in the two-dimensional ultrasonic vibration system are derived from the wave equation, and helps to establish a two-dimensional equivalent circuit model of the rectangular section of the fluid cavity. According to this model, the resonance frequencies of the two-dimensional normal mode are listed. Simulations using finite-element method with ANSYS software are used to demonstrate the validity of the model and help to select the best exciting frequencies.2. The diameter of the inlet and outlets of the fluid cavity is enlarged, so as to establish the flow in the channel. The benefits for the"swallow tail"structure nearby the inlet and outlets are further analyzed. The dimension of the fluid cavity of the MEMS ultrasonic separator is introduced based on the acoustic theory, and also the separators with two sizes are designed.3.An experimental platform based on two-dimensional ultrasonic separation is built, including the design of separator and the piping system, excitation of the normal mode in the fluid cavity, recorder of the separating results, preparation for the suspending liquid, etc. The experiments using single PZT to excite (2,1) normal mode and two anti-phase PZT to excite (1,1) normal mode have shown good results, and various factors influencing the separation performance are investigated, including the layout of PZT,concentrations of the suspending liquid, the wire connections, the power of ultrasonic excitation and so on. Experiments demonstrate that these factors can not fundamentally improve the separation performance, and the direction for further investigation is proposed.