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MEMS ultrasonic separation chamber of the two-dimensional normal modes of excitation technology research

Author: XiaoHanLi
Tutor: DingJieXiong
School: University of Electronic Science and Technology
Course: Precision instruments and machinery
Keywords: sweep MEMS acoustic separation two‐dimensional normal mode
CLC: TB559
Type: Master's thesis
Year: 2011
Downloads: 5
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Abstract

Acoustic separation technology combined with MEMS opens up new areas for the application in microfluidic system,which has great advantages and extensive application foreground. Initially, most of the reported separators employ in-plane standing waves(1D) for concentrating particels into pressure node planes of resonator. However, a less efficiency of separation related to structure(1D mode) is undesired in the development of the separator. In order to increase efficiency, research has turn to two-dimension ultrasonic waves field there is obvious advantage in flow cavity. Now, various MEMS device based on two-dimensional ultrasonic standing waves field is developing. Different strategies have been suggested for achieving 2D ultrasonic resonances in microfluidic device. There are many ways to excite 2D ultrasonic standing waves.A new way which two-dimensional normal mode is employed to build separator ultrasonic resonance is proposed. Theoretical model of excitation of normal mode in cavity is established and the validation experiment is completed. Separation experiment is carry out in this paper. The mian contents are listed as follows:1.The resulting ultrasonic field that occurs in the fluid gap trapped between the vibrating plan and the refecting surface is researched. By using of the relationship between plan surface vibration and ultrasonic field in the fluid, the exciting technology of the two-dimensional normal mode of cavity of separator is discussed. The spatial distribution of acoustic radiation force potential in the cross-section of the cavity is simulated with Matlab. It is valid that the two-dimensional normal mode exists in the cavity.2.The problem involving actual excitation of two-dimensional normal mode in the cavity has been researched and verified. It includes: relative shortage of acoustic radiation force caused by normal mode coexist in the cavity and absolute shortage of acoustic radiation force caused by fixed operation mode of separator. According to the theroy about interference of sound wave,a couple of sources and proportional factorηare involed to solve the problem of normal modes coexist in the cavity. A novel way which frequency modulating signal is input to transducer is proposed to improve absolute acoustic radiation force on particels. Combination of above solutions, two transducers mounted on the antinodes of sound pressure of separator driven with out-of-phase frequency modulating signal are employed to actuate (1,1)mode of cavity.3.An experimental platform is bulit. Experiment results have a good agreement with analysis. The (1,1)mode of the separator is excited, and separation is carried out. Various factors influencing the separation performance are inverstigated, including concentrations of the suspending liquid, experiment temperature, impedance characteristics of the separator and so on.

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