Study Of A Microdevice For Micro/Nano Particles Ultrasonic Separation

On the microparticles testing and identification, the first step is to separate different kinds of particles from the surrounding fluid medium. Therefore, an effective and uncontaminating separation method is very important. Compared with other methods for micro/nano particle separation, the ultrasonic method operates continuously, preserves the particles of interest in suspension for subsequent use without fouling the separation equipments, and can be used to separate those which are not charged particles, or nonmagnetic particles as well, so that the ultrasonic method is much more suitable for the bio-particle separation. Due to rapid development of MEMS technology over the past 20 years, the microdevices have great advantages in the volume, weight and cost price with the aid of MEMS technology, which brings up brand-new methods in designing and fabricating ultrasonic separation devices. The ultrasonic separation microdevices can realize the miniaturization of the device, achieve the on-chip microparticle separation, and will do some basic work for the particle testing on the same chip in further. This thesis proposes and investigates a MEMS based ultrasonic device for on-chip separation of micro and/or nano particles.On the basis of the principles of ultrasonic separation, the forces acting on particles in the microdevice are studied and the analytical mode of the forces is presented. And then, the motion and aggregation character of particles in the fluid medium in microdevice are analyzed, the factors affecting particles separation are studied in detail. Based on the analyses for different structures in the microdevice, the design of the device is finished and presented, and the process of the micromachining is fixed and realized. In this thesis, the analytical method and finite element method are used to analyze the vibration modes and the acoustic field of the microdevice. Two parts of the acoustic field, i.e., the acoustic pressure caused by the membrane vibration and the damping pressure caused by the fluid medium, are studied separately, and then the effective acoustic pressure acting on the particles is obtained. Moreover, with these analyses, we obtain the separation effects of different kinds of particles when the microdevice vibrates at different frequencies. Based on the work presented in this thesis, the conclusions and some suggestions for the research works on the same project in future are presented at last.