Study On The Quality Factor Control Technology Of The Microcantilever

Microcantilevers are nano-sensing devices with high sensitivity, wide applications in many areas such as the detection device used in atomic force microscopy, the transduction device applied in biosensors and so on. Quality factor is a physical parameter of microcantilever and an important pointer of the performance of microcantilever. Q is inversely proportional to the subjected damping of microcantilever. When a microcantilever works in the liquid condition, the quality factor decreases because of the effect of the liquid damping. For an atomic force microscopy, the decrease of quality factor of the key sensing device—the microcantilever will increase the scan speed but the sensitivity and resolution of microcantilever will decrease; however, if quality factor is too high, then the stability of the microcantilever will decrease accordingly; for biosensor, the resolution and sensitivity of microcantilever will increase because of the increase of the quality factor when the dynamic mode detection is used.In this thesis, the quality factor of the microcantilever based on dynamic mode of microcantilever is researched, and a digital quality factor controlling technique is designed. We tried to change the driving force and get the value of quality factor. The experiment results indicate that the function of digital control technique satisfies the preset requirement of the whole system. And, the amplitude-frequency curve and the phase-frequency curve of microcantilever will change accordingly in term of the quality factor.The followings are the main achievements of this thesis:1. Make research on the mechanism of quality factor and principles of controlling quality factor by solving the stimulated oscillation equation of microcantilever; the relation of oscillated microcantilever and exciting force is researched and the model to control quality factor is designed.2. Based on digital control technology, a system to control quality factor is developed, and the corresponding system control software is designed. Visual C language is applied for system programming.3. The designed control system of quality factor is applied to the microcantilever, and a Laser Doppler vibrometer is used to obtain its oscillation curve; comparisons of the experimental results of the oscillation curve of microcantilever with the control system of quality factor and without the control system are made. Thus the dynamic control of quality factor is realized.4. Analysis of the impact of circuit tuning of the quality factor on the phase-frequency curve and amplitude-frequency curve of the oscillated microcantilever and imaging interaction is made.