Research On Flow Rate Sensing Based On Closed-loop Fiber Optofluidic Manipulation

Microfluidic chip have been widely employed in the research and application of the drug screening,the chemical synthesis and analysis,and biological cell / macromolecule.It has a wide application prospect because of its high throughput detection ability.Among them,the control of microflow velocity plays a vital role in the application of these microfluidic chips.Of course,some microflow chip applications that require flow control,which can be met by the direct control of a high precision syringe pump.However,in other applications which need more accurate and real-time flow control,taking the time delay and flow rate deviation from the direct use of syringe pump and the high integration characteristics of microflow channel into account,it urgently needs a high precision,realtime and integrate friendly for monitoring flow rate.In this thesis,the optofluidic manipulator with the flat end and single-mode fiber applied to manipulate the polystyrene microspheres in the microfluidic environment.The flow rate of the microflow detected by monitoring the manipulation length of the microspheres in open loop manipulation mode and the output power of the laser in closedloop.In the open loop mode,and the manipulation length of the microsphere changes with the change of the microfluidic flow rate while the output power of the laser is constant.In the closed-loop control mode,the manipulation distance of the microspheres stabilized by feedback control,that is,the output power of the laser varied by microfluidic flow rate.In addition,in order to to meet the working environment which satisfy the open loop and closed-loop manipulation mode.We designed a closed-loop microfluidic steering platform in this project,which contains software and hardware implementation.The implementation of the hardware part is mainly to meet the closed-loop optofluidic manipulation of the closed-loop circuit.The software part completes the whole control flow,including the acquisition of the microscope image,the image processing and identify the location of the microsphere and feedback control,user interface interaction,information display and other functions.In order to understand the principle of optofluidic and the principle of flow rate sensing,this thesis has a brief theoretical analysis on the mechanism of light force and the application in microflow rate sensing.It verified that the feasibility of the flow rate sensing based on closed-loop optofluidic manipulation.The experiment of flow rate sensing tested the dynamic range,sensitivity,stability and repeatability of the measurement of the flow rate sensing scheme both in the open loop mode and closedloop mode.The lowest limit 10 nl/min of the flow rate measurement and the maximum manipulation distance 550 ?m achieved in the open loop measurement mode.In the closed-loop control mode.We obtain a maximum of 100,000 nl/min flow rate measurements under the condition of a pump laser with a maximum output power of 300 mW and wavelength of 980 nm,and the closed loop manipulation distance 15 ?m.Combined with the open loop and closed-loop control mode,the measurement range of amost 4 orders of magnitude is achieved,that is,the dynamic measurement range of 10 to 100000 nl/min.Finally,by comparing the flow rate sensors based on the different principle of flow rate sensing,it proves that the flow rate sensor proposed in this project can satisfiy the requirement of the dynamic measurement range while taking the measurement sensitivity into account.