Research On Improvement Of Microwave Sensor Performance Based On Active Device And Microfluidic Design

When the microwave incident signal radiates through the measured object,the difference of dielectric properties inside the material will result in the change of microwave detection parameters.Thus,the relation between a certain physical quantity and the corresponding parameter change can be constructed.When specifically designed microfluidic channels are integrated into microwave sensors,the detection path of the tested biochemical solution can be planed and the quantitative and formable tests can be ensured,excluding the direct interference of external environment.Therefore,microfluidic is helpful to improve the detection accuracy,sensitivity and other core parameters of the sensor.In addition,integrating active devices can increase power injection,improve quality factor and realize high resolution detection finally.In this paper,different microwave sensing units are designed for the composition analysis and concentration measurement of complex biochemical solution.And the working mechanism and sensing performance of different microwave units are studied.In this thesis,constructing the sensor microwave detection model is taken as the starting point,and a joint optimization scheme based on microfluidic channel and microwave sensor is used to improve the sensor sensitivity.The sensor resolution is further optimized by using the active device to compensate the loss of passive structure.Finally,the physical mapping relationship model between microwave parameters and biochemical samples is built and the microwave sensing mechanism is studied.The main research content of this thesis can be summarized as follows.(1)The influence of different microfluidic channels on the performance of microwave sensors is investigated.Firstly,a circular antenna detection structure combined with a complementary split ring resonator(CSRR)is designed.The ground of the microwave sensor adopts the partial ground structure design.The quality factor is improved to 76.5 by parameter optimization.Then,the influence of different microfluidic channels on the detection sensitivity is studied.Four microfluidic channels,including CSRR boundary,metal gap,metal region and serpentine line,are designed to characterize the concentration of ethanol solution by frequency shift,amplitude,phase and other parameters.The research shows that different microfluidic channels have distinct abilities to gather electric fields,so the appropriate design of microfluidic channels can improve detection sensitivity.This study provides an essential reference for the design of microfluidic channels for microwave solution concentration detection.(2)The miniaturization application scheme of microwave sensor is studied.Firstly,the structure of the inductive split-ring resonator(ISRR)and its integrated miniaturization scheme with the electrically tunable variable capacitance diode(VCD)are studied.Then,based on the analysis of coupling strength and electromagnetic loss between microstrip transmission line and resonant unit,the frequency modulation mechanism of loading VCD into the inductance region,capacitance region and coupling region of the ISRR unit is explored.Then,VCD is applied in the design of the array sensor.It can adjust the resonant frequency without changing the resonant element’s area and reduce the array design’s complexity.Finally,the concentration of the phosphate solution is measured by an array sensor.The results show that the sensitivity is higher at 3.095 GHz resonant frequency,the resonant frequency changes by0.007 MHz,and the resonant amplitude changes by 0.042 d B.This study expands the application of miniaturized microwave sensors and saves the unit area.(3)The influence of an active positive feedback loop in microwave sensors on detection resolution and sensitivity is studied.Firstly,a filter microwave sensor based on a curved line resonant element is designed.A low noise amplifier(LNA)is applied to the active,positive feedback loop,and its influence on the system quality factor is discussed.The LNA can compensate for the loss generated by the device and solution,and increase the quality factor from 47 to 295,thus improving the detection resolution.Then,the detection performance of the active microwave sensing system is analyzed,and the ethanol and glucose solutions are tested,respectively.The multiple linear regression method is used to analyze the measured data,including phase,amplitude and frequency.The linear regression correlation coefficient R~2 is 0.997.This method improves the detection accuracy.Finally,to broaden the application range of the sensor system,the detection ability for mixed solution is explored.The mixed solution of ethanol and glucose is used for testing.The principal component analysis method is used to process the detection results of the hybrid solution.It is found that the two components and their concentrations in the solution can be successfully distinguished by using amplitude and frequency.This study shows that the application of active devices can improve sensors’resolution and detection performance.