Research On High Resolution Active Microwave Sensor Based On Negative Resistance Compensation Technology

Microwave sensors are widely used in the detection of material composition,purity and quality in agricultural,biological,medical and industrial fields due to their advantages of fast response,simple operation and easy integration with circuits.With the advancement of science and technology,various fields have put forward higher requirements for the resolution,accuracy and sensitivity of microwave sensors,but traditional microwave sensors are difficult to meet the development needs of various industries today.Therefore,increasing the resolution,sensitivity and multifunctional integration of microwave sensors has become the mainstream direction of many researchers.Under this background,this paper designs and manufactures two integrated negative resistance circuit（NRC）high-resolution active microwave sensors is used for glucose concentration characterization and iron powder particle content detection in lubricating oil,respectively.The specific research results are as follows:（1）Research on high-resolution dual substrate integrated waveguide re-entrant cavity resonators（DSIW-RECRs）glucose active sensor based on negative resistance compensation technologyTwo passive SIW-RECRs are vertically stacked to implement a miniaturized dual RECRs sensor.Only one NRC is innovatively proposed to be connected with these two RECRs in the common stacked metal layer between them and implement an active dual RECRs sensor,and the corresponding equivalent lumped circuit mode is proposed to analyze the dielectric sensing characteristics.Then,the compensated power obtained from the NRC is simultaneously fed into these two RECRs embedded with two microfluidics,and the Q-factor of either of these two RECRs can be greatly enhanced by simply changing the bias voltages of the transistor and varactor in the NRC.Finally,the active sensor is utilized to perform high-resolution detection to glucose solutions in high concentration range from 100 to 1000 mmol/L and low concentration range from 1 to 50mmol/L.By gradually approximating the resonant frequency self-shift noiseΔf _Aself(Δf _Bself)of the active RECR-A（RECR-B）by the resonant frequency shiftΔf_s determined by glucose solutions,minimum detectable glucose concentration of 1 mmol/L is experimentally achieved.The linear relationship between theΔf_s and the glucose concentration is experimentally demonstrated,and shows good potential for glucose sensing.（2）High-resolution active folded substrate integrated waveguide re-entrant cavity resonator（FSIW-RECR）for detection of iron powder particle content in lubricating oil based on negative resistance compensation technology sensor researchBased on the conventional rectangular SIW,two capacitive columns are introduced to form a RECR,which is then folded by a folding technique to form a passive FSIW-RECR sensor.Using the negative resistance compensation technique,the NRC is integrated on top of the passive FSIW-RECR sensor to form a high-resolution active FSIW-RECR sensor for the detection of iron powder particles in lubricating oil.In order to facilitate the construction of the experimental platform,a rectangular groove is etched in the sensing area of the passive resonant cavity for placing the polytetrafluoroethylene（PTFE）tube loaded with the sample to be tested.When performing sample detection,the resolution can be adjusted by varying the dc bias voltage of the transistor and the varactor diode in the NRC to meet the high-resolution detection of iron powder particles in the lubricating oil.It is worth noting that a static magnet device is introduced in the sensing region to increase the sensitivity of the sensor and thus further improve the detection lower bound of the sensor.At the same time,the effect of different static magnetic field strengths on the detection of iron powder content has been explored experimentally.By making the resonant frequency shiftΔf caused by the changing content of iron powder particles in the lubricating oil gradually approach the resonant frequency self-shifting noiseΔf_self of the sensor,the lower detection limit of the sensor’s iron powder content is obtained experimentally as 200 mg/L...