The Investigation Of LC-Type Multi-Functional Passive Wireless Sensors

With the rapid development of internet of things and sensor network technology,more and more new requirements have been put forward for the design of sensor nodes due to the complexity and diversity of application scenarios.LC-type passive wireless sensors are based on magnetic coupling principle,which can transform the measured parameters into sensor's resonant frequency,and detect it wirelessly through a readout coil.LC sensors have many advantages,such as simple structure,battery-free and high adaptability,which have attracted wide attention from researchers around the world.A traditional LC sensor can only realize one parameter detection at a time,which is difficult to meet the diversified needs of different applications.This dissertation is devoted to the research on the underlying technology of LC passive wireless sensors,especially the accomplishment of multi-parameters measurement using double resonance technology.The main research contents and innovations of this dissertation include:(1)The theoretical basis of LC passive wireless sensors technology is generally introduced,and the coupling distortion when multiple sensors work together is deeply studied and discussed.The research shows that when different LC sensors are close to each other,the magnetic field coupling between their inductors will lead to the deviation of resonant frequencies and crosstalk between the readout signals,resulting in the distortion of detection results.(2)Two kinds of flexible LC-type single parameter sensors are proposed,which can wirelessly monitor humidity and pressure using graphene oxide and micro-structured PDMS as the sensing material.The sensors' potential applications in the intelligent packaging and wound monitoring are studied,and the substrate bending effect and dielectric environment effect on the sensors' performance are emphatically analyzed.The experiments show that the sensitivity of the humidity sensor was-136.1khz/%RH in the range of 20%RH to 95%RH,and the sensitivity of the pressure sensor was-284.9khz/mm Hg from 0mm Hg to 200 mm Hg.(3)A novel symmetric dual-resonant circuit is proposed.The theoretical and simulation results show that the circuit has two working modes which are independent of each other,and the two resonant frequencies are regulated by a different capacitor respectively,which can effectively avoid the effect of inductive coupling distortion.Based on the circuit,an LC-type dual-parameters sensor is designed and fabricated,which can achieve the simultaneous measurement of humidity and pressure using two different frequencies.The sensor's humidity and pressure sensitivity is-67.7 k Hz/%RH and-48.5 k Hz/mm Hg,respectively.This dissertation focuses on the challenge of multiple parameters monitoring,which is difficult for traditional LC sensors,and proposes a symmetric dual-resonant circuit as a solution,whose two independent frequencies can be used to characterize two parameters to be measured.In addition,through the multiple utilizing of resonant frequencies and Q values,the circuit will be able to further realize simultaneous measurement of up to four parameters,which provides theoretical support and feasible scheme for the design of LC type multi-parameters sensors in more applications scenarios.