| The polluted water environment may contain heavy metal ions,like Pb,Cd,Hg,Cu,As,Cr,etc.,which are harmful to human body,besides metal elements needed by human body such as Na,K,Mg,Ca.In addition,there are salts of N and P elements that are likely to cause eutrophication.Fast and convenient testing the elements containing in water is important for water quality control.Combining microfluidic technology with the high-Q LC resonance structure,the small changes in the properties of the solution can be detected by the LC wireless sensor frequency-amplitude change,and then it is expected to realize the wireless detection of the ions in aqueous solution.Low-temperature co-fired ceramic（LTCC）technology has advantages in three-dimensional microchannel construction and passive integration,and is an ideal carrier for obtaining wireless microfluidic sensors.This thesis focused on the design,fabrication,and characterization of LTCC based microfluidic wireless sensors.The results are summarized as follows:1.Based on the equivalent circuit model of the LC resonant circuit,a kind of high-sensitivity LTCC wireless microfluidic sensor was designed.The flat microfluidic sensors without collapse and stratification were fabricated by LTCC technology.The initial frequency of the sensor is 250 MHz,and the wireless sensors were used as wireless signal test platform for various solutions investigation.2.The selected metal ion solutions including heavy metal ions(Pb2+,Cd2+,Cu2+),alkaline earth metal ions(Mg2+,Ca2+)and alkali metal ions（Na+,K+）with the concentrations from 0 to 100 m M were tested by as model solutions,respectively.For all the metal ion solutions,the amplitude of S11 gradually decreased when the concentrations of the solutions increased.The resonance frequencies of the sensor are almost the same with the increase of the concentration of metal ion solutions when the concentrations are within 5 m M.When the concentration of the metal ions increased to above 5 m M,the resonance frequencies of the sensor decreased with the increase of concentration of metal ions.When the concentration is 0-1 m M,theΔS11 of Pb（NO3）2,Ca（NO3）2,and KNO3 has a linear relationship with the concentration and the slopes were 1.05,1.27,and 0.73,respectively.The PCA method can be used to distinguish each metal ion at a concentration of 0.5 and 1 m M.The detection limit of the sensors for metal ion solutions was 5μM.The normalized sensitivity could reach 0.47%,which is higher than the reported electromagnetic microfluidic sensor.Combining the equivalent circuit model of the plate capacitor filled with liquid and the least square model,the origin of the variation of resonance frequency and S11 were investigated.The change of S11 amplitude was mainly affected by the conductivity.When the concentration is lower than 5 m M,the resonance frequency is mainly related to the dielectric constant.However,when the concentration is higher than 5 m M,the conductivity would be the main influencing factor.3.The response characteristics of the sensors to different concentrations of Na3PO4,Na2HPO4,NaH2PO4,Na2SO4,Na2CO3,NaCl solutions and Pb（CH3COO）2,Cd（CH3COO）2,Cu（CH3COO）2 solutions had been studied.It was found that the variation of S11 amplitude and resonance frequency with concentration was like that of metal ion solution,but the sensitivity was different.The sensors can be used to distinguish heavy metal ion acetate and heavy metal ion nitrate solution.In conclusion,a kind of wireless microfluidic sensor based on LTCC technology for real-time detecting ions in water was proposed.The wireless sensor was composed of a planar spiral inductor and parallel plate capacitor（LC）resonant antenna,which integrates with microchannel in the LTCC substrate between the capacitor plates.The sensors were used to detect different ionic solutions.The correlationship between the ion type and concentration of the solutions and the sensor frequency-amplitude signal parameters was revealed. |
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