Research On Rf Sensor Based On Coplanar Waveguide With Limited Metal Thickness

As one of the important types of microwave planar transmission lines,coplanar waveguides have attracted the attention of scholars from various countries.However,the study of finite metal thickness coplanar waveguides is limited to theoretical research,and the research in practical aspects is blank.In the fields of industry,agriculture,biomedicine,and chemistry,the key analyzing a sample is how to accurately measure the change in the dielectric constant of the sample.Based on the theory of finite metal thickness coplanar waveguide transmission line and the principle of on-chip cancellation,the design and measurement of this RF sensor based on finite metal thickness coplanar waveguide are completed.The sensor signal transmission line is a coplanar waveguide transmission line with limited metal thickness,and is composed of two 3dB in-phase Wilkinson power splitters and a branch with a half-wavelength difference between the upper and lower paths.The structure has high symmetry and small volume.When working,the microwave signal input to the sensor is divided into two equal-amplitude in-phase signals by the Wilkinson power splitter,and then becomes two equal-amplitude inverting signals after passing through the upper and lower branches,and then used as a synthesis through the output The Wilkinson power divider of the device is synthesized.The reference object and the object to be measured are placed in the slots of the upper and lower branches respectively,and the offset effect is reflected by measuring the S parameter of the final signal to obtain the difference between the two materials.In this paper,two sensor structures with finite metal thicknesses of 35um and 70um were simulated,and the reference solution deionized water?dielectric constant 81?was placed on the upper and lower branches as the reference.The offset points S₂₁1 were-89.1dB and-90.7 dB,then place the lower half of the branch to be tested with dimethy-lacetamide?dielectric constant 37.8?,ethanol?dielectric constant 24.55?and propanol?dielectric constant 20.33?Simulation,as the difference between the dielectric constant of the test solution and the reference solution becomes larger,the frequency of the cancellation point and the change value of S₂₁ will be larger,which meets the theoretical expectations,and the structure with a metal thickness of 70um is respectively When equal amounts of acetamide,ethanol,and propanol with the same dielectric constant are added,the variation of offset point S₂₁1 and the reference is larger than the structure with a metal thickness of 35um,which effectively proves that thickening the metal thickness can improve the sensitivity of the device.In this paper,a tuning module is designed for the board used to deform the soft board easily,the error caused by the gold wire bonding technology,and some processing errors,and the tuning principle of the tuning structure is simulated and analyzed.The physical measurement verified the effectiveness of the tuning device and selected deionized water as the reference solution,anhydrous ethanol and n-propanol as the materials to be tested.The obtained test results were in line with the expectations of the simulation results.Correlation analysis and regression analysis were also performed on the data,and the correlation and regression function between the cancellation point frequency and S₂₁ and the dielectric constant were obtained,and the functional relationship between the dielectric constant and the cancellation point frequency and S₂₁ was fitted.Formula,through several sets of samples with different dielectric constants,to verify the validity of this functional relationship,it is obtained that the fitting error of the solution with a smaller dielectric constant is greater than that of the solution with a larger dielectric constant,the overall error is?0.48%¹.66%?,indicating that the RF sensor based on the coplanar waveguide with limited metal thickness has practical value.