Research On Wideband Microstrip Refractive-index Sensor Based On Metamaterial

The metamaterial is a periodic artificial electromagnetic material composed of subwavelength structure elements which exhibit negative permittivity and permeability in a specific frequency band,and havesome singular electromagnetic properties such as slow wave characteristics,negative Doppler effect and so on.Sensors based on metamaterialsare attracting more and more people's attention,which do not exist separation components and have the characteristics of miniaturization to integrate with other microwave devices easily.First of all,this paper summarized the research status of the metamaterial sensor,and further explored the working principle and analysis methods of the CSRR and SRR.The main contents of this paper are as follows:(1)The mechanism of the transmission line theory and the SRR and the CSRR are introduced in this paper.And the method of extracting the equivalent electromagnetic parameters from the S parameter is studied emphatically and we proved the method with simulation.In addition,we also studied the metamaterial sensor equivalent circuit model,which can help us to analyze and improve metamaterial sensors.(2)Two different resonant rings: the gear CSRR and double complementary helix DCSR are designed using the software of HFSS.Then,the two kinds of resonant rings with the same size are respectively loaded with the improved microstrip to simulate for getting resonant frequency and sensitivity of the sensor.The Results show that amplitude of the transmission coefficient S21 is linear with the dielectric constant of the material under test.In addition,several factors that affect the sensitivity of the sensor have been analyzed.The sensitivity of sensor based on gear complementary split ring resonators can be improved by increasing the thickness of material under test and the length of gears,and reducing the split width and radius of inner ring.(3)Finally,a differential metamaterial refractive index sensor is designed to improve the accuracy.This paper focuses on the analysis of splitter microstrip sections where each branch is loaded with a CSRR.If the structure exhibits perfect symmetry with regard to the axial plane,a single transmission zero at the fundamental resonance of the CSRR will be arose.Conversely,two notches appear if symmetry is disrupted and their positions are determined not only by the characteristics of the CSRRs but also by the length of the splitter sections.From the equivalent circuit model,we have obtained the necessary conditions that relative to the electrical length of the transmission line sections of the splitter,optimizing the sensitivity of the sensor,which efficiently improved the sensitivity and discrimination.