Abstract
A differential microwave permittivity sensor and comparator is designed using a microstrip transmission line loaded with a magnetic-LC resonator. The microstrip transmission line is aligned with the electric wall of the resonator. The sensor shows a single transmission zero, when it is unloaded or loaded symmetrically on both halves. A second notch appears in the transmission response by asymmetrical dielectric loading on the two halves of the device. The frequency splitting is used to characterize the dielectric properties of the samples under test. The sensitivity of the sensor is enhanced by removing the mutual coupling between the two halves of the magnetic-LC resonator using a metallic wall. The sensors’ operation principle is explained through a circuit model analysis. A prototype of the designed sensor is fabricated and measurements are used for validation of the sensing concept. The sensor can be used for determination of the dielectric properties in solid materials or detecting defects and impurities in solid materials through a comparative measurement with a reference sample.
Highlights
Metamaterials-based components, such as split-ring resonators (SRRs) and complementary split-ring resonators (CSRRs) have been widely used in the implementation of high performance compact microwave electronic components such as filters and antennas [1,2,3,4,5,6]
RF and microwave sensors are popular in various measurement and instrumentation applications due to their robust, real-time, and label free measurement compatibilities [7,8,9,10,11,12,13,14,15,16,17,18,19,20]
The measurement principle in a majority of microwave sensors is the frequency shift or notch magnitude variation, where any environmental or structural alterations leads to modification of the resonance characteristics [21,22,23,24,25,26,27,28,29,30,31]
Summary
Metamaterials-based components, such as split-ring resonators (SRRs) and complementary split-ring resonators (CSRRs) have been widely used in the implementation of high performance compact microwave electronic components such as filters and antennas [1,2,3,4,5,6]. The capacitive effect and as a result the fringing electric field provide by SRRs is smaller than the complementary counterparts such as CSRRs and magnetic-LC (MLCs) (complementary electric-LC (ELC)) [45] This causes a smaller sensitivity of the SRR-based sensors to the dielectric variations with respect to the complementary resonators-based sensors. The electric wall (a plane, where the electric fields are distributed symmetrically on its’ two sides) of the MLC is aligned with the horizontal symmetry line of the microstrip transmission line This leads to a balanced excitation of the two resonator halves causing a single notch in the transmission response of the bare sensor. Any unbalanced loading causes asymmetry in the resonator and excites the odd resonance mode causing a second transmission notch and frequency splitting This characteristic is used for differential characterization of the unknown test samples
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