Extremely Sensitive Microwave Microfluidic Dielectric Sensor Using a Transmission Line Loaded with Shunt LC Resonators

In this paper, a very high sensitivity microwave-based planar microfluidic sensor is presented. Sensitivity enhancement is achieved and described theoretically and experimentally by eliminating any extra parasitic capacitance not contributing to the sensing mechanism. The sensor consists of a microstrip transmission line loaded with a series connected shunt LC resonator. A microfluidic channel is attached to the area of the highest electric field concentration. The electric field distribution and, therefore, the resonance characteristics are modified by applying microfluidic dielectric samples to the sensing area. The sensor performance and working principle are described through a circuit model analysis. A device prototype is fabricated, and experimental measurements using water/ethanol and water/methanol solutions are presented for validation of the sensing mathematical model.

Parametric Investigation and Analysis of an Electric-LC Resonator by Using LC Circuit Model

Electric-LC resonators (ELCs) metamaterials, as a kind of common structures, have been extensively investigated from microwave to terahertz frequencies. In this paper, we present a LC circuit model to analyze electric-LC resonator. With the reliable and closed formulas of the effective inductance and capacitance, the expressions of electric and magnetic resonance frequencies were obtained, which is suitable to discuss the resonance characteristic under the normal incidence case. Meanwhile, the mutual relationships among the permittivity, permeability, refractive index, and structure parameters can be explored by using the obtained expressions. Numerical simulations and theoretical calculations reveal that the width and length of the gaps are some of the critical parameters determining the resonator frequency of the example metamaterial. This study provides valuable information for designing the desired left-hand metamaterial at some specific frequency points.

Microwave Differential Frequency Splitting Sensor Using Magnetic-LC Resonators

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.

An 550-650 MHz Digitally-Tunable Bandpass Filter: Design and Implementation

In this paper, a digitally-tunable band-pass filter is designed and implemented for applications of Cognitive Radio in middle Ultra high frequency television band from 550 to 650 MHz. This design is based on the 3th-order Chebyshev filter model in the combination with impedance inverters and series LC resonators, where capacitors are replaced by varactor diodes. The central frequency is tuned by means of a digital control board to adjust DC bias voltages of the diodes. Theoretical analysis, numerical simulation, and hardware implementation are described and carried out. The RF board is fabricated using SMV1736 varactor diodes with FR4-0.8mm material. The results show good match between simulations and measurements in terms of return loss, insertion loss, and fractional bandwidth over the operating range.