| With the rapid development of information technology and the advent of the Io T era,there is an increasing demand for the performance of microwave devices,whether the integrated communication systems responsible for signal transmission/reception or the sensors that interact with the environment.For frequency-selective devices in communication systems,the requirements are reflected in miniaturization,anti-interference,high selectivity,and low loss.For microwave sensors,the focus is mainly on sensitivity,resolution,and functional implementation.Traditional microwave technology has inherent flaws that make it challenging to keep up with the constantly evolving external demands.As a result,incorporating emerging technologies is essential to overcome technical barriers and achieve breakthroughs.Spoof surface plasmons typically arise from deep subwavelength periodic metal structures,which possess the ability to confine electric fields tightly,and can be used to design microwave devices with superior performance or unique functionalities.They can be divided into two forms:propagating and localized.The propagation-type（SSPP）is commonly used in the design of RF front-end filters,while localized-type（SLSP）are mostly used in microwave resonators/sensors.This paper focuses on the characteristics and mechanisms of spoof surface plasmons and conducts relevant microwave device designs.Firstly,a folded SSPP low-pass transmission line is proposed,which exhibits excellent signal selectivity due to large number of units,while the folded design avoids a significant increase in lateral dimensions.The compact folding solution could reduce the lateral size to nearly 2/5 of the original one.An additional optimization is performed on the bending section to avoid signal loss during sharp bends.Secondly,a quarter-mode 2.5-D SLSP microfluidic sensor is proposed for measuring the liquid permittivity.The 2.5-D structure has been proven to be an effective solution for enhancing the surface field confinement of the resonator.The quarter-mode design reduces the size and liquid consumption and solves the problem of modes clutter that full-mode structure have.The introduction of the amplification circuits successfully improves the quality factor.In experiment,the water-ethanol mixed solution was selected as the liquid to be measured,and the functional equations representing the performance of the sensor were successfully fitted.The sensor sensitivity reaches 0.16%on average,and has quality factor of 4247.Compared with similar works,the proposed sensor has the advantages of miniaturization,high sensitivity,and high resolution.Thirdly,a step spiral SLSP sensor for oily substances detecting is proposed.By setting channels inside the step structure and utilizing the SLSP resonator to concentrate the electric field,the liquid fully utilizes the strong electric field between the upper and lower metal layers,resulting in ultra-high sensitivity.Since this sensor exhibits particular sensitivity to low permittivity,it is used for detecting oily substances.The proposed sensor achieves an ultra-high average sensitivity of 8.5%in the permittivity range of 1-5 with an electrical size of only 0.06×0.0402.In the experimental,edible oil mixed with different concentrations of mineral oil was used as a sample,and the sensor’s ability to identify oil adulteration is successfully demonstrated.In conclusion,this paper designs high-performance microwave low-pass transmission lines and microwave sensors utilizing the natural advantages of spoof surface plasmons. |
