Sensing Systems Based On Spoof Surface Plasmons

Spoof surface plasmons(SSPs)are kinds of surface waves which exist on the surface of periodic metal subwavelength structures.It extends the properties and applications of Surface Plasmons(SPs)from optical frequency to microwave and terahertz band.According to its different characteristics of mode,SSPs are usually divided into spoof surface plasmon polaritons(SSPPs)and spoof localized surface plasmons(SLSPs).SLSPs can realize higher sensitivity and smaller size of planar integrated microwave resonator,which are of great value of application.This thesis focuses on the research of ultra-sensitive microwave sensing system based on SLSPs.A SLSP resonator with high sensitivity is designed and two kinds of SLSP sensing system with high integration and high performance are proposed.The main innovations are summarized as follows.1.An SLSP resonator with internal and external slots is designed.The resonator is composed of single-layer coaxial inward and outward spokes with the characteristics of strong electromagnetic field binding.By introducing a symmetry-breaking slit in the outer ring,a trapped mode is excited and the confinement is double folded.The trapped mode behaves as a mixture of the electric and magnetic plasmon dipoles.The simulation results show that the quality factor(Q-factor)of the resonator reaches 67.0.When the thickness of the upper space medium is 15 mm,the frequency sensitivity of its refractive index can reach 288 MHz / RIU,which has a high application value in the design of high sensitivity resonant microwave sensor.2.A frequency scanning sensing system is designed to detect the frequency shift of resonant peak quickly and precisely.The sensing circuit is mainly composed of voltage controlled oscillator(VCO),SLSP resonator,envelope detector(ED)and microcontroller unit(MCU).Compared with the traditional SLSP sensing detection method,it has a high degree of system integration.In the aspect of frequency scanning algorithm,after introducing the basic principle of scanning frequency to find the position of resonance peak,three optimization algorithms to find resonance peak are proposed,which maximizes the bandwidth of the system,improves the data rate by17.79 times the data accuracy by 63.5%.3.An intelligent frequency locking sensing system is designed,which mainly includes the design of resonant structure and frequency locking algorithm.The proposed laminated resonant structure has greatly improved the resonant intensity and sensing sensitivity.The Pound Drever Hall(PDH)program with the function of automatically determining the control parameters can track the resonant frequency,minimize the circuit hardware and consumed spectrum resources.The measured data rate can reach 2272 measurement points per second.This system can intelligently adapt to different resonance characteristics and communicate with mobile phones through bluetooth module,which providing a new solution for sensing the Internet of things.4.A compact and wireless sensing system tracking the resonance frequency shift of a SLSP resonator via a software-defined scheme is proposed.The SLSP resonator yields a deepsubwavelength size,enhanced sensitivity,and a good electromagnetic compatibility performance.The software-defined resonance tracking scheme minimalizes the hardware circuit and the consumed spectrum resources based on the improved Pound-Drever-Hall(PDH)technology,and makes the detection intelligently adaptive to the target resonance,with a signal-to-noise ratio(SNR)of 69 d B and a data rate of 2272 measuring points per second.The sensor has been validated via acetone vapor concentration sensing,while its applications can be widely extended by replacing the transducer materials.This approach provides compact,sensitive,accurate and intelligent solutions for resonant sensors in the Internet of things(IoT).