Research On Resonance Mechanism Of Typical Complex Structures And Filtering Detection Technology

In the realm of information and intelligentized warfare,the battlefield has progressively transformed into an intricate intersection of the"five dimensions"encompassing land,sea,air,space,and electricity.Herein,"electricity"refers to the intricate electromagnetic environment on the battlefield,encompassing powerful electromagnetic environments generated by nuclear electromagnetic pulses,high-power microwave weapons,electromagnetic pulse bombs,and so on.In the civilian realm,the escalating prevalence of electronic equipment has led to a progressively intricate electromagnetic environment,necessitating the urgent achievement of electromagnetic compatibility among electronic devices.Leveraging the theoretical foundation of electromagnetic compatibility research and uniform waveguide propagation,this thesis delves four structures into improved structures for coaxial lines,called filtering cables,improved microstrip line filters,called as mesh transparency filters,rectangular resonant cavities,and cylindrical resonant cavities.Employing existing research theories rooted in TEM mode,TM mode,and TE mode,we conduct in-depth derivation and analysis,propose and design multiple practical cases to solve different electromagnetic compatibility problems.The research works are mainly shown below:（1）A novel U-shaped defected filtering cable structure with a long axial length and small cross-section has been proposed.Designing and fabricating a new device with both transmission and filtering functions,called filtering cable.The filtering cable structure consists of four parts:inner cylindrical dielectric,defected conductor transmission structure,transmission dielectric and shielding layer,or three parts:inner conductor,transmission dielectric layer and defected conductor layer.Its resonance mechanism has been delved into through full-wave simulations and experiments.Both simulation and experimental results indicate that the attenuation of this low-pass filtering cable remains below 1.0 d B within the passband frequency range,while exceeding 35 d B in the stopband frequencies above 3.5 GHz.The effect of defective structures on the overall filter performance when they are located at different positions is investigated,which provides a solution to the electromagnetic compatibility problem of signal interference in cable transmission.（2）A flat plate mesh filter structure is proposed,with a transparent filter design aimed at achieving superior low-pass filtering performance.Based on the existingΠ-shaped defected ground microstrip line filter structure,leading to transparent dielectric substrates made of polyethylene terephthalate,and adding some mesh structures to the defected ground structure and microstrip lines.Then,analyzing the impact of the density and area of the mesh square holes on the performance and transparency of the new microstrip line filter.This provides a path for visualization applications.Two types of transparent low-pass filters for different applications are designed based on two different connectors,SAM and IPEX.By cascading the filters,the insertion loss in the stopband is increased.The transparent filter cutoff frequency is at 1 GHz and high optical transparency is achieved.（3）A test method for assessing the electromagnetic shielding effectivenes of board-level shielding enclosures featuring a nested cavity structure is presented.By analyzing the resonance mechanism of the rectangular cavity,a small rectangular resonant cavity with dimensions of 120 mm×81.8 mm×58.2 mm has been developed with a minimum operating frequency of 17.118GHz.The enclosure under test can be submerged in its internal field,allowing for precise measurement of electromagnetic leakage with a probe.This method enables efficient measurement of board-level electromagnetic shielding effectivenes,which is achieving values exceeding 80 d B.The proposed measurement system surpasses traditional counterparts in terms of its compact size and convenient use offering enhanced electromagnetic shielding effectiveness assessment.（4）The investigation focuses on electromagnetic parameter measurements utilizing a fusion of machine learning and perturbed resonant cavities.By analyzing the modal characteristics of cylindrical resonant cavities and leveraging their sensitivity to internal perturbations,the method for measuring different relative permittivity using microwave sensors in cylindrical cavities has been proposed.A new sensor for measuring changing in relative permittivity is designed,whose size is 120 mm×120 mm×23 mm.It can measure the moisture content of small substances such as capsules,and it has higher sensitivity than existing sensors.The measurement object can not only be moisture content,but also the powder content inside the capsule.Then,leading into two machine learning methods,PCA and NB,significantly enhanced the robustness and accuracy of sensor measurements for analyzing the magnitude and phase data of the S₂₁ parameter.