Research On Design And Electromagnetic Properties Of Flexible Microwave Frequency Selection Electromagnetic Structures

Frequency selection electromagnetic structures(FSESs)have been widely employed in controlling the electromagnetic wave radiation characteristics,acting as an important part of microwave technology.The combination of flexible electronics achieves the bend-able and stretchable FSESs,which provides a technical foundation for extensible applica-tions and realization methods,and makes it possible to add more functions to FSESs as well.However,there are still many urgent problems to be solved on key technologies such as structural design,preparation methods,and control methods due to the large deforma-tion and incompatibility with traditional fabrication process for the realization of flexible FSESs.Thus,it’s necessary to study the underlying mechanism of the change of elec-tromagnetic response of the flexible FSESs with large deformation.Proposing feasible flexible design methods to achieve the effective control of the relation between electro-magnetic response and deformation and exploring the application scenarios suitable for the flexible FSESs are of great significance to further promote the development of flexi-ble FSESs and broaden the functions of FSESs.In this dissertation,researches on typical FSESs,such as flexible ultrawide band an-tenna,flexible frequency selective surface(FSS)and flexible electromagnetically induced transparency(EIT)device,are carried out to study the electromechanical coupling charac-teristics and large-scale fabrication in the flexible design,aiming at developing the design method of FSESs based on the comprehensive design of flexible material and deformable structure and proposing the block design strategy suitable for large-scale flexible FSESs.Furthermore,the prototype fabrication and characterization of devices are also conducted.The main contents of the thesis are as follows:(1)Based on the combination of flexible materials and deformable structure,a flexi-ble ultrawide band antenna is first studied operating in the frequency range of 3.5 GHz to17.8 GHz.By O-shaped slot loading on traditional rectangular monopole antenna,the per-formance consistency is effectively improved before and after the antenna is conformed to the curved surface,and bandwidth of the antenna is also broadened to a certain extent.The results show that when the antenna is attached to a cylinder with a bending radius as low as 11 mm,its reflection coefficient remains below 10 d B within the operating frequency range,and the antenna can work normally.Meanwhile,the bandwidth of the antenna elim-inates its impedance mismatch in the frequency range of 6 GHz to 8 GHz compared with that without an O-shaped slot loading.Then,a conformal FSS that works in the X-band is designed.Based on the analysis of the coupling relation between transmission character-istics and bending deformation of FSSs,an FSS design with stable frequency response in the conformal applications is successfully obtained by adapting the zigzag and serpentine structures.The results present that the serpentine design FSS maintains stable frequency selection characteristics without frequency deviation when attached to the cylinder with the bending radian ofπ/3,π/2 andπ,which is greatly improved compared with the origi-nal straight and zigzag structures with the frequency offset of 10%and 5%.On this basis,a flexible EIT device based on”bright-bright”mode coupling is proposed and its underlying mechanism and electromagnetic response on deformation are also studied.At the same time,its potential applications are explored in electromagnetic detection,achieving the device with a quality factor of 10.6 and a sensitivity of 13.33 mm/RIU in the microwave frequency band based on EIT effect with spoof surface plasmons(SSPs)resonance,which makes the quality factor and sensitivity of the device maintain at a high level as a whole.(2)For the fabrication of large-scale flexible FSESs,a block design strategy is pro-posed.Based on the“definition-after-transfer”idea that transferring the precursor struc-ture to the flexible substrate before using laser processing method to functionalize the electromagnetic structures,it avoids the problems,such as incomplete transfer and low transfer accuracy,due to the direct transfer of separate elements onto a flexible substrate,and simplifies the fabrication process.Based on this strategy,a 250×250 mm~2flexible FSS was designed and fabricated.Three different block arrangement definitions are used to realize three defined FSSs with the same square loop precursor structure,presenting different electromagnetic characteristics on the strain.The mechanism of block defini-tion on coupling characteristics is also analyzed by electric field analysis and equivalent circuit model.The results show that three defined FSSs exhibit different response charac-teristics under the same strain conditions,achieving the reconfigurability of sensitivity of the electromagnetic response on deformation.Besides,the block design strategy is also employed to realize an EIT device with reconfigurable bandwidth and large group delay characteristics,indicating its universal feasibility.The results show that the obtained EIT device can achieve the dynamic control of its bandwidth and group delay characteristics in a wide range,adjust the sensitivity of the electromagnetic response on strain according to application scenarios and configure the dependence of the electromagnetic characteristics on deformation.Based on the same precursor structure,an EIT device is presented with tunable bandwidth or stable frequency response under strain loading of up to 30%.(3)To explore the applications of flexible FSESs in complex scenes,the design of flexible microwave FSESs based on origami structure and their performance control strate-gies are studied.The flexible EIT device based on origami structure is designed and fab-ricated.By changing the folding states and the arrangement of units,the devices with dynamic tuning of bandwidth and center frequency can be achieved.The designed me-chanically reconfigurable single-layer FSS based on this method can achieve a fractional bandwidth of 25%and a modulation depth of more than 300%,which significantly im-proves the bandwidth and tunable range of the single-layer FSSs and simplifies design and fabrication processes.Based on the analysis of the electric field and equivalent circuit,the mechanism of bandwidth reconfigurability of the FSS is explained.A design method of single-layer mechanically reconfigurable FSS is proposed based on the design of origami structure.