Design And Fabrication Of Microwave Absorbers Based On All-dielectric Metamaterial And Research Of Their Electromagnetic Characteristics

With the popularity and application of digital instruments and electronics,the production and living process has become more convenient and intelligent,while it has brought hazards at the same time.The electromagnetic interference and radiation problems have gradually developed into a new type of pollution,thus electromagnetic management is imminent.In addition,high-tech military technology like stealth technology constantly put forward new requirements for the absorber's performance in effectively absorbing electromagnetic waves.Developing novel electromagnetic absorbers to achieve efficient absorption and dissipation of electromagnetic waves is an important scheme to solve the above problems.Although conventional absorbing materials have achieved impressive performance in terms of microwave absorption,there exist defects such as narrow absorption bandwidth,high density,poor chemical stability,high preparation cost,and high load content.Carbon-based materials have excellent microwave properties due to their unique dielectric properties,rich porous structure,and high specific surface area,but the complex synthesis process limits their practical application.In recent years,the use of abundant and sustainable biomass materials to prepare derived carbon as microwave absorbing materials has attracted the interest of researchers.Biomass-derived carbon materials have promising applications contributed to availability,low cost,and require no tedious preparation processes,but the absorption bandwidth of a single coating does not meet the ultra-broadband requirements.The structural design concept of metamaterials provides a new direction for the development of absorbers.However,metamaterial absorbers generally use metals to construct their surface structures,which also has the problem of narrow bandwidth or high requirements for the process.Therefore,this paper proposed using biomass-derived carbon materials instead of metals to construct all-dielectric metamaterial absorbers,which achieved impedance matching in a wider frequency range and broadened the absorption bandwidth through the structured design of lossy materials.In this paper,a popcorn-derived carbon material was firstly prepared from corn kernels by a non-polluting and simple method(microwave thermal expansion and high-temperature graphitization),and its microstructure and electromagnetic properties were studied.Then,two types of all-dielectric metamaterial microwave absorbers with periodic unit structures were constructed based on this material.Finally,the models of the absorbers were prepared by combining with 3D printing technology,and their broadband absorption characteristics were verified through experiment tests.The absorption characteristics of hollow cross-type metamaterial microwave absorbers were analyzed in detail in Chapter 4,whose reflection loss(RL)was less than-10 dB in the range of 4.4-18 GHz and reached 97% absorption in the range of 5.6-18 GHz(RL <-15 dB).The outstanding absorption performance is attributed to the excellent dielectric loss of the popcorn-derived carbon material and the multiple resonances and edge diffraction effects brought by the macrostructure design,further improving the impedance matching characteristics and electromagnetic attenuation capability of the absorber.Thus,the all-dielectric metamaterial microwave absorber designed in this paper achieved broadband absorption.Additionally,with lightweight popcorn-derived carbon material coupled with the design of the hollow structure,a lower sample filling rate was achieved.It provides an important reference for the design and large-scale preparation of lightweight and ultra-broadband microwave absorbers.