Layered Three-dimensional Subwavelength Broadband Absorbing Materials

Nowadays from microwaves to optical bands,electromagnetic waves have a wide range of applications.Not only in the military we use radar to detect targets but also to transmit information in everyday life.With the continuous development of electromagnetic wave research,the harm of electromagnetic waves has gradually emerged,such as electromagnetic radiation on the human's body,electromagnetic interference on communications equipment,especially for modern information warfare,exposure to enemy radar are very dangerous.Therefore,the study of electromagnetic wave absorber is particularly important.Absorbing materials that are capable of absorbing and attenuating incident radiation have aroused much interest.Effectively absorbing the power of incident radiation is ever growing in different aspects of ongoing technologies from radio to optical frequencies.They are employed for sensing,light harvesting,thermo-photovoltaic and reducing the electromagnetic interference among microwave components.In military applications,they play key roles in reducing the radar signature of objects.Traditional absorbing materials,such as Jaumann absorbers and Salisbury screens,place the lossy film on a 1/4 wavelength thickness medium from behind the metal plate.The formation of a standing wave makes the energy confined to the medium through the surface of the lossy film and the loss of the medium to absorb the wave.However,with such a structure,electromagnetic waves for low-frequency bands face too large thickness,which is on the contrary to the development trend of today's absorbing materials which are "light,thin,wide,and strong".Therefore,we are not confined to the traditional two-dimensional structure and will extends the design of absorbing materials to the third dimension,so the new types of layered three-dimensional subwavelength broadband absorbers are being studied.This paper focuses on the layered three-dimensional sub-wavelength broadband absorbing materials for light weight and thin thickness.Expanding the absorption bandwidth and strong absorption characteristics,optimizing the absorption effect using parameters optimization and simulation,and mainly studying and designing three different kinds of novel sub-wavelength absorbing structures.The main work is summarized as follows:1.Studying and designing a new type of subwavelength absorbing material with frequency-tunable transparent window based on frequency selective surface.We use a sandwich structure to combine resistive frequency-selective surfaces with metal frequency-selective surfaces and attach them to other sides of the dielectric substrate to achieve a good absorption effect for electromagnetic waves of both X-band and Ku-band,and there is a transmission window with high transmission performance in the absorption band which can be achieved by adjusting the structural parameters of the metal FSS to tune transparent window.And by loading varactors and other lumped elements on the FSS,the advantages of electrically adjustable can be achieved.The study of the absorbing material with a transparent window is of great significance for applications such as radome2.A low-frequency subwavelength three-dimensional absorbing material based on split ring resonators is studied and designed.A single SRR can be equivalent to an LC resonant circuit.The resonant frequency is determined by its structural parameters.It has a narrow band with strong absorption peak at its resonant frequency.In order to broaden its absorption band,we arrange several SRRs of different sizes in the vertical direction as pyramid structure to achieve the coalescence of multiple absorption peaks.The structural parameters and the thickness of each layer are adjusted,and different resonance peaks are aggregated to form a broadband strong absorption structure.In order to further reduce its resonant frequency,enhance its resonance,we stagger the gaps of two adjacent rings to achieve a three-dimensional sub-wavelength low-frequency wave-absorbing structure.3.A 3-D ultra-wideband microwave absorbing structure based on ferrite and lossy materials was studied and designed,By using a spiral-shaped loss ring material to construct a broadband absorption,in order to further reduce the absorption band,the three-dimensional structure and the metal backplane a layer of ferrite is added between them to extend the low frequency to 500MHz to achieve a low-frequency broadband subwavelength absorbing structure.Furthermore,we optimize the spiral ring as a layered structure to maintain its absorption effect and facilitate further experimental verification.