The Regulating Effects Of Dielectric Metamaterials On Electromagnetic Wave

Metamaterials are a kind of artificially constructed materials,which are made up of artificial unit cells that are much larger than the particles in the natural material.Therefore,we can easily design and regulate the size and physical and chemical properties of artificial cells to obtain artificial materials with specific electromagnetic responses.Electromagnetic metamaterials can achieve zero or negative permittivity and permeability near the electromagnetic resonance frequency of artificial cells and we can freely control these electromagnetic parameters to meet our requirements.The extraordinary properties of metamaterials have attracted great attention from researchers around the world and the field of application of metamaterials has been expanded,with the development of metamaterials absorber and photonic crystals particularly rapid.According to Lewin's model,dielectric particles based on Mie-resonance can be used as artificial unit cell of metamaterials,which provides a new idea for the design of metamaterials absorber.However,the limited work frequency of metamaterials absorber and photonic crystals also hinders these applications and then currently the tunability becomes a hot spot of the metamaterial.This topic is devoted to design and prepare tunable metamaterials absorber and tunable photonic crystals by dielectric materials.An electrically controlled metamaterial perfect absorber(MPA)based on Mie resonance is demonstrated experimentally and modeled numerically.A ceramic dielectric cube is adhered to a specially shaped thin copper film sputtered on a quartz plate.By passing direct current(DC)through the film,the temperature of the cube can be varied,resulting in changing the cube's permittivity and shifting the absorption resonance frequency.The frequency rises as the increase of temperature and the absorption is over 99% throughout the tuning range.This method for constructing miniaturized tunable MPAs compares favorably to bulky alternative designs.It also provides a versatile route to broaden the absorption bandwidth and potentially expand the range of applications such as metasurfaces and cloaking devices utilizing nonuniform permittivity produced by temperature gradients.Mie-resonance terahertz absorbers by self-assembly method are designed and demonstrated in experiments and simulations.A monolayer of zirconium dioxide microspheres fixed on a copper film with designed grids that were manufactured by direct writing with a composite ink system composed of polydimethylsiloxane(PDMS).Magnetic resonance leads to near-unity absorption at about 0.4 THz in the samples.In addition,different spacing and array configurations are created economically and efficiently and we studied and demonstrated the effects of different spacing and configurations for absorption.Magnetically tunable terahertz photonic crystals(PCs)are designed and prepared.Flexible woodpile structures with different geometry parameters created by the direct-writing technology with a composite ink system composed of barium strontium titanate nanoparticles and PDMS are immersed in 5CB liquid crystals(LCs),where the orientation of LC molecule is modulated by external magnetic field.Experiments show that the photonic gaps of these PCs have a red shift with the spacing of rods increasing and the peaks keep the same position but become deeper with the increase of layer.In addition,ther e is about 7.5 percent fine tunability of photonic gap appearing with the orientation of magnetic field changing.