Dipoles with Lorentz-type resonant electromagnetic responses can realise negative effective parameters in their negative resonant region.The electric dipole and magnetic dipole can realise,respectively,negative permittivity and negative permeability,so both the field distribution forms of electric and magnetic dipoles are fundamentals in designing left-handed metamaterial.Based on this principle,this paper studies the field distribution in high-permittivity dielectric materials.The field distributions at different resonant modes are analysed based on the dielectric resonator theory.The origination and influence factors of the electric and magnetic dipoles are confirmed.Numerical simulations indicate that by combining dielectric cubes with different sizes,the electric resonance frequency and magnetic resonance frequency can be superposed.Finally,experiments are carried out to verify the feasibility of all-dielectric left-handed metamaterial composed by this means.
By using the coordinate transformation method,we have deduced the material parameter equation for rotating elliptical spherical cloaks and carried out simulation as well.The results indicate that the rotating elliptical spherical cloaking shell,which is made of meta-materials whose permittivity and permeability are governed by the equation deduced in this paper,can achieve perfect invisibility by excluding electromagnetic fields from the internal region without disturbing any external field.
By using coordinate transformation method,this paper obtains an useful equation of designing meta-material cloaks embedded in anisotropic medium.This equation is the generalization of what was introduced early by Pendry et al(2006 Science 312 1780) and can be more widely used.As an example of its applications,this paper deduces the material parameter equation for cylinder cloaks embedded in anisotropic medium,and then offers the numerical simulation.The results show that such a cylinder cloak has perfect cloaking performance and therefore verifies the method proposed in this paper.
Using (Ti(OC_4H_9)_4) and metal chlorates as starting materials, CoFe_2O_4/TiO_2 composite films were pre-pared by sol-gel method. The effects of heat treatment temperature and pH of the precursor on micro-structure and magnetic properties were studied. The phase structure of the samples was examined by X-ray diffraction. The microstructure was examined by scanning electron microscope, atomic force microscope and polarized microscope. The magnetic property was measured by vibrating sample magnetometer. The results show that the crystals of different phases grow up independently. CoFe_2O_4 is uniformly embedded into the TiO_2 matrix in the prepared composite films, and the growth of com-posite films is dependent on the heat treatment temperatures and PH of the precursor. The average size of CoFe_2O_4 crystal is 19 nm in Nanocomposite film prepared when the heat treatment temperature is 800℃ and the pH of the precursor is between 2 and 3. The magnetism of the composite films is en-hanced as the heat treatment temperature increases.
We simplify the material parameter equation for elliptical cylinder cloaks under transverse-electric and transverse-magnetic models,respectively,and confirm these simplified equations by numerical simulations.As a result,the number of the component parameters is reduced from three to two,which simplifies the design of meta-materials and thus opens up the possibility of achieving elliptical cylinder cloaks in an easy way.
A new metal-organic framework,{Zn[Zn3(BTA)3(μ3-OH)(H2O)3]2}n 1,has been synthesized under hydrothermal reaction of ZnCl2 and bis(5-tetrazolyl)amine(H2BTA),and characterized by elemental analysis,FT-IR,Raman spectrum,X-ray single-crystal diffraction,TGA and photoluminescence measurements.Compound 1 crystallizes in the trigonal system,space group P-3c1,a=13.667(3),c=12.981(3) ,V=2099.6(8) 3 and Z=2.The BTA2- ligand in 1 assumes the μ3 tetradentate mode with both 1,2-and 1,4-tetrazole bridges,generating an unusual 2-D layer,in which the [Zn3(μ3-OH)] triangular motifs act as three-connecting nodes and the mononuclear Zn atoms as six-connecting nodes that are inter-linked by organic ligands.Adjacent 2-D metal-organic layers are linked by strong hydrogen bonds to form a novel 3-D supramolecular framework.Complex 1 exhibits blue fluorescence emission in the solid state at ambient temperature.
CoFe2O4/TiO2 magnetic composite films were prepared using the sol-gel method with tetrabutyltitanate and metallic chlorates as starting materials. The effects of heat treatment temperatures on micro- structures and on magnetic properties were studied. The microstructure and properties of the samples at different heat treatment temperatures were characterized by X-ray diffraction, Raman spectrum, scanning electron microscopy, polarized microscopy and vibrating sample magnetometry. The results show that crystals of different substances grow up independently. Cobalt ferrite is evenly embedded into the titanium dioxide matrix in the prepared composite films. The magnetism of the composite films is enhanced with an increase of the heat temperature.
TIAN XiaoXia1, QU ShaoBo1,2, PEI ZhiBin1 & WANG BinKe1,2 1 College of Science, Air Force Engineering University, Xi’an 710051, China
By making a comparison between the acoustic equations and the 2-dimensional(2D) Maxwell equations,we obtain the material parameter equations(MPE) for acoustic elliptical cylindrical cloaks.Both the theoretical results and the numerical results indicate that an elliptical cylindrical cloak can realize perfect acoustic invisibility when the spatial distributions of mass density and bulk modulus are exactly configured according to the proposed equations.The present work is the meaningful exploration of designing acoustic cloaks that are neither sphere nor circular cylinder in shape,and opens up possibilities for making complex and multiplex acoustic cloaks with simple models such as spheres,circular or elliptic cylinders.
The piezoelectric,dielectric,and ferroelectric properties of the(LiCe) co-substituted calcium bismuth niobate(CaBi2Nb2O9,CBNO) are investigated.The piezoelectric properties of CBNO ceramics are significantly enhanced and the dielectric loss tan δ decreased.This makes poling using(LiCe) co-substitution easier.The ceramics(where represents A-site Ca2+ vacancies,possess a pure layered structure phase and no other phases can be found.The Ca0.88(LiCe)0.04 0.04Bi2Nb2O9 ceramics possess optimal piezoelectric properties,with piezoelectric coefficient(d 33) and Curie temperature(TC) found to be 13.3 pC/N and 960 C,respectively.The dielectric and piezoelectric properties of the(LiCe) co-substituted CBNO ceramics exhibit very stable temperature behaviours.This demonstrates that the CBNO ceramics are a promising candidate for ultrahigh temperature applications.
