Zhao Xiaopeng

Behaviour of Hexagon Split Ring Resonators and Left-Handed Metamaterials

We used a rectangular waveguide system to measure the X-band (8–12 GHz) transmission of hexagon split ring resonators (SRRs) alone and the left-handed metamaterials (LHMs) consisting of hexagon SRR array and wire array. The experimental results show that for an individual SRR, the resonance frequency increases with the azimuthal gap, but decreases with the radial gap. For two identical SRRs, the resonance peak has a shift because of the electromagnetic interaction, and the resonance frequency and the strength decrease with the separation distance. Finally, we demonstrate the left-handed effect of the LHMs.

Highly Symmetric Planar Metamaterial Absorbers Based on Annular and Circular Patches

We present the simple designs of metamaterial absorbers which are composed of a periodic array of copper annular (or circular) patches, FR4 substrate, and copper film. With appropriate geometrical parameters, these metamaterials can provide the electric and magnetic resonances overlapping in the given frequency range, and the experiments demonstrate the absorptivities of 97.6% and 96.7% with only a single layer of the metamaterial absorber. The surface currents and field distributions of these metamaterials are discussed to look straight into the resonance mechanism. Furthermore, our numerical simulations confirm that these metamaterial absorbers could be operated at wide angles of incidence. The simple and highly symmetric structures of the metamaterial absorbers proposed would greatly accelerate the practical applications in optics and electromagnetics.

Electrorheological Effects of Cerium-Doped TiO2

It is found that the doping of cerium ion into anatase TiO2 can improve the electrorheological (ER) effects of TiO2 and broaden the operational temperature range. Especially, the substitution of 7-11 mol% of the cerium dopant for Ti can obtain a relatively high shear stress, tau = 7.4 kPa (at 4 kV/mm), which is ten times larger than that of pure TiO2 ER fluid. Also, the typical Ce-doped TiO2 ER fluid shows the highest shear stress at 80 degreesC, but 40 degreesC for pure TiO2 ER fluid. The dielectric loss and dielectric constant at a low frequency of TiO2 is improved by the doping of cerium, and the temperature dependence of the dielectric properties shows an obvious difference between pure and doped TiO2 ER fluids. These can well explain the ER behaviour of doped TiO2. Furthermore, the change of rheological and dielectric properties is discussed on the basis of the lattice distortion and defects in TiO2 arising from the doping of cerium.

Numerical Study of Low-Loss Cross Left-Handed Metamaterials at Visible Frequency

We present a numerical study of left-handed metamaterials (LHMs) composed of double cross pairs at visible frequency. The S-parameter retrieval method is adopted to confirm the negative refractive characteristic of this design. Compared with fishnet LHMs, the proposed cross LHMs have a much lower loss, which will greatly facilitate practical applications. It is also found that, with the same size of resonant cells, the cross LHMs have a higher frequency than fishnet LHMs, which is explained using a simple effective LC circuit model.

The effects of stress ratio on fatigue threshold

Abstract Arising from the fact that there is a reverse compression stress around a fatigue crack, it is supposed that there is an equivalent compressive high-strain area. Based upon the eigenequation of crack growth, the critical value, K th c , of the compressive stress intensity factor is derived. The analytical expression for the change in fatigue threshold with stress ratio is derived from the similarity between the crack closure stress intensity factor and K th c . The fatigue threshold values for some materials are calculated using the results of this paper; it is found that the theoretical values are in good agreement with the experimental results.

Tunable Effect of Double-Connective Dendritic Left-Handed Metamaterials Based on Electrorheological Fluids

We present double-connective dendritic unit pairs which exhibit the left-handed property for electromagnetic wave normal incidence. Based on the tunable characteristics of electrorheological fluids (ERF) as the electric field, we experimentally study the influence of the distance of electrodes, the number of stacked layers, and the intensity of the external electric field upon the ERF to the left-handed transmission peak of the double-connective dendritic structure. The results show that the transmission could be enhanced with the increase of distance or the number of layers. Furthermore, by changing the intensity of the electric fields, the left-handed transmission peak can be modulated actively, and the maximum shift is up to 160 MHz.

Stopband Phenomena in the Passband of Left-Handed Metamaterials

Stopband phenomena are reported in the passband of left-handed metamaterials. The samples with linear defect are designed by removing one layer of split ring resonators (SRRs). It is shown that the left-handed transmission peaks have a distinct transform with the relative deviation of the SRRs centre from the wire centre δ, from a single left-handed peak, double left-handed peaks with different magnitude to no transmission peak, i.e. left-handed properties of metamaterials disappear. Numerical simulation shows that the change of δ makes the effective permeability shift at a frequency range, where stopband occurs. It is thought that the stopband in left-handed passband is due to the symmetry breaking between SRRs and wires in the metamaterials.

Effect of defect on the energy distribution inside the left-handed metamaterials

Abstract The electromagnetic field energy distribution inside the left-handed metamaterials (LHMs) with or without blank and line defects is firstly investigated. The LHMs consist of an array of periodic unit cells of copper hexagon split ring resonators (SRRs) and wires. The internal energy distribution of the LHMs is measured in a microwave measuring line device at X-band frequencies. It is found that the LHMs only respond to the electromagnetic field around the resonance frequency. The electromagnetic field amplitude inside the LHMs generally decreases with the introduction of defects. It is suggested that the electromagnetic field energy reduction may arise from the symmetry breaking in the LHMs. * Supported by the National Natural Science Foundation for Distinguished Young Scholars (Grant No. 50025207), the National Natural Science Foundation of China (Grant No. 50025207), the National Natural Science Foundation of China (Grant No. 50272054) and the Major State Basic Research Development Program of C...

A new formula for estimating fatigue crack propagation rates

Abstract Based on the eigenequation of crack growth in metals, a new analytical expression for estimating fatigue crack propagation rates is proposed. It takes into account the volume effect of the plastic zone ahead of crack tips and utilizes the concept that crack growth is controlled by the high-strain area (HSA) at the very tip of the crack. Factors such as the fatigue threshold values, ΔKth, the cyclic mechanical properties of materials, Youngs modulus of elasticity, the stress intensity factor range, ΔK, and the stress ratio, R, have been incorporated in the proposed model. The comparison between the theoretical curve and the experimental results for some materials indicates that the formula is correct for the determination of a crack propagation rate for da/dN