Zero Index Research Articles

Manipulation of elastic waves by zero index metamaterials

In this work, we investigated anti-plane transverse elastic waves transmission through a zero index metamaterials (ZIM) waveguide embedded with defect. Theoretical analysis and numerical simulations show that total transmission and total reflection of the impinging transverse elastic waves can be achieved by simply adjusting the parameters of the defect, and a ZIM waveguide embedded with a free-wall hole can be utilized as an elastic waves cloaking. Moreover, we present a two-dimensional (2D) phononic crystal (PC) to exhibit Dirac-like cones dispersion at the zone center. Effective medium theory finds that such PC can have effectively zero reciprocal of shear modulus and zero mass density, thus zero refractive index. Numerical simulations show that the PC system would be a good experimental candidate to achieve the intriguing transmission properties of the ZIM waveguide structure.

High-gain composite microstrip patch antenna with the near-zero-refractive-index metamaterial

A high-gain rectangular microstrip patch antenna which is covered by a single layer metamaterial (MTM) superstrate with the near zero refractive index is proposed. The refraction of the metamaterial at frequency 3.51GHz–3.57GHz is very close to zero. The metamaterial with the near zero refractive index is placed 42mm above an ordinary rectangular microstrip patch antenna. The effectively zero refractive index behavior of metamaterial superstrate can gather the wave emitted from the microstrip patch antenna and collimate it toward the normal direction of the antenna. The finite element method (FEM) and the finite difference time domain (FDTD) method are used to study the characteristics of this antenna. The results of the two methods indicate that the realized gain of the proposed antenna is increased by more than 6dB, and the antenna has a flatness high gain in the predicted frequency band, where the proposed MTM is designed to have a near zero index of refraction. Therefore, the high-gain antenna is effectively enhanced based on the near-zero-refractive-index metamaterial.

Quantification of loss and gain in performance using survey data: a study of earthquake-induced damage and restoration of residential buildings

This paper presents a method to assess and quantify changes in performance states of systems. The method is based on survey data containing performance states graded in a suitable scale. The changes in performance states are modelled using an association matrix obtained as a frequency table of measured performance states before and after an influential incident. Performance deviation, for both negative effects induced by a harmful incident and positive effects due to a constructive incident, is modelled. Relative change in performance is quantified by defining loss and gain matrices. Hadamard products of loss/gain matrices and the association matrix obtained from survey data are used to quantify performance deviation matrices. Finally, the overall change in performance is defined in terms of a performance deviation index, which is obtained by using the sum of the elements of performance deviation matrices. This index can be negative, zero or positive, and its value represents the degree of change in performance. A negative index indicates loss in performance; a zero index implies no measurable change, and a positive index means a gain in performance. An example application of the presented methodology for earthquake-induced damage and the subsequent restoration of residential buildings in South Iceland is presented.

Poisson-Transmission Problems for $$L^{\infty }$$ L ∞ -Perturbations of the Stokes System on Lipschitz Domains in Compact Riemannian Manifolds

The purpose of this work is to show the well-posedness in \(L^2\)-Sobolev spaces for a Poisson-transmission problem involving \(L^{\infty }\)-perturbations of the Stokes system on complementary Lipschitz domains in compact Riemannian manifolds. The technical details rely on the layer potential theory for the Stokes system and the invertibility of some perturbed zero index Fredholm operators by suitable compact operators. The compact part is provided by the \(L^{\infty }\)-perturbations of the Stokes system. An existence result for a related semilinear Poisson-transmission problem is also formulated.

Fatigue Behavior of Weld Repaired AISI 4130 Aeronautic Steel Used in Critical Flight Safety Structures

Since the 1950s, fatigue is the most important project and operational consideration for both civil and military aircrafts. For some aircraft models the most loaded component is one that supports the motor: the "Motor Cradle". Because they are considered critical to the flight safety the aeronautic standards are extremely rigorous in manufacturing them by imposing a "zero index of defects" on the final weld quality (Safe Life), which is 100% inspected by Non-Destructive Testing/NDT. This study has as objective to evaluate the effects of up to four successive TIG welding repairs on the axial fatigue strength of an AISI 4130 steel. Tests were conducted on hot-rolled steel plate specimens, 0.89 mm thick, with load ratio R = 0.1, constant amplitude, at 20 Hz frequency and in room temperature, in accordance with ASTM E466 Standard. The results were related to microhardness and microstructural and geometric changes resulting fromwelding cycles.

A high gain patch antenna based PN zero permeability metamaterial

AbstractA zero refractive index metamaterial is designed, and the zero refractive index is caused by the magnetic resonance. Based on the metamaterial, a zero index lens antenna is designed, fabricated, and measured. Due to the wave converging effect of the zero index lens, the gain of the new designed antenna reaches 11.7 and 4.8 dB higher than the original antenna without the lens. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:1065–1069, 2014

Universal Steganalysis Based on Differential Zero Coefficients and Index Co-Occurrence Matrix

为提高互联网通信的安全性和可靠性，提出一种针对图形交换格式(graphics interchange format，简称GIF)图像的隐密分析算法.该算法基于差分零系数(differential zero coefficients，简称DZC)和索引共生矩阵(index cooccurrencematrix，简称ICM)，提取对图像像素间颜色相关性和图像纹理特征变化敏感的36 维统计特征.结合支持向量机(support vector machine，简称SVM)分类技术，实现对GIF 图像中隐密信息的有效检测.实验结果表明，相比于同类算法，该算法对最佳奇偶分配(optimum parity assignment，简称OPA)、分量和(sum of components，简称SoC)、多比特分配(multibit assignment steganography，简称MBA)等典型隐密算法以及EzStego，S-Tools4，Gif-it-up 等网络上常见隐密工具的检测效果更佳，时间效率更高，且具备通用隐密分析的能力.;To improve the security and reliability of Internet communications, a steganalysis algorithm for graphics interchange format (GIF) images is proposed in this paper. 36-dimensional statistical features of GIF image, which are sensitive to the color correlation between adjacent pixels and the breaking of image texture, are extracted based on differential zero coefficients (DZC) and index co-occurrence matrix (ICM). Support vector machine (SVM) technique takes the 36-dimensional statistical features to detect hidden message in GIF images effectively. Experimental results indicate that the proposed algorithm has better detection performance and higher time efficiency comparing with other similar steganalysis algorithms for typical steganographic algorithms including optimum parity assignment (OPA), sum of components (SoC), multibit assignment steganography (MBA) and steganographic tools which are popular in the Internet, such as EzStego, S-Tools4 and Gif-it-up. Furthermore, the proposed algorithm has the ability of universal steganalysis.

A Real-Time Pulse Peak Detection Algorithm for the Photoplethysmogram

In this paper, we propose a simple and low complexity pulse peak detection algorithm using cascaded recursive digital filters and a slope sum function (SSF) with an adaptive thresholding scheme. The algorithm first eliminates noises in the photoplethysmogram (PPG) using the cascaded lowpass and highpass digital filters. The filters have been designed with 3-dB cutoff frequencies of 11 Hz and 0.5 Hz, respectively. The filtered PPG signal is then transformed by the SSF. The SSF simplifies detecting the pulse peaks by enhancing the upslope of the PPG signal and suppressing the remainder. A threshold for identifying SSF peaks is updated using the median filter with an order of 5. This update makes the threshold adaptive to variations of SSF heights. The detected SSF peaks localize ranges for pulse peak detection. Finally, the pulse peak is identified by picking the local maxima within the range from an onset index of the SSF signal to the following zero index. In order to cope with over-detected and missed information, the proposed algorithm employs knowledge-based rules as post- processing. The algorithm is tested on a database where PPG waveforms are collected from 127 subjects. The results are promising, suggesting that the method provides simpler but accurate pulse peak detection in real applications. 

Compact Microstrip Antenna Structures with Multiband, Broadband, and Band-Notched Properties, for Portable Devices

It is difficult to list all the current applications for microstrip antennas; it could be said that they are the transducers that control modern life. Yet, every year, new applications are required which challenge the performance limits of current designs. Some of those challenges are associated with controlling the spectrum performance and continuing to seek techniques to tailor the shape to the applications. This special issue brings some of the latest thinking in compact microstrip antenna design. However, the variety of approaches presented in the papers shows the possibilities that exist for future developments: this special issue is as much about setting out possibilities as it is about presenting new thinking. The papers in this special issue are as follows. An approach to design microstrip antennas is presented in “Design of arbitrarily shaped planar microstrip antenna arrays with improved efficiency” which considers improved radiation efficiency. Focusing on the application areas of Bluetooth and WLAN, a dual-band planar inverted-E antenna (PIEA) is presented in “Compact dual-band planar inverted-eshaped antenna using defected ground structure” with a novel ground. A mesh grid structure planar wideband zero index metamaterial (ZIM) antenna is presented in “Zero index metamaterial for designing high-gain patch antenna” that provides a bandwidth of 9.9GHz to 11.4 GHz.An arc H-shaped slot on the radiating patch provides dual bandnotched characteristics which is discussed in “Design and analysis of a novel dual band-notched UWB antenna.” The paper entitled “Printed modified bow-tie dipole antenna for DVB/WLAN applications” presents a printed modified bow-tie dipole antenna which consists of asymmetric feed and inserted slots. A frequency range of 3.1– 10.6GHz is achieved by an antenna of only 30mm × 36mm and is discussed in “A compact UWB diversity antenna.” Amodified compact planar ultrawideband (UWB) monopole antenna with triple controllable band-notched characteristics is presented in “A compact planar UWB antenna with triple controllable band-notched characteristics,” which consists of a modified staircased V-shaped radiating element and partial ground plane. The radiation pattern is controlled using elliptical and rectangular patches, which is discussed in “A compact size 4–19.1 GHz heart shape UWB antenna with triangular patches.”

Metamaterials with Zero Phase Delay

During the early years of research into metamaterials, some interest has shifted towards the realization of materials that exhibit zero or near-zero refractive index. A refractive index of zero implies that light enters a state of quasi-infinite phase velocity and infinite wavelength. Instead of strong resonance mechanism in metamaterials, the physical phenomenon of PhC is based on the special dispersion relations of photonic bands with weak loss. Several different metamaterials to realize zero phase delay are introduced in this paper. Their remarkable properties should have significant technological applications in photon delay lines with zero phase difference, information-processing devices, new optical phase control and measurement techniques.

Measuring disparities in sanitation access: does the measure matter?

Initiatives to monitor progress in health interventions like sanitation are increasingly focused on disparities in access. We explored three methodological challenges to monitoring changes in sanitation coverage across socio-economic and demographic determinants: (i) confounding by wealth indices including water and sanitation assets, (ii) use of individual urban and rural settings versus national wealth indices and (iii) child-level versus household-level analyses. Sanitation coverage by wealth for children and households across settings was estimated from recent Demographic and Health Surveys in six low-income countries. Household assignment to wealth quintiles was based on principal components analyses of assets. Concordance in household quintile assignment and estimated distribution of improved sanitation was assessed using two wealth indices differing by inclusion or exclusion of water and sanitation assets and independently derived for each setting. Improved sanitation was estimated using under five children and households. Wealth indices estimated with water, and sanitation assets are highly correlated with indices excluding them but can overstate disparities in sanitation access. Independently, derived setting wealth indices highly correlate with setting estimates of coverage using a single national index. Sanitation coverage and quintile disparities were consistently lower in household-level estimates. Standard asset indices provide a reasonably robust measure of disparities in improved sanitation, although overestimation is possible. Separate setting wealth quintiles reveal important disparities in urban areas, but analysis of setting quintiles using a national index is sufficient. Estimates and disparities in household-level coverage of improved sanitation can underestimate coverage for children under five.

Freeing Nonlinear Optics from Phase Matching

Optical metamaterials that have a refractive index of zero can boost the efficiency of nonlinear optical processes.

Epsilon-near-zero or mu-near-zero materials composed of dielectric photonic crystals

We theoretically demonstrate that at certain frequencies two-dimensional dielectric photonic crystals (PCs) may be regarded as either epsilon-near-zero or mu-near-zero materials. We show that the transmission through a slab of such materials upon normal incidence is normally non-unity and decays with slab thickness. However, when the incident angle increases slightly, the transmittance experiences a dramatic increase due to the Brewster effect. The combination of the tunneling and resonance effects makes such materials good candidates for almost perfect bending waveguides and cloaking in waveguides. The zero index also enables applications of focusing and directive emission. At last, the distinction between the single-zero and double-zero media is discussed. In all of the above results, the numerical simulations perfectly match with theoretical predictions from the effective medium analysis.

Total transmission and total reflection of acoustic wave by zero index metamaterials loaded with general solid defects

This work investigates acoustic wave transmission property through a zero index metamaterials (ZIM) waveguide embedded with a general solid defect. Total transmission and total reflection can be achieved by adjusting the parameters of the solid defect. We comprehensively study how longitudinal/transverse wave speeds of the solid defect affect the acoustic wave propagation through the waveguide. A two-dimensional (2D) acoustic crystals system with zero index is used to realize these intriguing transmission properties. Thus, our work provides more possibilities to manipulate acoustic wave propagation through ZIM.

Propagation of acoustic waves in a metamaterial with a refractive index of near zero

A metamaterial system with a refractive index of near zero for acoustic wave is realized. The designed system, which uses Helmholtz resonators, is analyzed using the equivalent circuit theory. Through the simulation and the experiment, we observed a large phase velocity in the metamaterial and a concentration of the energy density in the narrow normal waveguide directly coupled to the metamaterial. This is different to the metamaterial for the electromagnetic wave, because the concentration of energy density of the electromagnetic wave occurs in the metamaterial inside. The acoustic metamaterial system can be applied to the development of device for the acoustic energy concentrator and the acoustic filter.

AB0750 Comparative study between physical and ultrasound examination in rheumatoid arthritis patients with low disease activity or in remission

BackgroundImaging data indicates that Rheumatoid Arthritis (RA) patients in clinical remission (CR) may present persistent sub-clinical inflammatory activity. Positive Power Doppler Ultrasonography (PDUS) signal in joints is considered to be...

Effective zero index in locally resonant acoustic material

Abstract Here in locally resonant acoustic material, it is shown that effective zero refractive index can be constructed by the resonant unit-cells with coherent degenerate monopole–dipole momenta. Due to strong local resonances, the material layers with effective zero refractive index can function as a resonant cavity of high Q factor, where a subtle deviation from the resonant frequency may result in distinct increase of reflection. Full-wave simulations are performed to demonstrate some unusual wave transport properties such as invisibility cloaking, super-reflection, local field enhancement, and wavefronts rotation.

Total reflection and cloaking by zero index metamaterials loaded with rectangular dielectric defects

In this work, we investigate wave transmission property through a zero index metamaterial (ZIM) waveguide embedded with rectangular dielectric defects. We show that total reflection and total transmission (cloaking) can be achieved by adjusting the geometric sizes and/or permittivities of the defects. Our work provides another possibility of manipulating wave propagation through ZIM in addition to the widely studied dielectric defects with cylindrical geometries.

Space-coiling metamaterials with double negativity and conical dispersion.

Metamaterials are effectively homogeneous materials that display extraordinary dispersion. Negative index metamaterials, zero index metamaterials and extremely anisotropic metamaterials are just a few examples. Instead of using locally resonating elements that may cause undesirable absorption, there are huge efforts to seek alternative routes to obtain these unusual properties. Here, we demonstrate an alternative approach for constructing metamaterials with extreme dispersion by simply coiling up space with curled channels. Such a geometric approach also has an advantage that the ratio between the wavelength and the lattice constant in achieving a negative or zero index can be changed in principle. It allows us to construct for the first time an acoustic metamaterial with conical dispersion, leading to a clear demonstration of negative refraction from an acoustic metamaterial with airborne sound. We also design and realize a double-negative metamaterial for microwaves under the same principle.

Asymptotic for a Riemann-Hilbert problem solution

We solve an homogeneous Riemann-Hilbert problem, such that the density does not satisfy the zero index condition. Moreover, we find an asymptotic representation for the solution to this problem. As an application, the problem mentioned above appears in the construction of a Green operator for a linear partial differential equation with Riesz fractional derivative. Also, in order to estimate such operator the asymptotic representation is used.