负折射率材料的研究进展

负折射率材料由于其独特的性质引起了人们极大的兴趣。介绍了负折射产生的原理及其奇特性质，着重阐述了实现负折射材料的3种主要方法：双负介质实现负折射、左手介质实现负折射和光子晶体实现负折射。分析了各种方法在实现光频段低损耗负折射材料中的可行性及纳米技术发挥的重大作用。     

Image inversion and magnification by negative index prisms

A Dove prism and an anamorphic prism pair are investigated in negative index imaging systems. An equilateral triangular prism with refractive index of -1 operates as a negative index Dove prism that inverts as well as images the incident field. A negative index anamorphic prism pair acts as a negative index imaging system with magnification. The relationship between achievable magnification and aberrations is discussed. Both prism systems can be implemented by using negative index photonic crystals, and their performance is demonstrated numerically by the finite-difference time-domain method. These negative index prism structures enhance the functionalities of negative index flat lenses and broaden the applications of negative index materials.     

反铁电材料中负电卡效应的研究进展

电卡效应是指电介质材料中由于施加或去除电场导致的材料温度变化的现象, 包括正电卡效应和负电卡效应两种类型。电卡效应作为一种高效率、无噪音、环境友好的制冷效应, 在固态制冷特别是集成电路制冷领域显示出广阔的应用前景, 在过去的几十年中吸引了科研人员广泛的研究兴趣。研究表明, 通过结合正负电卡效应, 可以显著提高电卡效应的制冷能力。与正电卡效应不同, 负电卡效应因其独特的物理起源, 调控手段极为有限。本文以负电卡效应为中心, 重点介绍反铁电材料中负电卡效应的最新研究进展, 具体内容包括以下四个部分: 首先, 从电卡效应的研究历史出发, 介绍了电卡效应的制冷原理, 介绍了一个典型的能将正、负电卡效应结合的双制冷循环; 其次, 介绍了基于Maxwell关系的负电卡效应间接测试方法, 以及几种负电卡效应直接测试方法, 并讨论了不同方法的适用条件和优缺点; 再次, 以典型的负电卡效应材料——反铁电材料为例, 着重介绍了负电卡效应的物理起源, 综述了反铁电薄膜和反铁电块体材料中的负电卡效应, 并对其它铁电材料中的负电卡效应做了简要介绍; 最后, 对负电卡效应的研究进行了总结和展望。     

Negative Poisson's Ratio in Modern Functional Materials

Materials with negative Poisson's ratio attract considerable attention due to their underlying intriguing physical properties and numerous promising applications, particularly in stringent environments such as aerospace and defense areas, because of their unconventional mechanical enhancements. Recent progress in materials with a negative Poisson's ratio are reviewed here, with the current state of research regarding both theory and experiment. The inter‐relationship between the underlying structure and a negative Poisson's ratio is discussed in functional materials, including macroscopic bulk, low‐dimensional nanoscale particles, films, sheets, or tubes. The coexistence and correlations with other negative indexes (such as negative compressibility and negative thermal expansion) are also addressed. Finally, open questions and future research opportunities are proposed for functional materials with negative Poisson's ratios.     

带负吸功能的液体灌装阀

目的研发一种关阀后液体不滴漏的灌装阀。方法打破传统设计理念,将灌装阀设计成复合腔,即灌装腔和负吸腔,负吸腔在灌装腔内部。灌装阀关闭瞬间,负吸腔形成上腔和下腔,下腔具有负压,阀口周围残留的液体会自动顺着阀芯和负吸杆中间的毛细孔被吸入负吸下腔。结果灌装阀关闭后没有残留液体滴漏,避免了残留液体污染包装桶,省去了传统的接料盘或复杂的负吸装置。结论带负吸功能的液体灌装阀成功地解决了灌装阀滴漏的难题,而且结构紧凑、成本低。     

Axial evolution of the negative glow in a hollow cathode discharge.

The purpose of these studies was to examine the axial evolution of the negative glow in a hollow cathode discharge. The time-average negative glow profiles along the central axis of a hollow cathode were recorded for 81 pulse widths over the range of 5-25 microseconds in increments of 0.25 microseconds at a constant interpulse delay of 206.4 microseconds. Subsequent numerical processing yielded the instantaneous negative glow profile. The negative glow was viewed through a mesh-covered slot along the length of the hollow cathode. The negative flow profiles were imaged using a vidicon video camera. A PC-based frame grabber digitized the video images and stored them for subsequent processing.     

Evanescent surface-wave modes in a slab with application to miniaturised waveguide components

Characteristics of surface-wave modes in a slab with either negative permittivity or negative permeability are considered. It is shown that this kind of slab is a monomode structure which supports TM mode when the permittivity is negative and TE mode when the permeability is negative. It is shown that tightly bound surface-wave modes exist, also backward waves, in a slab with small thickness. These surface-wave modes will certainly have applications in trying to miniaturise waveguide components in microwave techniques and in optics. As an example, characteristics for a planar plasma waveguide are given     

An ‘electromagnetic wiggler’ originating from refraction of waves at the side edge of a Bragg reflector

Calculations are reported which predict that light incident on the side edge of a Bragg reflector can show varied and unusual refraction behaviour, including a rapid transition from positive to negative refraction. Although under certain conditions negative refraction can occur, it is concluded that perfect lensing based on it is unlikely to be realised in practice. However, it is shown that light incident obliquely on the structure can be made to propagate normal to the interface after refraction while exhibiting lateral oscillations of its Poynting vector, an effect that could possibly find application in an ‘electromagnetic wiggler’. It is also shown that negative group velocity rather than negative effective mass is required for the observation of the negative refraction, and in the case of low refractive index contrast, negative refraction occurs only when the size of the illumination spot exceeds a critical value, which is inversely proportional to the contrast of the refractive indices.     

Exploring the bibliometric and semantic nature of negative results

Negative results are not popular to disseminate. However, their publication would help to save resources and foster scientific communication. This study analysed the bibliometric and semantic nature of negative results publications. The Journal of Negative Results in Biomedicine (JNRBM) was used as a role model. Its complete articles from 2002–2009 were extracted from SCOPUS and supplemented by related records. Complementary negative results records were retrieved from Web of Science in “Biochemistry” and “Telecommunications”. Applied bibliometrics comprised of co-author and co-affiliation analysis and a citation impact profile. Bibliometrics showed that authorship is widely spread. A specific community for the publication of negative results in devoted literature is non-existent. Neither co-author nor co-affiliation analysis indicated strong interconnectivities. JNRBM articles are cited by a broad spectrum of journals rather than by specific titles. Devoted negative results journals like JNRBM have a rather low impact measured by the number of received citations. On the other hand, only one-third of the publications remain uncited, corroborating their importance for the scientific community. The semantic analysis relies on negative expressions manually identified in JNRBM article titles and abstracts and extracted to syntactic patterns. By using a Natural Language Processing tool these patterns are then employed to detect their occurrences in the multidisciplinary bibliographical database PASCAL. The translation of manually identified negation patterns to syntactic patterns and their application to multidisciplinary bibliographic databases (PASCAL, Web of Science) proved to be a successful method to retrieve even hidden negative results. There is proof that negative results are not only restricted to the biomedical domain. Interestingly a high percentage of the so far identified negative results papers were funded and therefore needed to be published. Thus policies that explicitly encourage or even mandate the publication of negative results could probably bring about a shift in the current scientific communication behaviour.     

On the possibility of creating artificial media simultaneously possessing negative permittivity and permeability

Artificial magnetodielectric media are considered which are composed of two subsystems-one, possessing a negative dielectric permittivity and another, possessing a negative magnetic permeability. It is shown that the resulting composite material is characterized by a negative refractive index only under certain special conditions: in the absence of a strong quasistatic coupling between the two subsystems.     

Estimate of the negative ion density in reactive gas plasmas

The negative ion density in a SF₆/Ar double plasma is estimated. Here, the density ratio of negative ions to positive ions is evaluated from the reduction rates of the ion and electron saturation current. Furthermore, the negative ion density obtained with this method is confirmed to agree with that calculated from the measured phase velocity of the ion acoustic wave (fast mode) when <0.6, where the positive and negative ion mass are obtained from the spectrum analysis with a quadruple mass spectrometer (QMS) system. The negative ion density in fluorocarbon ECR plasma is also estimated by means of the Langmuir probe method. It is found that in fluorocarbon ECR plasma is less than 0.5.     

Metamaterials with gradient negative index of refraction

We propose a new metamaterial with a gradient negative index of refraction, which can focus a collimated beam of light coming from a distant object. A slab of the negative refractive index metamaterial has a focal length that can be tuned by changing the gradient of the negative refractive index. A thin metal film pierced with holes of appropriate size or spacing between them can be used as a metamaterial with the gradient negative index of refraction. We use finite-difference time-domain calculations to show the focusing of a plane electromagnetic wave passing through a system of equidistantly spaced holes in a metal slab with decreasing diameters toward the edges of the slab.     

Magnetoactive Acoustic Metamaterials

Acoustic metamaterials with negative constitutive parameters (modulus and/or mass density) have shown great potential in diverse applications ranging from sonic cloaking, abnormal refraction and superlensing, to noise canceling. In conventional acoustic metamaterials, the negative constitutive parameters are engineered via tailored structures with fixed geometries; therefore, the relationships between constitutive parameters and acoustic frequencies are typically fixed to form a 2D phase space once the structures are fabricated. Here, by means of a model system of magnetoactive lattice structures, stimuli‐responsive acoustic metamaterials are demonstrated to be able to extend the 2D phase space to 3D through rapidly and repeatedly switching signs of constitutive parameters with remote magnetic fields. It is shown for the first time that effective modulus can be reversibly switched between positive and negative within controlled frequency regimes through lattice buckling modulated by theoretically predicted magnetic fields. The magnetically triggered negative‐modulus and cavity‐induced negative density are integrated to achieve flexible switching between single‐negative and double‐negative. This strategy opens promising avenues for remote, rapid, and reversible modulation of acoustic transportation, refraction, imaging, and focusing in subwavelength regimes.     

Optimum Conditions In Automatic Colour Printing

General principlss involved in automatic colour printing are discussed. A new concept is introduced: the reading value of a negative, i.e., the way the photocell registers the negative. Methods, by which reading and printing values of negative are matched, are indicated.     

A magnetic feedback modulator for improved FM carrier recording

Magnetic multivibrators are often used as voltage-controlled oscillators in FM carrier recording systems. These oscillators generally consist of two switching transistors connected to a center tapped coil on a square loop magnetic core. The transistors operate alternately in saturation, driving the core between its positive and negative saturation limits. Frequency then depends upon saturation flux and applied voltage. In the Magnetic Feedback Modulator, stability and linearity improvement of an order of magnitude is possible with a new method of applying negative feedback to a square-loop core magnetic multivibrator. In addition, circuit complexity is reduced considerably over previous methods using conventional frequency detectors to derive feedback voltage. Based on Faraday's Law, a voltage which is a function of frequency and flux change is derived from the magnetic circuit. This voltage is then used as negative feedback to the dc differential amplifier to drive the magnetic multivibrator. Since the magnetic circuit is included in the negative feedback loop, frequency errors occurring in the modulator cause corresponding changes in the magnetic feedback voltage. The errors are then reduced in magnitude by the negative feedback.     

A lossless negative dielectric constant from quantum dot exciton polaritons

Prospects for a lossless negative dielectric constant material for optical devices are studied. Simulations show that with sufficient gain, a mixture of two semiconductor quantum dots (QDs) can produce an effective dielectric constant that is lossless and negative. This permits, in concept, arbitrarily small scaling of the optical mode volume, a major goal in the field of nanophotonics. The proposed implementation of a lossless negative dielectric constant material based on colloidal QDs opens a tractable path.     

A composite medium with simultaneously negative permittivity and permeability

A new composite medium that possesses simultaneously negative permittivity and permeability in the microwave wavelength range is proposed. The medium is composed of evanescent waveguide structures responsible for the negative permittivity, with embedded cylindrical elements of a one-dimensional chiral medium accounting for the negative permeability. The evanescent waveguide structures exhibit blooming and antiresonances in the reflection coefficient.     

Metamaterials with negative compressibility — a novel concept with a long history

Metamaterials with negative compressibility are a very promising group of novel materials with a wide variety of potential application. A recent model proposed construction of the structures with three-dimensional negative compressibility by utilizing successive destabilization of stable or metastable states and inducing phase transitions mimicking negative compressibility. Here, we would like to show that similar concept is used by the nature and a nice example of this kind of metamaterial can be seen even in a glass of water.     

Negative thermal expansion structures constructed from positive thermal expansion trusses

The negative thermal expansivity of a type of space frame structure is investigated herein. On the basis of space frame structure consisting of tetrahedral representative volume elements, a volumetric thermal strain, and a volumetric coefficient of thermal expansion (CTE) models are developed in this article for a special category of tetrahedron that is made from two types of materials, each for the three apex and the three base rods. Based on these models, the conditions for attaining negative volumetric thermal strain and negative coefficient of volumetric thermal expansion are established. Plotted results reveal a trend in which the extent of negative expansivity is increased for lower apex-to-base rod length and CTE ratios, and higher base rod CTE.