Longitudinally driven giant magneto-impedance effect enhancement by magneto-mechanical resonance

Longitudinally driven giant magneto-impedance (GMI) effect in amorphous magnetostrictive Fe₂₄Co_11.82Ni_47.3Si_1.47B₁₅ ribbons was investigated. The experimental results showed that the magneto-mechanical resonance of the ribbons had significantly enhanced GMI effect. The strong magneto-mechanical coupling (MMC) interaction resulted in high MI ratio. Maximal GMI ratio of 1532% was obtained in the sample annealed at 340 °C under transverse magnetic field. The results are explained in terms of MMC and resonance of the magnetostrictive materials.     

基于硅基光子器件的Fano共振研究进展

硅基光子技术的发展为新型微纳光学功能器件和片上系统提供了高可靠、高精度的实现手段.采用硅基光子技术构建的具有连续(准连续)模式微腔与离散模式的微腔耦合产生的Fano共振现象得到了广泛关注.Fano共振光谱在共振波长附近具有不对称且尖锐的谐振峰,传输光的强度在共振波长附近从0突变为1,该机制可显著提高硅基光开关、探测器、...     

LC共振型巨磁阻抗效应的研究

采用化学镀方法成功制备了自带电容构成LC共振回路的CoP/Insulator/BeCu复合结构丝. 研究了这种新型复合结构丝产生LC共振型巨磁阻抗效应的特征,长度为l_m=95 cm的复合结构丝,当驱动电流频率为LC共振频率f_r=290 MHz时,LC共振型巨磁阻抗效应为4875%,磁场灵敏度为046%/A·m^-1,大于常规复合结构丝;远离此频率时的巨 关键词： 复合结构丝 LC共振')" href="#">LC共振 等效电路模型 巨磁阻抗效应     

Stochastic resonance: Linear response and giant nonlinearity

The response of a bistable noise-driven system to a weak periodic force is investigated using linear response theory (LRT) and by analogue electronic experiment. For quasithermal systems the response, and in particular its increase with increasing noise intensityD, are described by the fluctuationdissipation relations. For smallD the low-frequency susceptibility of the system() has been found in explicit form allowing for both forced oscillations about the states and periodic modulation of the probabilities of fluctuational transitions between the states. It is shown, both theoretically and experimentally, that a phase lag between the force and the response passes through a maximum whenD is tuned through the range where stochastic resonance (SR) occurs. A giant nonlinearity of the response is shown to arise for smallD and small frequencies of the driving force. It results in the signal induced by a sinusoidal force being nearly rectangular. The range of applicability of LRT is established.     

Interplay between out-of-plane magnetic plasmon and lattice resonance for modified resonance lineshape and near-field enhancement in double nanoparticles array

Two-dimensional double nanoparticle （DNP） arrays are demonstrated theoretically, supporting the interaction between out-of-plane magnetic plasmons and in-plane lattice resonances, which can be achieved by tuning the nanoparticle height or the array period due to the height-dependent magnetic resonance and the periodicity-dependent lattice resonance. The interplay between the two plasmon modes can lead to a remarkable change in resonance lineshape and an improvement on magnetic field enhancement. Simultaneous electric field and magnetic field enhancement can be obtained in the gap region between neighboring particles at two resonance frequencies as the interplay occurs, which presents “open” cavities as electromagnetic field hot spots for potential applications on detection and sensing. The results not only offer an attractive way to tune the optical responses of plasmonic nanostructure, but also provide further insight into the plasmon interactions in periodic nanostructure or metamaterials comprising multiple elements.     

Stochastic resonance in a parallel array of linear elements

This paper studies stochastic resonance (SR) phenomenon in a parallel array of linear elements with noise. Employing the signal-to-noise ratio (SNR) theory, it obtains the output SNR, and investigates the effects on the output SNR of the system with signal-independent noise and signal-dependent noise respectively. Numerical results show: the curve of the output SNR is monotone with signal-independent noise; whereas SR appears with signal-dependent noise. Moreover, the output SNR enhances rapidly with the increase of N which is the number of elements in this parallel array linear system. This result may provide smart array of simple linear sensors which are capable of acting as noise-aided amplifiers.     

Corrigendum: Stochastic resonance in a parallel array of linear elements

In this paper,we point out the errors occurring in the paper(Dong X J 2009 Chin.Phys.B 18 70) and present a correct conclusion.     

Stochastic resonance in multi-scale bistable array

This Letter explores a new mechanism of stochastic resonance (SR) that is induced by the multi-scale noise decomposed from the input signal, which is promising in signal detection and processing under heavy background noise. The input signal is firstly decomposed to multi-scale signals by orthogonal wavelet transform. Then, the approximate signal, which contains the driving signal, is processed by an uncoupled parallel bistable array with the detailed signal of each scale as the internal noise. At last, a SR mechanism combining the effects of colored noise and array SR is proposed. The simulation results show that a high quality output signal can be obtained by the new mechanism. The proposed model is more adaptive to input signal with high noise intensity than single bistable SR system, which can be seen from the signal-to-noise ratio curves and average noise intensity curves.     

硅薄膜太阳电池表面纳米线阵列光学设计

陷光结构的优化是增加硅薄膜太阳电池光吸收进而提高其效率的关键技术之一. 以硅纳米线阵列为代表的光子晶体微纳陷光结构具有突破传统陷光结构Yablonovith极限的巨大潜力. 通常硅纳米线阵列可以用作太阳电池的增透减反层、轴向p-n结、径向p-n结. 针对以上三种应用, 本文运用有限时域差分(FDTD)法系统研究了硅纳米线阵列在 300-1100 nm 波段的光学特性. 结果表明, 当硅纳米线作为太阳电池的减反层时, 周期P=300 nm, 高度H=1.5 μm, 填充率(FR)为0.282条件下时, 反射率最低为7.9%. 当硅纳米线作为轴向p-n结电池时, P=500 nm, H=1.5 μm, FR=0.55条件下纳米线阵列的吸收效率高达22.3%. 硅纳米线作为径向p-n结电池时, 其光吸收主要依靠纳米线, 硅纳米线P=300 nm, H=6 μm, FR= 0.349 条件下其吸收效率高达32.4%, 进一步提高其高度吸收效率变化不再明显. 此外, 本文还分析了非周期性硅纳米线阵列的光学性质, 与周期性硅纳米线阵列相比, 直径随机分布和位置随机分布的硅纳米线阵列都可以使吸收效率进一步提高, 相比于周期性硅纳米线阵列, 优化后直径随机分布的硅纳米线阵列吸收效率提高了39%, 吸收效率为27.8%. 本文运用FDTD法对硅纳米线阵列的光学特性进行设计与优化, 为硅纳米线阵列在太阳电池中的应用提供了理论支持.     

Controlling the focusing properties of a triangular-lattice metallic photonic-crystal slab：

This paper studies the focusing properties of a two-dimensional photonic crystal (PC) slab consisting of a triangular lattice of metallic cylinders immersed in a dielectric background. Through the analysis of the equifrequency-surface contours and the field patterns of a point source placed in the vicinity of the PC slab, it finds that both the image distance and image quality can be controlled by simply adjusting the refractive index of the background material.     

Coulomb excitation of double giant dipole resonances

We implement the Brink–Axel hypothesis for the excitation of the double giant dipole resonance (DGDR): the background states which couple to the one-phonon giant dipole resonance are themselves capable of dipole absorption. These states (and the ones which couple to the two-phonon resonance) are described in terms of the gaussian orthogonal ensemble of random matrices. We use second-order time-dependent perturbation theory and calculate analytically the ensemble-averaged cross section for excitation of the DGDR. Numerical calculations illuminate the mechanism and the dependence of the cross section on the various parameters of the theory, and are specifically performed for the reaction ²⁰⁸Pb + ²⁰⁸Pb at a projectile energy of 640 MeV/nucleon. We show that the contribution of the background states to the excitation of the DGDR is significant. We find that the width of the DGDR, the energy-integrated cross section and the ratio of this quantity over the energy-integrated cross section for the single giant dipole resonance, all agree with experiment within experimental errors. We compare our approach with that of Carlson et al. who have used a similar physical picture.     

双稳态系统中随机共振和相干共振的相关性

研究了加性噪声和乘性噪声共同驱动的双稳态系统中的随机共振和相干共振现象. 针对加性噪声和乘性噪声之间不存在关联性和存在关联性两种情形, 引入一种适当的能同时表征随机共振和相干共振的指标, 应用一阶欧拉方法, 通过数值模拟对系统的随机共振和相干共振现象进行研究. 结果表明在弱噪声驱动下, 随着加性噪声强度的增加, 当系统出现相干共振时, 如果给系统外加一个弱周期驱动力, 几乎在同一时刻, 系统也出现了随机共振现象; 但随着乘性噪声强度的增加, 仅当加性噪声和乘性噪声之间相关时, 此结论成立. 并且系统参数对相干共振和随机共振的影响是一致的. 关键词： 双稳态系统 随机共振 相干共振     

二值噪声驱动下二阶线性系统的随机共振

研究了二值噪声驱动下二阶线性系统的随机共振问题. 采用平均法推导出系统输出幅值增益的表达式,考察了幅值增益与系统频率、输入信号频率、噪声强度和噪声相关时间的关系,发现系统输出幅值增益随这些参量呈单峰共振变化. 另外,二值噪声的非对称性对共振峰值具有很大影响. 关键词： 随机共振 幅值增益 二值噪声 二阶线性系统     

Analysis of transmittance enhancement for a slab lens formed by sub-wavelength holes array on the metallic film

By investigating the transmittance and phase characteristics of the square holes on the metallic film, we find that the transmittance fluctuates with center distance between holes and appears resonant peaks, which attributes to the surface wave enhanced transmission phenomenon while the corresponding phase retardation through holes keeps constant. Based on this phenomenon, the slab lens can be optimized to a high transmittance by modulating the center distance of the holes. Design results show that the light intensity values at the focal spot of the slab lens can be enhanced from 3 to 14.5 in intensity scale when the center distance changes from 1.25λ to 0.95λ.     

一种单稳随机共振系统信噪比增益的数值研究

采用四阶Runge-Kutta数值求解方法, 发现一种单稳随机共振系统信噪比增益的随机共振现象, 并且在一定的条件下系统信噪比增益大于1.通过调节单稳随机共振系统参数可以改变信噪比增益.本文结果拓展了这类单稳的已有研究范围, 在信号检测与处理以及通信领域有着潜在的应用价值. 关键词： 单稳随机共振 信噪比增益 数值分析 非线性     

Near-field imaging of a square-lattice metallic photonic-crystal slab at the second band

Imaging properties of a two-dimensional photonic crystal slab lens are investigated through the finite-difference time-domain method. In this paper, we consider the photonic crystal slab consisting of a square lattice of square metallic rods immersed in a dielectric background. Through the analysis of the equifrequency-surface contours and the field patterns of a point source placed in the vicinity of the photonic crystal slab, we find that a good-quality image can form at the frequencies in the second TM-polarized photonic band. Comparing the images formed at different frequencies, we can clearly see that an excellent-quality image is formed by the mechanisms of simultaneous action of the self-collimation effect and the negative-refraction effect.     

Quality factor enhancement of plasmonic surface lattice resonance by using asymmetric periods

We report that using asymmetric lattice periods can enhance the quality factor of plasmonic surface lattice resonances(SLRs)in two-dimensional array of metal-insulator-metal nanopillars in asymmetric dielectric environment.Simulation results show that by adopting appropriate asymmetric lattice periods,the SLR quality factor can be enhanced by 24%compared with the scenario of symmetric periods.We find that the SLR quality factor is optimized when the resonance wavelength is closest to the Rayleigh cutoff wavelength.We also find that the SLRs effect is polarization sensitive in the proposed structure.We expect this work will advance the engineering of SLRs especially in asymmetric dielectric environments,and will promote their applications in sensing.     

Magnetic resonance image enhancement using stochastic resonance in Fourier domain

Objective

In general, low-field MRI scanners such as the 0.5- and 1-T ones produce images that are poor in quality. The motivation of this study was to lessen the noise and enhance the signal such that the image quality is improved. Here, we propose a new approach using stochastic resonance (SR)-based transform in Fourier space for the enhancement of magnetic resonance images of brain lesions, by utilizing an optimized level of Gaussian fluctuation that maximizes signal-to-noise ratio (SNR).

Materials and Methods

We acquired the T1-weighted MR image of the brain in DICOM format. We processed the original MR image using the proposed SR procedure. We then tested our approach on about 60 patients of different age groups with different lesions, such as arteriovenous malformation, benign lesion and malignant tumor, and illustrated the image enhancement by using just-noticeable difference visually as well as by utilizing the relative enhancement factor quantitatively.

Results

Our method can restore the original image from noisy image and optimally enhance the edges or boundaries of the tissues, clarify indistinct structural brain lesions without producing ringing artifacts, as well as delineate the edematous area, active tumor zone, lesion heterogeneity or morphology, and vascular abnormality. The proposed technique improves the enhancement factor better than the conventional techniques like the Wiener- and wavelet-based procedures.

Conclusions

The proposed method can readily enhance the image fusing a unique constructive interaction of noise and signal, and enables improved diagnosis over conventional methods. The approach well illustrates the novel potential of using a small amount of Gaussian noise to improve the image quality.