Surface plasmon-mediated energy transfer in heterogap Au-Ag nanowires

We report the observation of energy transfer from a gold (Au) nanodisk pair to a silver (Ag) nanowire across a 120 nm gap via surface plasmon resonance (SPR) excitation. The enhanced electromagnetic (EM) fields generated by Au SPR excitation induce oscillation of the conduction electrons in the Ag segment, transferring energy to it even though the Ag segment has only weak resonant interactions with the incident EM radiation. The induced Ag SPR produces strong EM fields at the position of the Ag segment, leading to a Raman signal approximately 15 times greater than when the Ag segment is alone (not adjacent to the Au nanodisk pair). The Raman intensity is found to depend nonlinearly on the incident laser intensity for laser power densities of 10 kW/cm(2), which is consistent with the results of EM theory calculations which are not able to account for the factor of 15 enhancement based on a linear mechanism. This suggests that energy transfer from the Au disk pair to the Ag segment involves an enhanced nonlinear polarization mechanism such as can be produced by the electronic Kerr effect or stimulated Raman scattering.     

A new compact circuit-level model of semiconductor lasers: investigation of relative intensity noise and frequency noise spectra

We introduce a new compact noise equivalent circuit model of semiconductor lasers (SLs) from the rate equation including Langevin noise sources. The noise sources are described in terms of the spectral properties of the relative intensity noise (RIN) and frequency/phase noise (FN). Unlike the previous noise equivalent circuit models, which are based on two different DC and small-signal circuit models, using only a single circuit model, the static and dynamic responses and also the noise characteristics of SLs, can be investigated. We examine the validity of the presented noise circuit model by comparing the simulated results with the analytical and numerical results available in the literatures.     

Probing the electromagnetic field distribution within a metallic nanodisk

A Co nanolayer is used as a local probe to evaluate the vertical inhomogeneous distribution of the electromagnetic (EM) field within a resonant metallic nanodisk. Taking advantage of the direct relation between the magneto-optical activity and the electromagnetic field intensity in the Co layer, it is shown that the nonuniform EM distribution within the nanodisk under plasmon resonant conditions has maximum values close to the upper and lower flat faces, and a minimum value in the middle.     

Equivalent circuit for high-voltage partial-core resonant transformers

An equivalent circuit model for the partial-core resonant transformer is presented. A model which omits core losses is first introduced and is verified on a sample air-core resonant transformer. Partial-cores are then introduced into the transformer and the resonant characteristics are re-measured. The model is modified to account for the core losses and then verified against the measured data. Comparisons and transformations between the model and the Steinmetz 'exact' transformer equivalent circuit are given. A procedure for measuring the equivalent circuit inductances is described and then used to investigate the inductance variation with core displacement characteristics of the sample transformer in both axial-offset and centre-gap arrangements. In a capacitive load test the sample transformer was linear to a significantly higher voltage when using the centre-gap arrangement.     

Breaking through Barriers: Ultrafast Microbullet Based on Cavitation Bubble

Micromotors hold great promise for extensive practical applications such as those in biomedical domains and reservoir exploration. However, insufficient propulsion of the micromotor limits its application in crossing biological barriers and breaking reservoir boundaries. In this study, an ultrafast microbullet based on laser cavitation that can utilize the energy of a cavitation bubble and realize its own hurtling motion is reported. The experiments are performed using high-speed photography. A boundary integral method is adopted to reveal the motion mechanism of a polystyrene (PS)/magnetic nanoparticle (MNP) microbullet under the action of laser cavitation. Furthermore, the influence of certain factors (including laser intensity, microbullet size, and ambient temperature) on the motion of the microbullet was explored. For the PS/MNP microbullet driven by laser cavitation, the instantaneous velocity obtained can reach 5.23 m s⁻¹. This strategy of driving the PS/MNP microbullet provides strong penetration ability and targeted motion. It is believed that the reported propulsion mechanism opens up new possibilities for micromotors in a wide range of engineering applications.     

Experimental characterization of on-chip inductor and capacitor interconnect: part I. Series case

Detailed experimental investigations described here show the overall characteristics of on-chip inductor and capacitor serial interconnects (L--Cs) on silicon substrates. Using a new equivalent circuit model and the measured S parameters obtained by deembedding techniques, we examine and compare a single inductor, single capacitor, and two sets of series L--Cs. Agreement between the measured and simulated S parameters is excellent. At low frequency, the first resonant frequency f/sub res/ of series L--Cs can be easily determined by f/sub res/=(2/spl pi//spl radic/(LC))/sup -1/, while at high frequency, parasitic parameter effects of both the substrate and the metal strips on f/sub res/ of the L--Cs circuit must be considered.     

Efficient tunability and circuit model of nested-U nanoresonators in optical metasurfaces

Tunable metasurfaces can be employed to physically or mechanically engineer and control electromagnetic wave properties like reflection and transmission and their associated spectral characteristics like resonance frequency. Here, we propose highly tunable and sensitive metasurfaces composed of an array of a nested double U-shaped (NDU) nanoresonators on elastic polydimethylsiloxane substrate, operating in infrared region. The mechanical deformation varies the spaces between the coupled resonator elements which in turn leads to corresponding variations in the equivalent capacitance and inductance between the U-shaped elements causing efficient tunability. In addition to the higher signal strengths, it is also reported that the resonant frequency of the proposed metasurface exhibits substantial spectral shift. The observed remarkable trends are adequately verified by the developed equivalent circuit model for the proposed NDU-structure.     

自由电子激光中的等效折射率

推导出适用于三维自由电子激光中的电子束的等效折射率，并说明高斯平面波分布的激光场是电子束等效折射率为平方分布率即类透镜介质的结果，对指数增长区的复数增益的三次方程作了改进，而且，还选用典型的自由电子激光的参数进行了数值计算，并对结果作了简要的分析。     

EM characteristics of the RAS composed of E-glass/epoxy composite and single dipole FSS element

From the methods to reduce radar cross section (RCS) such as shaping of the target, radar absorbing material (RAM), and radar absorbing structure (RAS), the RAS composed of frequency selective surface (FSS) screens and low-loss composite materials is used widely because the FSS screen transmits or reflects electromagnetic (EM) waves selectively and the composite material withstands external loads. In this study, the RAS composed of the E-glass/epoxy composite and single dipole FSS element was fabricated by printed circuit board (PCB) manufacturing process, and their EM transmission characteristics, such as a resonant frequency, a minimum transmission loss, and a transmission bandwidth, were measured in the X-band frequency range by the free space method with respect to the size of dipole element and its periodicity of array.     

被动湍流控制圆柱驰振能量收集的等效电路研究

为更好的预测驰振压电能量收获机的性能,首先建立了等效电路仿真模型(ECM)并通过实验验证,最大误差不超过10%。采用该方法分析了被动湍流控制(PTC)下圆柱驰振压电能量收集的仿真模型,且该方法可将驰振能量转化系统的质量-弹簧-阻尼(M-C-K)控制方程中各参数用等效电路的电子元件来表示,从而可以分析过往仿真手段所不能解决的直流电路耦合问题。其次,从能量收集效率角度分析了交流-直流等效电路中临界风速(Ucr)随外接载荷的变化规律,及输出电压与功率随不同风速和外界载荷的变化规律。结果表明,交流电路中Ucr随载荷的增大先增大后减小,直流电路中Ucr随载荷的增大逐渐减小。当风速达到Ucr的最大值时,驰振在任一电阻下均会发生。U≥Ucr时,驰振出现锁定现象,输出电压和功率均随着风速的增大而增大。当风速过大时,增长率有减小趋势。输出电压均随着电阻的增大而增大,功率随电阻的增大先增大后减小。相比于交流电路,直流电路的最佳负载由1.1 MΩ提高到2.0 MΩ,同时功率峰值从0.08 mW降低到0.04 mW。     

Broadbanding of A-sandwich Radome Using Jerusalem Cross Frequency Selective Surface

Enhancement of electromagnetic performance of A-sandwich radome using aperture-type Jerusalem cross frequency selective surface (FSS) is presented. The Jerusalem cross FSS array is embedded in the mid-plane of the core of Asandwich radome to enhance the EM performance parameters over the entire Xband. For modeling the Jerusalem cross FSS embedded radome panel and evaluation of its EM performance parameters, equivalent transmission line method in conjunction with equivalent circuit model is used. A comparative study of Jerusalem cross FSS embedded A-sandwich radome and A-sandwich radome of identical material and thickness (core and skin layers) indicate that the new wall configuration has superior EM performance as compared to the A-sandwich wall alone configuration. The excellent EM performance of Jerusalem cross FSS embedded A-sandwich radome makes it a desirable choice for the design of normal incidence radomes (hemispherical/ cylindrical), near-normal incidence radomes (paraboloidal) and highly streamlined airborne nosecone radomes.     

Reduction of the dependence of the frequency of a passive resonant surface acoustic wave sensor with magnetic coupling on the angle of rotation of the shaft

The effect of connecting a rotating ring joint on the frequency of a passive contactless surface acoustic wave resonant sensor with the combined use of a model based on connected transmission lines and its equivalent electric circuit with lumped elements is analyzed. The considerable reduction in the dependence of the frequency of the sensor on the angle of rotation of the shaft and the reduction in the error of measurements carried out on the shaft when both rotating ring joints are completely symmetrically connected are demonstrated.     

影响贵金属纳米颗粒表面等离子体共振因素评述

贵金属纳米颗粒具有可调的共振吸收谱,被广泛用于光能传送器、近场扫描光学显微学、表面增强谱学、化学和生物传感器等。系统地评述了颗粒尺寸、颗粒分布、颗粒形状、颗粒体积分数、颗粒组成和颗粒结构等因素对金属纳米颗粒等离子体共振吸收性能的影响,有利于深入理解等离子体共振吸收的物理实质和实现对等离子体共振频率的调控。     

Photoinduced switching of the current through a single molecule: effects of surface plasmon excitations of the leads

The photoinduced switch of the current through a single molecule is studied theoretically by including plasmon excitations of the leads. A molecule weakly linked to two spherical nanoelectrodes is considered resulting in sequential charge transmission scheme. Taking the molecular charging energy (relative to the equilibrium lead chemical potential) to be comparable to the molecular excitation energy, an efficient current switch in a low voltage range becomes possible. A remarkable enhancement of the current is achieved due to simultaneous plasmon excitations in the electrodes. The behavior is explained by an increased molecular absorbance due to oscillator strength transfer from the electrode plasmon excitations and by a net excitation energy motion from the electrodes to the molecule.     

Finite element analysis of underwater capacitor micromachined ultrasonic transducers

A simple electromechanical equivalent circuit model is used to predict the behavior of capacitive micromachined ultrasonic transducers (cMUT). The equivalent circuit model of the cMUT lacks important features such as coupling to the substrate and the ability to predict crosstalk between elements of an array of transducers. To overcome these deficiencies, a finite element model of the cMUT is constructed using the commercial code ANSYS(R). Calculation results of the complex load impedance seen by single capacitor cells are presented, then followed by a calculation of the plane wave real load impedance seen by a parallel combination of many cells that are used to make a transducer. Crosstalk between 1-D array elements is found to be due to two main sources: coupling through a Stoneley wave propagating at the transducer-water interface and coupling through Lamb waves propagating in the substrate. To reduce the crosstalk level, the effect of structural variations of the substrate are investigated, which includes a change of its thickness and etched trenches or polymer walls between array elements     

Effects of a parallel resistor on electrical characteristics of a piezoelectric transformer in open-circuit transient state

This paper investigates electrical transient characteristics of a Rosen-type piezoelectric transformer (PT), including maximum voltages, time constants, energy losses and average powers, and their improvements immediately after turning OFF. A parallel resistor connected to both input terminals of the PT is needed to improve the transient characteristics. An equivalent circuit for the PT is first given. Then, an open-circuit voltage, involving a direct current (DC) component and an alternating current (AC) component, and its related energy losses are derived from the equivalent circuit with initial conditions. Moreover, an AC power control system, including a DC-to-AC resonant inverter, a control switch and electronic instruments, is constructed to determine the electrical characteristics of the OFF transient state. Furthermore, the effects of the parallel resistor on the transient characteristics at different parallel resistances are measured. The advantages of adding the parallel resistor also are discussed. From the measured results, the DC time constant is greatly decreased from 9 to 0.04 ms by a 10 k(omega) parallel resistance under open output.     

Surface plasmon-assisted optical bistability in the quantum dot-metal nanoparticle hybrid system

We theoretically investigated optical bistability (OB) of a coupled excition–plasmon hybrid system in a unidirectional ring cavity. It is found that the threshold and the region of OB can be tuned by adjusting the center–center distance between the quantum dot and metal nanoparticle (MNP), the Rabi frequency of the control field and the radius of the MNP. Due to the significantly enhanced optical nonlinearity by the surface plasmon effect, the threshold of OB can be decreased greatly when the probe field is parallel to the major axis of the hybrid system. The enhanced OB may have promising applications in optical switching and optical storage.     

Resonant vibration investigations for piezoceramic disks and annuli by using the equivalent constant method

This paper presents the equivalent constant method to investigate the transverse vibration of piezoceramic disks and annuli. By comparing the characteristic equations of resonant frequencies between isotropic and piezoceramic disks, the named equivalent Poisson's ratio v is derived, then the transverse vibration characteristic equation can be expressed as a single formulation for these two materials. To verify this method, characteristic equations of transverse vibration for piezoceramic disks and annuli with many different boundary conditions are discussed and calculated for resonant frequencies. Numerical calculations based on the finite-element method (FEM) also are performed, and the results agree rather well with the theoretical predictions. With the aid of the relations between frequency parameter and equivalent Poisson's ratio in explicit form, the other application of equivalent Poisson's ratio is the inverse evaluation of material constants. The laser Doppler vibrometer (LDV) and impedance analyzer are used to experimentally obtain the resonant frequencies of transverse and radial extensional vibrations, respectively. By the experimental results for the traction-free piezoceramic disk, the planar Poisson's ratio v(p) and planar electromechanical coupling coefficient k(p) are determined.     

Inductive reactance component model for high-voltage partial-core resonant transformers

A model for the inductive reactance components of an equivalent circuit for high-voltage partial-core resonant transformers is presented. The self and mutual inductances of the transformer windings are calculated using a two-dimensional linear magneto-static finite-element model. Provisions are made for axial-offset and centre-gap tuning. The model can also predict the secondary voltage at which core saturation occurs under resonant conditions. Its performance was verified against test results of three sample transformers.     

An Improved Magnetic Equivalent Circuit Model for Iron-Core Linear Permanent-Magnet Synchronous Motors

The aim of this work is to establish an accurate yet simple method for predicting flux density distribution and iron losses in linear permanent-magnet synchronous motors (LPMSMs) for iterative design procedures. For this purpose, an improved magnetic equivalent circuit for calculation of the teeth and yoke flux densities in the LPMSMs is presented. The magnetic saturation of iron core is considered by nonlinear elements and an iterative procedure is used to update these elements. The armature reaction is also taken into account in the modeling by flux sources located on the teeth of motors. These sources are time dependent and can model every winding configuration. The relative motion between the motor primary and secondary is considered by wisely designing air gap elements simplifying the permeance network construction and preventing permeance matrix distortion during primary motion. Flux densities in different load conditions are calculated by means of the proposed model. The effects of saturation and armature reaction on the flux density distribution are shown in detail. Using these flux densities, iron losses in the motor are examined and its variations versus motor parameters are then studied. All results obtained by proposed model are verified by finite-element method based on an extensive analysis.