Particle Velocity Sensor and Its Application in Near-Field Noise Scanning Measurement

The Particle Velocity Sensor (PVS) is a kind of acoustic transducer which measures the particle velocity directly with figure-of-eight directivity. This paper proposes a near-field noise scanning technology based on the research of PVS, pressure-particle velocity (P-U) probe, and its application in noise source identification. Firstly, the principle and characteristics of PVS are presented. Secondly, a P-U probe is designed on the basis of PVS development. Finally, the noise measurement experiment for a single source is arranged and conducted. The result shows that the proposed P-U probe performs well in near-field noise source identification and localization.

A novel phase-sensitive scanning near-field optical microscope

Phase is one of the most important parameters of electromagnetic waves. It is the phase distribution that determines the propagation, reflection, refraction, focusing, divergence, and coupling features of light, and further affects the intensity distribution. In recent years, the designs of surface plasmon polariton （SPP） devices have mostly been based on the phase modulation and manipulation. Here we demonstrate a phase sensitive multi-parameter heterodyne scanning near-field opti- cal microscope （SNOM） with an aperture probe in the visible range, with which the near field optical phase and amplitude distributions can be simultaneously obtained. A novel architecture combining a spatial optical path and a fiber optical path is employed for stability and flexibility. Two kinds of typical nano-photonic devices are tested with the system. With the phase-sensitive SNOM, the phase and amplitude distributions of any nano-optical field and localized field generated with any SPP nano-structures and irregular phase modulation surfaces can be investigated. The phase distribution and the interference pattern will help us to gain a better understanding of how light interacts with SPP structures and how SPP waves generate, localize, convert, and propagate on an SPP surface. This will be a significant guidance on SPP nano-structure design and optimization.

Standing-wave spectrometry in silicon nano-waveguides using reflection-based near-field scanning optical microscopy

Utilizing reflection-based near-field scanning optical microscopy(NSOM) to image and analyze standing-wave patterns, we present a characterization technique potentially suitable for complex photonic integrated circuits. By raster scanning along the axis of a straight nano-waveguide in tapping mode and sweeping wavelength, detailed information of propagating waves in that waveguide has been extracted from analyses in both space and wavelength domains. Our technique needs no special steps for phase stabilization, thus allowing long-duration and environment-insensitive measurements. As a proof-of-concept test, in a silicon single-mode waveguide with a few of etched holes, the locations and reflection strengths of the inner defects have been quantified. The measurement uncertainty of the reflection amplitude is less than 25% at current stage. Our technique paves the way for non-destructively diagnosing photonic circuits on a chip with sub-wavelength spatial resolution and detailed information extraction.

Influence of the probe-sample interaction on scanning near-field optical microscopic images in the far field

We have studied the influence of probe-sample interaction in a scanning near-field optical microscopy （SNOM） in the far field by using samples with a step structure. For a sample with a step height of - λ/4, the SNOM image contrast between the two sides of the step changes periodically at different scan heights. For a step height of-λ/2, the image contrast remains approximately the same. The probe-sample interaction determines the SNOM image contrast here. The influence of different refractive indices of the sample has been also analysed by using a simple theoretical model.

RESEARCH ON A SCANNING NEAR-FIELD MICROSCOPY BASED ON A QUARTZ RESONATOR

A scanning near field acoustic microscopy(SNAM) used in imaging the topography of precise surfaces is presented. As a micro force sensor, a non encapsulated 1 MHz quartz resonator is damped by hydrodynamic forces when approaching an object. Thus the oscillating characteristics of the leg of the quartz resonator change. While measuring the decrease of the amplitude of vibrating, the shape of the object can be obtained. Based on the analyses of the principle and key parameters of SNAM, a SNAM is exploited. A lateral resolution of 0.5 μm and vertical resolution of 2 nm has been achieved in the experiments.

Optical polarization response at gold nanosheet edges probed by scanning near-field optical microscopy

Optical properties of metallic edge-like structures known as knife-edges are a topic of interest and possess potential applications in enhanced Raman scattering, optical trapping, etc. In this work, we investigate the near-field optical polar- ization response at the edge of a triangular gold nanosheet, which is synthesized by a wet chemical method. A homemade scanning near-field optical microscope （SNOM） in collection mode is adopted, which is able to accurately locate its probe at the edge during experiments. An uncoated straight fiber probe is used in the SNOM, because it s611 preserves the prop- erty of light polarization though it has the depolarization to some extent. By comparing near-field intensities at the edge and glass substrate, detected in different polarization directions of incident light, the edge-induced depolarization is found, which is supported by the finite differential time domain （FDTD） simulated results. The depolarized phenomenon in the near-field is similar to that in the far-field.

Scanning Head for the Apertureless near Field Optical Microscope

The design and characterization of a tip control unit for an apertureless scanning near field optical microscope (ASNOM) is reported. To make the instrument operation easier, the cantilever control parts (piezo excitation of the cantilever vibration for the dynamic mode feedback and the parts necessary for the optical lever scheme of the vibration control) were placed in a separate detachable assembly. To suppress the influence of vibrations of the setup, the assembly was made lightweight. Good optical access to the ASNOM tip from various directions is provided in the system. High long-term mechanical stability of the system (~50 nm lateral drift in 18 hours) as well as low sensitivity to seismic vibrations (~400 pm RMS) is demonstrated. It is shown that external sound is not a main source of noise in the topography image (~200 pm RMS). The light field distribution (with its amplitude and phase) around the ASNOM tip was acquired by scanning the focal spot around the tip, and a high optical quality of the system is demonstrated.

Far-Field Pattern Reconstruction from Positioning Errors Affected Near-Field Data Acquired via Helicoidal Scanning

In this paper, an effective technique to compensate the positioning errors in a near-field—far-field (NF-FF) transformation with helicoidal scanning for elongated antennas is presented and validated both numerically and experimentally. It relies on a nonredundant sampling representation of the voltage measured by the probe, obtained by considering the antenna as enclosed in a cylinder ended in two half-spheres. An iterative scheme is used to reconstruct the helicoidal NF data at the points fixed by the representation from the acquired irregularly spaced ones. Once the helicoidal data have been retrieved, those needed by a classical NF-FF transformation with cylindrical scanning are efficiently evaluated by using an optimal sampling interpolation algorithm. Some numerical tests, assessing the accuracy of the approach and its stability with respect to random errors affecting the data, are reported. Experimental tests performed at the Antenna Characterization Lab of the University of Salerno further confirm the validity of the proposed technique.

Spherical Near-Field - Far-Field Transformation for Quasi-Planar Antennas from Irregularly Spaced Data

An effective near-field - far-field (NF - FF) transformation with spherical scanning for quasi-planar antennas from irregularly spaced data is developed in this paper. Two efficient approaches for evaluating the regularly spaced spherical samples from the nonuniformly distributed ones are proposed and numerically compared. Both the approaches rely on a nonredundant sampling representation of the voltage measured by the probe, based on an oblate ellipsoidal modelling of the antenna under test. The former employs the singular value decomposition method to reconstruct the NF data at the points fixed by the nonredundant sampling representation and can be applied when the irregularly acquired samples lie on nonuniform parallels. The latter is based on an iterative technique and can be used also when such a hypothesis does not hold, but requires the existence of a biunique correspondence between the uniform and nonuniform samples, associ- ating at each uniform sampling point the nearest irregular one. Once the regularly spaced spherical samples have been recovered, the NF data needed by a probe compensated NF - FF transformation with spherical scanning are efficiently evaluated by using an optimal sampling interpolation algorithm. It is so possible to accurately compensate known posi- tioning errors in the NF - FF transformation with spherical scanning for quasi-planar antennas. Some numerical tests assessing the accuracy and the robustness of the proposed approaches are reported.

保偏光纤制备及其参数测试原理

为了研制工作波长为1310 nm的保偏光纤,采用改进的化学气相沉积工艺制备了保偏光纤预制捧和应力棒,经加工、拼接、清洗、拉丝工艺后,得到几何尺寸精确的高质量保偏光纤;同时搭建了高效测试系统,采用折射近场法、远场扫描法、视频灰度技术(传输近场),分别测量了预制棒的折射率分布和几何尺寸,保偏光纤模场直径、数值孔径、几何尺寸等关键参数。结果表明,此标准化测试系统操作流程简单、结果精确;模场直径为6.26μm,数值孔径为0.23,包涂直径80μm/135μm/165μm(精度±0.7μm);终检测试合格的光纤成品随机抽样16.25%,高低温老化实验后拍长、串音变化小。所研制的保偏光纤性能稳定,几何尺寸精确、结构均匀、损耗低,具有优良保偏性能,已广泛应用于实际生产中。

基于多面无相位近场数据的电磁干扰源等效建模

针对现有无相位近场数据的偶极子建模很难精确对干扰源进行等效的问题,对现有无相位近场数据的干扰源等效建模中所采用的双面迭代方法进行了改进,改进方法主要是采用2个以上不同高度的磁场幅度数据;对双面迭代方法中平面的选择以及改进方法中平面数量和起始面的选择进行了讨论;以干扰源辐射磁场重构的均方根误差(Root Mean Square Error,RMSE)作为偶极子建模准确度评价依据,与现有双面迭代方法及其他优化方法等效建模出的偶极子模型进行了对比验证,对比结果显示该改进方法具有更高的准确度。

Clustering study in Eu(DBM)_3Phen-doped polymer optical fibers by optical properties and near-field scanning microscopy

The clusters of Eu^3＋ ion in Eu（DBM）3Phen-doped polymethyl methacrylate （PMMA） have been studied by three means. The relative fluorescence intensity ratio of the ^5D0 → ^7F2 to ^5D0 → ^7F1 transitions with different concentrations of Eu^3＋ in Eu（DBM）3Phen-doped PMMA and metastable-state （^5D0） lifetime dependence on Eu^3＋ concentration axe analyzed. The analysis indicates that there axe no clustering effects in Eu^3＋ ions of Eu（DBM）3Phen-doped PMMA when the Eu^3＋ doping concentration is up to 1.0 wt.-%. At the same time, the clustering effect has not been observed by the scanning neax-field optical microscopy （SNOM） in Eu（DBM）3Phen-doped PMMA with 1.0 wt.-% of Eu^3＋ ions. The analysis reveals that a high concentration of Eu^3＋ can be incorporated into polymer optical fiber （POF） without clustering effect.

燃料电池控制器的电磁干扰分析

为了研究燃料电池控制器(Fuel Cell Controller,FCU)的电磁干扰(Electromagnetic Interference,EMI)特性,采用差分进化算法建立等效辐射源,基于近场扫描方法测试FCU的磁场,通过对比等效辐射源产生的磁场和测试的磁场,获得各频点在X、Y、Z方向的平均误差均在3%左右;利用重构模型对印制电路板(Printed Circuit Board,PCB)上方半空间的远场辐射进行仿真模拟.结果表明,仿真电场与实测电场的平均误差在4.1 dB左右,在测量频带范围内整体趋势一致,验证了差分进化算法重构的等效辐射源具有较高的精度,该方法可以用来预测辐射源的影响.研究了重构等效辐射源对金属外壳的影响,仿真结果表明,PCB板的远场辐射降低了10 dB左右,金属外壳能有效减少FCU向外产生辐射.

电磁近场测试平面扫描系统设计

设计了一种测量电子器件电磁场分布的近场扫描系统,用于电磁兼容测试。首先,设计了一种四层印刷电路板结构的磁场探头,其工作频率达12 GHz,空间分辨率为2 mm,仿真与实测结果吻合较好,并对探头进行了校准。其次,实现了近场扫描的自动化,采用LabVIEW设计上位机软件,STM32作为运动控制核心,通过串口接收上位机数据,并控制步进电机带动探头移动,实现定点扫描,上位机通过局域网与矢量网络分析仪实现通信,完成数据的读取与保存。最后,通过上位机对数据进行可视化处理,在扫描完成时对结果进行校准,并实时生成被测物体的场强分布图,实现电磁场分布数据可视化。场强测试结果与电磁仿真结果吻合较好,可用于分析电磁耦合路径及实现近场与远场的转换。

近场扫描技术中探头校准与源重构算法

随着通信技术的发展,电子设备的工作频率不断提高,同时设备自身的尺寸和间距也不断减小。微型化和高集成化带来了日益严重的电磁干扰问题。而传统的电磁干扰诊断方案效率低、精度差。近场扫描技术的出现和发展为分析和解决电子设备电磁干扰问题提供了有效方案,近场探头和源重构方法分别作为近场扫描技术的核心器件和主要算法,日益受到广泛的关注和研究。文章从介绍近场扫描技术、近场探头设计与校准和源重构算法的基本概念出发,概括总结这三个方面国内外的研究动态,并分析了当前研究存在的主要问题和机遇,旨在为近场扫描技术解决电磁干扰问题提供参考。

探测激子极化激元在超薄范德华微晶中的光传播

激子极化激元是一种准粒子,过渡金属二硫族化合物材料即使在室温下也能支持传播激子极化子,是非常好的纳米光子学研究平台.已有研究表明,通过散射型扫描近场光学显微镜可以对过渡金属二硫族化合物薄片中激子极化激元进行实空间探测,但波导厚度仅限于低至30 nm.本文采用三种不同波长的入射光(1550和1064 nm的近红外以及633 nm的可见光),通过基于原子力显微镜的散射型扫描近场光学显微镜测量,探测到MoS2和WSe2薄片中激子极化子普通横电模式的纳米光学成像.在厚度分别低至~3 nm(相当于4原子层)和~8 nm(相当于12原子层)的超薄MoS2和WSe2薄片上,可以清楚地观察到干涉条纹图案,大大打破了之前的测量厚度限制.当厚度接近几个原子层时,波矢量始终保持在1.6k0~1.7k0左右,而不是理论预言的1k0.这些模式的特性表明,体系是由近乎悬浮的过渡金属二硫族化合物薄片的三层对称波导构成,其对激子极性子的传播产生限域效应.研究结果为探索基于超薄过渡金属二硫族化合物材料的近红外区极化器件提供了深入的理解和开辟了新的途径.

基于人工智能高效近场扫描的瞬态强电磁干扰传导耦合路径可视化

在高压电子系统中,瞬态强电磁干扰会通过空间辐射、传导耦合等方式影响低压控制区的正常工作,在该工况下系统的电磁兼容问题较为突出。该文在时域电流测试与近场扫描结合的基础上,提出了一种改进的人工智能近场扫描算法,可实现强瞬态电磁干扰下传导耦合路径的高效可视化,据此采取了相应的整改措施并解决了系统中的电磁干扰问题。与传统近场扫描方法相比,该文提出的人工智能算法可大幅度提高测试效率。此外,还分析了不同参数的选择对该人工智能算法稳定性的影响,提出了一种自动停止扫描的判决标准,该判决标准使人工智能近场扫描算法不需要人为干预,从而具有更高的智能化与鲁棒性。

印制电路板电磁辐射等效偶极子建模与预测

提出了一种计算由印刷电路板产生的电磁辐射的新方法。这种方法是从近场扫描推导出的等效偶极子模型,建立了一系列可以产生相同辐射场的无穷小偶极子来代替PCB板。等效偶极子的参数直接由被测近场磁场决定,在封闭环境下仿真,等效的方法被推广应用到电介质平面偶极子模型,通过等效PCB基本物理特征来解决在PCB板和外壳之间的相互作用。通过用数学法求解等效模型来预测电磁辐射,极大的减少了仿真时间,提高了仿真效率。最后,以一块印制电路板为对象,通过对其进行电磁辐射仿真与试验测试,证明了利用本文方法建模与预测的正确性和高效性。

染色体的显微光谱

利用显微光谱技术在可见光范围内测定了蚕豆根尖染色体、小白鼠骨髓细胞染色体和小白鼠骨髓细胞微核的光谱，其光谱形状各具特征，峰值亦有差异。

平面近场扫描技术及其测量系统

简要介绍了平面近场扫描原理，据此研制成功的测量系统可实现平面、柱面、球面和极平面等多种方式的近场扫描、近远场变换以及数据分析和各种终端处理．