MR microscopy of micron scale structures

Magnetic resonance (MR) microscopy of up to 1–5-μm resolutions have been reported previously. The tested phantom structures, however, had widths one order of magnitude bigger than the reported resolutions, e.g., spherical beads or capillary tubes of tens-of-micron diameters or wall thicknesses have been imaged. In this study, we fabricated structures having a few micron widths on a silicon wafer and imaged them using our 1-μm-resolution MR microscopy at 14.1 T. Micron scale width structures were, for the first time, resolved by MR microscopy.     

An improved model for the cantilever NEMS actuator including the surface energy,fringing field and Casimir effects

The influence of the surface energy on the instability of nano-structures under the electrostatic force has been investigated in recent years by different researchers. It appears that in all prior research, the response of all structures becomes softer due to the surface effects. In the present study, the pull-in instability of a NEMS device incorporating the electrostatic force and Casimir intermolecular attraction for different values of the surface parameter is investigated by the Duan–Rach method of determined coefficients (MDC) in order to identify the remarkable effect of the surface energy. Although the obtained results verify the behavior of such structures in presence of the fringing field and the Casimir attraction same as the previous investigations, however the incremental effects of the surface energy cause the aforementioned structures to behave more stiffly in contrast.     

Understanding of optical readout accuracy with micromechanical sensor cantilever monitored by surface plasmon resonance

This paper reports a concept of micromechanical sensing of environmental condition using the surface plasmon resonance phenomenon. We calculate the resolution in the cantilever bending monitoring using the transfer matrix numerical method. We show that the cantilever deflection can be monitored with a resolution in the nanometer range. The SPs resonance behavior of the multilayer stack in the case of gold cantilever is discussed. We believe that this concept permits a low cost and ease of fabrication for a large bi-dimensional array of sensors with an enhanced signal-to-noise ratio.     

采用DDS的近场扫描光学显微镜探针-样品的纳米距离检测

近场扫描光学显微术中, 近场距离的检测和控制是需要解决的核心技术之一. 本文研究了基于DDS驱动的压电传感器, 在一个压电陶瓷片上, 电极被分成相同的两部分, 分别用于振动驱动和振幅检测. 近场扫描的光纤探针固定于此压电陶瓷片上. 振动驱动信号采用DDS, 在样品的远场时, 可以通过频率扫描得到误差在0.006 Hz以内的压电陶瓷片谐振频率驱动信号, 而当光纤探针处于样品的近场距离之内时, 压电陶瓷片的谐振频率偏离驱动信号频率, 振幅明显减小, 从而检测出近场距离. 高精度振动驱动源DDS和高灵敏度压电传感器的采用提高了检测灵敏度和工作稳定性.     

Direct observation of variations of optical properties in single quantum dots by using time-resolved near-field scanning optical microscope

We study the variations of optical properties of self-assembled In_0.5Ga_0.5As single quantum dots (QDs) in the spatial and time domains by combining a near-field scanning optical microscope with an ultrafast pulsed laser. Through the examinations of several tens of QDs, we find that the variations of photoluminescence (PL) intensity strongly depend on the condition of the initial carrier creation. The differences in quantum efficiency and those in the carrier flow rate into QDs cause the large distribution of PL intensity when the carriers are excited in the barrier layers. From the results of time-resolved PL decay measurements, we find that there are two types of QDs exhibiting quite different PL decay profiles.     

A general closed-form solution for the static pull-in voltages of electrostatically actuated MEMS/NEMS

In this article, an analytical method for calculating pull-in voltage is proposed. This method can accurately predict pull-in voltage of clamped-free, clamped-clamped and curved micro- and nano-beams. In this study, mid-plane stretching, axial stress, initial deformation and the effect of size are taken into account. To achieve this goal, governing equation of beam based on modified couple stress theory was first derived and then transformed to a single degree of freedom (D.O.F) model by Galerkin method. In this model, electrostatic force appears in integral form which is approximated to non-integral form employing Genetic Algorithm. This single degree of freedom model provides means for obtaining critical deflection of beam and is used to find the general closed-form expression for pull-in voltage. The validation of the method was carried out by comparing the results with the existing literature.     

The string theory landscape: a tale of two hydras

String theory is the leading theoretical approach to finding a consistent quantum theory that unifies gravity with the other three forces. However, the theory is only consistent in ten dimensions. In order for string theory to describe observable physics, the six extra dimensions must be sufficiently small to be unobservable. Originally it was hoped that there would only be one consistent way of doing this, but now it is realized that this problem may have as many as 10⁵⁰⁰ possible solutions. I describe where this number comes from and the approaches, both statistical and anthropic, taken in dealing with this superfluity of solutions.     

A general procedure for thermomechanical calibration of nano/micro-mechanical resonators

We describe a general procedure to calibrate the detection of a nano/micro-mechanical resonator’s displacement as it undergoes thermal Brownian motion. A brief introduction to the equations of motion for such a resonator is presented, followed by a detailed derivation of the corresponding power spectral density (PSD) function, which is identical in all situations aside from a system-dependent effective mass value. The effective masses for a number of different resonator geometries are determined using both finite element method (FEM) modeling and analytical calculations.     

Advances in the FDTD design and modeling of nano- and bio-photonics applications

In this paper we focus on the discussion of two recent unique applications of the finite-difference time-domain (FDTD) simulation method to the design and modeling of advanced nano- and bio-photonic problems. The approach that is adopted here focuses on the potential of the FDTD methodology to address newly emerging problems and not so much on its mathematical formulation. We will first discuss the application of a traditional formulation of the FDTD approach to the modeling of sub-wavelength photonics structures. Next, a modified total/scattered field FDTD approach will be applied to the modeling of biophotonics applications including optical phase contrast microscope (OPCM) imaging of cells containing gold nanoparticles (NPs) as well as its potential application as a modality for in vivo flow cytometry configurations. The conclusion provides a justification for the selection of the two specific examples and summarizes some of the insights that could open the opportunity for the application of the FDTD approach in new research areas.     

The Microwave Spectrum and Quadrupole Coupling Constants of cis-2-Chlorophenol

The rotational spectrum of cis-2-chlorophenol was observed from 5 to 12 GHz by molecular beam Fourier transform microwave spectrometer (MB-FTMW). The rotational and quadrupole coupling constants for the ³⁵Cl of the molecule were determined: A=2985.4479(22) MHz, B=1549.8591(3) MHz, C=1020.1915(1) MHz, χ_aa=−68.2429(83) MHz, χ₋=−0.922(20) MHz, χ_ab=−11.4(19) MHz. The quadrupole coupling constants of the chlorine nuclei of cis-2-chlorophenol were nearly equal to that of the chlorobenzenes. We concluded that the electric field gradient of the chlorine atom in cis-2-chlorophenol is similar to that of other chlorobenzenes, although the suggestion of intramolecular hydrogen bonding.     

A resonance tracking method for stable operation of a near-field scanning optical microscope in liquid environment

We report on the novel design of the near-field scanning optical microscope (NSOM) which operates in liquid environment. A resonance tracking digital scanning method is applied to compensate the resonance shift due to the evaporation of the liquid in the atmospheric pressure. By this method, stable operation of NSOM system is demonstrated by showing topographic images of the metallic grating embedded in liquid environment.     

基于前馈模糊逻辑的微波功率控制设计与分析

描述和设计了一类生产陶瓷载体的大型微波干燥控制系统;针对微波干燥过程中微波功率控制不准确、产品缺陷率高的问题, 分析了过程变量与控制变量之间的关系特点,并在现有算法基础上,设计了一种基于前馈模糊逻辑的微波功率控制模型;最后对此控制模型设计算法,并应用于实际进行实验分析,得出了很好的效果。     

金属覆层光纤探针近场特性研究

采用有限积分法对用于近场光学显微镜的旋转对称光纤探针进行了数值模拟计算,研究了光纤探针开口附近亚波长范围的电磁场及其能量密度的分布.计算结果表明,在探针外,光场为沿探针轴线方向的近逝波,其空间光场的分布与激励光场及其极化方向有关,在激励光场的极化方向出现了由感应电荷引起的边缘增强效应.同时研究了近场光纤探针的空间分辨率和样品处的电磁场能量,结果表明光纤探针孔的尺寸及其与样品的作用距离是影响探针的分辨率和样品内电磁场能量的重要因素.     

Effect of GMR and Magnetization Reversal on Microwave Absorption

Low-field microwave absorption has been measured as a function of magnetic field in a series of thin film structures exhibiting or not exhibiting the giant magnetoresistance effect (GMR). Although a close correlation has been found between the microwave absorption and GMR, an additional absorption due to magnetization reversal is shown to have substantial effect on the overall microwave response.     

微波检测机理与矢量分析

简要叙述了微波探测的机理，并对连续波辐射相干检测方法中的相位、幅度及矢量关系进行了分析和讨论。     

Microwave excitation of ultrasound in graphite-fiber reinforced composite plates

In this paper is demonstrated the effect of microwave beam polarization on the thermal generation of acoustic waves in continuous fiber-reinforced composite laminates. It is found that beam polarization strongly influences the dielectric interaction that leads to thermal losses, bulk expansion, and acoustic wave generation. The oriented graphite fibers in the composite laminate effectively short the microwave fields and reduce the generation efficiency nearly to zero. Ultrasonic waves at several hundred kHz generated in the composite are detected by air-coupled acoustic transducers located on the opposite side of the plate specimen from the 9.41 GHz incident microwave beam. With some averaging signal-to-noise ratios of better than 26 dB are obtained. Applying a conventional model of electromagnetic wave scattering in anisotropic media to this experiment yields good agreement between calculations and measured data. Implications for microwave-acoustic testing of graphite-reinforced composites are also discussed.     

A new positioning approach of fiber probe for near-field scanning optical microscope

A fiber probe-based positioning scan approach was established, whose precision can reach as high as 0.8 μm. And a set of modified microscope system was designed utilizing this approach, in which the scanning probe microscope (SPM) combined with an optical microscope was manipulated. The optical microscope and scanning probe can conveniently be switched through a switch panel. The observation period of samples can significantly be shortened. And more reliable images can be provided using this approach. Our design can effectively solve the inherent disadvantages of SPM technology, which makes SPM scan and image more reliably, conveniently, safely and rapidly.     

横卧式杨氏模量与组装台秤实验仪的设计

通过对横向放置的钢丝进行受力分析,推导出其杨氏模量的测量公式,进而运用该公式对其杨氏模量进行实验测量.再用该杨氏模量值作为已知参数,利用该钢丝作为压力的应变传感器件,反向设计出一款简易台秤,推导出其测量公式,并用来测定未知物体的重力.此设计将传统的验证性实验项目拓展改进成设计性实验项目,减小了原实验误差,丰富了实验内容.