数字伺服系统机械谐振频率偏移现象机制分析及实验研究

高刚度的伺服系统在柔性传动机构中极易引起机械谐振。为提高系统的鲁棒性，通常采用自适应陷波滤波器，但会产生机械谐振频率偏移现象，无法快速实现振动抑制。基于此现象，从系统阻尼、离散化周期以及陷波器串入3个角度对机械谐振频率的影响进行了定量分析，深入剖析机械谐振频率偏移现象的机制，揭示了谐振频率变化的本质原因。通过理论分析，得出在谐振出现偏移现象时最有效最快速的陷波频率仍是系统自然谐振频率（NTF）的结论。最后，通过MATLAB/Simulink和实验验证了理论分析的正确性与有效性。     

伺服系统机械谐振的在线检测及其抑制

伺服系统中的传动环节一般具有一定的弹性，会导致伺服系统产生机械谐振，需要准确检测谐振并将其抑制。在保证伺服系统性能的前提下，引入陷波滤波器抑制机械谐振。设计了一套基于振动信号频谱的陷波器参数整定策略，可以自动设定陷波器陷波频率、宽度、深度参数；设计了基于SDFT(滑动傅里叶变换)的频谱提取算法，可以快速准确获取当前系统的谐振频率，在不依赖于伺服系统机械参数的条件下自动整定陷波器参数，抑制机械谐振。实验证实谐振检测方法的准确性和陷波器参数整定的有效性，该方案可以准确地检测伺服系统谐振并完成谐振的自适应抑制。     

面向焊接的软开关有源功率因数校正仿真研究

在分析软开关有源功率因数校正电路原理的基础上，建立了一套软开关有源功率因数校正的仿真电路。通过仿真，研究了在不同静态负载下实现全程软开关的条件。并研究了谐振电容和谐振电感的参数对整个电路性能的影响，对谐振电容和谐振电感的选取具有指导意义。     

串联式感应加热输出回路伪谐振现象的探讨

串联谐振式结构是感应加热电源的基本谐振方式之一，其输出为方波电压源。如果在较大的范围内进行电源工作频率的调整。在调整的过程中将会发现输出回路将工作在谐振状态以及多个类似于谐振的状态（伪谐振状态）。工作在伪谐振状态下，电源的工作效率低、加热速度慢，因此要避免在频率自动跟踪过程中进入伪谐振状态。本文基于方波的傅立叶级数分解形式，对伪谐振现象的产生原因进行了分析，并针对电源工作频率自动跟随技术，提出了避免进入伪谐振工作状态的解决方法。     

谐振变流技术及其在弧焊逆变电源中的应用

本文介绍了谐振变流技术的发展概况，分析了恒频移相控制谐振技术的特点及工作原理，讨论了谐振变流技术在弧焊逆变电源中的应用。     

陶瓷基负磁导率材料的制备和性能

设计并制备了由开口谐振环（split ring resonators）周期性排列而成的陶瓷基负磁导率材料，采用微波波导法研究了陶瓷基板对负磁导率材料电磁谐振行为的影响。实验结果表明：负磁导率材料的谐振频率可由陶瓷基板介电常数调节，并且随陶瓷基板介电常数的增加而减小。当陶瓷基板的微波损耗增大时，其谐振效应减弱，并且可能伴随负磁导率的消失。陶瓷基板介电常数的增加导致开口谐振环单元的等效电容增加，从而引起谐振频率的减小。     

串联谐振式中频电源的节能效果分析

串联谐振是中频电源的一种谐振形式。介绍了中频电源电路的基本原理,比较分析了串联谐振和并联谐振的工作特性,通过在钢管加热中的应用实例来证明串联谐振显著的节能效果,指出在钢管加热中采用串联谐振式中频电源具有显著的节能价值。     

数控龙门铣床伺服进给系统谐振分析及减振方法

分析了大型龙门铣床数控化改造中所遇到的进给系统谐振问题,指出了速度环谐振频率和机械谐振频率对进给系统谐振特性的影响作用,并提出了相应的解决措施。     

一种新型逆变式感应钎焊电源频率自动跟踪技术

针对感应钎焊过程中谐振频率不断变化的问题，在常规以SG3525A为控制核心的逆变电源基础上，设计了一套基于PI调节的谐振频率自动跟踪技术。该技术充分利用了SG3525A芯片的功能，具有跟随速度快、频率跟踪准确、电路设计简单、工作可靠等优点，同时简化了串联谐振电源的起动方法，并对该技术的工作原理、电路设计以及实验结果等作了详细的分析和介绍。     

钛制硬盘的特性

谐振性能和阻尼性能可调节。随TiN层的不同厚度调节盘片的谐振峰值，适应不同的转速，降低磁道记录失真，提高硬盘性能。     

Measurement of the thickness of a cylindrical shell with a focused beam

The acoustic scattering from a cylindrical or spherical object immersed in water and insonified with plane wave has been theoretically and experimentally studied. The backscattering spectra show minima, which are related to the circumferential waves circumnavigating around the object. These waves are identical to the Lamb waves propagating in a plate. Two types of resonances are observed on ultrasonic spectra: the resonances related to the thickness and the resonances related to the stationary state that establish around the cylindrical shell from the circumferential waves. To eliminate the second type of resonances a focused beam is used to excite only the thickness resonances. The cylindrical shell thickness is calculated from these experimentally measured resonance frequencies.     

Optical near-field resonances in the system of interacting nanoparticles

Near-field interaction of two metallic nanoparticles is considered at small spacings between their centers in the field of an external optical radiation. Effective polarizations of valence electrons in nanoparticles are calculated with allowance for their interactions with the ion core. The effective polarizations are shown to contain near-field resonances whose frequencies differ substantially from the frequencies of resonances in isolated nanoparticles, and to depend on the distance between the centers of the nanoparticles and on the polarization of the external field with respect to the axis that connects the nanoparticle centers.     

Optical near-field resonances in a metastructural layer of metallic spherical nanoparticles

Based on the solution to the boundary problem of resonance optics in which a monolayer of metallic nanoparticles located on the surface of a dielectric interacts with a plane electromagnetic wave, optical fields inside and outside of the monolayer of metallic nanoparticles have been calculated. It is shown that the reflection and refraction of light is strongly affected by optical near-field resonances whose frequencies significantly differ from the natural frequencies of the spectrum of conduction electrons inside the nanoparticles and from the frequency of electrodynamic resonances of isolated nanospheres.     

Material removal mechanism of multi-layer metal-film nanomilling

Tip-based nanomilling via atomic force microscopy enables alterable feature sizes for fabrication of substrates for surface-enhanced Raman scattering (SERS) with tunable plasmonic resonances. Specifically, nanomilling of SERS substrates on a multi-layer Au/Ag/Au film was investigated. The material removal mechanism at close-to-atomic scale, plastic deformation of the sample material, as well as the formation of nanogrooves were characterized. The Raman enhancement mechanism of the SERS substrate was revealed via simulations. This work thus provides a new method for preparing SERS substrates with tunable plasmonic resonances.     

Radiation-induced shift and splitting of resonances in a system of metallic nanoclusters

A microscopic justification has been given for the experimentally observed shift and splitting of maxima of light scattering in silver nanoclusters upon changes in their size. It has been shown that the resonances of metallic nanoclusters can be strongly shifted with allowance for the self-effect in an optical-radiation field. A formula has been derived for the effective polarizability of valence electrons in a spherical metallic nanocluster when the self-effect of electrons in the field of an external optical radiation and the interaction of nanoclusters are taken into account. Using this formula, the optical properties of different optical systems composed of nanoparticles can be described, in particular, conditions were obtained under which the real index of refraction of these systems can take negative values. It has been shown that the shift of resonances in metallic nanoclusters makes it possible to reach an ideal antireflection coating of the surfaces of optical media coated by a layer of nanoparticles.     

Nonlinear acoustic characterization of micro-damaged materials through higher harmonic resonance analysis

A method developed for the analysis of nonlinear systems is applied for the first time to non-destructive testing of diverse materials using vibrations and elastic waves. This method allows to extract the vibrational/acoustical responses of the system, at the excitation frequency and importantly, also at higher harmonics, with the help of a nonlinear convolution signal analysis. It is then possible to make use of the robust nonlinear resonance method together with the harmonic generation method in order to analyze the nonlinear elastic resonances of a sample at excitation frequency harmonics. Definitions of the nonlinear hysteretic parameters associated to higher harmonic resonances are provided. The bases of the signal analysis method are also described. A higher sensitivity to the presence of gradual damage compared to the classical nonlinear resonance method is demonstrated experimentally for diverse materials and configurations.     

High resolution NMR and structural investigations of the 2-ammonium 2-methyl propanol dihydrogenodiphosphate [(CH3)2C(NH3)CH2OH]2H2P2O7

We report on high resolution ¹³C and ³¹P NMR and X-ray diffraction measurements of the organic dihydrogenodiphosphate (C₄H₁₂NO)₂H₂P₂O₇. The obtained ¹³C magic angle spinning (MAS) NMR spectrum at room temperature shows four resonances at 22, 23, 57 and 66 ppm which we attribute to the four magnetically inequivalent carbons of the organic cation, the two CH₃, the CH₂ and the quaternary carbon, respectively. The corresponding ³¹P MAS NMR spectrum presents two isotropic resonances at − 9.2 and − 6.9 ppm assigned to the two crystallographically inequivalent sites of the phosphorus atoms in the structure. The obtained NMR results are in quite good agreement with our X-ray data on the same sample. These results confirm the non-centrosymmetric structure of this material and its ability to exhibit non-linear optical properties.     

Magic angles (Lebed''s and others), and the phase diagram of the Bechgaard Salts

We present transport data on the metallic and Field Induced Spin Density Wave phases of the Bechgaard Salts (TMTSF)₂PF₆ and (TMTSF)₂ClO₄. The a and c axis resistivities (ρ_XX and ρ_ZZ) of these compounds have been measured for magnetic field rotations in the b-c planes (Lebed geometry) and striking resistance dips are observed at magic angles. We examine the differences between the two materials and the status of our understanding of the Lebed resonances. We then investigate the resistivities for magnetic fields rotated in the a-c plane. In this case we find a new set of resonances which for the first time allow direct measurements of the Fermi surface parameters of quasi-one- dimensional metals. Extending ρ_XX and ρ_ZZ measurements to 30 Tesla we have found that the phase boundary for the FISDW in (TMTSF)₂ClO₄ is most easily investigated by temperature dependent studies of ρ_ZZ at high field. We find a new phase below a nearly temperature independent and we discuss some of the properties of this phase.     

Pinning structure of dimensional phonon resonance in quantum wires

The dimensional phonon resonances in dimensionally-quantum semiconductor wires are considered. It is supposed that the absorption of light is caused by electron transitions between dimensionally-quantum subbands in potential wells with the participation of long-wavelength phonons. The influence of resonance electron-phonon interaction on a spectrum of one-dimensional electrons in quantum wires is investigated. It is shown that the spectrum contains two branches and also the splitting of the peak of the dimensional phonon resonance into two components; the distance between them is determined by the resonance electron-phonon interaction.     

Resonance modes of two-layer exchange-coupled ferromagnetic film

Ferromagnetic and spin-wave resonances in two-layer exchange-coupled ferromagnetic films have been investigated numerically at different intensities of a magnetic field when it is directed in parallel or perpendicular to the film plane. Layers of the film have finite thicknesses and possess anisotropy of the easy-plane and easyaxis types. It has been shown that at a nonzero parameter of interlayer exchange coupling the dynamic component of magnetization upon ferromagnetic resonance is distributed nonuniformly across the film thickness. Its change has been described when the external magnetic field decreases from the saturating field to zero.