Harmonic vibro-acoustography

Vibro-acoustography is an imaging method that uses the radiation force of two interfering ultrasound beams of slightly different frequency to probe an object. An image is made using the acoustic emission resulted from the object vibration at the difference frequency. In this paper, the feasibility of imaging objects at twice the difference frequency (harmonic acoustic emission) is studied. Several possible origins of harmonic acoustic emission are explored. As an example, it is shown that microbubbles close to resonance can produce significant harmonic acoustic emission due to its high nonlinearity. Experiments demonstrate that, compared to the fundamental acoustic emission, harmonic acoustic emission greatly improves the contrast between microbubbles and other objects in vibro-acoustography (an improvement of 17-23 dB in these experiments). Applications of this technique include imaging the nonlinearity of the object and selective detection of microbubbles for perfusion imaging. The impact of microbubble destruction during the imaging process also is discussed.     

简谐激励力作用下悬垂缆线的谐波共振

本文研究在简谐激励力作用下的悬垂缆线的谐波共振。用Hamilton原理导出悬垂缆线面内运动的非线性偏微分方程。通过假设悬垂缆线的挠度曲线，运用Galerkin方法将偏微分方程转化为常微分方程。用多尺度法研究悬垂缆线的超谐波共振和次谐波共振，得到了系统的定常周期解，平均方程和幅频曲线。研究了非线性对幅频曲线的影响和定常运动的稳定区域。     

Harmonic diffractive lenses

The harmonic diffractive lens is a diffractive imaging lens for which the optical path-length transition between adjacent facets is an integer multiple m of the design wavelength λ(o). The total lens thickness in air is mλ(o)/(n - 1), which is m times thicker than the so-called modulo 2π diffractive lens. Lenses constructed in this way have hybrid properties of both refractive and diffractive lenses. Such a lens will have a diffraction-limited, common focus for a number of discrete wavelengths across the visible spectrum. A 34.75-diopter, 6-mm-diameter lens is diamond turned in aluminum and replicated in optical materials. The sag of the lens is 23 μm. Modulation transfer function measurements in both monochromatic and white light verify the performance of the lens. The lens approaches the diffraction limit for 10 discrete wavelengths across the visible spectrum.     

包装的和谐化设计

文章归纳和总结了和谐美的精神所在,结合具体实例,从人与包装、包装与产品以及包装与环境3个层面论述了现代包装和谐化设计的必要性.提出作为设计师.只有更好地了解人的生理和心理需求,充分考虑到人类的生存环境这个大系统,才能设计出和谐包装符合人的需要适应社会的要求.     

Second Harmonic Reflected Light

A review is given of the laws of non-linear optical reflection which govern the direction, polarization and intensity of second harmonic light generated in reflection. The complex non-linear susceptibility of III-V and II-VI piezoelectric compounds has been measured over a range of frequencies and shows characteristic dispersive properties. Both the amplitude and the phase can be determined. When the medium has a centre of inversion, the reflected second harmonic production is several orders of magnitude smaller. The effect has magnetic dipole and electric quadrupole character and has been observed in silicon, germanium and several metals and alloys. In metals the contribution from core electrons and the conduction electron plasma have the same order of magnitude.     

Harmonic Analyzer/Generator

A method of measuring the phase angle and magnitude of "n" harmonics corresponding to a periodic signal is described. The method includes the generation of sinusoidal bursts to reproduce significant components of distorted and complex signals; burst amplitude, burst initial phase, and burst frequency correspond, respectively, to harmonic amplitude, harmonic phase angle, and harmonic frequency.     

Harmonic waves in thermoviscoelastic solids

The constitutive properties and time-harmonic wave propagation in thermoviscoelastic solids are investigated through the energy flux. First the dissipative character of the model is characterized by requiring that the divergence of the energy flux vector be non-positive. The attention is then restricted to planarly stratified solids and the governing equations are shown to satisfy a first-order system of the Stroh-form. The corresponding scalar energy flux is examined and shown to satisfy a decay property which, thanks to a previous result, provides existence and uniqueness for the reflection–transmission process generated by a layer. The required definiteness property of an appropriate matrix is shown to hold in particular cases.     

Acoustic Harmonic Generation at Diffusion Bonds

The distortion of a sinusoidal acoustic wave at unbonded interfaces has been determined in terms of the first and second harmonic amplitudes. The results demonstrate for the first time that the second harmonic can reach the theoretically predicted maximum value. As also predicted, the harmonic generation efficiency at unbonded interfaces first increases and then decreases with an externally applied compressive load. The technique has been applied to diffusion bonded specimens in an attempt to quantify their achieved strength. As already demonstrated earlier, the energy reflected from such diffusion bonds is also useful to characterize their strength. Indications are that a combination of reflected energy and harmonic generation data could be a powerful tool to quantify the strength of diffusion bonds, particularly those of nearly perfect strength. A strength determination of diffusion bonds by nondestructive evaluation is a necessity for the qualification of such bonds in critical applications.     

脉冲谐波混频器及应用

脉冲谐波混频器是一种具有广泛应用前景的频率变换电路。本文对脉冲谐波混频器的工作原理进行了详细分析，并给出了谐波混频器的工作条件及应用实例     

Angularly-resolved High-order Harmonic Generation in Helium

Abstract

Harmonics up to 119th have been generated in helium using a 1·053 μm, 1 ps chirped pulse amplification laser at intensities up to 3 × 10¹⁴W cm^?2, and their far-field spatial distributions have been measured. In the presence of considerable ionization, complex angular distributions are found for harmonics in the plateau region, while near the cut-off, their distribution narrows to approximately that predicted by lowest-order perturbation theory. The experimental results are found to be in good agreement with the predictions of a numerical propagation model which incorporates photoelectron dispersion and strong-field atomic data for the ionization rates and dipole moments.     

Harmonic wave generation in nonlinear thermoelasticity

The basic equations that describe nonlinear thermoelastic interactions in a continuous medium were derived under the simplifying monomode hypothesis to provide an effective basis for the investigation of nonlinear thermoelastic bulk wave propagation. The one-dimensional equations are solved for a semi-bounded region (half-space) subjected to a prescribed harmonic displacement at its boundary. Two methods of solution are used:

• 1.(i) The straightforward expansion in a small parameter for the near-field solution. The first two orders of approximation are obtained and briefly discussed. It appears, in particular, that the second order solution induces an alteration in the velocity of propagation of the fundamental mode due to thermal influence.
• 2.(ii) The multiple scale technique for the far-field solution. Here, the characteristic curves are investigated and the solution in the first approximation is obtained for points in the half-space not too far from the boundary. In particular, the formation of discontinuities is put in evidence. Comparison is established with the results obtained by the Poincaré expansion, thus establishing the limits of validity of the latter.

     

Harmonic admittance and dispersion equations--the theorem

The harmonic admittance is known as a powerful tool for analyzing the excitation and propagation of surface acoustic waves (SAWs) in periodic electrode arrays. In particular, the dispersion relationships for open- and short-circuited systems are indicated, respectively, by the zeros and poles of the harmonic admittance. Here, we show that a strict reverse relationship also exists: the harmonic admittance of a periodic system of electrodes may always be expressed as the ratio of two determinants, which have been specifically constructed to describe the eigenmodes of the open- and short-circuited systems. There is no need to solve these equations to find the admittance. The existence of a connection between the excitation and propagation problems was recognized within the coupling-of-modes theory by Chen and Haus (1985) and was recently used to model surface transverse waves by Koskela et al. (1998), but a rigorous mathematical proof was only found later by Biryukov (2000). Here, we reproduce this theorem in detail, give some examples of calculations based on this theorem, and compare the results with measured admittance curves.     

Harmonic oscillators of carbon nanotube arrays

The harmonic properties of single-walled carbon nanotube (10, 10) arrays in cantilever geometry of lengths, L = 1,000 to 10,000 nm and diameters, D = 15 to 70 nm have been measured recently, and a linear relationship between the first natural frequency and the ratio of array diameter and the square of the span length, D/L2 was postulated. In the present work the authors show that this relationship is highly nonlinear, especially for large values of the ratio, D/L2. In addition, for a given array length, L = 1000 nm, the first natural frequency of the cantilever is shown to vary little with diameters more than 30 nm and to become asymptotic to a value of 22 MHz as it is further increased. The present study is based on earlier work of the authors wherein the flexural stiffness of the single-walled carbon nanotube (CNT) array of hexagonal symmetry and of non-covalent bonding, due to van der Waals interactions, was predicted in terms of the chirality of the nanotubes and the shearing transfer efficiency between nanotubes when subjected to flexural deformation. In addition, predictions are shown to be in agreement with the experimental evidence wherein the flexural modulus of the CNT array decreases with an increase in array diameter.     

三相三线制有源电力滤波器谐波检测方法

针对三相三线制有源电力滤波器(Active Power Filter,APF)中的谐波检测,研究了基于瞬时无功理论的谐波电流快速检测算法,结合谐波检测过程中出现的频率混叠现象而搭建的二阶巴特沃斯低通滤波器,共同实现了有源电力滤波器高精度的谐波检测功能.实验结果验证了方法的正确性和可靠性,对于提高APF的补偿性能有很大的帮助.     

Pulse-Echo Harmonic Generation Measurements for Non-destructive Evaluation

Ultrasonic harmonic generation measurements have shown great potential for detecting nonlinear changes in various materials. Despite this, the practical implementation of the technique in non-destructive evaluation (NDE) has typically been limited to the through transmission setup case, with which problems arise in certain situations. Recently, works in the fields of nonlinear fluids and biomedical imaging have reported different application of the harmonic generation theory by making use of reflective boundaries and beam focusing. It is thought that such techniques may be similarly applied in the field of NDE to enable single-sided nonlinear inspection of components. In this paper, we initially describe a numerical model which has been used to determine the effects of attenuation and acoustic beam diffraction on measurements of the nonlinear parameter β. We then extend the model to incorporate first the effects of multiple reflecting boundaries in the propagation medium, then of focused source excitation. Simulations, supported by experimental data, show that nonlinear pulse-echo measurements have the potential to provide a viable (and practical) alternative to the usual through-transmission type as a means of measuring β in solids. Furthermore, it is shown that such measurements may be optimised, both by adjusting the excitation frequency, and by focusing the acoustic source at a certain point relative to the specimen boundary.     

Hyper-Raman Lines Produced During High Harmonic Generation

Abstract

The possibility of producing and detecting hyper-Raman lines in high-harmonic generation with short and strong laser pulses is discussed. It is shown that the strength and positions of the hyper-Raman lines depend very sensitively on the parameters of the laser pulse and the conditions which are required for an effective production are indicated. It is pointed out that the phenomenon of atomic stabilization can contribute to obtaining these conditions.     

压电谐振滤波器的高频谐波响应

提出压电谐振滤波器不能很好地滤除高频谐波的问题,结合一个具体例子理论推导了压电谐振滤波器存在许多干扰谐振频率,从而不能有效滤除一些特定频率的干扰信号．为了解决这个问题,提出一种改进型的静电激励谐振滤波器．为了说明其可行性,具体分析了改进型双端固支微梁静电激励谐振滤波器,理论推导证实基于双端固支微梁的各阶振型正交的原理,通过适当调整激振电容的间距,双端固支微梁的高阶振动模态受到很好的抑制,因此这种谐振滤波器可以有效阻止滤波器中心频率的高频谐波的通过．     

谐波治理技术应用研究

对谐波治理技术进行了分析和总结.首先对电能质量、谐波治理措施以及谐波治理技术在电力系统中的应用情况进行介绍;然后,重点分析有源滤波器的工作原理、系统组成及其主要部件;最后,通过具有代表性的实验,借助电能质量分析仪,对实验数据进行了分析总结.研究表明,采用有源滤波器的谐波治理效果可达92％ 以上.