用于自由电子激光的光学速调管的设计与测试

 详述了用于合肥自由电子激光用的光学速调管的物理设计与测试,以及光学速调管实际运行结果与升级计划。测试结果表明,考虑三维效应的OPERA3D场有限元计算法比解析设计更精确,多周期波荡器中任意周期磁场峰值受该周期外其它周期波荡器磁体的影响小于10%。     

Nonlinear sound and structure interaction in a fluid–filled flexible waveguide

In this study, a 2-D infinite flexible waveguide is considered. The waveguide carries a weakly nonlinear acoustic fluid. It is bounded on one side by a weakly nonlinear flexible membrane and the other side is rigid. The infinite waveguide is driven at the origin by a piston oscillating at a single frequency. However, we focus only on the positive side of the piston. As the coupled waves propagate in the membrane and the fluid, the modal interactions lead to resonances and beats which form the main focus of this work. A regular perturbation method is used to derive the linear and the quasilinear order equations which are then solved. At the linear order, the primary wavenumbers are solved for and the modes are found to be non-orthogonal because of the flexible membrane. Only the propagating waves are included in the analysis. Both self-mode and cross-mode interactions of the planar and the non-planar modes are considered. The novelty of this work lies in obtaining conditions and the closed form solutions for the resonances and beats along the spatial coordinate. It is found that the self-mode interactions lead to beats only. And in the self-mode interactions, the coupled planar mode plays an important role. On the other hand, the cross-mode interactions can lead to either resonances or beats.     

非线性波动方程的新数值迭代方法

提出了一种新的求解非线性波动方程的数值迭代法,它是一种半解析的方法.与完全的数值计算方法扰法相比,它能够考虑各阶谐波的相互作用,且能够满足能量守恒定律.用它研究了非线性声波在液体中的传播性质,结果表明,在微扰法适用的声强范围内迭代法也适用,在微扰法不适用的一个较宽的声强范围内迭代法依然适用.     

Calculation of acoustic scattering of a nonrigid surface using physical acoustic method

In this paper the physical acoustic method or the Kirchhoff approxima-tion is extended to treat the scattering of a nonrigid surface in order to estimatethe target strength of targets with absorbing coatings.By using the locally planewave approximation,the relationship between the sound pressure and its normalderivative on the surface can be represented by the plane wave reflectioncoefficient and the acoustic impedance of the surface.The resulting modifiedKirchhoff approximation involves the plane wave reflection coefficient.For aimpedance sphere,a comparison between the physical acoustic method and theexact solution shows that the physical acoustic method still is a good approxima-tion at higher κα values.     

Sonic stop-bands for cubic arrays of rigid inclusions in air

Extensive band structures have been computed for cubic arrays of rigid spheres and cubes in air. Complete stop bands are obtained for the face-centered-cubic (fcc) structure; however, there is no gap for the body-centered-cubic (bcc) and simple-cubic (sc) structures. These gaps start opening up for a filling fraction of (27%) for spherical (cubic) inclusions and tend to increase with the filling fraction, exhibiting a maximum at the close-packing. We also propose a tandem structure that allows the achievement of an ultrawideband filter for environmental or industrial noise in the desired frequency range. This work is motivated by the recent experimental measurement of sound attenuation on the sculpture, by Eusebio Sempere, exhibited at the Juan March Foundation in Madrid (Nature 378, 241 (1995)) and complements the corresponding theoretical work (Appl. Phys. Lett. 70, 3218 (1997)). Received: 24 October 1997 / Revised: 1 December 1997 and 26 January 1998 / Accepted: 6 March 1998     

Acoustic Analysis of the Interaction of Choral Arrangements, Musical Selection, and Microphone Location

Acoustic differences were evaluated among three choral arrangements and two choral textures recorded at three microphone locations. A choir was recorded when singing two musical selections of different choral texture, one homophonic and one polyphonic. Both musical selections were sung in three choral arrangements: block sectional, sectional-in-columns, and mixed. Microphones were placed at the level of the choristers, the conductor, and the audience. The recordings at each location were analyzed using long-term average spectrum (LTAS). The LTAS from the mixed arrangement exhibited more signal amplitude than the other arrangements in the range of 1000-3500Hz. When considering the musical selections, the chorus produced more signal amplitude in the region of 1800-2200Hz for the homophonic selection. In addition, the LTAS produced by the choir for the homophonic selection varied across the microphone locations. As for the microphone location, the LTAS of the signal detected directly in front of the chorus had a greater slope than the other two locations. Thus, the acoustic signal near the choristers differed from the signals near the conductor and in the audience. Conductors may be using acoustic information from the region of the second and third formants when they decide how to arrange a choir for a particular musical selection.     

Nonlinear acoustics of bounded solid

Reflection and refraction are investigated when the incidental angles of transverse waves are larger than the critical one. An interesting result is obtained that at this angle all the second-order displacements on the stress-free surface have a very strong maximum module and a phase leap; thereupon an appropriate second-order harmonic surface wave could be produced. Project supported by the National Natural Science Foundation of China (Grant No. 19334062).     

Discernment of non-Newtonian behavior in liquids by acoustic means

An experiment was conducted with the use of a „sonic viscometer” to demonstrate that a change in the constitutive nature of a fluid will alter the overtones that occur from the nonlinearity of the propagation of a sine wave through the fluid. Pure sine waves ranging octave-wise from 500 to 8000Hz were introduced into distilled water, and FFT analyses of the signals received were compared with those resulting from transmission of the same set of sine waves through a 1% solution of polyethylene oxide in distilled water. Differences in the FFT spectra which occur as the result of introducing the polymeric solute indicate that the device could prove viable in indicating small changes in viscous properties. Received: 10 February 1998 Accepted: 1 June 1998     

岩石等非线性介观弹性固体材料的谐波特性的超声研究

岩石、混凝土等非线性介观弹性固体材料显示出与经典的非线性声学不同的非经典非线性声学现象，比如滞后现象、离散记忆等。本文实验研究了超声波在岩石材料中产生的基波、二次、三次谐波随声源幅度的依赖关系，研究了岩石的超声衰减，与金属材料的进行了对比；并且将浸水后的混凝土与浸水前的混凝土的超声谐波特性进行了对比，对此实验现象作出了定性的解释。此研究有利于岩石等非线性介观弹性固体材料的无损检测的研究。     

析古戏台下设瓮助声之谜

传统古戏台下设瓮助声乃广为流传的说法，在国外亦有类似记述。作者对此作了考据和声学分析，认为事属妄传，当予澄清。