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本文从换能器的互易原理出发,利用平面波自易校准法获得换能器的自由场发送电流响应.根据平面活塞型换能器的衍射规律,推导出发射声功率的表达式.由此计算互易换能器在给定驱动电流(或电压)作用下的辐射超声功率.基于上述原理,使用自易校准装置测量了互易换能器的声功率一频率曲线.估计的测量不确定优于±20%. 相似文献
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在聚焦换能器的会聚球面波自由场互易校准法中,衍射损失修正系数是获得互易常数的一个关键参数。本文利用冲击响应函数积分法系统地计算了超声治疗头、机械扫描B超探头以及多普勒诊断探头的衍射损失系数,得出了一些典型参数下的计算曲线,可供不同类型的聚焦换能器会聚球面波互易校准时引用。与传统的瑞利积分法分析比较显示,本文中所采用的冲击响应函数积分法显著地提高了运算速度,同时基本保持了与瑞利积分算法计算结果的一致性。 相似文献
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基于铜互连电迁移失效微观机理分析建立一种Cu/SiCN互连电迁移失效阻变模型,并提出一种由互连阻变曲线特征参数即跳变台阶高度与斜率来获取失效物理参数的提取方法.研究结果表明,铜互连电迁移失效时间由一定电应力条件下互连阴极末端晶粒耗尽时间决定.铜互连电迁移失效一般分为沟槽型和狭缝型两种失效模式.沟槽型空洞失效模式对应的阻变曲线一般包括跳变台阶区和线性区两个特征区域.晶粒尺寸分布与临界空洞长度均符合正态对数分布且分布参数基本一致.阻变曲线线性区斜率与温度呈指数函数关系.利用阻变模型提取获得的电迁移扩散激活能约为0.9eV,与Black方法基本一致. 相似文献
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声能量非互易传递机理及声非互易系统构建是近年来声学领域的研究热点.本文开展了由非线性薄膜和两个不同尺寸声腔组成的实验系统中声能量非互易传递的实验研究.该系统利用简化为Duffing振子的薄膜频响函数的不对称性,实现了声能量的非互易传递.采用复化平均法获得系统频响函数的渐近解,理论计算结果与实验测量结果吻合.理论计算和实验结果表明:该系统理论上存在最大9.1倍的非互易量,实验测得的最大非互易量为4.3倍,归一化跳变区频率带宽为0.56.研究结果揭示了实验系统中声能量非互易传递机理,为实现空气介质声系统中声能量的非对称传递提供了一种新方法. 相似文献
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光学非互易性对建立量子网络和现代通讯技术都是不可或缺的.本文研究了双腔光力学系统在蓝失谐驱动下如何实现完美的光学非互易性.研究发现此系统中的光学非互易性来源于系统中的光力相互作用和腔模线性耦合相互作用之间的量子干涉效应.在应用光力学输入输出关系得出输出光场表达式后,给出了在此系统中实现完美光学非互易性的条件以及影响非互易谱线宽度的因素.另外还发现当系统参数(耗散速率)一定时,可以存在两套耦合强度来实现完美的光学非互易性.最后利用劳斯-霍尔维茨(Routh-Hurwitz)稳定性判据给出了系统的稳定条件. 相似文献
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基于等效原理和互易性定理研究了两个相邻目标的电磁散射问题,给出了这一复合电磁散射模型的二阶散射结果. 通常平面入射波的一阶散射结果容易求解,但由于耦合效应的复杂性,很难给出二阶散射结果的解析形式. 应用互易性定理给出了求解任意相邻导体/介质目标二阶电磁散射场的公式,并利用等效原理将求解散射场公式中的体积分简化为面积分的形式,从而降低了求解难度. 同时还推导了两个目标的二次散射场之间的关系. 最后应用给出的公式,求解了两相邻球形目标的复合散射场,对双站散射结果进行了讨论,同时与应用时域积分方程法求得的结果进行了比较.
关键词:
等效原理
互易性定理
电磁散射
相邻圆球 相似文献
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It is frequently assumed that sensitive museum materials follow the reciprocity principle of light exposures. Thus, equivalent exposure doses obtained by using either high-illuminance levels for short periods of time or lower illumination for longer exhibition periods are believed to cause similar degrees of damage to an object. Microfading spectrometry permitted the investigation of this phenomenon by evaluation of light-induced changes in a series of samples. The effects of equivalent exposure doses on materials such as Blue Wool 1, LightCheck Ultra, and various dyed silks from a reference collection were compared. The results indicate that reciprocity is obeyed by the most stable colorants, while materials with lower stability to light may experience deviations that are proportional to the intensity of illumination. This study confirms that reciprocity failure is associated with the use of high-intensity lamps during accelerated-aging trials. Therefore only those tests conducted at low-illumination intensity ranges where reciprocity holds should be employed when one estimates the extent of damage occurring in a museum environment. 相似文献
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拍摄脉冲全息肖象母版的研究 总被引:2,自引:1,他引:2
本文介绍了我们在拍摄脉冲全息肖象母版方面的研究工作.讨论了拍摄工作中所需要特别注意的若干问题.如:人眼安全、对易律失效、消除双频条纹、如何获得高亮度图象等问题.此外,还介绍了我们拍摄脉冲全息母版时,在未使用Q开关的情况下,同样获得了高质量全息肖象母版的经验. 相似文献
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W.J.N. de Lima 《Journal of sound and vibration》2003,265(4):819-839
The propagation of finite-amplitude waves in a homogeneous, isotropic, stress-free elastic plate is investigated theoretically. Geometric and weak material non-linearities are included, and perturbation is used to obtain solutions of the non-linear equations of motion for harmonic generation in the waveguide. Solutions for the second-harmonic, sum, and difference-frequency components are obtained via modal decomposition. Ordinary differential equations for the modal amplitudes in the expansion of the second-order solution are obtained using a reciprocity relation. There are no restrictions on the modes or frequencies of the primary waves. Two conditions for internal resonance are quantified: phase matching, and transfer of power from the primary to the secondary wave. 相似文献
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We study the applicability of the reciprocity principles in an underwater waveguide for the vector-scalar fields of multipole sources. We show analytically and numerically that multipole sources are divided into two groups according to this principle: in the first group, the sound pressure field and the horizontal projections of the vibration velocity vectors satisfy the reciprocity principle, while the vertical projections of these vectors do not. In the second group, the pressure and the horizontal projections of the vibration velocity vector do not satisfy the reciprocity principle, while their vertical projections do. We establish that the phase gradients and angles of arrival of signals in the vertical plane do not satisfy the reciprocity principle for the vector-scalar fields of volumetric sources with arbitrary directivity in the vertical plane. 相似文献
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The linear or phenomenological laws such as Ohm's law, Fourier's law and Fick's law are derived for a relativistic plasma in an electromagnetic field. It is shown that the choice of a reference frame as proposed by Landau and Lifshitz entails-in contrast to, for instance, the choice of Eckart-the validity of Onsager's reciprocity relations. 相似文献
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It has been shown by the Brussels School that there is a physical representation in which the evolution of the density matrix reveals the dissipative structure. In this article, we present a two-dimensional model of the collision operator with a singularity at the origin which characterizes a long-range force. The dissipativity and the approach to equilibrium in the physical representation are studied and it is shown that the second law may be established in spite of the failure of Boltzmann's kinetic equation. 相似文献
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应用于复杂结构中频声振分析的扩散场多自由度互易原理采用位移变量描述系统,实质为弹性波场互易原理,应用于声波场时会造成模型自由度数不必要的增加。建立基于声压描述的扩散声场受挡模型,利用声辐射模态描述扩散声场中结构的表面受挡声压;据此提出基于声压描述的扩散声场多自由度互易原理,发现扩散声场中结构表面受挡声压的互谱矩阵与该结构在自由空间中振动辐射声波的声阻矩阵成正比。该互易原理与传统的单自由度互易原理表达形式相似,但适用于任意自由度结构。该互易原理可用于扩散声场中复杂结构的表面受挡声压的自谱及相关分析,仿真研究表明当边界元网格尺寸小于声波波长的1/6(线性单元)或1/3(二次单元)时,数值解与理论解完全吻合。 相似文献