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在前期研究(声学学报;1991;16(3):161—169)的基础上,建立了改进的热源分布模型。利用积分变换和特征函数展开法,求解了强度简谐调制的电子束源在各向同性试样中所激发的各种Lamb波模式,以及耦合在试样背面的压电片的电压输出,并分析了扫描电子声显微镜(SEAM)的信号激发机理。结果表明SEAM是一种高分辨率的近场成像技术,它的最佳横向空间分辨率为22~(1/2)倍的电子束焦斑半径。实验结果表明SEAM的空间分辨率可优于0.5μm,小于试样的热扩散长度,从实验上证实了理论预计的SEAM的近场成像特征。
Based on the previous research (Acoustics; 1991; 16 (3): 161-169), an improved heat source distribution model was established. Using integral transform and eigenfunctions expansion method, the various modes of Lamb waves excited by the electron beam source with intensity harmonic modulation in isotropic samples and the voltage output of piezoelectric films coupled with the backside of the sample are obtained. The signal excitation mechanism of scanning electron acoustic microscope (SEAM) was analyzed. The results show that SEAM is a high-resolution near-field imaging technique with optimal lateral spatial resolution of 22-1 / 2 times the electron beam focal spot radius. The experimental results show that the spatial resolution of SEAM can be better than 0.5μm, which is less than the thermal diffusion length of the sample, and the near-field imaging characteristics of SEAM are theoretically verified.