Numerical analysis of sound pressure fields focused by phase continuous fresnel lens using finite difference time domain method
Numerical analysis of sound pressure fields focused by phase continuous fresnel lens using finite difference time domain method
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DOI：
10.1143/jjap.46.4990
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发表时间：
2007-07-01
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影响因子：
--
通讯作者：
Takeuchi, Yasuhito
中科院分区：
文献类型：
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作者：
Mori, Kazuyoshi;Miyazaki, Ayano;Takeuchi, Yasuhito
使用室温硫化（RTV）硅橡胶的凸透镜是典型的声透镜，其声阻抗与水的声阻抗匹配良好。然而，由于RTV硅橡胶中的衰减非常大，因此需要一些考虑来减小透镜的厚度。因此，我们提出了一种相位连续的菲涅耳透镜，其具有一些装置以在整个透镜孔径中保持相位连续，而在出射侧没有不相等的相位。该透镜是通过以阶梯形状去除其厚度而制造的，其中每个阶梯之间的差是波长的整数倍。在这项研究中，相位连续菲涅耳透镜聚焦的声场进行了分析，使用时域有限差分法（FDTD）。利用二维时域有限差分法，通过改变脉冲长度、入射角和频率，对聚焦区的声压场进行了测量。结果表明，相位连续菲涅耳透镜的透镜增益大于凸透镜的增益，聚焦特性依赖于声源信号的突发脉冲长度，聚焦点对频率有很强的依赖性。在另一个使用三维FDTD方法的分析中，我们发现主瓣与二维分析结果所示的相同，并且主瓣外的电平低于二维分析结果中的电平。
A convex lens using room temperature vulcanization (RTV) silicone rubber, whose acoustic impedance matches well with that of water, is a typical acoustic lens. However, some considerations are required to reduce the thickness of the lens because attenuation is very large in the RTV silicone rubber. Therefore, we have proposed a phase continuous Fresnel lens, which has some devices to keep the phase continuous in the entire lens aperture without an unequal phase on the exit side. This lens is fabricated by removing its thickness in a staircase shape in which the difference between each step is an integer multiple of wavelength. In this study, the sound fields focused by the phase continuous Fresnel lens are analyzed using a finite difference time domain (FDTD) method. Using a two-dimensional (2-D) FDTD method, we surveyed the sound pressure field of the focal region by changing the burst pulse length, angle of incidence, and frequency. Results show that the lens gain of the phase continuous Fresnel lens is greater than that of the convex lens, that focusing characteristics depend on the burst pulse length of sound source signal, and also that focal points strongly depend on frequency. In another analysis using a three-dimensional FDTD method, we found that the main lobe is the same as that indicated by 2-D analysis results and that the level outer of the main lobe is lower than that in the 2-D analysis results.