摘要:
数字显微全息技术由于具有三维、非接触和实时测量微小空间内流场的能力，已引起了国内外学者的广泛关注.利用数字显微全息方法测量微通道流场时，记录距离、颗粒尺寸、颗粒浓度、入射光波长、CCD分辨率等参数会对颗粒重建结果产生重要影响.为了评估颗粒浓度和样本空间深度对重建结果的影响，本文开展了数值模拟研究.采用基于洛伦兹-米散射理论的程序产生不同浓度的颗粒全息图，用小波变换重建算法对其进行重建.结果表明：在样本空间深度为24μm时，颗粒浓度ns在3.44×105 mm?3-13.77×105 mm?3范围内时，颗粒重建率Ep随着颗粒浓度ns的增大而迅速减小，在13.77×105 mm?3-55.08×105 mm?3范围内时，颗粒重建率Ep随颗粒浓度ns增大而缓慢减少.在颗粒浓度ns (13.77×105 mm?3)保持不变时，颗粒重建率Ep与样本空间深度满足单调递减的线性关系.当阴影密度不变时，重建率的变化呈现一定的规律性：当深度L较小时，样本空间深度对颗粒重建的影响要比颗粒浓度的影响大；当深度L较大时，颗粒浓度对颗粒重建的影响较大.
Abstract:
Digital holographic microscopy plays a key role in micro-fluid measurement,and appears to be a strong contender as the next-generation technology for diagnostics of three-dimensional (3D) particle field. However, various recording parameters, such as the recording distance, the particle size, the wavelength, the size of the CCD chip, the pixel size and the particle concentration, will affect the results of the reconstruction, and may even determine the success or failure of a measurement. In this paper, we numerically investigate the effects of particle concentration and the volume depth on reconstruction efficiency, to evaluate the capability of digital holographic microscopy. Standard particle holograms with all known recording parameters are numerically generated by using a common procedure based on Lorenz-Mie scattering theory. Reconstruction of those holograms are then performed by a wavelet-transform based method. Results show that on the premise that the value of volume depth is 24 μm, the reconstruction efficiency Ep decreases quickly until particle concentration reaches 6.89×105 mm?3, and decreases slowly with the increase of particle concentration from 6.89 × 105 mm?3 to 55.08 × 105 mm?3. And on the premise that the value of particle concentration is 13.77 × 105 mm?3, the reconstruction efficiency Ep decreases linearly with the increase of the volume depth. When shadow density is constant, the variance of the construction efficiency presents a certain regularity. When the volume depth is small, the effect of particle concentration on the reconstruction efficiency becomes larger than one of volume depth, while it comes to a completely opposite result with a larger volume depth.
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