基于DMD的阿达玛变换近红外光谱仪关键技术研究

发布时间：2018-04-07 17:52

本文选题：阿达玛变换　切入点：近红外光谱仪　出处：《中国科学院长春光学精密机械与物理研究所》2017年博士论文

【摘要】：近红外分析方法以其快速性,非破坏性,准确性等特点,已经广泛应用于定性和定量的成分分析多个行业。近红外光谱仪作为光谱获取设备,它的类型也有多种,应用最广泛的有傅立叶变换型和光栅分光型。傅立叶变换型光谱仪具有高分辨率、高信噪比的特点适合于实验室使用,光栅分光型光谱仪又主要有扫描光栅加上单点探测器的结构和固定光栅加上线阵探测器的结构这两种类型。单点探测器结构的速度较慢,适合速度要求不高的场合,如农产品的成分分析,而线阵探测器结构的速度较快,适合过程控制中使用。随着数字微镜阵列器件(Digital Micro-mirror Device,DMD)的出现,一种光栅分光、单点探测器检测信号、DMD进行光谱波长选通和调制、并且采用阿达玛变换来提高信噪比的光谱仪出现了,这种光谱仪综合性能卓越,价格优势明显。本文围绕着基于DMD的阿达玛变换光谱仪的关键的技术进行了研究。首先,按照仪器中的噪声产生的位置,将仪器的噪声分成了阿达玛编码前和编码后的噪声,详细推导了S矩阵、S互补矩阵、H互补矩阵等阿达玛编码矩阵的编码模板对编码前和编码后噪声抑制的比例系数,进行了MATLAB仿真,验证了推导结果的正确性。对比了多位学者的分析结果,说明了多位学者分析结果一致性和不一致性的原因。第二,设计和制作了基于DLP4500NIR型号DMD的近红外光谱仪,包括光学设计参数,电路设计方案,软件方案等内容。装调出了多台光谱仪样机,对多台样机进行了关键指标的测试。特别地,在对光谱仪的波长绝对值标定存在困难时,提出了基于吸光度曲线相关度的波长标定方法,使得不同样机之间的波长台间差在理论上小于0.2nm,符合模型转移的要求。第三,按照设计的光谱仪的参数,详细计算和测试了光谱仪的各种噪声。计算了电路噪声,光子噪声,测试了光源波动和背景噪声。指出光子噪声在本光谱仪可以忽略,并且提出了光源波动引起噪声的处理方法。最后,提出了各种阿达玛矩阵模板应用于阿达玛变换方法改善信噪比的条件,给出了光源噪声和探测器电路噪声应该满足的关系。分别测试了基于H互补矩阵、S矩阵、S互补矩阵等3种阿达玛变换方法在强光条件和弱光条件下对信噪比改善比例的数据,指出S矩阵具有最好的性能,但是在强光条件下的性能不如扫描方法。利用DMD可以调制光谱辐射幅值的特点,提出了恒功率S矩阵阿达玛模板,使得应用阿达玛方法时不论在强光条件下还是弱光条件下都能改善仪器的信噪比。
[Abstract]:Near-infrared analysis (NIR) has been widely used in qualitative and quantitative component analysis for its rapidity, nondestructive and accuracy.As a spectral acquisition device, Near-infrared spectrometer has a variety of types, the most widely used are Fourier transform type and grating type.Fourier transform spectrometer has the characteristics of high resolution and high signal-to-noise ratio.There are two types of grating spectrometer: the structure of scanning grating and single point detector and the structure of fixed grating and linear array detector.The structure of single point detector is slow, which is suitable for the situation where the speed requirement is not high, such as the composition analysis of agricultural products, while the speed of linear detector structure is faster, which is suitable for use in process control.With the emergence of digital micromirror array device Digital Micro-mirror device, a kind of spectrometer, which uses grating to separate light, detects signal by single point detector, switches and modulates spectrum wavelength, and uses Adama transform to improve signal-to-noise ratio (SNR) has appeared.This spectrometer has excellent comprehensive performance and obvious price advantage.The key technology of Adama transform spectrometer based on DMD is studied in this paper.First of all, according to the location of the noise in the instrument, the noise of the instrument is divided into the noise before and after the encoding of Adama.The scale coefficients of Adama coding matrix, such as S matrix and S complementary matrix and H complementary matrix, for noise suppression before and after coding are derived in detail. The MATLAB simulation is carried out to verify the correctness of the derived results.The analysis results of many scholars are compared, and the reasons of consistency and inconsistency are explained.Secondly, the near infrared spectrometer based on DLP4500NIR model DMD is designed and fabricated, including optical design parameters, circuit design scheme, software scheme and so on.Several spectrometer prototypes are installed and tested.In particular, when it is difficult to calibrate the absolute wavelength of spectrometer, a wavelength calibration method based on the correlation of absorbance curve is proposed, which makes the wavelength difference between different prototypes less than 0.2 nm theoretically, which meets the requirements of model transfer.Thirdly, according to the parameters of the designed spectrometer, the noise of the spectrometer is calculated and tested in detail.Circuit noise, photon noise, light source fluctuation and background noise are calculated.It is pointed out that the photon noise can be neglected in this spectrometer, and a method to deal with the noise caused by the fluctuation of light source is proposed.Finally, the condition of using various Adama matrix templates to improve SNR is proposed, and the relationship between the noise of the light source and the noise of the detector circuit is given.Three kinds of Adama transformation methods based on H complementary matrix and S matrix and S complementary matrix are tested to improve the SNR ratio under the condition of strong light and weak light respectively. It is pointed out that S matrix has the best performance.But the performance under the strong light condition is inferior to the scanning method.Using the characteristic that DMD can modulate the amplitude of spectral radiation, a constant power S-matrix Adama template is proposed, which can improve the signal-to-noise ratio (SNR) of the instrument under the condition of strong light or low light.
【学位授予单位】：中国科学院长春光学精密机械与物理研究所
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TH744.1

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