光声光谱检测装置中光声池的数值计算及优化

利用光声光谱技术进行痕量气体的检测具有独特的优势,光声池是系统装置中最为重要的核心部件,它决定着整机性能的优劣.以一圆柱形共振型光声池为研究对象,基于声学与吸收光谱学的基本理论,建立了光声池声场激发的数学模型;利用数值模拟方法对光声池空腔结构进行了声学模态仿真,获得了前8阶声学模态值以及声压可视化振型;在考虑热黏性声学损耗的作用下,对光声池进行了热-声耦合多物理场仿真计算;将仿真结果与解析计算和实验结果进行对比,明确了利用数值模拟方法来计算光声池有关指标的可靠性与可行性;针对光声池的优化问题,提出了一种将响应面代理模型与遗传算法相结合的优化算法,在将原光声池中的谐振腔两端形貌更改为喇叭口形的情况下,通过优化算法获得了以光声池品质因数Q及池常数C_(cell)为最大值寻优的Pareto最优解集;选取一组解进行考察,结果表明,代理模型预测值与数值模拟值指标最大误差仅为1.3%,优化后的新型光声池Q较之前增长了48.9%, C_(cell)增长了34.4%.研究方法可为光声光谱中光声池的优化设计提供参考借鉴.

Numerical calculation and optimization of photoacoustic cell for photoacoustic spectrometer

Photoacoustic spectroscopy (PAS) offers intrinsic attractive features in the detection of trace gases, including ultra-compact size and background-free absolute absorption measurement. The photoacoustic (PA) cell is a key component in the PAS system, which determines the performance of the PAS sensor. In this paper, a cylindrical resonant photoacoustic cell is taken as a research target. Based on the fundamental theory of acoustics and absorption spectrum, a mathematical model of acoustic field excitation in the PA cell is established. The acoustic resonance frequency, quality factor and cell constant of the PA cell are used as three key parameters to describe its performance. By employing advanced computer numerical calculation and finite element simulation technology, we establish a simulation model and impose the excitation load and boundary conditions on the model according to the actual working conditions. Then we calculate and simulate the acoustic modal of the PA cell, and the first eight acoustic modal values of the cavity and the visual vibration model of the acoustic pressure are obtained. With considering the acoustic loss, the thermo-acoustic coupling multi-physical field simulation of photoacoustic cell is carried out. Comparing with analytical calculation and experiment results, the reliability and feasibility of using numerical simulation method to calculate the relevant parameters of photoacoustic cell are demonstrated. In order to obtain a better structure of photoacoustic cell, an optimization algorithm combining response surface proxy model with multi-objective genetic algorithm is proposed. We try to change the shapes of both ends of the resonator in the original photoacoustic cell into the shape of the bell mouth. Take into account the case that the longitudinal acoustic normalization frequency of the PA cell is larger than 1000 Hz, Pareto optimal solution set with the maximum quality factor Q and cell constant C_cell of the PA cell is obtained. The results show that the maximum error between the predicted and simulated values of the proxy model of the PA cell Q and C_cell is only 1.3%. Comparing with the original PA cell, the Q factor and the C_cell of the optimized PA cell are increased by 48.9% and 34.4%, respectively. The performance of the optimized photoacoustic cell is obviously improved. The proposed algorithm of photoacoustic numerical simulation combined with multi-objective optimization design can provide helpful reference for designing the PA cell in PAS sensor development.