【作者】 余洋；

【导师】 熊庆宇；

【作者基本信息】 重庆大学 ， 软件工程， 2022， 博士

【摘要】 在微波加热过程中,由于空间分布不均的交变电磁场作用,使得被加热物料的温度变化呈现时变和非线性的特点,局部加热区域很可能产生热点。进一步地,在时变负载特性的作用下,被加热物料的温度将变得极不稳定,并可能产生燃烧、爆炸等一系列灾难性后果。因而,这就需要适于微波工业电磁场环境下的温度分布检测技术。超声测温技术因具有硬件成本低、非接触式测量、可扩展性强、对声波的曲线路径敏感度小等优点而广泛应用于工业温度检测领域。本文的研究旨在探索将超声测温技术应用于微波加热系统中加热腔体内部的温度测量的可能性,而所加热区域内的超声温度重建涉及两个关键问题,即为超声飞行时间测量和重建算法。因而,本文主要从飞行时间测量和重建算法两方面展开研究,以重建测量区域内具有较高精度的温度图像分布。然而在实验验证的过程中,由于微波加热系统中加热腔体对超声信号的干扰和屏蔽,使得飞行时间测量系统无法采集到可靠的时间数据。鉴于此,本文构建了一个带有热源的实验测试平台来模拟微波加热腔体内部的加热环境,以评估本文中所提出算法的重建性能。本文以超声飞行时间测量和重建算法为切入点,围绕高精度的温度图像重建目标,提出了可行算法,并通过实验测试平台验证了所提出算法的有效性和可行性,最后开发了一套融合有三种温度测量技术的超声测温系统。本文主要的创新性研究成果如下:1)根据文献综述结果,相当数量的文献并未构建一个超声飞行时间测量系统来获取真实的飞行时间数据,或缺乏对测量系统的详细描述。针对这一问题,本文从测量系统的组成单元功能、超声探头间的通信流程、信号的预处理过程等方面对所构建的超声飞行时间测量系统进行了详细的阐述,并分析了可能影响时间测量精度的因素。由于测量系统中所选用的超声模拟前端芯片TDC1000具有特定的阈值比较器模块,故采用阈值法来计算超声飞行时间。进一步地,在获取高精度且真实的飞行时间数据后,验证了经典的最小二乘法存在边缘温度信息缺失的问题,而基于径向基函数的重建算法则可重建出测量区域内的完整温度图像分布信息。2)测量区域内的超声温度重建过程等价于求解正则化的最小二乘问题,针对大型线性方程求解收敛缓慢的问题,本文创新性地发展了由Yang所提出的一种记为HBMR(Heavy Ball Minimal Residual)的Krylov子空间算法,将该算法扩展到正则化形式并求解正则化的最小二乘问题。本文称扩展的HBMR算法为正则化的HBMR算法,并简记为Reg HBMR算法(Regularized HBMR)。此外,本文还制定了迭代运算中所需的停机准则,并根据交叉验证法确立了正则化过程中的正则化参数。在实验上,本研究内容先基于三种数值温度模型从仿真角度验证了所发展的Reg HBMR算法的重建性能,再基于实验测试平台所得的飞行时间数据证实该算法的各项性能。3)重建模型中系统矩阵的病态性也是影响超声温度图像重建精度的因素之一,而径向基函数的选取与系统矩阵的病态性直接关联。为此,本文提出了融合指数函数(Exponential,Exp)和三次方函数Cubic的混合径向基函数Exp+Cubic。混合函数中的Cubic函数不受自由参数的影响,对系统矩阵的病态性几乎无关联;而Exp函数充分考虑了各数据点之间的距离和随机性,可视为最佳的线性无偏预测器。此外,由均方根误差计算出的结果确立了混合函数中自由参数的大小。在实验上,各径向基函数在条件数的比较验证了所提出函数具有最小的条件数。进一步地,基于实验测试平台进行了单峰对称和非对称的评估实验,实验结果验证了所提出混合径向基函数的温度图像重建性能。4)分析超声测温技术、光纤温度计、红外测温技术三种技术的优劣性,充分利用这三种测温技术在温度监测中的优势,将三种温度信息融合起来,以更好地辨识和监测测量区域内真实的温度分布,同时也开发了一套超声温度测量系统,用于显示出这三种温度信息。更多还原

【Abstract】 In the process of microwave heating,due to the effect of the alternating electromagnetic field with uneven spatial distribution,the temperature change of the heated material is time-varying and nonlinear,and hot spots are likely to occur in the local heating area.Also,due to time-varying load characteristics,the temperature of the heated material will become extremely unstable,and some catastrophic consequences such as combustion and explosion may occur.As a result,there is a need for temperature distribution detection techniques suitable for microwave electromagnetic field environments to meet practical needs.Acoustic temperature measurement techniques are widely used in industrial temperature detection due to their low hardware cost,noncontact measurement,scalability,and low sensitivity to the curve path of the acoustic waves.The aim of this thesis is to explore the possibility of applying acoustic tomography to the temperature measurement inside a heated cavity in a microwave heating system.Acoustic temperature reconstruction in the measurement area involves two key points,i.e.,acoustic time-of-flight(TOF)measurement and reconstruction algorithm.Therefore,this thesis focuses on the TOF measurement and reconstruction algorithm to reconstruct the temperature image distribution with high accuracy in the measurement area.However,the resonant cavity can screen signals from an ultrasonic transducer during the experiment.This behavior of the resonant cavity can seriously interfere with the propagation of ultrasonic signals,and thus the measurement system cannot collect reliable TOF data.To guarantee the validation of experiments,this thesis simulates the internal circumstance of the heating system on a measurement platform with a heat source.Taking the TOF measurement and reconstruction algorithm as the starting point,and aiming at the high-precision temperature image distribution reconstruction,this thesis proposes a problem-oriented algorithm.Then,the effectiveness and feasibility of the proposed algorithm are verified through the experimental test platform.Finally,this thesis develops a set of acoustic temperature measurement system integrating three types of temperature information.The main research results of this thesis are as follows:1)According to the results of the literature review,a considerable amount of literature does not build an ultrasonic TOF measurement system to obtain real TOF data,or lacks a detailed description of the measurement system.To this end,this thesis presents a detailed description of the TOF measurement system in terms of the component units of the measurement system,the communication flow between ultrasonic probes,the signal preprocessing process,and analyzes the factors that may affect the TOF measurement accuracy.Since the TDC1000 ultrasonic sensing analog front-end selected has a specific threshold comparator module,the threshold method is used to calculate the TOF.Once obtaining accurate TOF data,it is verified that the classical least squares method suffers from missing edge temperature information,whereas the radial basis function-based reconstruction algorithm can reconstruct the whole temperature image distribution within the measurement area.2)The acoustic temperature reconstruction process in the measurement area is equivalent to solving the regularized least squares problem.In order to solve the problem of slow convergence of large-scale system matrix,this thesis innovatively develops the Krylov subspace algorithm HBMR(Heavy Ball Minimal Residual,proposed by Yang),i.e.,extends the algorithm to solve the regularized least squares problem.In this thesis,the extended HBMR algorithm is referred to as the regularized HBMR algorithm and abbreviated as Reg HBMR.In addition,the stopping criterion required in the iterative process is formulated,and the regularization parameters in the regularization process are determined according to the generalized cross-validation method.Experimentally,the reconstruction performance of the developed Reg HBMR is first verified from a simulation perspective based on three numerical temperature models,and then its performance is confirmed based on the TOF data collected from the measurement system.3)The ill-conditioning of the system matrix in the reconstruction model is also one of the factors that affect the reconstruction accuracy of ultrasonic temperature images,and the selection of the radial basis function is directly related to the ill-conditioning of the system matrix.To this end,a hybrid radial basis function Exp+Cubic is proposed in this thesis,which combines the exponential function(Exponential,Exp)and the Cubic function.Specifically,the Cubic function is free of the shape parameter and has little relevance to the ill-conditioned system matrix,while the Exp function takes full account of the distance and randomness between the data points and can be regarded as the best linear unbiased predictor.In addition,the free parameters in the hybrid function are determined by the calculation of the root mean square error.Experimentally,the comparison of each radial basis function in terms of condition number verifies that the proposed hybrid function has the smallest condition number.Furthermore,single-peak symmetric and asymmetric experiments are performed according to the experimental test platform,and the experimental results verify the reconstruction performance of the proposed hybrid function.4)This thesis analyzes the advantages and limitations of acoustic temperature measurement technique,optical fiber thermometer and infrared temperature measurement technique,and then combines the advantages of these three temperature measurement techniques in temperature monitoring in order to better identify the true temperature distribution in the measurement area.On the other hand,an ultrasonic temperature measurement system is also developed to display these three temperature information.更多还原