牛奶质量超声检测基础理论及实验研究.pdf

天津大学
博士学位论文
牛奶质量超声检测基础理论及实验研究
姓名:孙选
申请学位级别:博士
专业:测试计量技术及仪器
指导教师:徐可欣
20070301
摘要
超声波检测技术作为一种绿色检测技术已经在生命医学、疾病诊断、石油化
工、食品、环境监测、材料分析等领域得到成功应用,取得举世瞩目的成就。在
液体成分分析领域也有许多成功应用案例。超声波检测技术在牛奶质量检测中也
具有突出优势和良好发展前景,但是至今还未很好地满足牛奶质量检测的生产实
际的需要,主要原因在于对“牛奶声学”研究的不足,包括超声波与牛奶的相互
作用机制以及超声波在牛奶中传输的研究。本文采取理论分析与实验研究相结合
的方法,就牛奶质量超声检测的作用机理和测量影响因素展开深入研究。建立了
符合超声波与牛奶实际作用过程的声学模型,解决了牛奶质量超声检测的理论难
题。研究了温度变化对牛奶测量的影响机理,分析了现有解决温度影响方法的特
点,提出了“温度动态测量法”,并针对基于这种测量方法的建模方法进行了系
统硏究,解决了牛奶质量超声检测的应用瓶颈。具体内容包括:
1)从超声波在理想液体中传输满足的三个基本方程出发,推导出超声波在
牛奶这种多元液体中传播的声速模型;在综合 Stokes经典吸收理论和 Kirchhoff
理论的基础上,结合牛奶的特性,给出牛奶对超声波吸收衰减模型:在经典散射
模型的基础上,推导出适合牛奶这一具体对象的散射衰减模型,从理论上理清了
超声波在牛奶中的传输特性和超声波与牛奶相互作用机理。通过实验对牛奶脂
肪、蛋白质的超声特性进行了研究,验证了声速模型、衰减模型的正确性。
2)系统分析了牛奶超声测量的关键影响因素一一温度问题。研究了温度变
化对牛奶超声测量的影响机理,通过实验确定了温度对超声测量影响程度,得出
温度变化0.1℃对牛奶声速和衰减系数的影响相当于牛奶中脂肪质量百分比浓度
改变0.1%或蛋白质浓度改变0.15%的影响,所以要想使脂肪和蛋白质的测量绝
对误差小于0.1%和0.15%,温度的控制或检测精度高于0.1℃的结论。为了减小
温度对超声测量的影响,提出了“温度动态测量法”。
3)将化学计量学方法引入到牛奶成分测量的建模方法中,通过系统分析优
选偏最小二乘线性回归算法作为建立超声参量、温度与牛奶成分浓度之间关联模
型的算法。为了提高模型预测精度和减小温度的影响,提出三种建立温度校正模
型方法,经过实验对比研究得出了最佳建模方法,即采用声速和衰减系数联合建
模的35℃+40℃的局部温度校正模型方法,用该方法建模预测精度最高,能够满
足工业实际测量的要求
关键词:牛奶质量超声检测声学机理温度影响偏最小二乘回归
ABSTTRACT
Ultrasonic measurement technology, a green measurement technology has already
not only applied successfully in some fields getting a world spotlight accomplishment
such as life medical science ,disease diagnosing, petrochemical industry, food
environmental monitoring, material analyse, but also in the field of liquid components
analyse. Ultrasonic measurement technology has prominent advantages and well
development prospect in milk quality measurement, however, it hasn't satisfied
production need of milk quality measurement so far. Main cause lies in the study
deficiency for"milk acoustics, including the efifect mechanism between ultrason
and milk and the research of ultrasonic transmission in milk. The dissertation studied
effect mechanism and measurement influencing factors of milk quality ultrasonic
measurement adopting theoretical analysis and experiment research, built the
acoustics moel acrin with the actual ef eot process between ultrasonic and milk,
resolved the theory difficult problem of milk quality ultrasonic measurement. Studied
effect mechanism of milk measurement by reason of temperature change, analysed
characteristic resolving temperature effect methods, brought forward the"temperature
dynamic measurement principle and studied specifically its modeling methods,
resolved the application choke point of milk quality ultrasonic measurement. Concrete
content is included
1 Deduced the ultrasonic sound velocity model transmitting in multiplicative
liquid milk starting off three fundamental equations that ultrasonic transmitts in ideal
liquid given out the milk absorbability attenuation model to ultrasonic on the basis of
Stokes absorbability theory, Kirchhoff theory and milk characteristic. The milk
dispersion at enuation model was deduced from classics dispersion model, opened out
the ultrasonic transmission characteristic in milk and effect mechanism between
ultrasonic and milk. studied the characteristic of fattiness and protein with
experiments, and validated the validity of sound velocity model a