【作者】 王琳；

【导师】 王黎明；

【作者基本信息】 中北大学 ， 信息与通信工程， 2022， 硕士

【摘要】 针对目前层叠结构、大深度探测的广泛应用,对其进行质量检测越来越重要,通常采用高频超声检测方式。但对于非连续阻抗结构,例如由高阻抗到低阻抗的层叠结构,传统的高频超声检测中超声波几乎无法透过高阻抗界面进入到低阻抗介质中,而探究这种层叠结构的内部情况又非常重要。为此,本文提出选用低频超声进行检测的方法。为探究低频超声在高阻抗到低阻抗的层叠结构中的传播规律,采用有限差分求解波动方程的方法,对低频超声在非连续阻抗结构中的传播特性进行仿真研究。首先,分析零相位激励和多相位激励两种不同的激励模式下,层叠结构中上层厚度从0到40mm变化时,两种激励模式对低频超声检测的影响,结合低频超声存在严重“拖尾”现象,得出多相位激励模式更符合低频超声检测需求。其次,仿真分析2MHz及其以下频率的超声波在层叠结构中的传播,得出50k Hz到100k Hz之间的超声信号最适用于层叠结构中的超声检测,为实际探头选型提供依据,并得到信号能量与激励频率之间呈幂函数形式衰减,且衰减关系式为y=3.55e10x^-6.11,拟合系数R²=0.9968。然后,研究激励频率一定时,层叠结构的厚度变化与透射信号能量之间的关系,得出用50kHz的低频超声进行仿真时,能量与模型厚度之间基本满足y=-0.00113x+0.7831的线性关系,由此确定采用脉冲透射法能够检测的最大厚度。最后,对低频超声传播特性进行实际应用,提出“一发两收”的低频超声测厚工艺,解决测厚精度不高问题,为低频超声高精度测厚提供理论依据。更多还原

【Abstract】 In view of the wide application of the current layered structure and large depth detection,it is more and more important to carry out quality inspection,and high-frequency ultrasonic inspection is usually used.However,for discontinuous impedance structures,such as high-impedance to low-impedance stacked structures,in traditional high-frequency ultrasonic testing,ultrasonic waves can hardly enter the low-impedance medium through the high-impedance interface.Very important.Therefore,this paper proposes a method of using low-frequency ultrasound for detection.In order to explore the propagation law of low-frequency ultrasound in high-impedance to low-impedance stacked structures,the finite difference method of solving the wave equation was used to simulate the propagation characteristics of low-frequency ultrasound in discontinuous impedance structures.First,analyze the influence of the two excitation modes on low-frequency ultrasonic testing when the thickness of the upper layer in the laminated structure changes from 0 to 40 mm under two different excitation modes: zero-phase excitation and multi-phase excitation.Combined with low-frequency ultrasonic,there is a serious "smearing".It is concluded that the multi-phase excitation mode is more in line with the requirements of low-frequency ultrasonic testing.Secondly,the propagation of ultrasonic waves with frequencies of 2MHz and below in the laminated structure is simulated and analyzed,and it is concluded that the ultrasonic signal between 50 k Hz and 100 k Hz is most suitable for ultrasonic testing in the laminated structure,which provides a basis for the actual probe selection and obtains the signal energy.Then,when the excitation frequency is constant,the relationship between the thickness change of the laminated structure and the energy of the transmitted signal is studied,and the linear relationship between the energy and the thickness of the model is basically satisfied when the low-frequency ultrasound of 50 k Hz is used for simulation.The maximum thickness that the transmission method can detect.Finally,the practical application of low-frequency ultrasonic propagation characteristics is carried out,and the low-frequency ultrasonic thickness measurement technology of "one transmitter and two receivers" is proposed to solve the problem of low thickness measurement accuracy and provide a theoretical basis for low-frequency ultrasonic high-precision thickness measurement.更多还原