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Theory Research of the Calculation of a Thin Layer on an Elastic Substrate with Finite Thickness

Author: DingLiLi
Tutor: CuiZhiWen
School: Jilin University
Course: Acoustics
Keywords: Ultrasonic testing Thin layer Resonance transmission frequency Numerical Simulation
CLC: TP274.53
Type: Master's thesis
Year: 2011
Downloads: 38
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Abstract

Ultrasonic testing is an important form of non-destructive testing, ultrasonic NDT ultrasonic propagation characteristics of the medium, to detect the presence of the target, the evaluation objectives characteristics. The thickness of a thin layer of ultrasonic detection current comparison hot. The application of ultrasonic testing related to the national economy nearly all industries and sectors related to almost all industrial sectors, such as aerospace, high-speed railway, the integrated circuit, the nuclear industry, oil and extractive industries and so on. Thickness is an important parameter to reflect the characteristics of the thin layer, it becomes feasible to carry out the study of the thin layer thickness measurement. Conventional ultrasonic detection thin layer thickness measurement method: the pulse-echo method and time domain to the frequency domain resonance method. Pulse echo method needs to be recorded of separable samples before and after interface echo Layer Thickness Measurement failure. Resonance method needs to cover the sample one or several resonance or anti-resonance frequency on the TLC terms, this requires that the ultrasonic transducer having a wide band range. Thin layer thickness detection involves inversion algorithm, the inversion of the functional form of the equation is complex, and generally can not be solved analytically, using numerical methods such as the Newton-Raphson iteration method, you need to initial parameters need to be studied and the limited parameters of convergence area, otherwise, may face a difficult search global zero minimum point corresponding to the optimal solution in the corresponding solutions from multiple local minimum point of the equation. In this paper, this case, the system model based on the desired adjacent to each other in the thin layer under the condition of two frequency points of the phase shift difference of not greater than π, deduced the analytical expression of the relationship between the thin layer thickness of the experimental data . By the expression can be seen, the thin layer thickness is only concerned with the known amount of the measurement data of the acoustic impedance of the acoustic impedance, etc., using the measurement data of two adjacent frequency points can be realized on the calculation of the layer thickness. The paper presents the transfer function of the reflected wave of the vertically incident ultrasound, to achieve the measurement of thickness of a thin layer of elastic liner method. Thin layer thickness calculated in two different cases, a situation is when the elastic lining thicker when a reflected wave of a reflected wave of the thin layer with the other layers of medium can be separated. Another situation is when the elastic lining is thinner, the thin layer of a reflected wave and a reflected wave of the liner superimposed together can not be separated. Study both cases, select three different acoustic impedance material as lining: aluminum, steel and plexiglass to study, and the study of the ability of anti-noise. In the actual project, the thin layer is often not exist independently or, generally with one or more layers lining and elastic lining is very thick, thin layer of reflective wave layer media reflected waves can be separated in this category typical thin measured, usually taken in the time domain from the entire ultrasound reflected signal to a reflected wave from the thin layer individually extracted, extracted from the thin layer of the reflected wave as a Fourier transform, to give this part of the signal transfer function , then inversion or characterization of the thin layer parameters. , Using one or more frequency intervals in the inversion of the thin layer thickness to calculate the thickness of the sheet material. In order to study its noise immunity, the relative error between the plus amplitude of 1% of the random noise in the ultrasonic reflection signal, the obtained measurement value and true value at around 2%, indicating that this method has some noise immunity , also confirmed the feasibility of the method. If the thickness of the lining is gradually becomes smaller, either in the time domain or frequency domain, the reflection information of the sheet material and liner after the interface echo information can not be separated, and therefore can not be extracted from the ultrasound reflection signals TLC The reflected signal to invert the thickness of the thin layer, then the resonance frequency point information to calculate the thickness of the thin layer of material using the reflection coefficient in the liner. Select three kinds of barrier material of the acoustic impedance of aluminum, steel and plexiglass same as the liner analysis liner resonance transmission frequency points at several points near the point of the same frequency interval, by the calculation result obtained into line, and obtain a slope minimum a straight line, this line is close to the true value, namely, the estimated value of the thickness of the sheet material. After analysis of its stability and noise immunity, plus ultrasonic reflected signal amplitude of 1% random noise to further validate the feasibility of measuring thin bed thickness.

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CLC: > Industrial Technology > Automation technology,computer technology > Automation technology and equipment > Automation systems > Data processing, data processing system > Automatic detection system using a variety of new technologies > Ultrasonic testing equipment
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