Simulating Structural Noise in Ultrasonic Flaw Detection Taking into Account Frequency-dependent Attenuation of Ultrasound
Abstract
The article considers a new method for mathematically simulating the structural noise produced during ultrasonic examination of materials having a heterogeneous structure. Structural noise is an unsteady random process, the specific feature of which is that both its dispersion and energy spectrum vary with time. Unsteadiness of the structural noise energy spectrum is caused by frequency-dependent attenuation of ultrasonic waves in the medium, due to which high-frequency components of the signal spectrum are attenuated more intensely than its low-frequency components. As a result, as time passes, the structural noise energy spectrum narrows and shifts toward low frequencies. The novelty of the proposed structural noise simulation method is that the frequency-dependent attenuation of ultrasonic waves excited in the examined material is taken into account for the first time. Structural noise is generated as a result of the superposition of the signals reflected from heterogeneities located in the material according to a random uniform law. The characteristics of the probing signal and the directional patterns of the transducers are taken into account. Since each of these elementary signals travels over different paths in the course of their propagation in the medium, undergoes different attenuation and, therefore, has its own different shape of the spectrum, the structural noise is simulated in the spectral domain. The simulation boils down to calculating the spectra of elementary signals and summing these spectra with due regard to the necessary delays. As a result, the structural noise realization spectrum is obtained, after which the structural noise realization as a function of time is determined using the inverse Fourier transform. The article presents an example of simulating the structural noise arising in ultrasonic sounding of material with a specified frequency dependence of ultrasonic wave attenuation coefficient in the medium. A comparison between the simulated and experimentally obtained realizations confirms the adequacy of the proposed structural noise simulation method. Limitations of the method and the most promising fields of its application are pointed out.
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Для цитирования: Карташев В.Г., Трунов Э.И., Шалимова Е.В. Моделирование структурного шума в ультразвуковой дефектоскопии с учетом частотно-зависимого затухания ультразвука // Вестник МЭИ. 2018. № 4. С. 145—151. DOI: 10.24160/1993-6982-2018-4-145-151.
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For citation: Kartashev V.G., Trunov E.I., Shalimova Е.V. Simulating Structural Noise in Ultrasonic Flaw Detection Taking into Account Frequency-dependent Attenuation of Ultrasound. MPEI Vestnik. 2018;4:145—151. (in Russian). DOI: 10.24160/1993-6982-2018-4-145-151.
