OPTIMIZING THE SENSOR DISPLACEMENT PITCH DURING ULTRASONIC THICKNESS MEASUREMENTS OF OBJECTS MADE OF HETEROGENEOUS MATERIALS
Keywords:
ultrasonic thickness measurements, displacement pitch, materials with heterogeneous structureAbstract
The article is devoted to studying the effect the sensor displacement pitch has on the value of signal-to-structural noise ratio in thickness measurements of objects made of materials with heterogeneous structure by ultrasonic echo method. The sensor has one emitting and one receiving transducers, each having a circular aperture with a diameter of a few wavelengths. It was assumed that the dimensions of object’s probing area are fixed; and the sensor moves within this area with a certain pitch. The analysis was provided both theoretically and experimentally. As a result of theoretical analysis it was established that there exists an optimal sensor displacement pitch, which is equal to half the transducer’s aperture diameter. When the sensor displacement pitch is larger than the optimal one, the signal-to-structural noise ratio is proportional to the square root of the number of soundings; if the displacement pitch is smaller than the optimal one, the signal-to-structural noise ratio remains constant despite the increase in the number of soundings. The experiment was conducted with a sample of cast iron with a thickness of 100 mm. The sensor consisted of two transduces with aperture diameter 20 mm. A short radio impulse with a length of one sine wave cycle was used as the sounding signal. The frequency of the sounding signal was 1.8 MHz. The sensor was moved over the article surface with various steps; the object was sounded from each position, and the received signals were saved into computer memory and then processed. The experimental results fully coincided with theoretical results. The optimal sensor displacement pitch was found to be equal to half the transducer’s aperture diameter. On the basis of the obtained results, practical recommendations on choosing the sensor displacement pitch during thickness measurements of articles made of materials with heterogeneous structure were drawn up.
References
2. Марков Г.Т. Антенны. М.: Энергия, 1975.
3. Карташев В.Г, Севалкин Д.А. Корреляционные характеристики структурного шума в ультразвуковой дефектоскопии // Вестник МЭИ. 2007. № 3. С. 100 — 105.
4. Карташев В.Г, Шерщак П.В. Построение оптимального алгоритма обработки сигналов в ультразвуковой дефектоскопии на основе уточненной модели формирования структурного шума // Вестник МЭИ. 2009. № 1. С. 57 — 62.
5. Карташев В.Г., Шалимова Е.В. Пространственно-временная обработка сигналов при зондировании неоднородных материалов поперечными акустическими или электромагнитными волнами с использованием метода синтезированной апертуры // Радиотехнические тетради. 2009. № 38. С. 38 — 42.
