Читать книгу Monument Future - Siegfried Siegesmund - Страница 360

The new ultrasound system was first tested in the laboratory on so-called ultrasound phantoms. The first phantom was a cylindrical bucket filled with water in which a rod (Ø = 90 mm) made of polyoxymethylene (POM) was placed. Tomography was performed with 24 ultrasound transducers.

Figure 3 shows the result of the evaluation. The rod made of POM is clearly visible as a yellow area. The sound velocity in water was calculated with approx. 1.500 m/s and the sound velocity in POM with approx. 1.900 m/s was calculated correctly. The second phantom was a cylinder made of Carrara marble which was artificially aged. The cylinder was then heated to 150 °C and thrown into cold water. Thus, the average speed of sound could be reduced to approx. 3.200 m/s. Figure 4 shows the results of the evaluation. These correspond well with the expected values.

After successful measurements in the laboratory, the system was tested on the columns (Ø = 550 mm) of the Marmorpalais in Potsdam (see Figure 2). These are heavily weathered and show cracks, some of which have been filled.

Figure 5 shows the found structure of the marble. Although signals could be received at this object, they had large interference components. An automatic detection of the signal beginnings and thus an evaluation of tomography was not possible. The performance limit of the system was reached because of the strong fissuring of the stone.

Figure 5: typical structure of the marble columns of the Marmorpalais in Potsdam.