RESUMO
A metal object is computer visualized by registration of the amplitudes of the transmitted through the object short acoustic pulses. The pulses are separated by time, because of the presence of holes and internal compact components in the longitudinal section (structure along the propagation direction of acoustic wave). The acoustic field transmitted through the object is composited from a field presenting Fourier transformation of the hole shape and field, transmitted through the metal components in the longitudinal section of the object. A computer Fourier transformation of the digital data of the amplitude fields transmitted through the object components is performed instead of converging lens. The Fourier series of the object obtained as digital data after the transformation is multiplied with a term, describing the angle distribution of the field on spatial frequencies. The reconstruction of the image of the metal components is performed by reverse transformation, i.e. summing up in all spatial frequencies. 3D visualization of the transmitted through the hole acoustic field determines the hole geometry (circular, square, rectangular). It is shown that at the transmission of a short acoustic pulse through the components with different thicknesses and holes, presenting Fourier and non-Fourier transformation can be registered separately in contrast to the optics.
RESUMO
A multibeam Fabry-Perot interferometer is used for measuring very small periodic displacements (SPD). The steepness of such an interferometer as well as the high gain of the photomultiplier and the powerful laser allow one to measure SPD of the order of 10(-19) m at room temperature. Analysis of all the noise factors restricting the sensitivity (heat fluctuations of the surfaces of the mirrors, shot effect, radiation pressure noise) shows that at room temperature the heat noise is the most important.