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Novel modes of operation and contrast for phase sensitive acoustic microscopy

Grill W.

Prace Naukowe Instytutu Telekomunikacji i Akustyki Politechniki Wrocławskiej. Konferencje

2001

Vol. 83, nr 27

39-39

Scanning acoustic microscopy with high resolution phase and amplitude contrast gives access to a variety of modes of operation and contrast schemes. Concerning the information in the phase images, non-local response will lead to phase singularities. The presence of such structures will generally not allow to track the phases in images. Phase tracking is needed to derive for example topographical images from phase contrast images obtained in the reflection mode. Image processing has been developed to localize singularities and to identify related pairs and a connecting path. For sufficiently simple objects, these procedures can be used to establish reliable phase tracking conditions. Non-confocal imaging in the transmission mode has been performed with temporal and spatial apodization. This allows to achieve a line shaped point spread function between the focal points of the focusing transducers. For axial alignment the obtained point spread function is ideally suited for tomographic imaging respectively imaging schemes averaging along parallel lines through the object under investigation. Presented are measurements of the point spread function compared to numerical simulations and applications involving NDT and NDE of graded materials. From this detection scheme images in various contrast modes representing the velocity of longitudinally and transversely polarized ultrasonic waves, the Poisson ratio, Young's modulus and the shear modulus have been derived. Phase sensitive imaging in the reflection mode has been performed in combination with three dimensional scanning. The information based on spatial selection by confocal alignment and detection of the phases of the signals resulting from reflection in the focal region has been used to determine the reflectivity of biological samples corrected for the tilt of the imaged surface respectively interface elements. This allows to derive a normalized contrast representing the actual reflectivity as observed for vertical orientation with respect to the axis of observation. Applications aiming at the determination of the mechanical properties of living microscopic aquatic species (daphnia) are presented. An overview concerning the available imaging schemes based on phase sensitive acoustic microscopy (PSAM) concludes the presentation.