A new focusing ultrasonic transducer and two foci acoustic lens for acoustic microscopy.

The textured piezoelectric film of a new organic-based material produced by vapor deposition was used as an active element of a focusing ultrasonic transducer. The transducer exhibits near theoretical lateral and axial resolution, unipolar pulse response to a step voltage, and 30 dB insertion losses in an octave frequency band. The transducer is acoustically transparent over a wide frequency range and can be fabricated on a concave spherical surface of the standard acoustic lens. The resulting double transducer and two foci acoustic lens are capable of improving the quality of the surface structure imaging or of being used in continuous wave reflection acoustic microscopy.

Temperature effects in the focal region of acoustic microscope.

New analytical expressions that account for radial and axial heat flow in a medium and immersion liquid are derived for the case of a Gaussian-shaped ultrasonic beam pattern near a focus of an acoustic microscope in thin or semi-infinite absorbing materials for two cases corresponding to the studying of biological or solid-state samples. In the first case, it is assumed that the sample together with the immersion represents a medium uniform in its thermal properties. In the second case, it is supposed that heat conductivity of a sample material is much more than that of the immersion liquid. Solutions are given for temperature growth along the axis of symmetry of acoustic lenses. The use of these equations in estimation of the temperature growth gives a maximum value of one degree for biological samples with the absorption coefficient ten times more than that of water and 10(-3) degrees C for samples of silicon for the microscope with a maximum ultrasonic intensity of 10(3) W/cm(2) at 500 MHz and with water as an immersion liquid.

[Effect of ultrasound on the membrane potential and embryonic development of sea urchin eggs]. / Vliianie ul'trazvuka na membrannyi potentsial i émbrional'noe razvitie iaitsekletok morskogo ezha.

Eggs of sea urchin Strongylocentrotus intermedius were exposed to continuous wave ultrasonic energy at a frequency of 2 MHz for 3 min. Ultrasonic treatment results in the appearance of monstrous embryos that die at the latest stages of their development. The number of dead embryos sharply grows with the increase in the spatial average intensity from 0.4 W/cm2 up to 1.6 W/cm2, when it comprises 100%. Dramatic decrease from 99% to 17% in the absolute value of transmembrane potential for both fertilized and unfertilized eggs was observed after ultrasonic treatment. These results seem to be caused by the action of stable cavitation. The given estimations show that for ultrasonic intensities more than 0.2 W/cm2 and providing the presence of gaseous bubbles in the vicinity of eggs shell the value of shear stress in an egg shell becomes great enough to cause the cytoplasmic gel fragmentation.