Diffraction method for focusing of acoustic fields radiated by extended borehole antennas

One way to make a focusing borehole antenna using diffraction focusing of the acoustic field is considered. The primary attention is paid to the methods of partition of an extent borehole antenna cylindrical aperture into areas with antiphase excitation for the formation of a cylindrical zone lens. It is shown that, there is also an alternative method besides the classical Fresnel zones partition. Specific features of the elastic field distributions in the massif, created by different zone lenses, are examined. Applicability of focusing borehole antennas, designed as zone lenses, in geotechnologies is discussed.