Abstract
Detailed measurements have been done and compared to analytical models of the beam pattern and on-/off-axis pressure in the near-field region of plane circular transducers in order to model the reflection and transmission of ultrasonic waves from and through steel pipes (casing) and plates immersed in oil. It is shown that for broadband and pure tone pulses in the near field, for free field conditions and through a curved or planar layered media, the sidelobes are smaller and the half-power beamwidth is narrower than in the far field. The beamwidth is slightly dispersed (<1 deg) through the casing and plates of similar thickness, being larger through the planar geometry. Off-axis pressure through these elastic structures reveals condensing and dispersing effects (<2 mm) in the curved and planar geometry, respectively. On-axis pressure, however, for λ < structure’s thickness and plane ultrasonic transducers with size a/λ>5, where a is the transducer radius, the reflected and transmitted sound field is the same from and through both structures and behaves as a well-collimated beam in the near-field region. [Work supported by the University of Texas at Austin and the Mexican Petroleum Institute.]
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