High order asymptotics of the near field, radiated by a normal or angled beam fluid couple ultrasonic transducer, into an elasic plate or a half-space

The reasonable formalization of the radiation problem for the case of normal or angled beam fluid coupled ultrasonic transducer is discussed in context of NDT needs. The Green tensor is introduced first in the frequency domain. In the plate it is represented in the modal form. The radiated field is expressed as a convolution integral using effective contact loading. The field is analyzed into the first Fresnel zone where the characteristic wavelength is comparable with the zone size. As known, this problem is usually most time consuming. The high frequency asymptotics of the field under highly oscillating load on the contact spot with smooth contour are derived. For the rectangular transducer the leading asymptotics are obtained in the special geometrical zones. Numerical examples are presented and discussed. The research is performed in the frame of RFBR project 08-08-00855 which is gratefully acknowledged.