Numerical simulation of directivity for angle probe and surface defect

An ultrasonic testing uses the directivity of the ultrasonic wave which propagates in one direction. The directivity is expressed as the relationship between the propagate direction and i ts sound pressure. This paper studied the directivity of shear waves emitted from angle probes and scattered from surface defects by using visualization method. These experimental results were compared with the theory which was based on the continuous wave. The applicability of continuous wave theory was discussed in terms of the parameter d/λ where d is transducer or defect size and λ is the wavelength. In the case of angle probes, the experimental results show good agreement with theoretical directivity on the principal lobe. When defect size was smaller than the wavelengths, clear directivity in the reflected wave was observed. In the case of the same ratio of defect size to wavelength, the directivity of reflected waves from the defect show almost the same directivity in spite of frequency differences. When the d/λ is greater than 1.5, measured directivities almost agreed with the theoretical one.