Ultrasonic flaw sizing is an important issue for insuring structural reliability and remaining life prediction of industrial plants. The Time-of-Flight Diffraction (TOFD) method is one of the effective tools for sizing flaws. However, due to the difference of the acoustic impedance between the wedge and specimen, unexpected SV and Rayleigh wave are generated at boundary by mode conversion. These waves occasionally disturbs the received TOFD signal hence it is important to reduce the mode conversion waves. In this study, a Line-Focus SUS wedge longitudinal wave probe is developed to reduce mode conversion waves for possible application to TOFD method. The probe is composed of a cylindrical wedge and piezoeleciric transducer adhered to the cylindrical surface of the wedge from 20 to 70 degree. This probe can excite the longitudinal wave which is incident on the specimen surface at almost all angles from 20 to 70 degree simultaneously. In addition, this probe is expected to reduce the mode converted SV and Rayleigh wave. In this research, for the basic performance evaluation, the directivity of the Line-Focus SUS wedge longitudinal wave probe is evaluated with the examination using half-cylindrical steel specimen and the two dimensional numerical simulations.
