[en] After having recalled the problems due to standard ultrasonic probe properties and structure, the authors report the development of new specifications for ultrasonic non destructive testing making use of a new concept, the 'effective ultrasonic beam', related to a part of the beam which may be considered as cylindrical, and in which the sensitivity may be considered as constant. This concept is particularly useful when applied to 'shaped beams' like focused beams. These new specifications are based of experimental results and apply as well for longitudinal as for shear wave testing, and enable the flaw size to be determined with a given and known accuracy