An apparatus for in-situ monitoring of a welded joint in a workpiece includes an ultrasonic sending transducer and a receiving transducer. The ultrasonic sending transducer includes a probe head disposed on a plurality of individually-activatable piezoelectric elements, and a plurality of waveguide probes projecting orthogonally from a planar surface. A wave attenuator is disposed between individual ones of the waveguide probes. A receiving transducer is disposed therein. The workpiece is insertable between the waveguide probes of the ultrasonic sending transducer and the receiving transducer. The ultrasonic sending transducer urges the probe head towards the receiving transducer such that the waveguide probes physically contact the welded joint in the workpiece. The piezoelectric elements individually excite the waveguide probe that is in physical contact with the welded joint in the workpiece. The acoustic receiving transducer is disposed to monitor the welded joint in the workpiece.