Ultrasonic probe and method for monitoring materials processing in screw driven extruders

An ultrasonic probe and method for noninvasively monitoring materials processing in screw driven extruders. The noninvasive probe includes at least one ultrasonic transducer operable to transmit an ultrasonic signal on a signal path intersecting an inner sidewall of a barrel of the extruder and material between the inner sidewall of the barrel and an outer surface of a screw within the barrel. Information about the state of the material intersected by the ultrasonic signal is ascertainable from an elapsed time between reception of a first reflection of the ultrasonic signal and reception of a second reflection of the ultrasonic signal. The first reflection results when the ultrasonic signal exits the inner sidewall of the barrel and the second reflection results when the ultrasonic signal reaches one of the outer surface of the screw and partially solid material.