an ultrasonic device to characterize the flow of resin entering and exiting an injection mold during the phase of impregnation , by the resin , of a preform contained in the mold . the device includes two ultrasonic sensors arranged respectively in the vicinity of the inlet port where the resin enters the mold and in the vicinity of the outlet port where the resin exits the mold . each sensor emits an ultrasonic wave towards the end of the mold in the vicinity of which it is positioned , and receives the ultrasonic wave reflected by the medium . preferably , the device determines the stabilization of the flow of resin passing through the mold based on the signals received by the sensors . a method for implementing the device to determine the completeness of the operation of impregnating , with resin , a preform positioned in an injection mold into which the resin is introduced .