Temperature measurement using an ultrasonic sensor consisting of a piezoelectric transducer and an ultrasonic waveguide is presented. The waveguide is a clad rod consisting of a steel core and a stainless steel cladding together with two discontinuities created near the probing end. The temperature information is obtained from information about the time delay between the ultrasonic echoes reflected from these discontinuities and the probing end surface as a function of the temperature. The temperature measured ultrasonically is in good agreement with that obtained by using a commercial thermocouple.

On-line ultrasonic monitoring of polymer co-extrusion and gas-assisted injection molding are presented. During the coextrusion of high density polyethylene (HDPE) and Santoprene ultrasonic sensors consisting of piezoelectric transducers and clad ultrasonic buffer rods are used to detect the interface between these two polymers and the stability of the extrusion. The same ultrasonic sensor also measures the surface temperature of the extruded polymer. The results indicate that temperature measurements using ultrasound have a faster response time than those obtained by conventional thermocouples. In gasassisted injection molding the polymer and gas flow front positions are monitored simultaneously. This information may be used to control the plunger movement.