Many of the traditional NDE techniques of the past are today being investigated for their potential role as process control sensors for materials processing [1]. Ultrasonics appears one of the most promising because of its ability to penetrate opaque bodies and allow determination of microstructure variables (such as grain size), process variables (such as internal temperature distribution) and detect internal discontinuities (cracks, pores and inclusions). A key problem with the traditional approaches to ultrasonic measurements is the need to contact the body being probed with piezoelectric transducers. These transducers are fragile, require couplants, and fail when exposed to temperatures of more than a few hundred degrees Celsius. Their use during processing may thus require practices that unacceptably interfere with the process.