Reliable NDE techniques for green-state (unfired) ceramics are needed (1) to evaluate ceramic powder processing and compaction methods and (2) to screen out defective ceramic components prior to the costly densification process. Past work in the application of ultrasonic NDE to green-state ceramics has been hampered by the lack of an efficient yet safe means to obtain ultrasonic coupling, since conventional coupling fluids (water, gels, oils, etc.) have a detrimental effect on fragile green-state materials. In early work, direct contact pressure was used to obtain dry coupling between transducer and specimen [1]. This approach was later improved upon by placing an elastomer membrane between the transducer and specimen; this method provided efficient coupling at significantly lower contact pressures [2]. In the study presented here, an acoustically transparent plastic membrane was held against the ceramic specimen by atmospheric pressure [3]. The advantage of this technique is that it allows the use of ultrasonic immersion techniques as well as contact transducers.
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