Design and perfomance of a broadband 10 MHz transducer for elevated temperature, leave-in-place applications

This paper describes the novel design of an ultrasonic normal beam transducer for prolonged use in elevated temperature environments. Through the use of a Carbon/Carbon composite backing layer, prolonged exposure to elevated temperature had minimal effect on transducer performance. The conductive nature of the Carbon/Carbon allowed for an innovative electrical coupling technique. A clamping mechanism combined with the use of an annealed gold quarter-wave matching layer allowed for joint-free, dry coupling. This simple design allows for easy field assembly and eliminates temperature dependencies in the acoustic coupling. The transducer was tested initially at room temperature for reference data. Further tests after 100+ hours of exposure to a 77°C environment showed little overall change in the transducer performance. The transducer showed consistent -6dB bandwidths on the order of 54-67%, along with negligible change in centerline frequency. The insertion loss as a function of temperature showed an increase from approximately 6.8dB to 8.5dB over a temperature range from 25°C to 85°C. Regression lines show bandwidth changes of -0.01% per °C and insertion loss changes of 0.03dB per °C. These results show potential use for a transducer of this design at even higher temperatures.