AN AIR COUPLED TRANSMISSION MODE ACOUSTIC MICROSCOPE FOR ON-LINE NON-DESTRUCTIVE EVALUATION

ULTRASONIC NDE SYSTEMS SUFFER A MAJOR DIFFICULTY WHICH PREVENTS THEIR USE IN MANY INTERESTING APPLICATIONS. THIS IS, OF COURSE, THE NECESSITY OF PROVIDING A FLUID COUPLING TO THE SAMPLE BEING INSPECTED. THIS PREVENTS THE USE OF THESE SYSTEMS IN VERY HOT ENVIRONMENTS, OR WHERE THE MATERIALS BEING PROCESSED CANNOT BE CONTAMINATED WITH WATER OR OTHER FLUIDS. WE PROPOSE TO USE A TRANSMISSION TYPE ULTRASONIC MICROSCOPE OPERATING IN AIR IN THE 1 MHZ FREQUENCY RANGE TO ADDRESS THESE APPLICATIONS. WE SEE SUCH A SYSTEM IN USE FOR INPROCESS EVALUATION OF MANY STRUCTURAL MATERIALS SUCH AS COMPOSITES AND GREEN CERAMICS. THE KEY TO THESE TYPE OF SYSTEMS IS THE DESIGN AND CONSTRUCTION OF HIGHLY EFFICIENT AIR-COUPLED TRANSDUCERS AND DRIVING AND RECEIVING ELECTRONICS. WE WILL MAKE MORE EFFICIENT AND BROADBAND ULTRASONIC TRANSDUCERS IN AIR THAN HAS BEEN PREVIOUSLY DONE. THESE DEVICES WOULD HAVE AN INSERTION LOSS OF ABOUT 35 DB, SIMILAR TO THAT MANY STANDARD ULTRASONIC SEARCH UNITS.