Applications and Advantages of Dry Coupling Ultrasonic Transducers for Materials Characterization and Inspection
Practical self-coupling (dry coupling) piezoelectric ultrasonic transducer designs have been optimized for center frequencies up to at least 25MHz for longitudinal wave generation and at least 20MHz for zero degree incidence shear wave generation. While originally developed for examination of materials which would be damaged by liquid contact, they have been found to have practical and technical advantages for many materials characterization, discontinuity evaluation and gaging requirements.
Saving the time which would otherwise be required for the application and removal of liquid couplant is the most obvious advantage. Liquid intrusion is likely to cause unreliable data from porous materials and other materials which absorb water. Self-coupling facilitates the examination of assemblies with components such as electronic circuitry which could be damaged by liquids. Proper application of couplant is quite tedious for zero degree incidence shear wave examinations. Verification of complete removal of couplant is required where residue could interfere with subsequent processes such as chemical milling. For examination of low acoustic impedance materials, self-coupling provides increased transmission of ultrasonic energy into the test object and also improved near-surface resolution. Examples of several types of advantageous applications will be presented.
KeywordsLongitudinal Wave Delay Line Acoustic Impedance Test Surface Petroleum Jelly
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