Shear wave ultrasonic coupling performance of different adhesives

Adhesives are regularly used in the manufacture of piezoelectric ultrasonic transducers and can be used as a couplant. Both applications rely on the adhesive successfully transmitting the ultrasonic waves into adjoining material. Four adhesives were tested: Araldite 2014, Loctite Superglue, Ablefilm 5020k and Circuitworks' silver-loaded epoxy. Shear polarised piezoelectric elements are used to manufacture low-frequency transducers used for long-range ultrasonic testing. The elements were bonded to steel blocks and the amplitude of the reflected pulse was measured as the adhesive cured to study the quality of the acoustic coupling. In the case of the thermosetting adhesive (Ablefilm), the samples were repeatedly heated to investigate the piezoelectric element's degradation. Using Superglue produced the largest initial reflected amplitude but using the silver-loaded epoxy produced the greatest final amplitude.