PolyCMUTs for ultrasonic nondestructive testing of carbon fiber reinforced plastic: a feasibility study

Abstract

The following thesis describes the research conducted in between May and October of 2019 on the topic of PolyCMUTs and their usability for nondestructive evaluation of carbon fiber reinforced plastics. The first step was to calculate the acoustic and mechanical material properties of a provided CFRP test plate and the test of those values with a commercially available CMUT probe. The next part is the explanation of the manufacturing process of new prototypes and the many difficulties that occurred during this process. After several trials a working air coupled ultrasonic transducer was fabricated and then thoroughly characterized. The characterization showed some unexpected behaviour which was then investigated and contributed to a so-called Helmholtz resonance. The resonance phenomena was further explained and the possible benefits in PolyCMUT fabrication were evaluated. The last step was to evaluate these phenomena for further improvement to the technology. The result is that PolyCMUTs can indeed be used for NDE but they need further research and development. A commercial usage is not yet possible.