Influence of accelerated aging on the acoustic properties of a ceramic microsystem for structural health monitoring

Carbon fibre reinforced polymers (CFRP) are widely used wherever weight has to be reduced without compromising the mechanical properties of parts. One popular application is in aerospace. To reduce failure analysis (maintenance) time and eventually detect impacts even during flight it is necessary to durably mount an array of miniaturized sensors on CFRP elements. Especially the acoustic properties of the interface (adhesive) between ultrasound transducer and CFRP need to be constant over time (or at least show an predictable behaviour). LTCC-based transducers allow the integration of reliable electronics into the ultrasound sensor. For electrical circuits on ceramic substrates, lifetime predictions are basically known. In contrast, no investigations about the “acoustic lifetime” of an ultrasound sensor interface are known. The paper describes the fabrication and assembly of realistic test specimens as well as the accelerated aging by temperature cycling and temperature / humidity test. To evaluate the adhesive, lifelike ultrasound signals are sent and received with different types of solid mount LTCC-based sensors. Furthermore the electrical impedance of the piezoelectric transducers is analyzed.