A Phase Variation-Based Smart Structure for Crack Detection on Metals Using Cold Spray Additive Manufacturing

This article presents a novel zero-power smart structure for metal cracks' detection. We fabricated a sensitive one-port structure that receives the interrogation signal at 2.45 GHz and reflects the sensing information through its phase parameter. Damage on the ground surface of the structure causes variations in the phase delay of the reflection signal. This study combines the microwave sensing methodology with the innovative solid-state additive manufacturing (AM) technology to facilitate an in situ structural health monitoring (SHM) for a wide range of harsh environment applications. A sensing structure with a conductive comb-like pattern made from Cu powder is simulated and fabricated through the cold spray deposition (CSD) additive technology. Samples of aluminum including sharp rectangular machined grooves with different widths (constant 2 mm depth and 25 mm long) were fabricated to explore the sensor's detection ability in cases close to the natural cracks' scenario. It is shown from the simulations and experiments that the printed sensors on defected samples provide different phase delay parameters when compared with baseline healthy samples. As expected, increased diameter or width value of cracks results in a higher phase delay, and the best sensitivity of 138°/mm is obtained for sharp rectangular cracks. This experiment opens a new door for simple, low-cost fabrication and in situ repair of battery-free smart infrastructures by integrating metalized dielectrics on metallic substrates. Finally, the presented smart structure can be a part of a wireless sensing node and hence a node of the wireless sensor network for the internet-of-things applications.