Fatigue-critical metal structures such as ship hulls, propellers, rotor blades and aircraft wings would benefit from sensors built directly into the load-bearing material. Through the DARPA SENSE program, the NDML and collaborators at UT Austin are developing a hybrid manufacturing process that embeds wireless strain and temperature sensors inside metal parts made by laser powder bed fusion. The build is paused so that a custom micro-cold spray system can deposit ceramic insulating films and metal traces into a cavity, forming a chipless RFID sensor from a printed coil and interdigitated capacitors. Printing then resumes to seal the sensor inside the part. Strain shifts the resonant frequency of the sensor and temperature changes its quality factor, so each sensor can be read wirelessly through an external coil. Simulations showed a temperature resolution of 0.4 °C and a strain resolution of 1.75×10−5, and complete parts with embedded sensors have been fabricated and tested.
The figure above shows the concept for a beam with embedded x-, y- and z-axis strain sensors read through coupling inductors on the side of the part.