3D printed "smart screw" with built-in LC sensing circuit for wireless monitoring

This work presents a novel "smart screw" with built-in electrical circuit for sensing. Comparing to conventional screw for industrial application, the designed smart screw contains an inductor-capacitor resonant circuit, of which the resonance frequency is determined by the gap of the structure inside the smart screw. As the gap is changed due to external force or the deformation of the smart screw, the resonance frequency will shift or vanish and be detected wirelessly by an inductive reader in real-time. As a proof-of-concept, M24 smart screws were fabricated by metallic three-dimensional printing. The LC circuit, formed by selective-laser-melting of titanium together with the screw body, is found to have the initial resonance frequency 162.77 MHz. It showed −2.7% and 10.5% frequency shifts during compression and bending tests, respectively. As the deformation exceeded certain level, the resonance even vanished. Both the shift and vanishment of resonance are sensing indicators. This work enables an innovative scheme for wireless built-in sensing application for high-value mechanical components.