Low-frequency Inductive Power Transmission for Piezo-Wafer-Active-Sensors in the Structural Health Monitoring of Carbon-Fiber-Reinforced-Polymer

Structural Health Monitoring (SHM) using surface applied or embedded Piezo-Wafer-Active-Sensors (PWAS) to generate and measure Lamb-waves on fiber-reinforced materials is the main target of this study. Wireless power transmission was achieved implementing the principle of inductive coils. The characteristics of the material where the coil system is located have a direct impact on the strength of the magnetic-field. Carbon Fiber Reinforced Polymer (CFRP) is known to behave as a conductor and depending on their frequency; radio waves can be shielded by such materials. Therefore, a new interest to evaluate the direct operation of PWAS via inductive coils at the low-frequency range, where the effect is lower, has been raised. A low-frequency wireless SHM system is achieved by combining the PWAS, in this case bonded to the surface, with an inductive coil in resonance. A CFRP plate with surface bonded PWAS was prepared in order to evaluate the power transmission; not only between antenna coils but also the energy necessary to stimulate the PWAS was measured. To enable this direct excitation of the PWAS, the same frequency which is provided on the primary side is used on the secondary side. Typical values of a PWAS are obtained form an electrical model based on its measured impedance.