Preliminary Investigation of an Innovative RF Sensor for Deformation and Failure Evaluation in Composite Materials

This paper introduces the design of a high-sensitivity, low-cost, easy-integrable radiofrequency sensor for structural health monitoring. The hardware system is composed of an array of three self-resonant planar spiral coils, working in the 100-300 MHz frequency range, inductively coupled to a fed strip line. The design of the sensing spirals is the result of the corresponding Q-factor maximization through an optimization process, thus ensuring a good compromise between penetration depth and sensitivity of the resonant elements. The analysis of the resonance frequency shift and of the amplitude variation of the system input impedance are both exploited to identify the deformation state or the presence of defects inside the composite. In order to validate the methodology, we performed full-wave simulations to evaluate the radiating system performance in presence of normal conditions, deformation of the composite, occurrence of delamination, and presence of a crack within the sample. The obtained results validated the introduced theoretical approach, confirming both the ability to identify the presence of an irregularity within the composite material and also its spatial position. Therefore, the proposed sensing system is a promising alternative to non-destructively assess the current or future condition of a composite material, thus enhancing safety, availability, and reliability while reducing maintenance costs.