A novel phased-array thermography concept for non-destructive testing

Phased array technology involves the coordinated control of multiple elements to steer and focus elastic, electromagnetic, light, seismic, and radio waves in a specific location or direction. In structural integrity applications, it enables the precise inspection of materials and the identification of flaws/defects in structures. In this paper, we proposes a novel phased array method based on the steering and focusing of thermal waves, not previously explored for applications in NDT, named Phased-Array Thermography (PAT). This new three-dimensional approach aims to overcome the main limitations of most of the Active Infrared Thermography (IRT) methods that uniformly heat the component surface and generate a normal temperature gradient, resulting in lack of control in the gradient direction and, ultimately, limiting the identification capabilities of IRT. PAT leverages an array of heating elements to precisely steer and control the thermal wavefront. A closed-form analytical solution of the thermal wave propagation is derived and validated against numerical simulations. Then, the accuracy of proposed method is assessed via thermal Finite Element (FE) simulations of an aluminium plate by comparing PAT with a commonly used IRT technique such as the Pulsed Thermography (PT). Finally, experimental analyses of an aluminium plate with flat bottom holes and a composite plate with impact damage are performed to validate the proposed methodology. This novel approach to thermal wavefront steering via phased array technology introduces a previously unexplored mechanism for controlled heat wavefront, with transformative potential for non-destructive evaluation, structural health monitoring, and adaptive manufacturing systems.