Non-destructive inspection systems (10) and methods for inspecting structural flaws that may be in a structure (15) based on guided wave thermography. The method may include sweeping a frequency-phase space to maximize ultrasonic energy distribution across the structure while minimizing input energy, e.g., via a plurality of actuators. The system may include transducer elements (12, 14, 16, 17) configured to predominantly generate shear horizontal-type guided waves in the structure to maximize thermal response from any flaws.