Ultrasonic de-icing systems are energy-efficient solutions for ice protection. The systems generate high levels of stress in the ice by inducing vibrations in the substrate, resulting in bulk or adhesive ice failure and, ultimately, ice removal. For this purpose, two types of resonant modes can be excited: flexural and extensional modes. The extensional modes have the interesting ability to de-ice substantial areas of the underlying surface as long as they are pure and do not interfere with the flexural modes. However, the coupling between extensional and flexural modes occurs naturally for thin ice-covered substrates. The inertial effect that explains this coupling is demonstrated in this paper by means of the Euler–Lagrange approach. The Euler–Lagrange model also shows how the inertial effect can be eliminated by carefully adjusting the ratio of Young’s modulus to substrate density to be close to that of ice. Finally, the paper details how multilayered or architectured materials can be used to design piezoelectric plate-like structures to achieve pure extensional modes for de-icing. The ultrasonic de-icing capabilities are demonstrated on prototypes covered with freezer ice.