For underwater applications and manufacture of sonar for autonomous underwater vehicles (AUV), large areas of piezoelectric materials with very good electromechanical properties are often needed. Piezoelectric single crystals (typically the compositions PMN-PT or PZN-PT1) are high-performance materials (high yields), but are difficult to manufacture in large areas while maintaining homogeneous properties. This study on the behavior of piezoelectric single crystals will be conducted with the use of a finite-element code (ATILA) which was developed at ISEN in collaboration with the French Ministry of Defense. The results confirm the good fit between the models and experimental results after a phase of optimization.