Motorcycle transportation is widely used in densely populated regions, leading to frequent traffic accidents in which head injuries remain the leading cause of fatality. Helmets are therefore essential protective gear designed to reduce impact-induced damage to the human head. Beyond their traditional role, helmets can be regarded as sensor-interacting structures that not only absorb impact energy but also transform external mechanical stimuli into measurable physical responses. During an impact event, stress waves and deformation propagate through the helmet and are transmitted to the head, producing acceleration signals closely associated with injury severity. In this sense, acceleration serves as a key sensing output linking structural response to biomechanical evaluation. Finite element analysis is employed to investigate the dynamic behavior of a helmeted human head under various impact conditions. A three-dimensional model incorporating nonlinear expanded polystyrene behavior is developed to represent energy absorption characteristics. Multiple impact orientations are considered to evaluate stress distribution, displacement, and time-dependent responses. The results show that impact direction affects stress concentration patterns, whereas impact velocity governs the magnitude and evolution of the response. This sensing-oriented approach helps clarify the relationship between mechanical behavior and measurable signals, providing insights for helmet design optimization and advanced protective equipment.