Hierarchically gradient PMN-PT/PVDF piezoelectric composites for human motion monitoring

Visual monitoring of human motion signals using piezoelectric sensors offers critical insights for personalized exercise training and health rehabilitation. However, conventional piezoelectric sensors often face a fundamental trade-off between mechanical strength and electrical output, limiting their effectiveness in these applications. Here, we propose a hierarchically gradient structure based on lead magnesium niobate-lead titanate (PMN-PT) and polyvinylidene fluoride (PVDF) piezoelectric nanocomposite to alleviate this dilemma. This design leverages the exceptional flexibility of PVDF and the superior electrical properties of PMN-PT to enhance piezoelectric output and mechanical strength simultaneously. Both experimental tests and finite element analysis simulations reveal that the proposed gradient architecture facilitates stress redistribution and enhances crystallinity of the composite, synergistically improving its electromechanical coupling performance. Consequently, the fabricated sensor exhibits a 2.36-fold higher sensitivity (83.1 mV/N) compared to pure PVDF, along with nearly doubled flexibility (27 % elongation at break). Experimental validation confirms that the gradient-structured sensor can conformally adhere to various locations for motion monitoring. This system offers a reliable approach for dynamic biomechanical capture, enabling quantitative assessment and personalized guidance during exercise training and rehabilitation programs.