Analysis of Piezoelectric Properties of Coaxial Sensor Based on Ferro/Piezoelectret

Ferroelectret coaxial sensors (FCSs) combine a coaxial structure with high piezoelectricity, flexibility, lightweight, demonstrating great potential in biomedical applications. However, due to its complex structure and materials, theoretically predicting and analyzing the piezoelectric properties of FCS is challenging. This article initially proposes a theoretical model based on piezoelectric equations to determine the equivalent moduli of FCS’s ground and shielding electrode and outer jacket, respectively, which are experimentally verified to be 40 and 35 MPa, respectively. Subsequently, a finite element (FEM) model considering the ferroelectret’s anisotropic hyperelastic properties is developed and validated. The study further explores the impacts of material properties, structural dimensions, and prestress on FCS piezoelectric properties to guide the optimization of designed strategies. The results demonstrate that increasing the core electrode diameter can significantly improve FCS’s piezoelectric performance. Selecting a ferroelectret film with a high ${d}_{{31}}$ effect not only enhances the piezoelectric response but also improves the linearity. In contrast, introducing a large amount of prestress during manufacturing will noticeably reduce the piezoelectric properties of FCS. Finally, the real-time tracking capability for key physiological parameters-including respiratory rate (1225 breaths/min) and heart rate (60100 b/m)-has been successfully measured through FCS-based smart textile, confirming their efficacy in vital signs monitoring.