Development of P(VDF-TrFE)/KNN/rGO-based flexible dual-modal sensor for synchronous acquisition of heart sound and electrocardiogram

This study proposes an electrospun flexible piezoelectric composite membrane based on poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)), potassium sodium niobate (KNN), and reduced graphene oxide (rGO) for sensing weak, low-frequency physiological vibrations on the body surface. The synergistic incorporation of KNN and rGO enhances the piezoelectric performance of the porous membrane. Scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR) analyses show that KNN and an appropriate amount of rGO optimize the fiber morphology and promote the formation of the electroactive β phase. At KNN and rGO contents of 2 wt% and 0.5 wt%, respectively, the fabricated device achieves a maximum open-circuit voltage of 37.34 V and a short-circuit current of 23.88 μA. The optimized membrane exhibits a good response over 20–500 Hz, with a more pronounced output at 20–150 Hz, and a linear force–voltage relationship with a sensitivity of 1.22 V/N. Based on the optimized membrane, a dual-modal sensor integrating surface electrodes for electrocardiogram (ECG) recording and a flexible piezoelectric sensing unit for phonocardiogram (PCG) recording was developed. The sensor enables synchronous acquisition of electrophysiological and mechanical cardiac signals. After preprocessing, ECG R peaks and Q points and PCG S1 and S2 components were reliably identified, allowing extraction of heart rate (HR), R–R interval (RR), electromechanical activation time (EMAT), and left ventricular systolic time (LVST). These results demonstrate the potential of the P(VDF-TrFE)/KNN/rGO piezoelectric porous membrane for wearable cardiac monitoring.