Flexible Shielded Sensors Based on Biocompatible Ferroelectrets for Heart Rate Monitoring

In the medical field, flexible sensors based on biocompatible materials monitoring biosignals ex and in vivo are essential. In this work, we present a flexible ferroelectret sensor with high sensitivity and additional shielding against electromagnetic interference, suitable for heart rate monitoring. The sensor structure is manufactured by 3D printing filament onto biocompatible bulk polylactic acid (PLA) film, thermally fusing bulk PLA film onto the 3D printed filament, and fully encapsulating the structure with biocompatible silicone rubber. We compare the normalized signal amplitude and signal-to-noise ratio (SNR) of a shielded and encapsulated sensor with a non-shielded sensor in an ex vivo experiment on the human common carotid artery. The optimized sensor outputs a voltage amplitude 2.54 times higher due to the improved structure, and the shielding improves the SNR by 10.58 dB. Additionally, we demonstrate the functionality of the sensor in an in vivo experiment on a pig in a medical environment, measuring both heart rate and signal amplitude. During ongoing operation, the heart rate is reliably monitored with sufficient signal amplitude, detecting each heartbeat consistently. Using a low-cost additive manufacturing approach with biocompatible materials, we present an adaptable sensor with high sensitivity for medical applications, suitable for long-term heart rate monitoring on transplants and in vivo applications.