Improved Sensitivity of Printed Piezoelectric Sensor Arrays for Large Area Ballistocardiography

Holst Centre is an applied research institute specializing in the development of flexible and thin electronics through industrially relevant fabrication methods. Our mission over the past two decades has been to drive technological advancements that enable the industrialization of printed electronics systems, transforming future concepts into tangible realities.<br/><br/>Ballistocardiography (BCG) is a non-invasive technique that examines the heart's activity by measuring the ballistic forces generated during each heartbeat, eliminating the need for on-skin sensors, unlike electrocardiography (ECG). This unique characteristic makes it an unobtrusive measurement method.<br/><br/>To achieve sensors with optimal sensitivity, we have successfully demonstrated a universal method for enhancing effective transverse charge constants. Our methodology has been validated using a printable piezoelectric polymer called poly(vinylidene fluoride-co-trifluoroethylene) (P(VDF-TrFE)). Through our research, we have shown that discrete sensors can accurately detect displacements of less than 1 µm, dynamic forces of approximately mN, and accelerations of around 1 mm/s², precisely meeting the requirements for high-quality BCG measurements.<br/><br/>By employing printable sensors, we have scaled up our demonstration to a "human-sized" prototype measuring 60 x 90 cm, equipped with 255 piezoelectric sensors. This enabled us to measure spatially resolved BCG measurements of an individual with exceptional quality. The heart rate obtained from our measurements has been corroborated optically using photoplethysmography (PPG). The universality of our approach allows for the creation of increasingly sensitive piezoelectric sensor architectures, crucial not only in healthcare but also in various sensing and actuating applications.