A low-cost, flexible sensor patch for non-invasive respiratory monitoring capable of suppressing motion artifacts

Respiration is a fundamental vital function that ensures the vital exchange of oxygen and carbon dioxide in the body, but non-invasive and continuous respiratory monitoring remains challenging. Conventional monitoring methods often rely on specialized clinical equipment, whereas wearable systems are susceptible to motion artifacts. This study presents a wearable sensor matrix patch for respiratory monitoring with capabilities for suppressing artefacts that originate from body motions. The flexible sensor patch was realized in a hybrid manufacturing process that combines double-sided printed carbon resistors with standard flexible printed circuit board technology. The array of sensing carbon resistors was printed onto a polyimide (PI)-based flexible printed circuit board (FPCB) to form two-resistor voltage dividers with a quasi-half-bridge configuration. Instead of relying solely on backend signal processing to eliminate motion artifacts, the FPCB was designed so that mechanical decoupling suppresses motion artifacts at their source by separating the detection of local body bends from global body deformations. The resulting functional flexible sensor array was integrated with a breathable and moisture-wicking kinesiology tape made of elastic textile and a medical adhesive tape to create the final wearable patch. The printed sensing elements showed good bending response, with single-resistor gauge factors ranging from 5.60 to 7.43. The complete sensor patch also exhibited robust performance, with no electrical failure observed during 10,000 bending cycles. It demonstrated excellent resistance to motion artifacts under 6% stretch and during five distinct body motion patterns. This low-cost, non-invasive, and motion-tolerating sensor array patch not only offers a promising approach for easy to use and comfortable respiratory monitoring but also shows potential for future use with infants and other populations who cannot voluntarily control their body movements.