The project involved more than just fabricating a sensor and attaching it to a subject’s chest area. Piezoelectric sensors are subject to unwanted motion artifacts (which appear as noise), so the team minimized those by using a pair of identical tattoos placed adjacent to each other and then looking at their difference, in effect filtering out the common-mode signal.
Even placement of the e-tattoo is an issue, so they painted the chest of an adult male with a random speckle pattern and used a pair of cameras set at a 30-degree angle to capture the surface of the chest for 16 seconds at a 500-Hz frame rate. Three independent PVDF e-tattoos were attached at different locations on the chest to determine the location dependency and optimum placement of the ECG/SCG sensor.
Full details on the project, including rationale, principles, materials, fabrication, electrical schematic diagrams, test arrangements, captured waveforms, processing algorithms, and analysis of results are in their paper “A Chest-Laminated Ultrathin and Stretchable E-Tattoo for the Measurement of Electrocardiogram, Seismocardiogram, and Cardiac Time Intervals” published in Advanced Science (Wiley), along with a Supporting Information posting. The research was funded by the Office of Naval Research, the Air Force Office of Scientific Research, the National Science Foundation, the National Institutes of Health, and Texas Health Catalyst at Dell Medical School.
This article was first published on Electronic Design – www.electronicdesign.com