The soft device ecosystem consists of 4 skinlike electronic devices. The first combines ECG, PPG, and skin temperature sensing in a single device placed on the chest. The second monitors PPG from the forehead. The third captures ECG from the chest. Finally, the fourth monitors PPG from the ear.
Nanomembrane electrodes composed of copper, chromium, and gold layers electron-beam deposited on polyimide film similarly exceed the SNR typically obtained rigid devices for ECG measurement. the interconnect and electrode serpentine profiles reduce local strain for a given overall device strain. A custom flexible printed circuit board (fPCB) was designed to use an nRF52 microcontroller.
Interfaced with this via the SPI protocol is a 24-bit ADS1292 analog-to-digital converter (ADC) sampling at 250Hz for ECG collection. PPG was collected via the 18-bit, MAX30102 sampling red and infrared absorbance at 50Hz, interfaced with the microcontroller via I2C. Sharing this I2C bus was a TMP117 12-bit temperature sensor sampling at 1Hz. The device used a 120mAh battery, which provided nearly 24 hours of continuous monitoring ability at a steady-state current draw of 5mA.
