Fig. 3: Self-powered box knot pulse-wave sensor device.

a Schematics to illustrate the pulse wave detecting mechanisms of SBKP (i), the device set of SBKP-1.1 (SBKP-ECG-PPG paired system prototype 1.1. version) after integration (ii), and its representative photo of SBKP-1.1, monitoring human vital signals wirelessly (iii). b Representative pulse waves obtained from PPG and SBKP simultaneously. The pulse waves of the SBKP were collected from three different positions of the human body such as c wrist, d cheek, and e neck. Also, PPG and ECG signals were collected simultaneously for verification. f The measured heart rate every hour during the daily routine of subject #7 using SBKP-1.1.