Development and Evaluation of a Wristwatch-Type Photoplethysmography Array Sensor Module

In this paper, we address a new photoplethysmography (PPG) signal-sensing method using a wristwatch-type PPG array sensor. According to the development of the ubiquitous health care system, the many types of medical equipment and treatments have been improved. In conventional PPG signal-sensing approaches, the finger-type PPG probe has been used. However, the finger-type PPG probe requires tight fitting that restricts movement, meaning that patients should endure dome discomfort while wearing it. To solve this problem, we propose a novel PPG array sensor module with a wristwatch-type design. The proposed module measures the PPG signal from the radial artery and the ulnar artery of the wrist, whereas previous methods obtained it from the capillaries of the skin. Moreover, we place phototransistors and infrared-emitting diodes in an array form to improve the PPG signal sensitivity and level of accuracy. Various arrays are considered for optimization, and a conductive rubber wristband is employed to reduce external noise. In the experiments, the proposed module is assessed and compared with the commercial product. This comparison between the commercial finger-type probe dataset and the PPG array module wrist-type probe dataset shows that the degree of similarity between the two signals is greater than 91.2%.