Area-Based Photo-Plethysmographic Sensing Method for the Surfaces of Handheld Devices

摘要

Capturing the user's vital signs is an urgent goal in the HCI community. Photo-plethysmography (PPG) is one approach; it can collect data from the finger tips that indicate the user's autonomic nervous system (ANS) and offers new potentials such as mental stress measurement and drowsy state detection. Our goal is to set PPG sensors on the surfaces of ordinary devices such as mice, smartphones, and steering wheels. This will offer smart monitoring without the burden of additional wearable sensors. Unfortunately, current PPG sensors are very narrow, and even if the sensor is attached to the surface of a device, the user is forced to align and hold the finger to the sensor point, which degrades device usability. To solve this problem, we propose an area-based sensing method that relaxes the alignment requirement. The proposed method uses two thin acrylic plates, a diffuser plate and a detection plate, as an IR waveguide. The proposed method can yield very thin sensing surfaces and gentle curvatures are possible. An experiment compares the proposed method to the conventional point-sensor in terms of LF/HF discrimination performance with the participant in the resting state, and the proposed method is shown to offer comparable sensing performance with superior usability.