Artifact-resistant power-efficient design of finger-ring plethysmographic sensors

A miniaturized, telemetric, photoplethysmograph (PPG) sensor for long-term, continuous monitoring is presented in this paper. The sensor, called a "ri ng sensor," is attached to a finger base for monitoring beat-to-beat pulsat ion, and the data is sent to a host computer via a radio-frequency transmit ter. Two major design issues are addressed: one is to minimize motion artif act and the other is to minimize the consumption of battery power. An effic ient double ring design is developed to lower the influence of external for ce, acceleration, and ambient light, and to hold the sensor gently and secu rely on the skin, so that the circulation at the finger may not be obstruct ed. Total power consumption is analyzed in relation to characteristics: of individual components, sampling rate, and CPU clock speed. Optimal operatin g conditions are obtained for minimizing the power budget. A prototype ring sensor is designed and built based on the power budget analysis and the ar tifact-resistive attachment method. It is verified through experiments that the ring sensor is resistant to interfering forces and acceleration acting on the ring body. Benchmarking tests with FDA-approved PPG and electrocard iogram reveal that the ring sensor is comparable to those devices in detect ing beat-to-beat pulsation despite disturbances.