Ring-Embedded Micro-Power mm-Sized Optical Sensor for Accurate Heart Beat Monitoring

Abstract

This paper presents a wearable optical health monitoring device embedding a monolithic sensor chip with newly designed pixels, and an optical module optimized for photoplethysmography (PPG). The monolithic optical sensor at the heart of this device implements an array of novel pixels designed specifically for PPG and featuring a quantum efficiency (QE) as high as 85 %. The sensor readout chain, as well as the logic circuits, implements low power design techniques leading to only 60 µA current consumption at 122 Hz operation frequency, including digital communication. Thanks to the high QE and optical module optimization, medical grade PPG recordings are enabled with less than 10 µA emitter current. The optical sensor is embedded in an ergonomic ring device together with system electronics in order to enable in-field test of beat detection accuracy on 7 subjects. The ring device detects correctly 97.87 % of the beats on a total of 72.21 hours of recording. The inter-beat interval (IBI) estimation from these recordings features a mean absolute error (MAE) as low as 8.10 ms. This performance is achieved with less than 70 µA current consumption at the level of the PPG module.INDEX TERMS CMOS image sensor, heart beat detection, low power integrated circuit, monolithic optical detector, photoplethismography sensor, wearable electronics.

Advances in Medical Wearable Biosensors: Design, Fabrication and Materials Strategies in Healthcare Monitoring

“…Fiber-free optical sensing and detection systems exist, including near-infrared spectroscopy to probe skin tissues to measure and analyze tissue oxygen saturation and blood flow [ 108 , 109 ]. A pulse oximeter is one such device, which is a non-invasive optical sensor working on the photoplethysmogram (PPG) technique used for blood volume (Hb) and blood oxygen (HbO 2 ) changes [ 110 , 111 ].…”

Towards ultrasound wearable technology for cardiovascular monitoring: from device development to clinical validation

“…PPG-based optical solutions offer two key advantages over ultrasound: low power consumption (50.58 mW in [18], in comparison to circa 4 W for ultrasound [19]) and higher compactness (module size: 3.8 mm x 7.1 mm x 0.6 mm [20]). However, clinical validation has revealed their subpar accuracy, with errors in systolic blood pressure (SBP) and diastolic blood pressure (DBP) reaching up to 15 mmHg and 10 mmHg, respectively [17].…”

Wearable Optical Fiber Sensors in Medical Monitoring Applications: A Review

“…Wearable devices based on fiber optic sensors have proven to be effective and comfortable solutions for monitoring vital signs (ankle [ 23 , 28 , 29 , 30 , 31 , 32 , 33 ], blood [ 22 , 34 , 35 ], spine [ 36 ], heart rate [ 22 , 37 , 38 , 39 , 40 ], breathing [ 10 , 22 , 41 , 42 , 43 , 44 ], shoulder and neck [ 45 ], joint angle [ 21 , 29 , 30 , 37 , 42 , 46 ], etc.). The characteristics of optical fibers allow them to be embedded in textiles such as T-shirts and elastic belts for sensing applications, enabling respiratory monitoring [ 47 ].…”