Solar powered wrist worn acquisition system for continuous photoplethysmogram monitoring

Abstract

We present a solar-powered, wireless, wrist-worn platform for continuous monitoring of physiological and environmental parameters during the activities of daily life. In this study, we demonstrate the capability to produce photoplethysmogram (PPG) signals using this platform. To adhere to a low power budget for solar-powering, a 574 nm green light source is used where the PPG from the radial artery would be obtained with minimal signal conditioning. The system incorporates two monocrystalline solar cells to charge the onboard 20 mAh lithium polymer battery. Bluetooth Low Energy (BLE) is used to tether the device to a smartphone that makes the phone an access point to a dedicated server for long term continuous storage of data. Two power management schemes have been proposed depending on the availability of solar energy. In low light situations, if the battery is low, the device obtains a 5-second PPG waveform every minute to consume an average power of 0.57 mW. In scenarios where the battery is at a sustainable voltage, the device is set to enter its normal 30 Hz acquisition mode, consuming around 13.7 mW. We also present our efforts towards improving the charge storage capacity of our on-board super-capacitor.

Monitoring of Vital Signs with Flexible and Wearable Medical Devices

“…For example, in their design of a solar-powered pulse oximeter, Dieffenderfer et al included a low-power mode with lower duty cycle for cases when suffi cient solar power is not available. [ 117 ] However, since monitoring health is of utmost importance, the duty cycle must be adjusted with care to ensure that the reliability of the sensing, data analysis, or communication is not compromised. Also, although reducing the duty cycle reduces the average power, the peak current is typically not impacted.…”

“…So, if coupled with a battery large enough to compensate for the daily variation in light intensity experienced by most people, PV can be a very useful energy source. There have therefore been multiple recent demonstrations of commercial photovoltaic REVIEW modules powering wearable health monitoring devices, such as a pulse oximeter wristband including a crystalline silicon solar module along with a battery and supercapacitor, [ 117 ] and fl exible amorphous silicon solar modules wrapped around the arm or wrist powering temperature sensors. [ 146,147 ] There is a great deal of research in the photovoltaics community on low-cost, solution-processable photovoltaic materials such as organics and perovskites, because they can be deposited by printing processes under ambient conditions, reducing the cost per unit area of the solar module.…”

Low-Power Wearable Systems for Continuous Monitoring of Environment and Health for Chronic Respiratory Disease

“…However, in an effort to lower the power consumption, a green wavelength (Fig. 15) was selected to increase the signal-to-noise ratio (SNR) and allow for a lower power requirement [28], [29]. …”

“…This necessitates a proximal distance between the LEDs and the photodiode, which was selected as 6.5 mm for both devices. Our previous work has shown the use of PPG to be successful with the radial artery in the wrist [28] and other literature has shown PPG to be compatible with the chest region [30]. In order to minimize the movement of the optical probe, we placed a double sided film (Tegaderm, 3M, Saint Paul, MN) on top of the probe, offering adhesion to the tissue and simultaneously allows breathability of the skin.…”

Flexible Technologies for Self-Powered Wearable Health and Environmental Sensing

“…The first version of this platform, Soliband (Fig. 10) [17], is solar powered and demonstrates the capability to produce photoplethysmogram (PPG) signals while providing inertial measurement based activity monitoring using COTS integrated circuits. To adhere to a low power budget for solar-powering, a green light (574 nm) source was used to obtain PPG from the radial artery with minimal signal conditioning.…”