The authors observed that the flexible batteries integrated in the glucose monitoring smartwatch would be fully charged (up 6.0V) within one hour under outdoor sunlight, enabling the system to then operate up to 8h with a cut-off potential of 3V. Even under relatively low illuminance (in a lit room), the solar cells would still charge the batteries to 4.2V in under 2 hours, to support system functions for about an hour.
Although their prototype proved to be sufficiently self-powered to operate without external power sources both indoor and outdoor, the researchers are confident they could still optimize their design to lower the system’s overall power budget.
To provide clear signals to the wearer, the smartwatch display only gives out threshold-based alarm signals switching from “low” to “medium” and from “medium” to “high” according to the output currents of the sensors at glucose concentrations below 40μM, then over 40μM but under 120μM, and finally over 120μM, respectively. These simple alarm signals, instead of reading out and updating glucose concentration values, also contribute to limit the E-ink display power consumption.
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