Knowledge of energy flow in a microwatt-class energy harvesting system is essential to reliable deployment and scheduling of sensing, computation, communication, and actuation tasks. However, existing techniques for monitoring energy flow fail to meet the basic requirements for in-situ realtime monitoring systems by failing to be efficient and failing to perform accurately across a wide dynamic range. The proposed system, µMonitor, makes use of a highly power-optimized "Coulomb counting" implementation to achieve less than 1.7 microampere current draw, 94% efficiency in-situ, and high energy flow measurement accuracy across four orders of magnitude.

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Blood glucose measurement is commonly used to screen for and monitor diabetes, a chronic condition characterized by the inability to effectively modulate blood glucose that can lead to heart disease, vision loss, and kidney failure. Early detection of prediabetes can forestall or reverse more serious illness if healthy lifestyle adjustments or medical interventions are made in a timely manner. Current diabetes screening methods require visits to a healthcare facility and use of over-the-counter glucose-testing devices (glucometers), both of which are costly or inaccessible for many populations, reducing the chances of early disease detection. We therefore developed GlucoScreen, a readerless glucose test strip that enables affordable, single-use, at-home glucose testing, leveraging the user's touchscreen cellphone for reading and displaying results. By integrating minimal, low-cost electronics with commercially available blood glucose testing strips, the GlucoScreen prototype introduces a new type of low-cost, battery-free glucose testing tool that works with any smartphone, obviating the need to purchase a separate dedicated reader. Our key innovation is using the phone's capacitive touchscreen for the readout of the minimally modified commercially available glucose test strips. In an in vitro evaluation with artificial glucose solutions, we tested GlucoScreen with five different phones and compared the findings to two common glucometers, AccuChek and True Metrix. The mean absolute error (MAE) for our GlucoScreen prototype was 4.52 mg/dl (Accu-Chek test strips) and 3.7 mg/dl (True Metrix test strips), compared to 4.98 mg/dl and 5.44 mg/dl for the AccuChek glucometer and True Metrix glucometer, respectively. In a clinical investigation with 75 patients, GlucoScreen had a MAE of 10.47 mg/dl, while the AccuChek glucometer had a 9.88 mg/dl MAE. These results indicate that GlucoScreen's performance is comparable to that of commonly available over-the-counter blood glucose testing devices. With further development and validation, GlucoScreen has the potential to facilitate large-scale and lower cost diabetes screening. This work employs GlucoScreen's smartphone-based technology for glucose testing, but it could be extended to build other readerless electrochemical assays in the future.