Wearable sweat sensors are essential for providing insight into human physiological health. The currently developed microfluidic sweat sensors have demonstrated the function of collecting and storing sweat. However, they detect more average concentrations of substances based on time periods, which leads to the fact that in situ real-time measurement for multiple biomarkers remains a grand challenge. Here, we propose a wearable epidermal microfluidic patch with integrated microfluidic pumps and micro-valves for accelerated and continuous collection of the sweat, where the micro-pumps ensure the complete separation of old and new sweat for real-time detection of real concentration of biomarkers in sweat. The biomarker concentration at different time periods is detected by introducing a burst valve, which is used to assist in the analysis of the real-time detection. A quantitative relationship between the minimum burst pressure difference required for sequential collection and the size of the microchannel structure is established to overcome the effects of additional resistance at the gas–liquid interface. Additionally, the sensing modules, including sodium ion, chlorine ion, glucose, and pH level in sweat, are integrated into the patch to realize in situ, real-time detection of multiple biomarkers in the human sweat, decoding the correlation between changes in substance concentrations and physiological conditions. This work provides a unique and simplifying strategy for developing wearable sweat sensors for potential applications in health monitoring and disease diagnostics.
An investigation of the possibility of controlling the evolution of jets into the far field is presented. Driven by practical concerns the study examined a highly turbulent jet flow. To enhance controllability of the flow evolution the virtues of non-circular nozzles and active flow excitation were combined. The study examined an air jet, Reae = 8ooo, average turbulence intensity 1.8% issuing into stagnant room air out of a triangular nozzle, which had piezoceramic actuators mounted on the flat sides. The evolution of the jet flow field was examined over the range of o <~XID <~ 3o.Small amplitude, single mode, excitation with frequency as the varying parameter was found to be ineffective for controlling the far field evolution. In contrast, excitation of the jet with non-integer and counter propagating azimuthal modes yielded marked changes in the jet streamwise evolution. The most notable changes in the far field were the transition of the cross section from round to elliptical, increased jet cross sectional area based on half centerline velocity contour, asymmetric threedimensional flow, and an increase in the entrainment rate. The entrainment of ambient air by the jet increased slightly more than twofold for non-integer and counter propagating azimuthal modes, compared with the unexcited jet, and only a 5o% increase in the entrainment for single, integer, mode excitation.While excitation of the jet with modes m = o and I resulted in symmetric evolution of the jet in the x-y-t space, excitation at non-integer and counter propagating modes resulted in time-dependent asymmetric motion. The near field induced jet column motion is controlling the far-field evolution of the examined jet.
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