A self-powered wearable electrocardiography (ECG) system is demonstrated. The ECG sensing circuit was fabricated on a flexible PCB and powered by a wearable thermoelectric generator (w-TEG) using body heat as the energy source. To allow the TEG to obtain a large temperature difference for high power generation and also be wearable, a polymer-based flexible heat sink (PHS) comprised of a superabsorbent polymer (SAP) and a fiber that promotes liquid evaporation was devised. Parametric studies on the PHS were conducted, and the structure of the w-TEG was also optimized for the PHS. The output power density from the w-TEG with the PHS was over 38 μW/cm2 for the first 10 min and over 13 μW/cm2 even after 22 consecutive hours of driving the circuits. This power level is high enough to continuously drive the wearable ECG system, including the sensors and the power management circuits.

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An inverted flag with the free leading edge and fixed trailing edge has been widely adopted in an energy harvesting system due to its highly unstable characteristics in a flow. In the present study, the non-zero inclination angle is set on the fixed trailing edge of the inverted flag to increase its instability and improve the energy harvesting performance. The effects of the bending rigidity and the inclination angle on the energy harvesting efficiency are numerically analyzed where the interaction between the flag and the surrounding fluid is considered by using an immersed boundary method. The inverted flag shows five flapping motions depending on the bending rigidity and the inclination angle: straight, symmetric, asymmetric, biased, and the over flapping modes. The mode change is observed from the straight mode to the flapping mode by increasing the inclination angle from the zero to non-zero degree, which is favorable in terms of the energy harvesting performance. The optimal efficiency is obtained by the inverted flag at the inclination angle of around 40°–45° corresponding to the biased flapping mode. In the biased flapping mode, the strain energy is continuously produced without a period where energy production drops to zero. The strain energy is quantitatively scaled based on a vortex formation that consists of factors associated with the kinematics of the inverted flag.

Pulsed electron deposited thin films of Ru substituted La(1-x)Pb(x)Mn(0.8)Ru(0.2)O(3) (0.2≤x≤0.4) show an increase in the magneto-resistance ratio by ∼5-15% at the respective metal to insulator transition (T(MIT)) temperature when compared to the parent La(0.6)Pb(0.4)MnO(3) thin film. A systematic decrease in T(MIT) is observed from ∼310 to ∼260 K when the hole (Pb) concentration varies from 40 to 20% with constant 20% Ru substitution at the Mn site. The x-ray rocking curve and high-resolution transmission electron microscopy (HRTEM) images of the thin films suggest that Ru occupies the Mn site and shows epitaxial growth of the films on the LaAlO(3) (LAO) substrate. Transport and magneto-resistive properties show that Ru substitution maintains a considerable hole carrier density (due to Mn(4+):t(2g)(3)e(g)(0)/Ru(5+):t(2g)(3)e(g)(0)) even for La(0.8)Pb(0.2)Mn(0.8)Ru(0.2)O(3) (8282) composition, which influences the double exchange interactions.

Epitaxially grown thin films of La1−xPbxMn0.8Ru0.2O3 (0.2⩽x⩽0.4) on LAO (001) substrate using pulsed electron deposition technique shows a systematic decrease in metal to insulator transition from 300to250K when hole concentration varies from 40% to 20%. However, an increase in magnetoresistance ratio by ∼5%–15% is observed for Ru substituted films at the respective Curie temperatures when compared to the parent La0.6Pb0.4MnO3 film. Transport and magnetoresistive properties show that Ru substitution maintains a considerable hole carrier density even for La0.8Pb0.2Mn0.8Ru0.2O3 (8282) composition to stabilize the double exchange interactions.