A square cylinder with a V-shaped groove on the windward side in the piezoelectric cantilever flow-induced vibration energy harvester (FIVEH) is presented to improve the output power of the energy harvester and reduce the critical velocity of the system, aiming at the self-powered supply of low energy consumption devices in the natural environment with low wind speed. Seven groups of galloping piezoelectric energy harvesters (GPEHs) were designed and tested in a wind tunnel by gradually changing the angle of two symmetrical sharp angles of the V-groove. The GPEH with a sharp angle of 45° was selected as the optimal energy harvester. Its output power was 61% more than the GPEH without the V-shaped groove. The more accurate mathematical model was made by using the sparse identification method to calculate the empirical parameters of fluid based on the experimental data and the theoretical model. The critical velocity of the galloping system was calculated by analyzing the local Hopf bifurcation of the model. The minimum critical velocity was 2.53 m/s smaller than the maximum critical velocity at 4.69 m/s. These results make the GPEH with a V-shaped groove (GPEH-V) more suitable to harvest wind energy efficiently in a low wind speed environment.
In recent years, with the development of the Internet of Things (IoT) and wearable technology, the research and exploration of thermoelectric materials have been greatly promoted. However, traditional thermoelectric materials are rigid and brittle. Thermoelectric devices made of these materials usually cannot be closely attached to the heat and cold sources that provide temperature differences, thus limiting the application of thermoelectric materials. Therefore, manufacturing new high-performance flexible thermoelectric devices is still a huge challenge. In this work, polyimide/copper (PI/Cu) substrate was deposited by electron deposition technology. The flexible thermoelectric thin film device was fabricated by bonding [Formula: see text]-type and [Formula: see text]-type bismuth telluride (Bi2Te[Formula: see text] slurries onto the PI/Cu substrate. Then, the PDMS film was coated on the device to make the device waterproof and oxidation resistant. The output voltage and maximum power of this device, at the temperature of 80 K, reach 97.5 mV and 60 uW, respectively. After 200 cycles of cyclic bending experiments, 90% high conductivity retention can be maintained. It demonstrates that the new flexible thermoelectric thin film has good flexibility and excellent stability. This work provides a simple method for the preparation of flexible thermoelectric thin films and opens up a new way for its application in the sensing equipment and wearable device of the IoT.
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