摘要
In this paper, we present investigations on energy harvesters for wireless sensors inside pipes. The harvesters are of flexible piezoelectric PVDF （Poly-Vinylidene-Di-Fluoride） and aluminum-foils as electrodes. The layers were stacked alternating on each other and wound to a spool. An LDPE （low-density polyethylene）-film wraps the spool and prevents the inflow of liquids. A ring shaped bluff body was placed inside the pipe to induce turbulence in the fluid stream. As the harvesters have been arranged downstream of the bluffbody, they were forced to oscillate independent of the media. This led to a polarization and a separation of electrical charges. Experiments were carried out in a wind channel as well as in a water pipe. In air, the spool oscillates with a frequency of about 30 Hz, at a wind speed of about 7 m/s. A voltage of about 4 V （peak-peak） was measured. This delivers in case of impedance adjustment power values of about 0.54 p.W. In water, oscillation starts at a speed above 0.6 m/s. The average oscillation frequency is about 18 Hz. At a velocity of 0.74 m/s, a peak-peak-voltage up to about 2.3 V was found. In case of impedance adjustment, the power was about 0.33 μW. This power is stored in a capacitor. Assuming a data transmission unit consumes about 0.2 mWs during one operational period of I s, the duty cycle can be calculated to about 6.2 min for air harvesting and 10.1 min for harvesting in water.
