Piezoelectric flow harvesting for in-pipe metering systems

For supplying water monitoring systems at points of use over their entire application period an in-pipe flow harvester is proposed. It eliminates the maintenance requirements of current energy supplies such as batteries. This harvester exploits the piezoelectric properties of Polyvinylidenedifluoride (PVDF) to convert turbulence-induced oscillations into electrical energy. It is intended to be used in water pipes with diameters of ¾ in. and above. Turbulences induced by an upstream arranged ring-shaped bluff body force a wrap of piezoelectric films to oscillate, thus generate electrical charge. The wrap consists of two layers of 30 μm thick and 12 mm wide PVDF layered alternately with two centered 6µm thick and 8mm wide aluminum electrodes. It is sealed by a shell of polyethylene. A bottom-fixed wrap with 3 windings is characterized in a 1in. water pipe at a flow velocity of 0.75 m/s. It delivers a constant power output of 0.53 μW at a 2.3 MΩ load and an effective voltage of 1.1 V. Considering the extremely low power requirements of modern sensors, several harvesters may be combined to supply such devices.