Power source for wireless sensors in pipes

Abstract

In this paper, we present investigations on wireless sensors for fluid control inside a pipe. Autarkic sensors are in the technical trend. They are typically connected with a transceiver unit for data transmission. Sensors usually need a lower amount of energy than data transceivers. Therefore, they are commonly supplied via wires or batteries with electricity. With common technologies, this request leads to high requirements on tightness in liquids since poor sealing could easily lead to failures. Replacement of batteries inside pipes is complicated and almost accompanied by a flow interruption. The application of energy harvesters as power supply is therefore a good alternative. In our studies we used flexible piezoelectric energy harvesters of PVDF (Poly-Vinylidene-Di-Fluoride). All harvesting units consist of piezoelectric PVDF-foils as active layers and Aluminum-foils as electrodes. The layers were stacked alternating on each other and wound to a spool. A LDPE-film wraps the spool and prevents the inflow of liquids. The device has following parameters: No. of windings: 4 in air, 4, 5, 7 in water  Dimensions: 15mm; Ø 22mm  Materials: o PVDF: 25µm; o Aluminum: 6µm; o LDPE:25µm 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 bluff body, they were forced to oscillate independent of the media. In each case, deformation of the active layers 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 30Hz, at a wind speed of about 7m/s. A -Voltage of about 4V (peak-peak) was measured. This delivers in case of power adjustment, power values of about 0.54µW. In water, the velocity of the fluid was limited to nearly one tenth. Oscillation starts only at a water speed above 0.6m/s. The average oscillation frequency is about 18Hz. At a velocity of 0.74m/s, a peak-peakVoltage up to about 2.3V was found. In case of impedance adjustment, the power was about 0.33µW. This power is stored in a capacitor. Assuming a data transmission unit consumes about 0.2 mWs during one operational period of 1 second, the duty cycle time can be calculated to about 6.2 minutes for air harvesting and 10.1 minutes for harvesting in water.

Power Source for Wireless Sensors in Pipes

“…Typical concepts to achieve this are the piezoelectric conversion used [4][5][6][7][8][9][10]. Additionally, electromagnetic conversion was presented in Refs.…”

“…Piezoelectric harvesters show a distinctly promising scalability. Last year's research results show a focusing towards at least two piezoelectric materials: PZT (lead-zirconate-titanate) [5,6] and PVDF [4,8,9]. PVDF has much lower piezoelectric coefficients than PZT and let expect relatively low converted power.…”

“…[4,7,8,14]. The basic idea is the creation of mechanical stress oscillations in piezoelectric materials by means of turbulence flow-induced in the wake of a bluff body.…”

“…If the application cannot fulfill any of the criteria, it is better to supply consumers with electrical energy by batteries or the power grid. The identified criteria are listed below [4]: (1) …”