Wireless Power Supply for Low Power 'Smart Sediment Particle'

Abstract

Studying the entrainment process in riverbeds has been an ongoing research at the Civil and Environmental Engineering department at the University of Auckland. The ‘smart sediment particle’ is a device developed over the years, to assist this study to characterise river sedimentation. It can monitor its own three dimensional motion with the aid of accelerometer and gyroscope sensors. The gathered data is processed in a microcontroller and stored for later retrieval. When needed that data is downloaded to a computer for mathematical processing to obtain the three dimensional trajectory of the device. Using this data forces acting upon it can be determined to comprehend the entrainment characteristics of the smart sediment particle. This project was to design a wireless power supply for this micro-miniaturised device while optimising its power performance. An inductive power transfer based wireless charging unit has been developed successfully to charge the smart sediment particle. A small secondary pickup coil embedded in the device, with additional circuitry, couples magnetically with the primary side to extract power from a primary coil loop and recharges the power supply module of the device. A rechargeable, hybrid power module has been designed to replace the standard alkaline battery previously used to power the smart particle. This consists of a supercapacitor array and a rechargeable lithium-ion battery as a backup source. The supercapacitors are the primary power sources and the battery will be utilised when the supercapacitors are discharged. The key feature of the system is that simple discrete components have been utilised as much as possible to simplify operation and minimise device dimensions. The power consumption of the new design is nearly half that of its predecessor. This has been achieved by changing the onboard microprocessor and sensors, and also by replacing functions of additional components with software techniques. Extensive testing on the power supply module proved that the novel hybrid power supply has been successful. However more investigations are required to optimise the supercapacitor array in terms of rated voltage, capacitance and dimensions. Further work is needed to fully optimise the design for device dimensions and better power transfer, by designing a three dimensional power transfer system, optimising the supercapacitors and redesigning the printed circuit board layout to optimise for space etc.