Philipp Becker

Energy harvesting from human motion: exploiting swing and shock excitations

Modern compact and low power sensors and systems are leading towards increasingly integrated wearable systems. One key bottleneck of this technology is the power supply. The use of energy harvesting techniques offers a way of supplying sensor systems without the need for batteries and maintenance. In this work we present the development and characterization of two inductive energy harvesters which exploit different characteristics of the human gait. A multi-coil topology harvester is presented which uses the swing motion of the foot. The second device is a shock-type harvester which is excited into resonance upon heel strike. Both devices were modeled and designed with the key constraint of device height in mind, in order to facilitate the integration into the shoe sole. The devices were characterized under different motion speeds and with two test subjects on a treadmill. An average power output of up to 0.84 mW is achieved with the swing harvester. With a total device volume including the housing of 21 cm3 a power density of 40 μW cm−3 results. The shock harvester generates an average power output of up to 4.13 mW. The power density amounts to 86 μW cm−3 for the total device volume of 48 cm3. Difficulties and potential improvements are discussed briefly.

Efficient Energy Harvesting With Electromagnetic Energy Transducers Using Active Low-Voltage Rectification and Maximum Power Point Tracking

This paper reports on efficient interfacing of typical vibration-driven electromagnetic transducers for micro energy harvesting. For this reason, an adaptive charge pump for dynamic maximum power point tracking is compared with a novel active full-wave rectifier design. For efficient ultra-low voltage rectification, the introduced active diode design uses a common-gate stage in conjunction with supply-independent biasing. While this active rectifier offers low voltage drops, low complexity and ultra-low power consumption, the adaptive charge pump allows dynamic maximum power point tracking with implicit voltage up-conversion. Hence, efficient energy harvesting with high-resistive transducers, e.g., electromagnetic generators, becomes possible even at buffer voltage levels far above actual transducer output voltages. Both interfaces are fully-integrated in a standard 0.35 μm twin-well CMOS process. The designs are optimized for sub-mW transducer power levels and wide supply voltage ranges. Thus, these presented transducer interfaces are particularly suitable for compact micro energy harvesting systems, such as wireless sensor nodes or medical implants. The active diode rectifier achieves efficiencies over 90% at a wide range of input voltage amplitudes of 0.48 V up to 3.3 V. The adaptive charge pump can harvest with a total efficiency of close to 50%, but very independent of the actual buffer voltage. This charge pump starts operating at a supply voltage of 0.8 V, and has an input voltage range of 0.5 V-2.5 V . Finally, results of harvesting from an actual electromagnetic generator prototype are presented.

Energy Harvesting from Fluid Flow in Water Pipelines for Smart Metering Applications

In this paper a rotational, radial-flux energy harvester incorporating a three-phase generation principle is presented for converting energy from water flow in domestic water pipelines. The energy harvester together with a power management circuit and energy storage is used to power a smart metering system installed underground making it independent from external power supplies or depleting batteries. The design of the radial-flux energy harvester is adapted to the housing of a conventional mechanical water flow meter enabling the use of standard components such as housing and impeller. The energy harvester is able to generate up to 720 mW when using a flow rate of 20 l/min (fully opened water tab). A minimum flow rate of 3 l/min is required to get the harvester started. In this case a power output of 2 mW is achievable. By further design optimization of the mechanical structure including the impeller and magnetic circuit the threshold flow rate can be further reduced.