This paper presents an electrostatic energy-harvesting device for electrical energy extraction from vibrations. We successfully fabricated prototypes of completely packaged micro-generators with a chip size of 5 mm by 6 mm. This was achieved using a modified SOI technology developed for inertial sensors at HSG-IMIT. Micro-generators produce a maximum rms power of 3.5 μW when they are excited at their resonance frequency with an input excitation of 13 g. During a long-term experiment over a period of 2 h, the electrostatic energy harvester generated a total net energy of 13.38 mJ corresponding to an average power of 1.58 μW. The effect of mechanical stoppers and the bias voltage on the generated power is also evaluated. In order to get a more profound understanding of the dynamic behaviour of the micro-generator, we have developed a signal-flow model for numerical simulation of the electrostatic transducer on system level. This model includes a mechanical and an electrical domain which are coupled by electrostatic forces. The limited displacement of the proof mass is also considered using an elastic stopper model. We show that the numerical model is capable of providing good predictions of the device behaviour.

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 shocktype 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 cm 3 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 cm 3 . Difficulties and potential improvements are discussed briefly.

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This paper reports on a self-adaptive energy harvesting system, which is able to adapt its eigenfrequency to the operating conditions of power units. The power required for frequency tuning is delivered by the energy harvester itself. The tuning mechanism is based on a magnetic concept and incorporates a circular tuning magnet and a coupling magnet. In this manner, both coupling modes (attractive and repulsive) can be utilized for tuning the eigenfrequency of the energy harvester. The tuning range and its center frequency can be tailored to the application by careful design of the spring stiffness and the gap between tuning magnet and coupling magnet. Experimental results demonstrate that, in contrast to a conventional non-tunable vibration energy harvester, the net power can be significantly increased if a self-adaptive system is utilized, although additional power is required for regular adjustments of the eigenfrequency. The outcome confirms that active tuning is a real and practical option to extend the operational frequency range and to increase the net power of a conventional vibration energy harvester.

Abstract. 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.