Energy harvesting could provide power-autonomy to many important embedded sensing application areas. However, the
available envelope often limits the power output, and also voltage levels. This paper presents the implementation of an
enabling technology for space-restricted energy harvesting: Four highly efficient and fully autonomous power
conditioning circuits are presented that are able to operate at deep-sub-milliwatt input power at less than 1 V<sub>pk</sub> AC input,
and provide a regulated output voltage. The four complete systems, implemented using discrete components, include the
power converters, the corresponding ancillary circuits with sub-10 μW consumption, start-up circuit, and an ultra-lowpower
shunt regulator with under-voltage lockout for the management of the accumulated energy. The systems differ in
their power converter topology; all are boost rectifier variants that rectify and boost the generator’s output in a single
stage, that are selected to enable direct comparison between polarity–dependent and –independent, as well as between
full-wave and half-wave power converter systems. Experimental results are derived over a range of 200–1200 μW
harvester output power, the system being powered solely by the harvester. Experimental results show overall conversion
efficiency, accounting for the quiescent power consumption, as high as 82% at 650 μW input, which remains in the 65–70% range even at 200 μW input for the half-wave variant. Harvester utilisation of over 90% is demonstrated in the sub-milliwatt
range using full-wave topologies. For the evaluated generator, the full-wave, polarity-dependent boost rectifier
offers the best overall system effectiveness, achieving up to 73% of the maximum extractable power.
Health and usage monitoring systems (HUMS) are being incorporated into an increasing number of applications, e.g.
monitoring safety critical components in civil, aerospace, mechanical and other structures. A good example is the use of
HUMS in monitoring transmission and drive train components on rotary-wing aircraft. These transmission HUMS have
enjoyed success in predicting the deterioration of components, however, current system implementations rely on highbandwidth
hardwired sensors and significant data processing capability to perform feature extraction and classification,
limiting the locations where they can be installed. To extend HUMS capability into new application areas, such as wind
turbine blades or helicopter rotor head components, and other applications impossible to hard wire, the functionality of
HUMS needs to be implemented within a wireless sensor network (WSN). The power, processing and packaging
constraints of a WSN present many challenges. This paper initially considers the performance requirements of a
conventional wired HUMS and contrasts this with that available from state-of the art WSN components. Technical issues
related to power supply, sensor technologies, signal conditioning, damage detection and prognostic algorithms for low
power microprocessors, robustness and data integrity on wireless radio are discussed. The paper further considers
different approaches reported in the literature to overcome system limitations, such as the use of intelligent sensor nodes
which perform local signal processing and transmit only a reduced dataset. Finally, simple statistical measures are
executed on a low power microcontroller to demonstrate the potential of such devices for damage diagnostics.
We consider the performance of a vibration based energy harvester with realistic topologies for the electrical
circuit, including power conditioning through a rectifier. Specifically we apply a novel perturbation approach to
describe the time-varying power harvested in the system, including a rectifier in the circuitry. This approach
considers the full electromechanical coupling between the mechanical and electrical components, including the
amplitude and phase of the mechanical response. The resulting analysis is able to describe the behavior of the
system as the mechanical response is detuned from resonance by the electrical load. In addition, the charging of the circuit over time is also captured by the analysis. Finally, the analytical results are compared against the numerical simulations of the original equations of motion to verify the analytical approach.
Vibration powered electrical generators produce a raw AC electrical output that often needs to be converted into DC for use by the load systems. There are many possible ways to achieve this conversion (rectification) however the specific application of vibration energy harvesting requires a solution that is a delicate balance between efficiency, converter quiescent loss and impact upon the resonant generator operation. In this paper we investigate how vibration powered generators interact with typical rectification schemes and assess the overall system performance, comparing it to the theoretical maximum power that could be generated. Further to this we present practical circuits that address the inherent problems of passive rectification techniques including a unity power factor power converter, realised at ultra low powers, suitable for energy harvesting applications. Numerical models are validated with measured results.
Vibration powered electrical generators typically feature a mass/spring resonant system to amplify small background vibrations. The compliance element in these resonant systems can become non-linear as a result of manufacturing limitations, physical operating constraints, or by deliberate design. The characteristics of mass/spring resonant systems with non-linear compliance elements are well known but they have not been widely applied within the field of energy harvesting. In this paper analysis of non-linear system behaviour using the harmonic balance method is presented, giving an insight into the potential benefits of non-linearities in energy harvesting applications. The design of a vibration powered energy harvester is reviewed and it is shown how the deliberate incorporation of non-linear behaviour within a design can be beneficial in improving magnetic loading and also in extending the range of frequencies over which the device can generate useful power.