Lr Clare

Tuning a resonant energy harvester using a generalized electrical load

A fundamental drawback of vibration-based energy harvesters is that they typically feature a resonant mass/spring mechanical system to amplify the small source vibrations; the limited bandwidth of the mechanical amplifier restricts the effectiveness of the energy harvester considerably. By extending the range of input frequencies over which a vibration energy harvester can generate useful power, e.g. through adaptive tuning, it is not only possible to open up a wider range of applications, such as those where the source frequency changes over time, but also possible to relax the requirements for precision manufacture or the need for mechanical adjustment in situ. In this paper, a vibration-based energy harvester connected to a generalized electrical load (containing both real and reactive impedance) is presented. It is demonstrated that the reactive component of the electrical load can be used to tune the harvester system to significantly increase the output power away from the resonant peak of the device. An analytical model of the system is developed, which includes non-ideal components arising from the physical implementation, and the results are confirmed by experiment. The − 3 dB (half-power) bandwidth of the prototype energy harvester is shown to be over three times greater when presented with an optimized load impedance compared to that for the same harvester presented with an optimized resistive only load.

Vibration energy harvesters with non-linear compliance

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.

A Resonant Generator with Non-Linear Compliance for Energy Harvesting in High Vibrational Environments

This paper considers a resonant generator (RG) powered by ambient vibrations, in an environment where the level of vibration is significant. The target application of the RG is to provide power for wireless sensor nodes performing structural health monitoring. The RG is of moving magnet design and optimisation of the magnetic circuit to maximise power density has resulted in a RG with significant reluctance forces. These reluctance forces sum with the mechanical compliance to produce an overall non-linear compliance response, as a result the resonant behavior of the RG differs considerably from a simple second-order model. The approach taken to design has been experimental in nature. Results of a simulated RG are presented along with the realisation and testing of a prototype RG.

Energy Harvesting From Vibrations With a Nonlinear Oscillator

In this paper we present a nonlinear electromagnetic energy harvesting device that has a broadly resonant response. The nonlinearity is generated by a particular arrangement of magnets in conjunction with an iron-cored stator. We show the resonant response of the system to both pure-tone excitation and narrow-band random excitation. In addition to the primary resonance, the super-harmonic resonances of the harvester are also investigated and we show that the corresponding mechanical up-conversion of the excitation frequency may be useful for energy harvesting. The harvester is modeled using a Duffing-type equation and the results compared to the experimental data.Copyright

An electromagnetic inerter-based vibration suppression device

This paper describes how an inerter-based device for structural vibration suppression can be realized using an electromagnetic transducer such as a linear motor. When the motor shaft moves, a difference of voltage is generated across the transducer coil. The voltage difference is proportional to the relative velocity between its two terminals. The electromagnetic transducer will exert a force proportional to current following the Lorentz principle if the circuit is closed around the transducer coil. If an electronic circuit consisting of a capacitor, an inductance and a resistance with the appropriate configuration is connected, the resulting force reflected back into the mechanical domain is equivalent to that achieved by a mechanical inerter-based device. The proposed configuration is easy to implement and very versatile, provided a high quality conversion system with negligible losses. With the use of electromagnetic devices, a new generation of vibration absorbers can be realized, for example in the electrical domain it would be relatively uncomplicated to synthesize multi-frequency or real time tunable vibration absorbers by adding electrical components in parallel. In addition by using resistance emulators in the electrical circuits, part of the absorbed vibration energy can be converted into usable power. Here an electromagnetic tuned inerter damper (E-TID) is tested experimentally using real time dynamic substructuring. A voltage compensation unit was developed in order to compensate for coil losses. This voltage compensation unit requires power, which is acquired through harvesting from the vibration energy using a resistance emulator. A power balance analysis was developed in order to ensure the device can be self sufficient. Promising experimental results, using this approach, have been obtained and are presented in this paper. The ultimate goal of this research is the development of autonomous electromagnetic vibration absorbers, able to harvest energy, convert it into usable power, and use it for vibration control and health monitoring.

Power Conditioning for Energy Harvesting

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.

Switched-Mode Load Impedance Synthesis to Parametrically Tune Electromagnetic Vibration Energy Harvesters

Energy harvesters based upon resonant mass-spring-damper systems can only generate useful power over a narrow range of excitation frequencies. This is a significant limitation in applications where the vibration source frequency changes over time. In this paper, an active electrical load is presented which can overcome the bandwidth limitations by parametrically tuning the overall harvester system. The electrical tuning technique synthesizes an optimum reactive load with high-efficiency switch-mode electronics, which also provides rectification, feeding the energy harvested into a dc store. The method is shown to be effective at increasing the power frequency bandwidth of resonant type harvesters and offers the capability of autonomous operation. The theoretical basis for the technique is presented and verified with experiment results. The paper illustrates the challenges of implementing the power electronic converter for a low-quiescent power overhead and in choosing the control architecture and tuning algorithms.

Technological challenges of developing wireless health and usage monitoring systems

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.

Novel wireless sensors for in situ measurement of sub-ice hydrologic systems

Abstract Wireless sensors have the potential to provide significant insight into in situ physical and biogeochemical processes in sub-ice hydrologic systems. However, the nature of the glacial environment means that sensor deployment and data return is challenging. We describe two bespoke sensor platforms, electronic tracers or ‘ETracers’, and ‘cryoegg’, for untethered, wireless data collection from glacial hydrologic systems, including subglacial channels. Both employ radio frequencies for data transmission, are designed to endure harsh environmental conditions and can withstand low temperatures, high pressure, turbulence and abrasion. We discuss the design, optimization and field testing of the ETracers and cryoegg, culminating in test deployments beneath the Greenland ice sheet. The small, low-cost ETracers were able to travel through subglacial drainage channels, from where they returned water pressure measurements through 100 m of ice, and could measure water depth in crevasses. The larger cryoegg was able to return multi-parameter data from moulins through 500 m of wet ice to receivers up to 2 km away, and from 12 m depth in a proglacial lake to a receiver on the shore. The tests demonstrate that the cryoegg and ETracers are low-power, versatile, robust wireless sensor platforms suitable for glacial environments, which may be used with portable, low-cost receiving equipment.

Inductive power transfer in e-textile applications: Reducing the effects of coil misalignment

Wireless power transfer (WPT) is an attractive approach for recharging wearable technologies and therefore textile implementations are of interest. Such textile WPT systems are inherently flexible and prone to misalignments of the inductively coupled coils which affects performance. This paper investigates two methods to reduce the effect of coil misalignment in inductive WPT in e-textile applications: a single large transmitter coil and a switched transmitter coil array. Transmission efficiency and maximum received power are determined for both methods, and compared against the baseline system that uses a single small transmitter coil. All coils used in this study were fabricated using automated stitching of PTFE insulated flexible wire onto a polyester/cotton textile. This fabrication method allows coils to be sewn directly to existing garments.