Sandpit: Mobile Energy Harvesting Systems

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This is a collaborative proposal from 7 universities aimed at progressing the technology of kinetic energy harvesting in order to reduce the battery burden on dismounted soldiers. Dismounted soldiers in the British army carry a variety of electrical and electronic systems including torches, personal radios, the Bowman communications system and electronic counter measures. These devices are powered by both primary and secondary cells, from the ubiquitous AA cell to large Li-ion batteries. For an average foot patrol lasting 6 hours the weight of batteries carried by an individual can be up to 10 kg. This may be part of a total burden of up to 75 kg, much of which is irreducible (i.e. water, ammunition, etc). Such large burdens severely limit the mobility of the soldier and can lead to long term health problems. Hence it is imperative that weight be saved in the non-irreducible parts of the burden such as the batteries. Due to the expected improvements in battery energy density and the power consumption of mobile systems, it is envisaged that not only can the battery burden be reduced significantly, but that a considerable fraction of the total power demand of the dismounted soldier can be harvested from ambient energy sources such as thermal, solar or kinetic. This proposal addresses the issue of the harvesting of kinetic energy from the mobile soldier in order to provide charging currents for the secondary cells powering his/her electronic systems. It is proposed that such harvesting systems, in the context of advances in low power electronics, could help eliminate or reduce the replacement battery burden of the soldier.Whilst kinetic energy harvesting systems have previously been shown to under-perform compared to theoretical expectations, the systems developed have rarely been optimised throughout the whole of the system. That is they fail to match all parts of the system - mechanics, transducer and electronics - to each other and, perhaps crucially, to the source of power, in this case the human body. Hence this project aims to succeed by addressing the whole system, harnessing skills in biomechanics, dynamics, transducer design, materials selection and electronics to produce an optimised system. The project will address how energy can best be harvested from three different corporeal sources: footfall, limb articulation and burden acceleration. However, in producing a practical demonstration, it will focus on the use of burden (or proof mass) acceleration to power a personal communications radio. The demonstration will therefore incorporate advances in low power RF design to enable the radio to be powered solely from the stored energy produced from kinetic energy harvesting.Previous attempts at harvesting energy from body motion have often resulted in a negative reaction from users as suboptimal systems impose a noticeable reactive load to the movement, resulting in changes of gait which can increase fatigue. Hence it is an aim of the project to develop a system methodology that will not only reduce the impediment to the wearer but may even be used to reduce the impact of loading on the body. For example, it is proposed that harvesting devices can be used to support and reduce load to the knees. The electrical power extraction from such devices would be managed so that they absorb impact during compression of the knee, but present minimal impedance during extension.The overall aim of the project is design, develop and demonstrate kinetic energy harvesting systems for the dismounted soldier which could in concert provide renewable power of the order of 10 W. Whilst much of the project will be based around a conventional transducer type (piezoelectrics), one workpackage will concentrate on developing a novel form of transduction between kinetic and electrical energy, employing the converse electro-osmosis effect.