Sandpit: Mobile Energy Harvesting Systems

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.

The proposed research will have both direct and indirect impacts. The direct impacts will be those that result from the short to medium term implementation of the technology outcomes from the project upon the provision and management of electronic systems for the dismounted soldier. Whilst the project is not expected to produce complete solutions to power all the soldiers electronic systems within the 2 year term of the project, it will produce a demonstrator that proves the feasibility of the concept and establish the detailed principles by which kinetic energy may be harvested from the individual from several positions on the body. Hence in the medium term the work is expected to result in a reduced burden on soldiers due to a reduction in the number of replacement batteries each individual would need to carry, providing benefits in terms of increased agility and a reduction in fatigue. Secondary benefits would be the savings in the supply of replacement cells to soldiers on the front-line. Correct implementation of the technology will also result in biomechanical benefits to the soldier, in that harvesting devices will be configured to provide support to joints, such as the knees, in the high impact phase of the gait, but not during the extension phase. Such benefits are impossible to estimate in monetary terms. Indirect benefits will encompass two aspects, the transfer of the technology outcomes to other arenas and the application of the component advances in science and engineering produced during the project to other research activities. The exponential expansion of mobile electronic devices in our every day lives (e.g. mobile phones, PDAs, music players, laptop computers) has fuelled an enormous demand for high energy density batteries which need to be either replaced or recharged periodically. The freedom limitation this places on the individual is currently perceived as the major shortcoming of such devices, such that the battery life is regarded as a key competitive selling point. For example a mobile phone consumes approximately 10 mW on standby but up to 1 W during wide bandwidth communication. The ability to trickle charge at rates of around 10 to 100 mW would dramatically increase the time required between conventional charges for a mobile phone. Clearly, a successful energy harvesting technology must be invisible to the ordinary user and hence self-contained proof-mass solutions, such as scaled-down versions of that proposed here for the personal military radio, are the most viable. The impact of such technology on the market place would be substantial, giving the first phone manufacturer to market a major advantage in promoting sales of its products. This would be repeated across other sectors including not only all personal communications, computing and entertainment devices, but also medical devices such as glucose in blood readers and heart monitors. Also included in the indirect benefits from the project is the transfer of the scientific and engineering techniques to other research and development areas. Hence the development of the biomechanical modelling techniques and software would have applications beyond those of energy harvesting. The demonstration of novel materials and principles of energy harvesting will be transferred to new transducer designs, such as pressure and vibration sensing in harsh environments. The device modelling research has the potential to bridge the gap between the technology, device, circuits and systems communities. Hence beneficiaries of the project will include not only those in the military, but also potentially a wide range of electronic device manufacturers and ultimately the general public.