The market for vibration harvesters will increase perhaps one hundred fold when they are broad band so they can be fitted without tuning - or with auto tuning - to the vibration encountered. Ideally they should be made to standard battery sizes and sold as a non polluting, long life battery replacement. The race is therefore on for the truly broad band vibration harvester that does not need forces of 1g or more because that can mean that users shun them because they do not want their electronic devices to suffer such forces. It was therefore appropriate that Dr Steve Beeby of the University of Southampton in the UK spoke on Strategies for Increasing the Bandwidth of Vibration Energy Harvesters at the recent IDTechEx Energy Harvesting and Storage conference in Munich.
He gave an overview of fixed frequency inertial generators, including methods for increasing the practical bandwidth, increasing damping and size, multiple generators, electrical and mechanical frequency tuning mechanisms and variable frequency generators at Southampton. He considered energy harvesting networks. He noted that the majority of generators are inertial devices where the mechanical structure resonates at characteristic application frequency and the design depends upon the nature of the mechanical energy, sadly making it application specific.
Nonetheless, there are applications for such harvesters if they are wide bandwidth, an example being rail wagons because they have very high levels of vibration and yet frequency pattern and train speed change require wide bandwidth. Perpetuum electrodynamic vibration harvesters work well here, he noted. Like some other researchers at the event he saw improvement if one could exploit non linearity and use piezoelectrics. Another approach is to make tuning easier. For example, he noted that electrostatic forces have been used to tune resonant MEMS sensors and the same principle can apply to energy harvesters, though a constant electric field is required.
He assessed many other options, finishing by describing how EPSRC in the UK recently announced its decision to support the Energy Harvesting Network http://eh-network.org/. Founding Members are:
- Southampton University (ECS)
- Bristol University (Aerospace Engineering)
- Imperial College London (Dept. of Electrical and Electronic Engineering)
- Cranfield University (Department of Materials)
- Strathclyde University (Dept. of Electronics & Electrical Engineering)
- Cambridge University (Dept. of Engineering)
- The National Physical Laboratory
- Perpetuum Ltd
- TRW Conekt
- e2v Technologies
- Tyndall National Institute (Ireland)
Its objectives are
- 1. To define the new research challenges required to deliver on the potential of EH, to catalyse the creation of the new multidisciplinary teams required to address these challenges and to ensure the submission of a range of research proposals to potential funders. The formation of collaborations will seek to support young academics in particular in establishing their research careers.
- 2. To facilitate the interaction and mobility of researchers. This is particularly important given the wide range of expertise and facilities required to design and build EH devices.
- 3. To ensure that the advances in the science and the developments of the technology are more widely disseminated particularly to the potential end user communities not currently particularly aware of the state of the art and commercialisation efforts.
Top image of Southampton University source: Wikipedia
For more read : Energy Harvesting and Storage for Electronic Devices 2009-2019