The following is a paper by H. Aspden published in Proceedings, 26th Intersociety Energy Conversion Engineering Conference (IECEC), American Nuclear Society, (1991).
Abstract: The conversion of environmental energy, whether stored as heat in a familiar form or stored in movement and electrical displacement of something wholly unfamiliar that constitutes the vacuum field, to produce useful electrical output is discussed. There are several routes to this objective, but the physical principles underlying the three ways in which this author is particularly interested will be presented. The object is not to disclose structures which warrant research and development and are deemed of a proprietary nature at this time, but rather to share an insight into the basic factors involved, so that the 'free energy' challenge to win through and revolutionize the energy scene can involve more people with design skills and resources.