Ultra-Light Electromagnetic Wave Concentrator with Variable Focal Length

In this paper, we present an ultra-light electromagnetic wave concentrator with a variable focal length (EMC/VFL), and its representative applications to a solar ray concentrator for solar thermal propulsion (STP) and solar power station (SPS). The EMC/VFL consists of a pair of rectangular reflectors of ultra-light thin materials such as reflective polymer membrane, each of which has a line focus due to appropriate bending moment and axial force. The variable bending moment and axial force make the reflector a highly precise paraboloidal concentrator with variable focal length, and its characteristics as a concentrator are estimated by calculation. The two focal lines intersect each other perpendicularly so that a point focus can be formed at the intersection. Unlike a conventional paraboloidal concentrator including an inflatable type, the EMC/VFL can be folded very compactly, and hence an extremely wide area for an electromagnetic wave receiver would be available in space. Because of its variable focal length, applications in various fields are possible, as a radar antenna with variable gains, a solar furnace with variable heating patterns, and a concentrator for STP or SPS with variable solar image, especially in space due to its very high level of compactness.