Infrared Visualization of the Cavity Effect Using Origami-Inspired Surfaces

Surface temperature and apparent radiative surface properties (emissivity, absorptivity) may be controlled by varying surface topology through a phenomenon known as the cavity effect. Cavities created by origami folds offer the potential to achieve dynamic control of apparent radiative surface properties through actuation. To illustrate this phenomenon, a thin (0.0254 mm) stainless-steel, specularly reflecting surface (emissivity, ε = 0.117) was resistively heated (6.74 W). Accordion-shaped folds (1.27 cm panels) were used to create V-shaped grooves that transition from 29° at the center to 180° near the edges. Thermocouples were attached to the center of each cavity panel (Figure (a)). An IR image of the surface (Figure (b)) reveals that the apparent temperature increases as the cavity angle decreases and is not necessarily indicative of the actual surface temperature. This increase is due to an increase in the number of specular reflections associated with the cavity effect. A similar folded surface was placed 7 cm from a blackbody radiator at 1000° C, to illustrate the change in apparent absorptivity with cavity angle. The cavity angle was held constant across the surface and varied between tests from 180° to 37° (Figure (c), top to bottom). The increase in apparent temperature is a direct result of the increase in apparent absorptivity for decreasing cavity angle, despite constant heating conditions.