EMC-Optimized Transparency: Reducing Electromagnetic Emissions in Surveillance Camera Domes

Abstract: Electromagnetic compatibility (EMC) is a crucial aspect to product development. Companies need to make sure their products live up to the standards that exists around the world. One way of reducing electromagnetic emissions is to shield the product, using some conducting material, for instance, copper. An issue arises, though, when transparency is needed, like it is for cameras. At Axis Communications some cameras require a large aperture in its chassis, which increases emissions. This thesis aims to find solutions for transparent shielding of cameras with a dome-surface. This was done by creating prototype shields of different materials. The materials tested are an indium tin oxide film, a silver film, a galvanized steel wire mesh and an aluminium wire mesh. Shielding using aluminium foil with an aperture around the camera lens was also tested. These prototypes were then evaluated based on reduction of emissions, while taking image quality and cost into account. The electromagnetic emissions were measured both from a comb generator circuit and an Axis camera. A comb generator is a harmonic signal generator that served as a consistent noise source. The measurements were made with near field probes and in an EMC chamber. The results show that the prototypes manage to reduce emissions across a spectrum, some better than others, using both the comb generator and camera. The materials had varying transparencies, with some being indistinguishable with a regular camera lens. However, all prototypes, except for the aluminium foil with an aperture, had problems with infrared light. Thus, more research is needed before the materials can be implemented on real products.