A Semiconductor work by Ruth Jarman and Joe Gerhardt. Audio Data courtesy of CARISMA, operated by the University of Alberta, funded by the Canadian Space Agency. Special Thanks to Andy Kale. Made for the exhibition Invisible Fields at Arts Santa Monica in Barcelona Spain. lighthouse.org.uk/programme/invisible-fields 20 Hz observes a geo-magnetic storm occurring in the Earth's upper atmosphere. Working with data collected from the CARISMA radio array and interpreted as audio, we hear tweeting and rumbles caused by incoming solar wind, captured at the frequency of 20 Hertz. Generated directly by the sound, tangible and sculptural forms emerge suggestive of scientific visualisations. As different frequencies interact both visually and aurally, complex patterns emerge to create interference phenomena that probe the limits of our perception.