The number of start-up companies in the field of electro-magnetic wave energy harvesting and energy transport through the air increased significantly few years ago. However, ultrasonic and radiofrequency still present low performance and have not experienced any significant development. Conversely inductive and infrared technologies are doing well with applications currently dedicated to the military sector (charging of submarine batteries, PV panel in space to charge devices in desert locations...).
Source  ENGIE R&T Division, 2017. Emerging Technologies expected to change ‘our’ world - Report from 2016 watch
Sign up for the ENGIE Innovation Newsletter