Dave Jones from EEVBlog made a debunking video on uBeam. They apparently tried to to do ultrasonic wireless charging, which seems to fit your description. Here'

Dave Jones from EEVBlog made a debunking video on uBeam. They apparently tried to to do ultrasonic wireless charging, which seems to fit your description. Here's the video, it's mostly about efficiency/coupling loss (beam forming has it's limits) and IIRC also about being potentially harmful for humans: https://www.youtube.com/watch?v=A8dqzVlhFkA https://www.youtube.com/watch?v=A8dqzVlhFkA