The following submission statement was provided by /u/lughnasadh:

Submission Statement

Ultrasound energy transfer is already the basis of one of ultrasound's most well-known applications, ultrasound medical scanning.

We often tend to think of robots as large and humanoid, if their design wasn't burdened by the need for a power source, it's not hard to imagine useful robots on the same scale as insects, and perhaps just weighing a few grams.

Please reply to OP's comment here: https://old.reddit.com/r/Futurology/comments/zg3xf5/us_researchers_have_created_metamaterials_that/izevwpe/