I recently contributed an article on acoustic levitation to Frontiers for Young Minds. This is part of a collection on acoustics called A World of Sound. The article is aimed a young readers and was edited by a young reader. It is written in accessible lenguage (at least, that was my aim) and so may also be of interest to older readers wanting simple explanations of acoustic levitation.
The article can be found here – https://kids.frontiersin.org/articles/10.3389/frym.2021.678021
Acoustic levitation uses sound waves to hold objects in mid-air. We are all familiar with the power of sound to make us dance and change our moods, but sound can also exert a physical force that is strong enough to levitate objects. To harness this force, we use loudspeakers to form a sound pattern so that the object is surrounded by very loud sound. Scientists have used these ideas to levitate small objects such as insects, as well as extremely small objects like individual cells. They can then manipulate these objects, much like a robot would, but without any moving parts. So far, only relatively small levitating forces have been generated but, in theory, much higher forces could be produced and levitation of objects even the size of humans might be possible. Despite this exciting possibility, you might not want to be acoustically levitated yourself, for good reason!