This little robot relies on vibration to generate its adhesion. By vibrating its flexible disk, it generates low pressure in the thin air layer between the disk and the surface. The force created is strong in the normal direction — meaning that the robot won’t come off the surface, even when carrying large weights — but relatively weak in the plane of the surface, allowing the robot to move freely. The system does have some disadvantages, though. It requires a relatively smooth surface to work, and the necessary frequency of vibration is around 200 Hz — well inside of human hearing — which makes the robot very noisy. (Image, video, and research credit: W. Weston-Dawkes et al.; via IEEE Spectrum; submitted by Kam-Yung Soh)