Ultrasound transducer arrays can be used to create tactile sensations (haptics) using a fields projected in 3d. A recent Kickstarter for this type of device is

Ultrasound transducer arrays can be used to create tactile sensations (haptics) using a fields projected in 3d. A recent Kickstarter for this type of device is Emerge[1], and a more mature company is Ultrahaptics[2]. Have not tried either though, so do not know how well it works in practice. Ultrasound can also be used for gesture sensing in 3d. Elliptic Labs is one of the companies in that space. mmwave radar is also an option here, along with optical methods. 1. https://www.kickstarter.com/projects/emergehome/emerge-home-a-social-vr-experience-you-can-feel https://www.kickstarter.com/projects/emergehome/emerge-home-... 2. https://www.ultraleap.com/haptics/ https://www.ultraleap.com/haptics/