Hand movement used to control the acoustic levitation

British engineers have unveiled a prototype of the slot machine based on ultrasonic acoustic levitation. It consists of several rings floating in the air of a small ball that follows the position of the finger of the player through the sensor to track hand movements. Development was presented at the conference CHI 2020.

Ultrasonic acoustic levitation is based on the interference of sound waves from a variety of sources, from where the air formed a stable region with a variety of sound pressure. Including they form a small area of low pressure surrounded by an area with a high. If in this area to put enough light and a small object, it will stay in it without falling. A regulation of the amplitudes and phases of the waves in the array of ultrasonic sources allows you to shift the area of low pressure and the object it in the right direction.

Mostly acoustic levitation is considered as the basis for contactless devices that can move small objects, requiring careful handling. In particular, there are already prototypes of soldering devices and manipulators for moving chips to the chip using this effect. But, as often happened with other spectacular technologies, engineers are also trying to use it for entertainment purposes. Orestis George (Orestis Georgiou) of the company Ultraleap with his colleagues created a simple game based on acoustic levitation.

The apparatus for levitation is usual for such devices design. It consists of two arrays of size 9 to 27 emitters operating at a frequency of 40 kHz. They face each other and spaced at a distance of 18 inches. Between some of the emitters engineers put a thin ring of plastic or the more massive, consisting of acoustically transparent fabric (organza or acrylic felt). As the levitating object developers chose polystyrene beads with a diameter of from one to three millimeters, which are also standard for this task.

The unusual setting makes the control a levitating ball. For this it uses the motion sensor the Leap Motion hands, who with the help of infrared cameras and emitters in real time creates a three-dimensional model of the hand and transmits commands to the arrays of ultrasonic emitters

The player can control the ball by moving the index finger in the right direction and thus to hold it through the rings. It works only extended his thumb, and if it is pressed to the brush, the ball stops.

Acoustic levitation is also used for prototyping the surround screens, and for several years they have become much more sophisticated. In 2016, we talked about the display of several unevenly colored balls, working on the principle of electronic ink. And in 2019, the engineers first created a screen in which the balls keep a small canvas for projection, and then connecting the group presented a screen that uses only one ball, but it moves at a speed of several meters per second and with high-speed projector allows you to draw in air dimensional color figures.

Gregory Copies

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