Engineers at Northwestern University have developed a drone called "Phantom Twist" that rotates at high speeds in the air, becoming almost imperceptible to the human eye.
Until now, making drones invisible to the naked eye mostly involved reflective surfaces or various camouflage technologies. Researchers from Northwestern University in the USA have now taken a different approach to this issue. The prototype drone called "Phantom Twist," developed by engineers at Northwestern, becomes almost imperceptible to the eye by rotating at high speeds in the air.
The drone utilizes an effect known as motion blur, which makes it difficult for the eye to perceive fast-moving objects as a clear shape. The human eye does not perceive images as instantaneous single frames; it collects visual signals over a certain time interval. This creates an effect similar to a camera sensor's exposure time. When an object moves fast enough, its images at different positions are combined by the eye, and the distinct edges of the object become blurred. Phantom Twist takes advantage of this effect.
Propeller and Body Rotate in Opposite Directions
In traditional drones, only the propellers rotate, whereas in Phantom Twist, the entire drone, including its body, rotates at high speed. However, not every part of the drone rotates in the same direction. The drone has a single motor and a single propeller. While the propeller rotates in one direction, the drone's body rotates in the exact opposite direction. This is what causes the motion blur effect to emerge at high speeds.
The drone is made to rotate 25 times per second. This speed makes it difficult for the human eye to clearly distinguish details during movement. As a result, the observer begins to see a slight blur or a transparent haze in the background instead of a distinct drone body flying in the air. According to the perceptual measurement system developed by the researchers, the Phantom Twist is approximately 10 times less visible compared to a traditional quadcopter drone.
The drone's components are placed in three dimensions at different heights and angles, with gaps between them. This prevents the parts from overlapping to form a single, distinct silhouette when the drone rotates. The movement of components such as the motor, propeller, circuit board, battery, and balance weight is visually centered with the background image, making it difficult to perceive the drone as a distinct object.
Artificial Intelligence Was Also Utilized in the Design Process
Instead of creating the Phantom Twist's design directly through trial and error, researchers utilized computer models and artificial intelligence. In the initial phase, approximately 20,000 different drone configurations were created. In these designs, the positions of the motor, propeller, battery, circuit board, and balance weight were altered to produce various options that could both maintain flight stability and be less visible.
Subsequently, how each design would appear while rotating in the air was simulated in a computer environment. The models were placed over 100 different real-world backgrounds, ranging from skies to trees and buildings. Then, using a perceptual model that approximately mimics the human visual system, each design was given a visibility score. The most successful designs were advanced to the next stage.
From the initial 20,000 designs, 500 with the lowest visibility scores were selected, and the optimization process was re-executed on these designs. The algorithms repeatedly adjusted the positions of components, while maintaining engineering constraints like flight stability, to minimize the drone's visibility as much as possible. Ultimately, the researchers converted one of the most successful designs from the computer environment into a physical prototype.
As seen in the video, while the drone approaches invisibility when rotating, its high noise level makes its presence quite obvious. Researchers aim to further reduce the Phantom Twist's visibility in the future by using more transparent materials and quieter propulsion systems.
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