Robots Team Up to Use Sound Waves to Move Objects

Through teamwork, certain types of insects, such as ants and bees, can achieve far more than any individual ever could alone. Ants have been known to team up to build bridges that span gaps, or lift objects that are too heavy for any individual, for example. Engineers at University College London took notice of this natural phenomenon, and wondered if similar behaviors could help groups of robots to achieve greater things than any one alone could achieve.

Their solution is a swarm robotics system capable of contactless cooperative transport, using sound waves to levitate and move small objects through the air without physical contact. Drawing direct inspiration from the way ants coordinate during group transport missions, the team created a system that allows multiple robots to levitate, hold, and manipulate small airborne objects with precision.

Levitation is made possible through the use of ultrasonic transducers, which are devices that emit high-frequency sound waves beyond the range of human hearing. When arranged into a phased array and carefully synchronized, these transducers generate localized acoustic pressure fields. These fields act as invisible hands, creating areas strong enough to trap and levitate lightweight objects in mid-air. The robots, equipped with these transducers and controlled by a custom system, can move these pressure fields around to carry the levitated items from place to place.

Two different approaches to transport were investigated in the work: independent and cooperative. In the independent mode, a single acoustic robot generates and controls the pressure field alone. In the cooperative mode, multiple robots synchronize their movement and acoustic output to form a combined pressure field, allowing them to carry larger or more complex objects together.

While generally more useful, cooperation required a high-precision synchronization mechanism. The team developed this mechanism using a combination of field-programmable gate arrays and infrared-based signaling, allowing the robots to align their clocks down to the microsecond. This tight synchronization ensures that their sound waves combine correctly, forming stable pressure fields even while the robots are in motion.

To validate their approach, the team measured the stability of the levitation using microphones, tracked the movement of objects using a high-speed motion capture system, and confirmed synchronization accuracy with an oscilloscope. The results confirmed that both independent and cooperative modes of transport are not only feasible but can be executed with a high degree of stability and efficiency.

While the research is still in its early stages, this system opens the door to contactless material handling and micro-assembly, where precise manipulation of delicate or sterile objects is necessary. Biomedical applications, such as handling sensitive tissues or operating in environments that require strict hygiene, are also strong candidates for this technology. Ultimately, just as ants can accomplish incredible feats through cooperation, so too may future swarms of robots.