Toyota Researchers Build Insect-Sized Drone
Researchers from Toyota Central R&D Labs have built an insect-sized flying robot with flapping wings that operates using wireless radio-frequency technology. The drone, described in a paper in Nature Electronics, is based on a radio-frequency energy receiver with a specific power of 4900 W/kg.
“Small drones typically have very limited flight time because of their power source. The goal of our recent study was to overcome this limitation. Contactless power sources using electromagnetic waves are currently finding practical use in various products, but it is unknown how far they can be applied to small flying robots”
The main goal of Ozaki and his colleagues was to power an insect-sized flying robot using contactless wireless charging technology. The robot they created essentially consists of an oscillating piezoelectric actuator powered by a 5 GHz dipole antenna.
"Insect-sized flying vehicles are useful tools for communication, environmental exploration and the inspection of confined spaces. However, the lack of lightweight batteries with high power density limits the flight duration of these micro flying vehicles. Wireless power transfer using radio-frequency electromagnetic waves could potentially provide penetration through obstacles, wave steering/focusing capabilities and non-mechanical control of vehicles using phased antenna arrays. However, the use of radio-frequency power transfer has so far been limited to larger vehicles," the study says.
“One of the key features of our robot is the highly efficient wing-flapping actuation, achieved by using a powerful single-crystal piezoelectric material and a low-loss layout in which the two wings face each other, like clapping hands. This design delivers a power-to-weight ratio comparable to the efficiency of living insects”
A key challenge faced by engineers trying to build miniature robots is thermal runaway caused by power losses. To overcome this problem, Ozaki and his colleagues optimized the circuit design of their robot, ensuring that heat-generating components are not placed close to or next to each other.
In addition, the researchers used a radio-frequency energy receiver with a specific power significantly higher than that of standard lithium-polymer batteries of similar mass. This substantially improved the robot's efficiency and flight time.
“I think our most important finding is that a sub-gram circuit can receive and process high power of more than 1 W at a distance via radio-frequency waves. This suggests that not only flying robots but also various other devices that require high power at small sizes could be realized without batteries”
To evaluate the effectiveness of their design, Ozaki and his colleagues conducted a series of experiments. In these tests, they were able to make the insect-sized robot take off smoothly, without the need for batteries or wires.
The robot built by this research team weighs just 1.8 g, making it more than 25 times lighter than other radio-frequency-driven micro vehicles developed in the past. As a result, it could prove very valuable in the future for complex tasks such as entering cracks, pipes or other very confined spaces.
“In this paper, we successfully demonstrated takeoff. The next step will be to combine this power transfer technology with orientation control to make this robot hover and move freely in the air. We believe this is technically feasible, since we have already managed to control the robot's position using wired power”
Micro air vehicles (MAVs) could potentially be used for environmental sensing, communication, search and rescue, and autonomous inspection of confined or hazardous areas. However, regulations for such devices are tightening due to the risk of accidents. For example, in the US, drones weighing more than 250 g must be registered, and drone flight areas are strictly restricted.
Japan has also recently announced that the threshold weight for small drones will be lowered from 200 g to 100 g. In particular, since the impact energy of a falling aircraft depends heavily on its mass, the safety of MAVs can be improved by designing and developing lightweight insect-sized devices.
The researchers believe that a fully functional untethered MAV with insect-level mass can be realized by optimizing the vehicle design and adding new features. These include integrating a flight control system and using a beam focusing/steering system for the energy transmitter.
