They dance extremely slowly to the ground: based on the model of winged plant seeds, researchers have developed micro-planes the size of grains of sand that can be equipped with electronic elements. Their potential lies in the investigation of the air: the delayed descent enables the tiny creatures to optimally collect measurement data. In the future, their components could also be made from biodegradable materials so that the environment is not polluted with electronic waste, say the scientists.
The propeller-shaped structures of the maple trees are probably the most famous example: the seeds of some plant species have aerodynamically adapted structures that allow them to stay in the air for a particularly long time. This creates turning movements that provide more air resistance and stabilization when descending. With this design, the plants increase their potential for spreading. “Evolution was the driving force behind the sophisticated aerodynamic properties of many types of seeds,” says John Rogers of Northwestern University in Evanston. “These biological structures are designed to fall slowly and in a controlled manner so that they can interact with the wind patterns for as long as possible. This property maximizes the lateral distribution via purely passive, airborne mechanisms, ”explains the researcher. The technical potential of this natural patent is therefore obvious and so Rogers and his colleagues devoted themselves to implementation.
Cleverly dancing micro-planes
To do this, they first studied the natural models: They analyzed the structure and aerodynamic properties of various winged plant seeds. The seeds of the tropical Tristellateia plants turned out to be ideal models for a technical implementation. They have star-shaped wing structures that convey a rotational movement, whereby the seed slowly sinks to the ground. “We took up this design concept, adapted it and applied it to electronic circuit platforms,” says Rogers. In order to determine an ideal structure, the scientists carried out computer modeling of the air currents around various prototypes.
This resulted in micro-fliers with three wings that are similar in shape and angles to those of the Tristellateia seeds. As the researchers report, they can be made in different sizes and versions. In addition to the flight membranes, they consist of electronic functional components that can extend into the wings. The weight is distributed in such a way that the structure performs a stable rotational movement in the air and thus sinks to the ground in a delayed and controlled manner. As the researchers report, their micro-planes even overshadow their natural role model: They dance to the ground on more stable trajectories and at lower speeds than the seeds. “We were also able to make these helicopter flight structures much smaller than the natural models,” says Rogers. The smallest versions are only as big as a grain of sand.
Potential for environmental analysis
For production, the researchers first produce flat precursors to the flying structures. These flat blanks are then glued to a slightly stretched rubber substrate. When the material is then relaxed, there is a controlled buckling process through which the wings fold into precisely defined three-dimensional shapes, the scientists explain. “This strategy of building 3D structures from 2D precursors is very practical, since all existing semiconductor components can be manufactured in planar layouts,” says Rogers.
The micro-planes can thus be equipped with sophisticated micro-technology. In the previous examples, the scientists installed sensors, data storage devices and an antenna that can transmit data wirelessly to receiving devices. It is also possible to integrate a power source that generates energy from light. In experiments, the researchers demonstrated that the micro-planes can detect particles in the air, for example. They imagine the concrete application of the technology on a large scale: You could drop a swarm of micro-planes from an aircraft or a building and have them distributed over a wide area, for example to monitor environmental remediation measures after a chemical accident or air pollution at different altitudes in a city to eat.
However, there is a problem with this, the researchers admit: the tiny electronic devices would pollute the environment after use. But apparently there is a solution that the researchers are now working on: It is possible to manufacture many electronic elements from biodegradable substances. Just recently, for example, researchers presented a pacemaker that dissolves in the body by itself after its use. “We want to use degradable polymers, compostable conductors and dissolvable circuits in our technology, which naturally turn into environmentally friendly end products when exposed to water,” says Rogers.
Source: Northwestern University, Article: Nature, doi: 10.1038 / s41586-021-03847-y
Credit: nature video