Lightning is one of the natural phenomena that causes great damage to human society.
Although various lightning countermeasures have been implemented for critical infrastructure, including the NTT Groups communications facilities, lightning damage has not been eliminated even today, and the damage is estimated to be 100 to 200 billion yen per year in Japan alone (*1).NTT aims to significantly develop the technology it has cultivated to protect communications facilities from lightning and to realize technology that will eliminate lightning strikes on critical infrastructure and cities altogether.Conventional lightning countermeasures have widely used methods that use lightning rods, but the range that lightning strikes is limited, and there are also cases where it is difficult to install lightning rods, such as wind turbines for wind power generation and outdoor event venues.
NTT is conducting research into drone lightning induction (*2), which uses drones, which have been developing rapidly in recent years, to move drones according to the position of thunderclouds, actively induce lightning, and then guide them to a safe place.On this occasion, to demonstrate drone lightning resistance technology that prevents drones from malfunctioning or breaking down even if they are hit directly by lightning, and lightning induction technology that uses electric field fluctuations to actively make lightning strike a drone, Fujitsu conducted a drone lightning induction experiment under an actual thundercloud.2.
Experimental Overview and ResultsA lightning-triggering experiment using a drone was conducted at an altitude of 900m in the mountainous area of Hamada City, Shimane Prefecture, from December 2024 to January 2025.
In this experiment, a device called a field mill (*3) was used to observe the electric field on the ground, and when the electric field strength in the vicinity increased due to the approach of thunderclouds, a drone equipped with a unique lightning-resistant cage was flown to attempt to induce lightning (Figure 1).Figure 1 Lightning-resistant droneWhen the electric field strength observed by the field mill rose when the thundercloud approached on December 13, 2024, the drone with the wire was flown to an altitude of 300 m, and a switch installed on the ground was used to connect the drone to the ground (Figure 2).
As a result, it was confirmed that a large current flowed through the wire, and at the same time, the surrounding electric field strength changed significantly.
Furthermore, it was confirmed that a voltage of more than 2000 V was generated between the wire and the ground just before the lightning was induced, and lightning was induced in the drone by suddenly changing the electric field strength around the drone.
This is the first successful lightning induction using a drone in the world.In addition, at the same time as the lightning was induced, a popping sound, lightning was emitted from the winch, and part of the drones lightning-resistant cage was melted.
On the other hand, it was confirmed that the drone equipped with the lightning-resistant cage continued to fly stably even after the lightning was induced.Figure 2.
Drone-triggered lightning experiment system3.
Key Points of the TechnologyIn order to trigger lightning by drones, the drone must continue flying even when lightning strikes.
Furthermore, since it is difficult to strike lightning by simply flying a drone under a thundercloud, it is necessary to actively induce lightning.
To achieve this, we proposed and demonstrated the following two technologies (1) and (2).(1) Lightning resistance technology for dronesWe have devised a design method for a lightning-resistant cage that will not malfunction or break even if the drone is hit directly by lightning, and that can be installed on drones in the city.
The lightning-resistant cage is a metal shield that prevents the lightning current from flowing through the drone body by diverting the large current that flows when the drone is hit directly by lightning.
In addition, by making the lightning current flow radially, the strong magnetic fields generated by the large current cancel each other out, reducing the magnetic field effect on the drone (Figure 5).Figure 5.
Lightning-resistant design for large currents and strong magnetic fieldsFurthermore, we conducted an artificial lightning application test on a drone equipped with a lightning-resistant cage.
As a result, we confirmed that the cage covers more than 98% of natural lightning strikes, and that the drone will not malfunction or malfunction even when artificial lightning of 150kA, which is five times the average value of natural lightning strikes, is applied.(2) Lightning triggering technology using electric field fluctuationsTo induce lightning, we devised a method to connect a flying drone to the ground with a conductive wire, attach a high-voltage switch to the ground side, and change the electric field strength around the drone by operating the switch.
The switch connects the drone to the ground at the optimal timing, and the electric field strength around the drone is suddenly increased, which can help induce lightning (Figure 6).Figure 6 Principle of lightning induction technology using electric field fluctuations4.
Future DevelopmentsNTT aims to protect cities and people from lightning damage by flying drones that will not break down even if struck directly by lightning to highly accurately predicted lightning locations, inducing lightning and guiding the drones to safe locations.
In the future, we will continue to promote research and development into highly accurate lightning location predictions and the mechanisms behind lightning generation in order to increase the success rate of drone-induced lightning as demonstrated in this study.
Furthermore, we will also work on research and development into methods for storing lightning energy, with the aim of storing and utilizing the energy of induced lightning (Figure 7).[Terminology]*1Institute of Electrical Engineers of Japan Technical Report No.
902: 2002*2Lightning triggering: Actively inducing lightning and guiding it to a safe location*3Field mill: An instrument for measuring atmospheric electric fieldsTop Photo: Figure 7 NTTs vision for a world in which drones are used to protect cities from lightning damage and store lightning energy.Source: NTT