25-10-2021 | By Robin Mitchell
Recently, DARPA announced its interest in wireless power transmission and has asked the industry for solutions. What advantages does wireless laser power transmission offer, why may DARPA be looking for such technologies, and what challenges does it face?
In the field of electronics, it seems that most things are now wireless to some degree. Wi-Fi provides wireless internet, NFC provides contactless payment options, and RFIDs allow devices to be identified even without needing a local power source. However, transmitting power wirelessly has proven to be a significant challenge and unlikely to be achieved anytime soon due to the many physical limitations imposed by the universe.
If wireless power transmission could be achieved with great efficiency, it would bring many advantages that could rapidly change society. For one, wireless power transmission to electric vehicles could allow for constant driving without recharging. Another potential application of wireless power transmission would be in electric aircraft; beamed energy to a plane could remove the need to carry fuel and provide carbon-free transportation over long distances.
Wireless power could even be taken further with the replacement of cables in power distribution. Depending on what technology was used, towers containing waveguides or transceivers could direct beams of energy across the nation while eliminating the challenges presented by cables such as electric shock risk, cost, and maintenance.
Recently, DARPA announced that it is looking towards the industry to develop wireless power technologies to improve its military capabilities. Specifically, it is looking for laser-based technologies that can fire intense laser light beams to a target that can absorb the energy and convert it to electricity.
Such a system would enable aircraft to remain in the air without refuelling or relying on sunlight for energy. As laser beams can travel a great distance while losing little energy (they do not follow the inverse square law as they are parallel beams), they would, in theory, be able to power aircraft at great distances and possibly even satellites in orbit.
To help realise this goal, DARPA has broken down the challenge into three specific areas; high-energy, high-efficiency, and relay technology. High-energy refers to producing beams with massive amounts of power, high-efficiency refers to transmission and reception methods that can maximise the energy converted, and relay technologies involve those that can redirect the energy with minimal losses.
One major challenge that DARPA has acknowledged is the safety aspect of the beam. Their power requirements have been stated to be between 1kw per square meter and 100kw per square meter, but any individual hit with this beam would suffer a major injury. As such, whatever system is used must be able to detect a break in the beam and immediately turn off the beam to prevent injury.
Unlike a typical laser beam, a power delivery system would have an intended target that would expect n amount of power. If the target detects any deviation in power received, a message sent via radio would instruct the power source in a matter of microseconds.
Another major challenge faced is that laser beams have a tendency to heat up their target, making it difficult to fully convert the delivered energy into electricity. In fact, this is the very mechanism that laser cutters rely on, and these devices operate at hundreds of watts, not hundreds of kilowatts. Heat can be converted to electricity using thermocouples, but these are very inefficient.
However, this technology does not necessarily need to be used in power transmission alone; it could lead to the development of long-range laser communication. Unlike radio, laser communication is virtually impossible to hack as laser beams are not detectable outside of the beam. For someone to eavesdrop on a laser beam communication line, they would need to intercept the beam, which is no small feat.
Overall, wireless power transmission is a challenging goal to achieve due to the many limitations of the universe. Still, the very attempt in developing such technology could open the world to new technologies not currently realised.