In recent years, Unmanned Aerial Vehicles (UAVs), commonly known as drones, have rapidly evolved from niche technology to indispensable tools for various industries and military applications. However, one of the most significant challenges for UAVs has always been their limited flight time due to onboard battery constraints. To overcome this limitation and unlock new possibilities for UAV swarm operations, the Defense Advanced Research Projects Agency (DARPA) has developed an innovative solution: the Whisper Beam wireless power system. In this article, we will explore how DARPA’s Whisper Beam technology is poised to revolutionize UAV swarm operations by providing unlimited flight endurance and transforming the future of aerial missions.
The Limitations of UAV Flight Endurance
UAVs have found applications in reconnaissance, surveillance, cargo transport, and even search-and-rescue missions. However, their effectiveness is often limited by their reliance on batteries with finite energy capacities. This constraint restricts the amount of time UAVs can remain airborne, necessitating frequent landings and recharging, which can be both time-consuming and logistically challenging in certain scenarios.
Defense and Security have also deployed advanced UAVs for a wide variety of critical missions. They provide capability to fight effectively in urban areas against widely dispersed forces, while minimizing collateral damage and achieving information superiority. The UAVs have become one of the essential constituents of all militaries to perform intelligence, surveillance, and reconnaissance missions. Their roles have expanded to areas including electronic attack, suppression or destruction of enemy air defense, network node or communications relay, combat search and rescue and many others. The increasing demand and reliance on UAV in warfighting and peacekeeping operations has doubled the pace of UAV-related R&D in recent years.
The employment of UAVs by various industries and in Defense and Security missions are enabled by their propulsion system to provide them with the necessary power to propel the aircraft for forward flight or hover. Propulsion systems can advance the flight time or endurance of a UAV which is influenced by the propulsion technology used and is dependent on the aerodynamic design and amount of fuel carried. To fulfil the energy requirements of a large variety of UAVs, several variants of piston-engines and electric motors have been designed by the market players.
Propulsion is also crucial for Drone swarms. DARPA OFFensive Swarm-Enabled Tactics (OFFSET) plans drone swarms of up to 250 unmanned aircraft enter battle alongside small teams of soldiers. The agency believes these small drone armies could soon help soldiers in clear buildings in urban areas and conduct reconnaissance.
Wireless power transfer (WPT) for Drones and Drone swarms
Now researchers have turned to Wireless power transfer (WPT) for Drones and Drone swarms. Wireless power transmission, wireless energy transmission (WET), or electromagnetic power transfer is the transmission of electrical energy without wires as a physical link.
For in depth understanding on Wireless Power Transfer technology and applications please visit: Wireless Power Transfer 101: A Beginner’s Guide
In a wireless power transmission system, a transmitter device, driven by electric power from a power source, generates a time-varying electromagnetic field, which transmits power across space to a receiver device, which extracts power from the field and supplies it to an electrical load. The ability to power devices remotely to eliminate the need for replaceable batteries or reliance on environmental inputs such as sunlight to provide energy offers attractive benefits.
One of the advantages of Whisper Beam is that it enables UAVs to fly for longer periods of time without having to return to a base station to recharge or swap out batteries. This can increase the range and endurance of UAVs, as well as their overall effectiveness in carrying out missions.
Wireless power techniques mainly fall into two categories, near field and far-field. In near field or non-radiative techniques, power is transferred over short distances by magnetic fields using inductive coupling between coils of wire, or by electric fields using capacitive coupling between metal electrodes.
In far-field or radiative techniques, also called power beaming, power is transferred by beams of electromagnetic radiation, like microwaves or laser beams. These techniques can transport energy longer distances but must be aimed at the receiver. Proposed applications for this type are solar power satellites and wireless powered drone aircraft.
DARPA Is Exploring Ways to Wirelessly Charge Drone Swarms
DARPA’s Whisper Beam technology is a wireless power transmission system designed to provide continuous and uninterrupted power to unmanned aerial vehicles (UAVs) in flight.
Whisper Beams use a new “non-gaussian” electromagnetic wave that focuses itself at the intended receiver, making it economic and practical to deliver kilowatts of power at kilometer distances. A UAV can carry a compact receiver to draw power while in flight. Swarms of UAVs can form a transmission array relaying power over several kilometers, such as from a main base to a forward base.
How Whisper Beam Works
a. Ground-based Power Transmitters: At the heart of the Whisper Beam system are the ground-based power transmitters, which convert electrical power into a directed microwave or laser beam. These beams are precisely aimed at the UAV swarm, providing a continuous stream of energy to keep them aloft.
b. Airborne Receivers: Each UAV in the swarm is equipped with specialized receivers that capture the incoming microwave or laser energy from the ground-based transmitters. The receivers then convert this energy back into electrical power, effectively recharging the UAV’s onboard batteries or directly powering the aircraft’s systems.
A startup called Electric Sky was awarded $225,000 award from the Defense Advanced Research Projects Agency to build first Whisper Beam transmitter to provide tightly focused wireless power to drones in flight.
The first phase of the project calls for the construction and testing of a laboratory-bench demonstration system that will operate over short distances. Those experiments are expected to supply data that can be used to upgrade the system for higher power and longer range.
With DARPA SBIR Phase I funding, we will build and demonstrate the first radio-frequency Whisper Beam transmitter at a lab-bench scale,powering a short-range UAV in flight. The technology readily scales to power large UAV swarms at kilometer altitudes, and/or wirelessly transfer power from a main base to a forward base several kilometers away. We will also analyze swarm patterns to optimize power levels over long distances.
As a first step, Electric Sky’s CEO and co-founder Robert Millman looked at the main existing technology used to send power through the air wirelessly. Known as a Gaussian beam, that technology has a number of significant limitations that make it ill-suited for power beaming to distant aircraft.
First and foremost, Gaussian beams lose power as they go, meaning the farther away an aircraft is from the power station sending it energy, the weaker the beam. This also means that the power generation platform would lose way more energy than ever reaches the aircraft. That would defeat one of the key benefits of power beaming, namely energy efficiency.
Another limiting factor is the dangers associated with Gaussian beams. Specifically, anything that flies between the emitter array and the receiving aircraft would be bombarded with massive amounts of electromagnetic energy. This means that birds, drones, and even other aircraft would be at significant risk every time they fly over a power transfer beam. Combined with the power loss experienced by these types of power beams and the massive amounts of energy required to compensate for that power loss to adequately fuel an aircraft in flight, a Gaussian beam would represent a costly, immediate danger to anything that crosses its path.
“You want to put high power on the vehicle without putting high power on everything in between,” Millman explained. Fortunately, he says, there are types of wireless radio wave beams, known as non-Gaussian beams, that can be custom-shaped so the peak power is at the aircraft and the space between the transmitter and aircraft is a low power zone.
“The way this beam works, it is actually the lowest power directly between the transmitter and the receiver,” Millman told The Debrief. Of course, he notes, no commercial applications of power beaming with non-Gaussian beams currently exist, but the base technology itself has been around for decades.
“The major issues have been worked out,” Millman said. “The engineering issues, how to turn this into a practical application. Let’s say that there are many solved problems that have been solved over the last 4 or 5 decades, so it’s not like we are solving new stuff.”
For Whisper Beam, Millman says the next practical steps are what he and his team are undertaking now, mainly reducing the non-Gaussian radio wave emitters to a lightweight transmission system that can send the power directly to an aircraft in flight.
“These are all things that have been done, either in the world of radio or wireless communication, that we will apply to our wireless power transmission,” Millman explained. “It’s a mound of work that we look forward to going through.”
Following the success of their light bulb experiments in January, Millman and Greason say they have some attainable, yet admittedly ambitious, goals. One such target is the burgeoning industry of drone-style people carriers, often called air taxis or flying cars.
“A substantial amount of the total energy budget (for flying cars) is used in climbing to altitude,” Millman explained. “If instead, you could enter the cruise phase, at altitude, at 100% charge, that electric vehicle now has more range. And if you again charge coming back in on landing, that vehicle can turn around faster at the gate. So it is more economical as well.”
For winged aircraft that would employ the Whisper Beam system, Millman says that the placement of the transmitter would also be designed to help vehicles tackle the massive power used during take-off and landing, reducing flight times and making electrically powered flight more energy efficient.
“With electric craft, you could position a transmitter near a runway, and you could be powering take-off and climb,” Millman explained.
Millman also pointed out that while his team is working on improving and scaling up their power-beaming technology with goals of building “bigger and more powerful” beaming arrays, they also have goals of designing fully electric aircraft that can cruise at altitudes well above 70k feet. Still, he cautioned, as a company looking to upend over 100 years of aircraft aviation and usher in an entirely new era of electrically powered flight, they need to take things one step at a time.
“We decided, ‘let’s attack that (power beaming) first.’ Because, if you don’t have power transmission, you can have the best electric propulsion system in the world, but if you don’t have a power source at altitude, it doesn’t get you anywhere.”
As far as the distant future and where power beaming could ultimately go, Millman says they have modeled a system that can send power as high as 740 kilometers. This extreme altitude is well into low earth orbit, meaning their technology could not only power aircraft of the future but could also power spacecraft or space stations that operate in low earth orbit.
One example used by Millman is the International Space Station (ISS), which typically hangs out at about 350 Km, an altitude that is well within the range of Whisper Beam simulations. As such, the ISS, Millman notes, would be an ideal long-term candidate since it currently employs massive solar arrays to generate around 100 kW of useable power.
Electric Sky isn’t the only venture focusing on wireless power for drones. Seattle-based PowerLite Technologies, for example, is working on a laser-based system that could power unpiloted aerial vehicles as well as 5G base stations. but Electric Sky’s proprietary technology takes a different approach.
Laser and microwave beams usually start out strong, but get weaker as they move outward. In contrast, the transmission of the whisper beam starts out weak but becomes stronger near the receiver. “Whisper Beam Technology is the electromagnetic equivalent of a whispering gallery,” Millman said in a news release:, “In a whispering gallery a lone listener across the room can hear the speaker, but no one else, not even those standing directly between the speaker and the listener. The voice is too weak for them to hear. ,
Radio waves sent by Electric Sky’s transmitter self-focus on the receiver, enabling the drone to draw kilowatts of power in any kind of weather.“It’s a myth that long-distance power transmission is impossible,” Greyson said. “It just has never been economical. This new method reduces the cost of a ground transmitter and the size of a vehicle’s onboard receiver.”
Greyson said the beaming system could be used with any type of electric aircraft. “Whisper Beam technology is particularly helpful in the power-hungry phases of takeoff and climb, helping vehicle designers meet other requirements to increase range, increase flight safety, reduce peak load on the battery and reduce ground turnaround time. enables,” he said.
In March 2023, Seattle, Washington-based aviation technology company Electric Sky has announced a significant breakthrough involving its Whisper Beam power beaming technology.
Advantages of Whisper Beam for UAV Swarm Operations
a. Unlimited Flight Endurance: With the Whisper Beam technology, UAVs no longer have to worry about running out of battery power. This unlimited flight endurance opens up new possibilities for extended aerial missions, persistent surveillance, and continuous data gathering.
b. Enhanced Mission Flexibility: Whisper Beam allows UAVs to stay airborne for extended periods, reducing the need for frequent landings and mission interruptions. This flexibility is particularly valuable in dynamic situations where rapid response and continuous monitoring are essential.
c. Scalability and Swarm Coordination: The Whisper Beam system can cater to large UAV swarms, ensuring seamless power supply to multiple drones simultaneously. This scalability is critical for coordinated swarm operations, where the collaboration of multiple UAVs can greatly enhance mission effectiveness.
Once commercially available, Whisper Beam will be perfectly poised to herald a dramatic shift in how passenger aircraft, flying taxis, drones, and satellites carry and consume the energy that keeps them aloft.
Addressing Concerns and Challenges
While the Whisper Beam technology presents exciting prospects for UAV swarm operations, it also raises some concerns that require careful consideration. Safety measures are paramount to ensure that the wireless power transmission does not interfere with other communication systems or pose risks to personnel and wildlife. DARPA has dedicated significant efforts to address these concerns, incorporating robust safety protocols into the Whisper Beam system’s design.
DARPA’s Whisper Beam wireless power system represents a paradigm shift in the capabilities of UAVs and holds the potential to redefine aerial operations. By eliminating the constraints of limited flight endurance, this groundbreaking technology empowers UAV swarms to perform extended missions with unmatched persistence and flexibility.
As the Whisper Beam technology advances and integrates with various UAV platforms, we can anticipate a future where aerial swarm operations become more efficient, adaptable, and potent in diverse applications, ranging from defense and reconnaissance to disaster response and environmental monitoring. Through DARPA’s relentless pursuit of innovation, the Whisper Beam system stands at the forefront of wireless power, propelling UAV swarm operations into a new era of limitless possibilities.
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