Alleviating the battlefield battery burden with wireless powerStory
December 17, 2013
Wireless power, a new technology already poised to change the way we recharge everything from smart phones to electric vehicles, has the unique potential to transform war fighting of the future and alleviate the battlefield battery burden for both soldiers and manned and unmanned vehicles on land, in the air, and undersea. The U.S. military goals of digitizing dismounted soldiers, sensing their environment, and sharing information could require as much as twice the power as is required by warfighters today; the already burdensome tasks of carrying, operating, and maintaining multiple batteries, cords, and connectors will only be exacerbated unless dramatic changes in power management are implemented using highly resonant Wireless Power Transfer (WPT) systems.
In a typical 72-hour mission, warfighters carry as many as 70 primary cells, and seven types of batteries weighing over 20 pounds1. In addition to the physical burden of carrying backup batteries, relying on an array of individual cells introduces dependence on a complex supply chain, user error, wasted time, and device failure. Today’s military-battery burden extends well beyond soldier-based systems to manned and unmanned aerial, ground, and underwater vehicles and systems that use extensive amounts of electric power, are often range-limited by battery life, and rely on manual battery recharging and/or replacement techniques.
Together, these challenges point to a fundamental need to rethink, automate, and future-proof battlefield power distribution through the implementation of new technologies that dramatically reduce the battery burden. Wireless power offers the unique potential to quickly, safely, cost-effectively, and automatically recharge virtually any mobile military device or system that relies on batteries.
First applications and next steps
The first use of wireless power by the U.S. military will likely be to automatically recharge batteries embedded in Unmanned Ground Vehicles (UGV) used on the battlefield. In addition to the obvious benefits of improving and automating the battery-recharging process, a primary motivation for using WPT in this application is to eliminate exposure when soldiers leave the safety of armored vehicles to manually replace UGV batteries. Initial prototypes embedded in QinetiQ Talon robots are being deployed to Afghanistan for field testing this year to recharge batteries when a robot is docked to an armored vehicle.
Building upon this initial success, the next step is to focus on enabling other high-use, high-power, and high-availability devices and systems. For example, wireless power – combined with intelligent power management – has the potential to more than halve the battery weight and number of primary cells carried by dismounted warfighters and reduce the energy storage requirements on unmanned vehicles. Cutting dependence on primary cells will ensure device availability and allow warfighters to focus on a single power source, eliminating potential errors in high-stress situations.
The basics of highly resonant wireless power transfer
Highly resonant WPT can occur when two high-quality-factor electromagnetic resonators are tuned to the same frequency and are within range to couple magnetically.
The power sources and capture devices include specially designed magnetic resonators that efficiently transfer power over mid-range distances via the magnetic near-field. These proprietary source and device designs and the electronic systems that control them support efficient energy transfer over distances that are multiples of the size of the sources/devices themselves.
This highly resonant WPT technology provides advantages over traditional magnetic induction that requires source and capture devices to be very close to one another – within millimeters – to transfer power efficiently.
Energy transfer via magnetic near-field can penetrate and wrap around obstacles, and can provide for safe, non-radiative energy transfer. Scalable designs enable solutions from milliwatts to kilowatts, while flexible geometries allow WPT systems to be embedded in vests, helmets, weapons, cameras, sensors, and other gear.
The efficiency of WPT systems is limited by the relative size, orientation, alignment, and distance between source and device resonators, as well as by the operating frequency and efficiency of the power electronics. In applications such as electric-vehicle charging, end-to-end efficiencies in excess of 90 percent are achievable over gaps of 20 cm or more.
Toward the wireless warfighter
WPT is a maturing technology already applicable to a host of today’s military applications. To reach its maximum potential and meet the demands of tomorrow’s wireless warfighter, however, the technology must continue to evolve, develop, and grow in sophistication and intelligence. Next-generation components, systems, and devices must also be designed and developed with WPT in mind to optimize form, fit, and function and also to ensure that the systems are efficient, safe, and accurate Over the course of the past year, a large number of potential defense-related use cases for WPT have emerged, such as:
- Soldier vest-to-helmet WPT to power helmet-mounted devices
- Soldier helmet-to-goggle WPT to power devices and defog optics
- Vehicle seat back-to-soldier vest WPT to recharge central batteries
- Operating base rack-to-soldier vest WPT to recharge central batteries
- Simple, smart, and wireless power managers
- In-vehicle, drop-in, multi-device WPT recharging boxes
- Operating base, drop-in, multi-device WPT recharging boxes
- Vehicle-to-Unmanned Aerial Vehicle (UAV) WPT systems
- Other vehicle-to-UGV WPT systems beyond the Talon robot
- Vehicle-to-Unmanned Underwater Vehicles (UUVs) WPT systems
- Wireless rechargeable batteries and multi-battery recharging boxes
- Soldier vest-to-affixed device WPT to recharge batteries
- Soldier vest-to-handheld device WPT to recharge batteries
Recent progress and ongoing activities
In addition to the ruggedized systems wirelessly recharging Talon robots from armored vehicles, proof-of-concept prototypes are being developed to move energy wirelessly between vest-embedded batteries and small helmet-mounted batteries used to power mounted electronics such as night vision and radio devices. This reduces the size and weight of helmet-mounted batteries and eliminates the need for a power cord connecting the helmet to the vest-mounted battery pack.
Figure 1: Prototypes of vest-pocket batteries to power helmet lights and other soldier-worn electric devices have been successfully demonstrated.
(Click graphic to zoom by 1.9x)
Proof-of-concept prototypes developed for the Defense Advanced Research Projects Agency (DARPA) that transfer power wirelessly from military vests to handheld devices contained in vest pockets have also been demonstrated successfully. A new project funded by the U.S. Army will explore the feasibility of transferring power between a vehicle seat back to a soldier-worn vest so that as warfighters sit in vehicles, their central battery can be recharging.
WiTricity engineers recently demonstrated the ability to wirelessly transfer several hundred watts of power through seawater. In the future, WPT systems will likely be encased in sealed enclosures to allow several kilowatts of power to be transferred through water with a high degree of spatial freedom. WiTricity envisions UUVs being recharged simply by floating alongside a dock, larger vessel, or other power source, eliminating the need for tight mechanical coupling and allowing power to be transferred underwater safely, reliably, and efficiently.
In the years to come, expect developers of defense systems to utilize wireless charging systems in a wide variety of systems and devices to improve operational efficiency and convenience. In doing so, they will be leveraging a disruptive technology capable of dramatically reducing the battery burden, supporting an overhaul of power management in military systems, and significantly augmenting mission effectiveness for the warfighters of tomorrow.
1 Dr. Ed Shaffer, U.S. Army Research Laboratory (ARL) Battery Technology Industry Day, McLean, Va.; February 16, 2011; http://www.arl.army.mil/www/?article=564.
Jeff Muhs is Director of Business Development for WiTricity Corporation where he directs business development in military, automotive, and industrial markets for the technology provider of wireless power-transfer systems. He can be contacted at [email protected]
WiTricity Corporation 617-926-2700 www.witricity.com