A review of long-range wireless power technologies–the future is now (Reader Forum)
Wireless technologies have been popular with consumers for several decades now (think Wi-Fi, cordless phones, etc.). The proliferation of smart devices has only fed the need for wireless advances, which have largely come in the form of vastly improved computing power, network connectivity and sharp increases in speed, ease of use and utility. But as accustomed as consumers have gotten to many of the benefits of wireless technology, one important aspect of these devices has remained short on innovation until just recently: wireless power.
Wireless power technologies deliver electricity to charge and power devices without plugs and without batteries. Unlike magnetic induction (“Qi”) charging pads, which require direct contact and careful alignment with a phone, long-range wireless power has taken the next step in this evolution and holds the promise of meaningfully charging smartphones and other smart devices from meters away. Smart home appliances, such as the Google and Amazon smart speakers, or smart locks and light fixtures, could be powered without the need to be placed close to power outlets. Batteries – and the inconvenience of replacing them or constantly having to charge battery powered devices – would have less sway over our lives.
Batteries not included
Why do so many of our products still use batteries and power cords – technologies that were invented and popularized decades ago? The simple answer comes down to design and proven functionality.
A good example of the benefits and deficiencies of cord-connected devices and battery-powered, wireless technology can be found in indoor security cameras. A security camera, such as one provided by Ring, gives you two options: cord powered, and battery powered. Corded versions offer more functionality such as video streaming but are limited by close proximity to a power outlet or the labor of running a powerline to the camera. The battery-powered version is easier to install but may only be able to stream a tiny amount of video each day, limiting the general utility of the devices. There is a more innovative way to power devices without as many convenience drawbacks – truly wireless power.
True long-range wireless power delivery – what you need to know
There are two key attributes for long-range wireless power delivery: distance and power. Distance is limited by the physical phenomenon of diffraction while power is limited by safety regulations.
Diffraction is a physical property of waves. It deals with how beams diverge – become wider – as they exit the source of the energy beam.
To understand diffraction, think of a person trying to drink from a garden hose. Water is delivered from the hose into the person’s mouth. The water stream starts with a small diameter, and the farther away the person is from the hose, the wider the diameter of the water stream. At a distance, only a small percentage of that available water will be captured because the water stream widens and the water “receiver” (the person’s mouth) is small compared to the diameter of the stream. Water will be wasted or displaced onto the ground.
When a power beam becomes wider, the distance of the transmitter from the receiver impacts the power-capture ability. If only a small portion of transmitted energy is captured by the receiver, efficiency is reduced and much more energy needs to be sent from the transmitter to power the device. Additionally, energy that is not captured by the receiver bathes the environment, potentially creating unwanted effects for people, pets, and plants.
One option to improve efficiency would be to increase the receiver size, but creating a larger receiver makes the technology less practical for phones or other small portable devices.
Another theoretical option to deliver the energy despite low efficiency is to increase the transmission power. However, depending on the type of energy, one might quickly reach the allowable safety limits as defined by government regulators.
Thus, to deliver wireless power at a distance we need a technology that can efficiently be captured by a small receiver at a distance yet stays within the safety limits.
Wireless power – finding the sweet spot
When engineers start thinking about wireless power delivery, Radio Frequency (RF) may seem like the best way. RF is used for communications technologies, it is a widely accepted and standardized means of transmission with many commoditized components available.
But because of diffraction, RF is very limited for practical power transmission. It is best suited for peripheral devices like wireless mice or keyboards in a desktop environment—applications that require very modest power at modest distances. Supporting the wide range of consumer products that would deliver real world solutions is not possible with RF technology. The same effect that makes RF so suitable for communication (it spreads so well) makes it less relevant to deliver power wirelessly efficiently and safely. IR, by contrast, possesses traits that meet the needs of 21st Century consumer technology in several important ways.
By packing infrared power in a tight beam, power resists diffraction and can carry over longer distances. Like a laser pointer that can focus light and not dissipate its light energy, IR can carry over distance without losing shape or power. One could calculate that at room-sized distances, delivery of several Watts of power using IR is feasible, more than enough to power most smart devices.
Wireless power presents significant opportunities to move beyond power cord dependent and battery-operated devices and the technology to implement new innovations is available today. With long-range wireless power, indoor cameras would install with ease and provide streaming video. Smart door locks could add face recognition, video streaming and cloud storage. Personal assistance speakers could be placed freely in the room without the burden of a power cord. Wireless power does not power your TV yet, but it has the potential to bridge the gap between batteries and wired connections in the very near future.