Wireless Power Unlocked Through Volumetric Absorption

Power Relay Technology utilizes light to transfer high power over long distance using a small footprint receiver.

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Prototype Power Relay demonstrating wireless power transfer via light. Light is absorbed volumetrically by the receiver allowing for higher efficiency and a smaller footprint.

Prototype Power Relay demonstrating wireless power transfer via light. Light is absorbed volumetrically by the receiver allowing for higher efficiency and a smaller footprint.

Written by Alexander Diggins, Cofounder & CTO, Nimbus Engineering, Inc.

Wireless Power is typically found on phone charging pads and more recently in experiments powering EVs. As the world becomes increasingly electric and automated, wireless charging will become more common. There are a few major challenges facing the wireless transfer of energy. In the case of inductive charging the major limitation is distance. In the case of RF (Radio Frequency) wireless power, the limitation is high power with high efficiency using a realistic receiver size or footprint. Both technologies have legitimate tradeoffs.

In the case of Power Relay Technology, this gap is being bridged with a solution that can provide high power over long distance, efficiently and in a practical form factor. The key to unlocking this potential is volumetric absorption of light.

Photovoltaic cells or solar cells are excellent for absorbing a narrow band frequency of light to produce power. They can even be made relatively efficient to sunlight and are plummeting in price over time. All of this is great for optical energy technologies but there is one inherent disadvantage. Photovoltaic cells are typically thin to reduce materials cost, and either way, light is absorbed within nanometers or micrometers from the surface of semiconductor layers. This results in a very thin surface absorbing large amounts of energy and rising quickly in temperature. If the goal is to beam high intensity light many times the brightness of the Sun at such a surface, it would simply melt or require enormous receiver panels over an impractically large space to receive the light without super heating.

A Volumetric Approach

This is where volumetric absorption comes in. The ability to spread out a narrow beam of ultra-high intensity light and then absorb that energy through kilograms of photoluminescent material rather than grams of solar cells allows for Relays to barely rise in temperature as they absorb intensely powerful light at great range. Remaining at relatively low, room temperature also allows the system to operate much more efficiently.

Exploded CAD diagram of Power Relay Receiver and distribution of light throughout volumetric material.

Utilizing LED spotlights and laser diode technologies, Power Relays can achieve 100 meter or greater transmission with minimal optical attenuation loss. The most efficient optical emitter devices have achieved over 82% WPE (Wall Plug Efficiency) which is essentially how well they can convert electricity into light. This and band gap matched photoluminescent absorber material allow this approach to achieve round trip efficiencies well above 30%. With these performance metrics, Relay Technology can bring wireless power to the world of autonomy and beyond.

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