Capturing energy in the air to power electronics

From cell phones to televisions to hospital equipment, there's energy in the air all around us. Now, researchers have discovered how to harness this ambient energy and use it to power other devices.

From cell phones to televisions to hospital equipment, there's energy in the air all around us. Now, researchers from the Georgia Institute of Technology have discovered how to harness this ambient energy and use it to power other devices.

I spoke yesterday with Manos Tentzeris, an engineering professor who is leading the research. Below are excerpts from our interview.

How do you capture and harness energy transmitted from TVs, radios and other devices?

We investigated different ways to scavenge energy by analyzing it over the whole spectrum in the ambient environment. There is a significant amount of energy all the way from FM radio up to WiFi. Previous efforts were scavenging only from narrow bands. That led to tiny amounts of power. In order to have a significant amount of power, we thought we should be able to scavenge energy from the whole frequency range. To do that, we developed extremely wide-band antennas. We managed to do this in a very cost-effective and environmentally-friendly way. We developed in-house ink jet printer technology where we can ink jet print circuits or metals on very low cost substrates like paper or plastic.

The third trick we utilized was finding efficient ways to keep storing this energy. It's like having to collect small droplets of water [from all different directions] in a single cup. We developed some ways using a super-capacitor where we can store this energy. After we reach the amount of power we want, we utilize it in a spurt and that activates a sensor or some very small communication device.

Previous efforts haven't been able to capture this much energy this way before?

Exactly. They were doing it over very narrow bands. We stretched it to much wider frequency bands. We're able to accumulate small amounts of power, but over a wide frequency range that will net a significant amount.

And the antennas are produced using ink jet printers?

Yes. The whole system depends on the wide-band antennas. Those will receive some energy over all the frequency ranges. A diode converts the energy, so it can be stored. That had been quite a challenge. We monitor the interconnect, as well. It will allow the device to power some practical electronic device.

What types of devices could the energy be used to power? Could it be used to power a cell phone, for instance?

Not yet. To give you an idea of where we stand now, with most of the conventional scavenges, we get minuscule amounts of power -- about 10 to 50 microwatts. We can push it almost all the way up to one milliwatt. The devices [we power with this] could be wireless sensors or devices that detect the structural strength of a large building. The third type are bio-monitoring devices, like a wireless electrocardiograph or [a device that does] temperature monitoring of a patient. We're trying to push it to some new devices, like glucose monitoring devices. There is an abundance of magnetic fields in hospitals or medical environments. That's the new generation we're developing right now. We're trying to scavenge magnetic energy from medical environments for medical devices.

Do you have anything else to add?

This is an extremely low cost and an extremely easy way to realize scavenges. If you're talking about the next generation of the sensing revolution, which in my opinion is the next revolution after the Internet, you're going to have billions of sensors. Batteries are not the solution.

This approach can be easily expanded to different frequency ranges. This is quite scalable and quite expandable.

This is very flexible. Typically scavenges are often very solid, rugged, planar constructions. That's one of the reasons they have not been generalized. Our approach could make this applicable for smart grid applications where you could place them very close to the high-voltage transmission lines, very close to transformers and so on.

Photo: Manos Tentzeris displays an inkjet-printed rectifying antenna used to convert microwave energy to DC power / By Gary Meek

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