Physics question - how useful is this power harvesting research?

[aceplace57]

Yeah, I rolled my eyes at this one to. Until I read closer and confirmed the Applied Physics Letters is peer reviewed. The research is coming from Duke University.

I have an associates degree in electronics. I recall studying AM/FM and tv receivers. The signal levels they receive are tiny. It required a lot of amplification to get anything useful. I’ve never studied microwave receivers. My focus was consumer electronics, radio/tv servicing in the 80’s.

I’d appreciate hearing from people with more physics training. How useful and practical is this research?
to
Anyone have a subscription to Applied Physics Letters? Any additional info there?
main article
http://www.eurekalert.org/pub_releases/2013-11/du-wdc110713.php

Another one with pictures.

New device harvests electricity from background radiation like Wi-Fi

DURHAM, N.C. – Using inexpensive materials configured and tuned to capture microwave signals, researchers at Duke University’s Pratt School of Engineering have designed a power-harvesting device with efficiency similar to that of modern solar panels.

The device wirelessly converts the microwave signal to direct current voltage capable of recharging a cell phone battery or other small electronic device, according to a report appearing in the journal Applied Physics Letters in December 2013. (It is now available online.)

It operates on a similar principle to solar panels, which convert light energy into electrical current. But this versatile energy harvester could be tuned to harvest the signal from other energy sources, including satellite signals, sound signals or Wi-Fi signals, the researchers say.

The key to the power harvester lies in its application of metamaterials, engineered structures that can capture various forms of wave energy and tune them for useful applications.

Undergraduate engineering student Allen Hawkes, working with graduate student Alexander Katko and lead investigator Steven Cummer, professor of electrical and computer engineering, designed an electrical circuit capable of harvesting microwaves.

They used a series of five fiberglass and copper energy conductors wired together on a circuit board to convert microwaves into 7.3V of electrical energy. By comparison, Universal Serial Bus (USB) chargers for small electronic devices provide about 5V of power.

“We were aiming for the highest energy efficiency we could achieve,” said Hawkes. “We had been getting energy efficiency around 6 to 10 percent, but with this design we were able to dramatically improve energy conversion to 37 percent, which is comparable to what is achieved in solar cells.”

“It’s possible to use this design for a lot of different frequencies and types of energy, including vibration and sound energy harvesting,” Katko said. “Until now, a lot of work with metamaterials has been theoretical. We are showing that with a little work, these materials can be useful for consumer applications.”

[Grey]

The big claim is that they’ve achieve efficiencies on par with solar cells ~30% or so.

We had been getting energy efficiency around 6 to 10 percent, but with this design we were able to dramatically improve energy conversion to 37 percent, which is comparable to what is achieved in solar cells."

Of course harvesting 37% of 1mW/m[sup]2[/sup] compared to harvesting 37% of 800,000 mW/m[sup]2[/sup] is a less impressive headline.

It strikes me as interesting but not game changing.

[aceplace57]

I suspected the signal strength had to be miniscule. Hard to imagine it even charging a cell phone.

[california_jobcase]

I saw a project plan similar to that idea back in high school ('78). It was a receiver circuit tuned to 60 Hz. If you built one near a substation, the plans said you could get a few volts good for about a hundred mA.

[lazybratsche]

Couldn’t this be really useful for something like RFID tags? Wiki sez there are RFID tags in the microwave band, but they require power for active transmission. These tags have higher data transmission rates but aren’t cheap because of the need for a power source. With a 5-fold increase in power harvesting you might be able to make cheaper passive RFID tags that use microwave frequencies.

(I suppose that would have to be MFID for the pedants.)

[Dallas_Jones]

This was all the farther I needed to read:

“The key to the power harvester lies in its application of metamaterials”

[Trinopus]

Dallas Jones: it isn’t as bad as it might seem. “Metamaterials” is a real branch of engineering/physics/science. It involves creating real materials which display certain desired properties which might not exist in ordinary materials. For instance, there is a way to create a surface that exhibits a negative coefficient of refraction.

So…don’t throw away the real science here, just because the name being used seems absurd. “Dark Energy” isn’t stupid just because the name is.

[Princhester]

I know there is a lot of inaccuracy in science reporting but they lost me at this:

They used a series of five fiberglass and copper energy conductors wired together on a circuit board to convert microwaves into 7.3V of electrical energy. By comparison, Universal Serial Bus (USB) chargers for small electronic devices provide about 5V of power.

Volts ain’t power. I could probably get a few hundred volts out of a cat and a comb on a dry day: doesn’t mean I’ve got any power worth speaking of.

[aceplace57]

The abstract from the Journal is worded more precisely. The article is available online but costs $4. Cheap for a peer reviewed article.
http://scitation.aip.org/content/aip/journal/apl/103/16/10.1063/1.4824473

We present the design and experimental implementation of a power harvesting metamaterial. A maximum of 36.8% of the incident power from a 900 MHz signal is experimentally rectified by an array of metamaterial unit cells. We demonstrate that the maximum harvested power occurs for a resistive load close to 70 Ω in both simulation and experiment. The power harvesting metamaterial is an example of a functional metamaterial that may be suitable for a wide variety of applications that require power delivery to any active components integrated into the metamaterial.