editor's blog
Subscribe Now

Harvesting Microwaves

We have just looked at an approach to wireless power transfer using low MHz electromagnetic field oscillations. But such a concept is only “power transfer” if the whole reason for the signal in the first place is to transfer power. If such a signal exists for some other reason – like communications – then doing the exact same thing wouldn’t be power transfer: It would be energy harvesting.

And indeed folks are trying to harvest energy out of all of the waves running rampant through our environment. The issue is efficiency, however, and you don’t really see a lot of practical discussion of this type of harvesting as being on its way to commercialization.

But there are some interesting things going on. And they involve “metamaterials” – artificial matter that can achieve characteristics – like a negative index of refraction or negative permittivity – that aren’t possible in nature. We took a look at some of these a couple years ago.

I have tended to think of metamaterials as the careful stacking and arranging of materials at the nano level; apparently that’s not always the case. Some folks at Duke University created a microwave energy harvester using a macro-sized metamaterial.

The fundamental unit of this “material” is the split-ring resonator. These can be very small, and would need to be on the order of 10s of nanometers across to respond to optical wavelengths, but the one Duke used was not that small: the outer diameter was 40 mm, and the gap was 1 mm. It was tuned for 900-MHz resonance.

Split_ring_resonator.png

 

Image courtesy ??(Wikipedia contributor)

My initial thought was that these were made out of a metamaterial, but no: they’re made out of copper, and an array of these becomes the resonator. They used five of them (5×1 array) in their experiments.

It’s interesting to me that one of these rings bears a remarkable resemblance to the structure that WiTricity uses as source and capture resonators, albeit at lower frequencies. I suspect that’s no accident.

While simulation suggested they might get into the 70% efficiency range, their results were closer to 37%. There wasn’t really an explanation of that discrepancy; I’m going to assume that will be the focus of more work.

You can read more details about their work in their paper (PDF).

Late update: there’s another “out of thin air” technology that’s more than harvesting. It will be the topic of a future piece

Leave a Reply

featured blogs
Apr 8, 2020
Here are some tips that will help you transition to your new environment. But more importantly, it will help you when having to go back into the office. Working remotely can be hard to adjust to psychologically. To help make the transition, take a disciplined approach to mana...
Apr 7, 2020
Have you seen the video that describes how the coronavirus has hit hardest where 5G was first deployed?...
Apr 7, 2020
In March 2020, the web team focused heavily on some larger features that we are working on for release in the spring. You’ll be reading about these in a few upcoming posts. Here are a few smaller updates we were able to roll out in March 2020. New Online Features for Ma...
Apr 3, 2020
[From the last episode: We saw some of the mistakes that can cause programs to fail and to breach security and/or privacy.] We'€™ve seen how having more than one program or user resident as a '€œtenant'€ in a server in the cloud can create some challenges '€“ at leas...

Featured Video

Industry’s First USB 3.2 Gen 2x2 Interoperability Demo -- Synopsys & ASMedia

Sponsored by Synopsys

Blazingly fast USB 3.2 Gen 2x2 are ready for your SoC. In this video, you’ll see Synopsys and ASMedia demonstrate the throughput available with Synopsys DesignWare USB 3.2 IP.

Learn more about Synopsys USB 3.2