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
Sep 25, 2018
Robots are a hot topic these days. From helping doctors in the operating room to helping survivors of a natural disaster, it'€™s clear that robots are poised to play an important role......
Sep 25, 2018
CDNLive India took place a few weeks ago and we are just trying to catch our breath! If you missed it, I'm going to be posting two cool videos before the weekend with the highlights. Here are two blogs by the veteran blogger Paul McLellan - one on Asynchronous Design and...
Sep 24, 2018
One of the biggest events in the FPGA/SoC ecosystem is the annual Xilinx Developers Forum (XDF). XDF connects software developers and system designers to the deep expertise of Xilinx engineers, partners, and industry leaders. XDF takes place in three locations this year.  Sa...
Sep 21, 2018
  FPGA luminary David Laws has just published a well-researched blog on the Computer History Museum'€™s Web site titled '€œWho invented the Microprocessor?'€ If you'€™re wildly waving your raised hand right now, going '€œOoo, Ooo, Ooo, Call on me!'€ to get ...