Entries Tagged ‘Small Device’

Extreme Processing: RF Energy Harvesting

Friday, May 28th, 2010 by Robert Cravotta

[Editor's Note: This was originally posted on the Embedded Master]

In this post I will explore RF energy harvesting – harvesting energy from radio waves. I spoke with Harry Ostaffe, Director of Marketing and Business Development at PowerCast to learn more about RF energy harvesting. Ostaffe informed me of another energy harvesting resource site. The Energy Harvesting Network focuses on disseminating the current and future capabilities of energy harvesting technologies to users in both industry and academia. The site currently lists contact information for 25 academic and 37 industrial members that are involved with energy harvesting.

The effectiveness of energy harvesting depends on the amount and predictable availability of an energy source; whether from radio waves, thermal differentials, solar or light sources, or even vibration sources. There are three categories for ambient energy availability: intentional, anticipated, and unknown. Building a device that powers itself in an environment with unknown and random sources of ambient energy is beyond the scope of this post. If you have experience with these types of designs, please contact me.


Building a device that relies on anticipated energy sources takes advantage of infrastructure that is already in place in the environment.  For RF systems, this could include scavenging ambient transmissions from cell phones, mobile devices, as well as television and radio broadcasts located in the area. A challenge for systems that rely on anticipated energy sources is that available energy can fluctuate and there is no guarantee that there will be enough energy to scavenge from the environment.

Intentional energy harvesting designs rely on an active component in the system, such as an RF transmitter, that can explicitly provide the desired type of energy into the environment when the device needs it. PowerCast’s approach to support an intentional energy source is to offer a 4W 915 MHz RF transmitter. The intentional energy approach is also appropriate for other types of energy, such as placing an energy harvesting on a piece of industrial equipment that vibrates when it is operating. Another example could involve placing an energy harvesting near a light source that will emit light when the device will be operating and is no longer asleep. Using an intentional energy source allows designers to engineer a consistent energy solution.

An “obvious” frequency sweet spot for RF energy harvesters should be 2.4GHz because so many consumer devices work at that frequency. Ostaffe says that while they have made components that work in the 2.4GHz range, they are currently not publicly available. There is the potential for consumer frustration with a 2.4GHz harvester that currently makes offering harvesters in this frequency range a problematic idea. The first logical spot someone with one of these devices is likely to put them is near their 2.4GHz wireless access point. The problem is that these routers typically transmit in the 100mW range (versus 4W for the 915 MHz transmitter) and that does not provide enough energy for most harvester applications – especially because the energy drops off at 1/r2 from the source. The consumer is likely to attribute the poor performance of the device to a flaw in the device rather than an insufficient power source issue.

If you would like to be an information source for this series or provide a guest post, please contact me at Embedded Insights

Extreme Processing: New Thresholds of Small

Friday, May 21st, 2010 by Robert Cravotta

[Editor's Note: This was originally posted on the Embedded Master]

While the recent stories about the DNA-based Robot and the Synthetic Organism are not techniques that are available to current embedded developers, I think they point out what type of scale future embedded designs may encompass. In short, the stories relate to building machines that designers can program to perform specific tasks at the molecular or cellular level. Before I relate this to this series, let me offer a quick summary about these two announcements.

The synthetic organism is a synthetic cell that the creators at J. Craig Venter Institute claim is completely controlled by man-made genetic instructions. The new bacterium is solely a demonstration project that tests a technique that may be applied to other bacteria to accomplish specific functions, such as developing microbes that help make gasoline. The bacterium’s genetic code began as a digital computer file, with more than one million base pairs of DNA, which was sent to Blue Heron Bio, a DNA sequencing company, where the file was transformed into hundreds of small pieces of chemical DNA. Yeast and other bacteria were used to assemble the DNA strips into the complete genome, which was transplanted into an emptied cell. The tam claims that the cell can reproduce itself.


There are two types of DNA-based robots that were announced recently. Each is a DNA walker, also referred to as a molecular spider that move along a flat surface made out of folded DNA, known as DNA origami, that the walker binds and unbinds with to move around. One of the walkers is able to “follow” a path, and there is a video of the route the walker took to get from one point to another. The other type of walker is controlled by single strands of DNA to collect nano-particles.

These two announcements relate to this series both from a size scale perspective and to our current chapter about energy harvesting. The synthetic organism article does not explicitly discuss how the bacterium obtains energy from the environment, but the molecular robot article hints at how the robots harvest energy from the environment.

“The spider is fueled by the chemical interactions its single-stranded DNA “legs” have with the origami surface. In order to take a “step,” the legs first cleave a DNA strand on the surface, weakening its interaction with that part of the origami surface. This encourages the spider to move forward, pulled towards the intact surface, where its interactions are stronger. When the spider binds to a part of the surface that it is unable to cleave, it stops.”

Based on this description, the “programming” is built into the environment and the actual execution of the program is subject to random variability of the molecular material positioning in the surface. Additionally, the energy to enable the robot to move is also embedded in the surface material. This setup is analogous to designing a set of tubes and ruts for water to follow rather than actually programming the robot to make decisions. When our hypothetical water reaches a gravity minimum, it will stop, in a similar fashion to the robot. Interestingly though, in the video, the robot does not actually stop at the end point, it jumps out of the target circle just before the video ends.

I’m not trying to be too critical here; this is exciting stuff. I will try to get more information about the energy and programming models for these cells and robots. If you would like to participate in a guest post, please contact me at Embedded Insights.