Energy harvesting chips: The next big thing for a connected world

If you can imagine a world of connected sensors embedded in walls, roads and consumer goods you probably don’t want to imagine having to change the battery on them every six months or year. Even as we build out more connected products we’re still limited by battery life. But at companies such as Qualcomm, Texas Instruments, ARM and many more, researchers are doing their best to make chips that can generate their own energy and then build out systems that can store and use that precious power.

Without delving into physics, energy is all around us, and the challenge for chip firms is figuring out how to capture enough energy and then to store it for usage later. Sources like solar or kinetic energy aren’t always available. An additional challenge is figuring out how to build sensors that can take advantage of the lower amounts of energy harvested by such processors.

There are generally four different types of energy harvesting chips that are in use:

Kinetic: Motion-based power has been around for decades. These chips might be used to charge a watch or even a sensor that is attached to a moving gear.

Thermal: A chip based on this design get its energy from a temperature differential. So it might power something you wear close to your skin if the surrounding air is much warmer or cooler.

Light: Imagine a really tiny solar panel. As in all solar panels, the challenge is to capture the most energy possible without needing a huge surface area.

Electromagnetic frequency: Companies have been trying to harvest power from radio waves for decades, but the trick is pulling enough energy and to target a wide range of frequencies.

A chart from TI showing the available power from different energy harvesting chips and what's needed to power selected devices.

A chart from TI showing the available power from different energy harvesting chips and what’s needed to power selected devices.

This technology isn’t new, but the market for wireless sensors is expanding greatly thanks to the development of the internet of things. Companies now have a larger incentive to build out more efficient harvesting chips and systems that can use them. So whether it’s an implanted medical device that might use kinetic energy in the body or a solar cell to charge a sensor embedded in the road, this is an area of growing research.

For example, on Thursday Alta Devices introduced a solar cell that it said produces up to five times more power from indoor light than other commercially available solar technologies. So for a given power requirement, an Alta Devices solar cell powering a wireless sensor can be a fifth of the size, making the technology easier to embed in more objects.

Meanwhile, at the University of Washington, researchers are trying to build a device that can capture power from radio transmissions. The researchers have found a way to use existing radio waves (from cellular, TV or existing Wi-Fi networks) to bounce messages from one device to another without requiring a power source. They call it ambient backscatter.

Kinetic sensors could also see a boost if research from the University of Florida pans out. Yuan Rao, a doctoral student, has figured out how to make a ping-pong-ball-size device that can harvest energy from bidirectional motion, instead of from motion going in only one direction. This greatly increases the amount of energy one can harvest from the device.

Improvements in energy harvesting chips are one element of building sensors or wearables that don’t need a power cord. But battery technology is also important. Sensors should have backup or rechargeable batteries in case the harvesting component fails (especially if it is an essential sensor). But those batteries could be better. Not only are researchers trying to make them smaller, but they are also trying to put them in more flexible packages, making them fit for clothing for example.

And of course, the microcontrollers and radios that might be part of any sensor package also have to consume less power. On the radio side, protocols such as ZigBee and Bluetooth Low Energy are one solution, while power management via sleep and wake cycles are another. Microcontrollers might also incorporate designs that let them go from “sleeping” to wake using a far smaller difference in voltage.

There are a lot of variations inside silicon that will lead us to longer-lasting and more powerful sensors that won’t need a power cord or constant battery changes. And rest assured, as we embrace the internet of things, researchers are exploring all of them.