An architectural innovation in chip-scale energy harvesting pioneered by the Analog Garage has the potential to make the Internet of Things practical – if not outright possible – in some cases.
The utopian vision for the Internet of Things – a future where deadly diseases are spotted in time to contain, crop infestations are quickly detected and eradicated, and faltering components driving factory equipment are flagged before they fail – hinges on insight garnered from continuous streams of measurements collected by sensors deployed, well, everywhere.
Of course, the sensors will need power to operate. In many cases, that’s easier said than done. Batteries add size, weight and cost to sensor nodes. And that doesn’t include the added maintenance burden of charging or replacing batteries. With billions of nodes deployed everywhere from factories and farms to rivers and roadways, that could become downright untenable.
Energy harvesting, which draws energy from environmental forces like sun, wind, motion – even radio waves – increasingly is being viewed the solution to this formidable challenge. And this solution has great market potential. IDTechEX is forecasting the overall energy harvesting market to reach $998 million in 2024, a tenfold jump from $94.5 million in 2016. And the wireless sensor portion of the market is forecasted to total $450 million in 2024, or 45 percent of the total, which is a key area for Analog Devices.
Analog Devices greatly amplified its energy harvesting portfolio earlier this year when it bought Linear Technology, a pioneer in the segment. A new area with great potential for powering sensors is thermoelectric energy harvesting. The Analog Garage is developing a chip-scale Thermoelectric Generator, or TEG, that can be used to generate power in spaces where temperature differentials exist.
The principle behind thermoelectric energy harvesting is known as the Seebeck effect, named for the Baltic German physicist Thomas Johann Seebeck. Seebeck discovered that when a temperature differential is maintained across a conductor, a voltage is generated. As it turns out, all materials exhibit the Seebeck effect to some degree (some better than others). The way this is quantified is the Seebeck coefficient, which can be understood by the following formula:
That is, the voltage generated is the product of the Seebeck coefficient S and the temperature difference ΔT. The best thermoelectric materials, those with the highest values of S and most often used in TEGs, are semiconductors.
The greater the temperature difference ΔT, the higher the voltage and the greater the power that can be generated. The power output Pout of a TEG is approximately proportional to the square of ΔT:
So by affixing a TEG to a window in a climate-controlled building, for example, enough power could be harvested to run a motion sensor to detect when people enter the room.
The Analog Garage is focusing its efforts on improving energy density for a given device area, and has developed some promising techniques for boosting power output significantly beyond the current state of the art. Once productized, these new devices will be able to power a wide range of sensor-to-cloud applications, like monitoring equipment and environmental conditions in smart buildings.