Is energy harvesting viable for powering medical wearables?
June 16, 2015
The trend towards medical wearables could be the killer application for which the energy harvesting industry has been waiting, given the potential the body has for generating power and the need for medical wearables to operate unattended for long periods. But some in the industry believe the potential of the human body is overestimated and the costs involved outweigh the benefits.
“Among the key challenges of wearables are energy efficiency and battery management,” Sylvain Gardet, business development manager at Freescale, told M2M Zone. “There will be no mains supply, so they have a battery. It has to be a small battery and the products have to deal with energy efficiency requirements. But energy harvesting is possible. The body produces energy sources such as temperature, motion and exposure to light. We could have solar cells in our clothes. If you are running or walking, you can generate energy.”
Most of these products, he said, had to be always on and energy harvesting was interesting additional source of power.
“But the main source today is still the battery,” he said. “So we need to look at how to manage the battery in the best way. Products will need to go into deep sleep mode and still monitor someone’s heart rate and then wake up when it is needed for, say, communications.”
Jim Davis, senior product marketing manager at California-based Cypress Semiconductor, added: “The entire market is going for extreme low power. As they add functions, they need charging more frequently, so that power consumption has to come down.”
His colleague at Cypress, Kendall Castor-Perry, added: “Products such as the Apple Watch have a powerful processor and need charging every day, then there are data loggers that do nothing more than log data and squirt it up through a radio link. They can last for a week or more.”
He said in both cases energy harvesting could help. “People are always moving or going through changes of temperature. We need to look at that. Energy harvesting for a conventional wrist watch has been around for decades; you don’t need much energy to do that. To get a health monitor down to that level of power consumption is a real challenge.”
But David Andeen, director of reference designs at California-based Maxim Integrated, thinks the technology has reached a hurdle.
“Energy harvesting is interesting,” he said. “There is a lot of energy in the human body with temperature gradients and motion. This was a hot topic six years ago and some companies came out with energy harvesting front ends.”
Interest though, he said, had faded because from a technology point of view it had not delivered as much energy as people hoped.
“You need a bigger temperature gradient,” he said. “On motion or light, you still need a good sized front-end device to harvest that energy. We have not got it to the point where it is convenient for people to use. But I do hope people are working on this. It is an invaluable endeavour.”