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New generation of sensors increase smartwatch battery life

26 April 2017

EPFL startup ActLight, introduced a new generation of sensors that consume five times less energy and cheaper to produce.

New generation of sensors developed by EPFL startup ActLight consumes five times less energy (Credit: EPFL/ActLight)

Nearly 80 percent of the battery power in smartwatches is used up by the heart-rate monitor. ActLight’s sensors can measure the wearer’s pulse with the same precision but only consume one-fifth of the energy, ultimately increasing the battery life. 

The sensors have been tested and calibrated by Maher Kayal’s laboratory and are now ready to be mass produced for use in new models of smartwatches. “The longer battery life certainly makes things easier for the user, but it also offers major savings in terms of electricity consumption,” said Kayal. 

According to EPFL, the secret behind the energy-saving sensors lies in signal processing. In order to grasp how the company’s ‘dynamic photodiode’ sensor works, we must first understand how sensors in most smartwatches currently work: Two diodes located on the back of the device – nestled against the wrist – emit light that penetrates the upper layers of the skin, and blood flow determines how much light is reflected back. A sensor placed between the diodes detects these light waves and transforms the information into electrical current, which is then translated into the pulse displayed on the watch.

Instead of converting the light into a current and then measuring the current’s amplitude, ActLight’s dynamic photodiode sensors turn the current back into light. The sensors use the pulse of light to identify the moment at which the current is triggered. The result is a small reduction in energy consumption with every heartbeat, but repeated more than 50,000 times per day it adds up to considerable energy savings.

The new sensors are also attractive in terms of cost savings: “They are less expensive to produce because they do not require as much silicon for the same level of manufacturing,” said Sergei Okhonin, the company’s CEO. Numerous other applications are also being targeted, such as gesture control for video gamers, as well as and use in solar cells and data transfer.

Video courtesy of École polytechnique fédérale de Lausanne (EPFL)

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