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Scientists in Singapore have developed a microchip that can continue to function even when its battery has run out.

Currently, batteries in Internet of Things (IoT) devices are much larger and up to three times more expensive than the single chip they power. Their size is determined by the sensor node lifetime, which directly affects how often they need to be changed. This has an important bearing on maintenance cost and impact on the environment when batteries are disposed. To extend their overall lifetime, batteries are usually recharged slowly by harvesting some limited power from the environment, such as using a solar cell.

However, existing IoT devices cannot operate without a battery, and small batteries are fully discharged more frequently. Hence, battery miniaturization often results in highly discontinuous operation of IoT devices, as they stop functioning every time the battery runs out of energy.

To address this technology gap, a team of engineers from the National University of Singapore (NUS) has developed an innovative microchip, named BATLESS, that can continue to operate even when the battery runs out of energy. BATLESS is designed with a novel power management technique that allows it to self-start and continue to function under dim light without any battery assistance, using a very small on-chip solar cell.

Battery indifference is the ability of IoT devices to continue operations, even when the battery is exhausted. It is achieved by operating in two different modes: minimum energy and minimum power. When the battery energy is available, the chip runs in minimum energy mode to maximize the battery lifetime.

However, when the battery is exhausted, the chip switches to the minimum-power mode and operates with a tiny power consumption of about half a nanowatt—this is about a billion times smaller than the power consumption of a smartphone during a phone call. Power can be provided by a very small on-chip solar cell that is about half a square millimeter in area, or other forms of energy available from the environment, such as vibration or heat.

The chip’s ability to switch between minimum energy and minimum power mode translates into aggressive miniaturization of batteries from centimeters down to a few millimeters. The BATLESS microchip enables the uncommon capability to uninterruptedly sense, process, capture and timestamp events of interest, and for such valuable data to be wirelessly transmitted to the cloud when the battery becomes available again.

Despite being in minimum-power mode when battery is not available, the reduced speed of the microchip is still adequate for numerous IoT applications involved in the sensing of parameters that vary slowly in time, including temperature, humidity, light and pressure. Among many other applications, BATLESS is well suited for smart buildings, environmental monitoring, energy management and adaptation of living spaces to occupants’ needs.

“BATLESS is the first example of a new class of chips that are indifferent to battery charge availability. In minimum-power mode, it uses 1,000 to 100,000 times less power, compared to the best existing microcontrollers designed for fixed minimum-energy operation,” said Associate Professor Massimo Alioto of NUS, who led the team.

“At the same time, our 16-bit microcontroller can also operate 100,000 times faster than others that have been recently designed for fixed minimum-power operation. In short, the BATLESS microchip covers a very wide range of possible energy, power and speed trade-offs, as allowed by the flexibility offered through the two different modes,” he added.

This article was originally published on www.asianscientist.com can be viewed in full

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