Conventional sensor nodes stop functioning when a battery runs of energy. A new microchip from the National University of Singapore allows the detectors to run without interruption, even when the battery is only intermittently available.

Thanks to a 0.5mm2 on-chip solar cell, the ‘BATLESS’ microchip continues to function under dim light – without any assistance from the battery.

“This capability is particularly valuable in Internet of Things (IoT) sensor nodes since the longevity of the battery can be sacrificed, thus allowing its miniaturization,” said lead researcher and Associate Professor Massimo Alioto from the Department of Electrical and Computer Engineering at the NUS Faculty of Engineering.

With a power consumption of under 1 nW, the self-starting chip substantially reduces the size of batteries required to power sensor nodes, says Alioto, making the components 10 times smaller and cheaper to produce.

Professor Alioto spoke with Tech Briefs about how the BATLESS microchip will impact the IoT ecosystem.

Tech Briefs: What inspired the idea for BATLESS?

Prof. Massimo Alioto: Our research was inspired by the initial observation that the battery dominates the form factor of IoT sensor nodes, as well as their lifetime and the cost of next-generation single-chip nodes.

Accordingly, we started focusing on how to shrink the battery by making IoT sensor nodes indifferent towards batteries. Our ultimate goal is to eliminate batteries altogether, which will take some more years of research. So far, we feel we are on track to achieve this ambitious goal.

Tech Briefs: Where do you see this microchip being most useful?

Prof. Alioto: BATLESS can be used in several applications. As a simple example, let us consider the case of sensor nodes for energy management in smart buildings. If the battery energy is adequate, the sensor node can communicate with the cloud any time, responding to occupants’ needs in real time.

Instead, if no battery energy is available, the sensor node runs in purely-harvested mode and continues to capture and time-stamp data and events. When the battery energy will be available again, these events will be transmitted to the cloud, so that the machine learning model governing the energy management can continue to learn, make better predictions, and refine the energy decision making.

Other applications can be biomedical implants where the patient should not be regularly exposed to surgery to just replace batteries.

Associate Professor Massimo Alioto (center) and his team with the BATLESS microchip. (Image Credit: NUS)

Tech Briefs: How does the chip operate even when the battery runs out?

Prof. Alioto: When the battery runs out of energy, the IoT sensor node adapts its power consumption to fit the very small power delivered by the energy harvester.

Essentially, it is reconfigured to a special minimum-power mode. In this mode, the power consumption is even lower than the intrinsic transistor leakage, and comes at the cost of slower speed. The latter is acceptable in many IoT applications, in which power is typically much more stringent than speed.

Tech Briefs: How does it self-start?

Prof. Alioto: In BATLESS, we have developed a novel power management scheme that ensures that the system draws very limited current during the start-up, so that start-up can occur even with the very limited power provided by the energy harvester.

For example, our chip was tested to start up correctly at light intensity as low as 55Lux, which is commonly experienced at twilight.

Tech Briefs: What’s next regarding the technology and its testing?

Prof. Alioto: We are now exploring new solutions to build complete battery-indifferent systems that cover the entire signal chain, from sensors to wireless communications. This builds on our recent work on microcontrollers and power management.

We aim to demonstrate a solution that shrinks the battery to the scale of millimeters, with the long-term goal of completely eliminating the need for it. On a broader scale, mitigating the need for batteries will make our planet greener other than smarter, as it will reduce our reliance on pollutants such as lithium.

What do you think? Will BATLESS impact the IoT ecosystem? Will the microchip lead to smaller, cheaper IoT devices? Share your comments and questions below.