Photovoltaic-powered sensors promise long-term reliability

MIT develops photovoltaic sensors for IoT
MIT researchers have designed photovoltaic-powered sensors that use energy harvesting to eliminate the need for batteries and can transmit data for years before requiring replacement. (MIT)

While IoT sensors are rapidly gaining in usage, these devices face the issue of having to undergo downtime to replace batteries, which could affect long-term monitoring. MIT researchers have designed photovoltaic-powered sensors that could potentially transmit data for years before they need to be replaced.

In a pair of papers published in the journals Advanced Functional Materials and IEEE Sensors, MIT Auto-ID Laboratory and MIT Photovoltaics Research Laboratory researchers mounted thin-film perovskite cells, known for their potential low cost, flexibility, and relative ease of fabrication, as energy-harvesters on inexpensive radio-frequency identification (RFID) tags.

The researchers reported using the sensors to continuously monitor indoor and outdoor temperatures over several days. The sensors transmitted data continuously at distances five times greater than traditional RFID tags—with no batteries required. Longer data-transmission ranges mean, among other things, that one reader can be used to collect data from multiple sensors simultaneously.

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“In the future, there could be billions of sensors all around us. With that scale, you’ll need a lot of batteries that you’ll have to recharge constantly. But what if you could self-power them using the ambient light? You could deploy them and forget them for months or years at a time,” said lead researcher Nithin Kantareddy, a PhD student in the MIT Auto-ID Laboratory, in the story on MIT’s website. “This work is basically building enhanced RFID tags using energy harvesters for a range of applications.”

Depending on certain factors in their environment, such as moisture and heat, the sensors can be left inside or outside for months or, potentially, years at a time before they degrade enough to require replacement.

In recent attempts to create self-powered sensors, other researchers have used solar cells as energy sources for internet of things (IoT) devices. But those are basically scaled-down versions of traditional solar cells—not perovskite. The traditional cells can be efficient, long-lasting, and powerful under certain conditions “but are really infeasible for ubiquitous IoT sensors,” Kantareddy said.

The scientists sought to combine a low-cost power source with low-cost RFID tags, which are battery-free stickers used to monitor billions of products worldwide. The stickers are equipped with tiny, ultra-high-frequency antennas that each cost around three to five cents to make.

The researchers’ sensor comprises an RFID tag built on a plastic substrate. Directly connected to an integrated circuit on the tag is the perovskite solar cell array. As with traditional systems, a reader sweeps the room, and each tag responds. But instead of using energy from the reader, it draws harvested energy from the perovskite cell to power up its circuit and send data by backscattering RF signals.

The RFID circuit was prototyped to only monitor temperature. Next, the researchers aim to scale up and add more environmental-monitoring sensors to the mix, such as humidity, pressure, vibration, and pollution. Deployed at scale, the sensors could especially aid in long-term data-collection indoors to help build, say, algorithms that help make smart buildings more energy-efficient.

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