Perovskite solar powered RFID sensors for the IoT

Technology News |
By Nick Flaherty

The researchers created the sensors by mounting thin-film perovskite solar cells — known for their potential low cost, flexibility, and relative ease of fabrication — as energy-harvesters on inexpensive radio-frequency identification (RFID) tags. In addition to working under various lighting conditions, say the researchers, the solar-powered sensors were capable of greater data-transmission distances and multiple sensors could be integrated onto a single radio-frequency ID (RFID) tag.

“In the future, there could be billions of sensors all around us,” says Sai Nithin Kantareddy, a PhD student in the MIT Auto-ID Laboratory. “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. This work is basically building enhanced RFID tags using energy harvesters for a range of applications.”

When testing the sensors by using them to continuously monitor indoor and outdoor temperatures over several days, the researchers found that the sensors transmitted data continuously at distances five times greater than traditional RFID tags. The longer data-transmission ranges mean, among other things, say the researchers, that one reader can be used to collect data from multiple sensors simultaneously.

The sensors could potentially be left inside or outside for months or even years at a time – depending on environmental conditions such as heat and moisture – before they degrade enough to require replacement. This would be ideal for any application requiring long-term sensing, indoors and outdoors, including tracking cargo in supply chains, monitoring soil, and monitoring the energy used by equipment in buildings and homes.

Most previous attempts to create solar powered sensors have relied on small traditional silicon solar cells. While such cells can be efficient, long-lasting, and powerful under certain conditions, say the researchers, they are infeasible for ubiquitous IoT sensors.

For example, traditional solar cells are bulky and expensive to manufacture and at the same time are inflexible and unable to be made transparent – a useful feature for temperature-monitoring sensors placed on windows and car windshields. They’re also really only designed to efficiently harvest energy from powerful sunlight, say the researchers, not low indoor light.

On the other hand, Perovskite cells offer the following advantages:They can be printed using easy roll-to-roll manufacturing techniques for a few cents each 

  • They can be made thin, flexible, and transparent
  • They can be tuned to harvest energy from any kind of indoor and outdoor lighting.

The idea then, say the researchers, was combining a low-cost power source with low-cost RFID tags – battery-free stickers equipped with ultra-high-frequency antennas used to monitor billions of products worldwide. RFID tags rely on backscatter – a communication technique that transmits data by reflecting modulated wireless signals off the tag and back to a reader device. The reader pings the tag, which powers up and backscatters a unique signal containing information about the product it’s attached to.

The tags harvest some of the RF energy sent by the reader to power up an integrated chip that stores data, and uses the remaining energy to modulate the returning signal. But in a traditional RFID system that amounts to only a few microwatts of power, which limits their communication range to less than a meter.

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

The initial RFID circuit was prototyped to only monitor temperature, but, say the researchers, their aim is 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.

For more, see “PV-powered RFID: enabling lowcost self-powered IoT sensors” and “Self-Powered Sensors Enabled by Wide-Bandgap Indoor Photovoltaic Cells.”

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