Passive RFID tags are everywhere. The market is expected to grow from USD 14.95 billion in 2025 to USD 39.11 billion by 2035. Yet these tags do very little. They wake up only when a reader is nearby, broadcast an ID, and go silent again. No sensing, no real geolocation, no data between two checkpoints.
Next-generation smart tags promise much more: continuous temperature, humidity or movement monitoring, active location, and communication over Bluetooth LE or other wireless networks. What has held them back is power.
That is the subject of a new white paper published by Dracula Technologies, written in collaboration with e-peas, Energous and Powercast: RF + PV: Powering Next-Generation Smart Tags with Dual Energy Harvesting.
The white paper was unveiled at The Things Conference in Amsterdam, where e-peas presented its latest work on energy harvesting for Ambient IoT.
Batteries don’t scale
Adding a battery to a tag makes it active, but it also makes it heavier, bigger and more expensive. It forces the device to save energy by transmitting less often and over shorter distances. And once you deploy thousands or millions of tags, replacing batteries becomes a logistical and environmental dead end, especially when tags sit in places no one can easily reach.
Ambient IoT offers another way. Devices harvest energy from their environment, store it in a small rechargeable element, and never need a battery replacement.
One source is good. Two are better.
Far-field RF energy, delivered by dedicated transmitter networks such as Energous PRO hubs or Powercast PowerSpot® transmitters, is a powerful source for smart tags. But RF has blind spots. A pallet of metal parts moved to the wrong place, some RF contention, a tag drifting too far from its hub, and the tag loses power. In simple setups, RF networks are often estimated to provide 85 to 90% visibility. For critical assets, the remaining 10 to 15% can be unacceptable.
Indoor photovoltaics fill that gap. Dracula Technologies’ organic PV (OPV) is optimized for low indoor light: a 1.5 cm² module delivers around 65 μW at 3 V under typical 1,000 lux LED lighting, and it can be sized to match the exact needs of each tag. PV has its own limits (shading, orientation, dark periods), but these are not the same as RF’s.
Combining the two creates continuity. When one source drops out, the other takes over.
What dual harvesting brings
The white paper details the benefits of an RF + PV architecture:
- Continuous operation and higher transmission frequency than with a single source
- Robustness through redundancy when one source is temporarily unavailable
- Near real-time monitoring, since both sources can harvest simultaneously
- Extended coverage of each RF hub, meaning fewer transmitters for the same facility
- More freedom in tag placement, with less need for detailed RF site surveys
- Near-zero maintenance and a lower total cost of ownership at enterprise scale
The role of power management
Harvesting from two independent, unpredictable sources takes dedicated power management.
This is where e-peas’ AEM13921 comes in. This dual-input PMIC manages RF and OPV on two fully independent channels, each with its own MPPT or constant-voltage regulation, plus an optional 5 V charging input.
Key features covered in the white paper:
- Cold start from as little as 1.5 μW from either source
- Operates on one source, or on stored energy alone once cold-started
- Supports a wide range of storage technologies, with built-in protection
- Programmable via GPIO or I²C, with real-time power metering, energy thresholds and temperature alerts
- 94%+ conversion efficiency with a Dracula Technologies 3-cell OPV at 1.8 V
For engineers, I²C access means full visibility into how much energy is harvested and consumed in real conditions. That is the fastest way to validate that a design will remain energy-positive over time.
From the smart factory to the smart home
The white paper looks at applications in asset tracking, cold chain, smart factories and smart buildings. It also covers the smart home, where “set and forget” is non-negotiable. Consumers won’t replace batteries or run cables to dozens of sensors. With RF + PV harvesting, a single base sensor could detect a leak under the sink, a light left on or an attic overheating, without maintenance. The same approach also opens the door to battery-free remote controls, computer mice and headphones.
RF + PV: Powering Next-Generation Smart Tags with Dual Energy Harvesting is the first edition of this work. An updated version will follow in the coming months.
Want to go further with dual-source harvesting?
