Energy Harvesting Roundup: 4 New Designs Tap Into Ambient Energy
With more low-power IoT devices flooding the market, researchers and developers are getting creative with power solutions—with some turning to unique energy harvesting techniques.
Industry and academic researchers have developed four new energy-harvesting solutions for low-power devices. For applications where batteries or wall-connected power isn’t feasible (or would greatly increase cost and complexity), energy harvesting presents an alternative for continual energy conversion and storage.
Researchers recently developed a device that harvests energy from vibration (more below). Image used courtesy of Tohoku University
Energy harvesting generally requires an application-specific solution due to the presence or absence of ambient energy sources in different environments. As such, this article delves into four new techniques that can be used to harvest energy in a variety of situations to give designers an update on the state of the technology and provide a glimpse into how the technologies could enable new applications and architectures.
Vibration Energy Harvesting
First is a new development from researchers at Tohoku University who have successfully fabricated a vibrational energy harvesting solution using piezoelectric materials. Piezoelectric materials have the unique ability to convert mechanical stress to electric energy, allowing the harvester to use vibrations from the environment to power sensors.
The piezoelectric vibration energy harvester can be used to store energy over time for infrequent transmissions, allowing connected sensors to be entirely battery-less. Image used courtesy of Tohoku University
The durability and low weight of the new piezoelectric vibration energy harvester (PVEH) make it well-suited for IoT applications, with simulations and tests showing sustained performance after 100,000 bendings. Preliminary results showed that after collecting energy with an output capacitor, the PVEH could power over 15 LEDs, showcasing its ability to power sensors using ambient energy.
Battery-less Animal Sensors
In a similar vein, another group of researchers has developed a mechanical energy harvester targeting wildlife tracking. Instead of using vibrational energy, however, the wildlife energy harvester, named Kinefox, uses microgenerators in conjunction with control and sensing electronics to monitor wildlife without batteries or solar panels.
The Kinefox uses a microgenerator in tandem with supporting electronics to periodically transmit the animal’s location using only the energy produced by the animal. Image used courtesy of PLoS ONE
The Kinefox was tested on five animals (three domestic dogs, one wisent, and one Exmoor pony) to gain a sense of its abilities. Overall, the energy generated depends heavily on the specific animal and its activity. However, even with the minimum energy observed, the animals powered two GPS transmissions over three days using only the Kinefox, with one dog producing over 10 J of energy in a single day. So, while it may not be the best solution for all sensors, microgenerators seem to offer a new tool for designers and scientists to leverage for long-term studies with infrequent data transmissions.
BLE Energy Harvesting
In the IoT space, e-peas, in partnership with InPlay, has developed an energy-harvesting BLE sensor beacon platform to unite energy harvesting and sensing/communications for the future of the IoT. The solution leverages two primary components: an e-peas power management IC compatible with a photovoltaic (PV) cell and energy storage element and an InPlay BLE beacon.
The AEM10330 power management IC requires only four external components, creating a small solution for PV integration for energy harvesting sensors. Image used courtesy of e-peas
The solution is aiming to provide designers with a battery-less sensor to simplify dense IoT deployments while also maintaining functionality. As with many IoT sensors, size is a critical aspect, which is aided by the small footprint of the AEM10330 power management IC. In addition, the ultra-low power of the IN100 NanoBeacon ensures that BLE communications won’t create too large of a power requirement for the PV cell.
Indoor Solar Solution
Dracula Technologies has recently reported a 25% performance improvement of its PV cells under indoor light conditions compared to traditional PV cells. Since indoor light is typically much less intense than outdoor, indoor solar energy harvesting for IoT can be quite challenging. With Dracula Technologies’ LAYER technology, however, new efficiency may be found for indoor solar.
The LAYER module allows engineers to make better use of indoor lighting to power electronics without requiring dedicated research and development costs. Image used courtesy of Dracula Technologies
Dracula Technologies has reported that its LAYER technology works best in 5–1,000 lux light—as dim as an emergency exit light. In its latest results, a LAYER module could provide 750 µW of power under 1000 lux, providing a new energy source for low-power IoT applications. In addition, with potential future regulation surrounding the use of non-rechargeable batteries, a new indoor energy source may help keep IoT sensors small.
Tapping into Ambient Energy
While there may not be one best energy source for every application, the abundance of new sources is indicative of a trend toward ambient energy harvesting for new low-power applications. And as sensors become smaller and lower power, next-generation devices may no longer require dedicated power supplies.
As the technology evolves alongside sensors and communications, it will be interesting to see how energy harvesting is balanced with communications efficiency. With wireless energy harvesting, Wi-Fi beamforming reduces the amount of ambient RF energy by only sending energy to the needed device. As such, RF energy harvesters may have to employ dedicated RF wireless chargers. Regardless, the tools seen here may benefit designers, who now have many more options when exploring how to power the next generation of connected sensors.