Energy Harvesting for Ambient IoT and Battery-Free Devices


IoT is facilitating a smarter and more connected world—so how do we enable IoT devices to reach their full potential?

Internet of Things (IoT) sensors are tiny electric devices that feature a microprocessor to process sensor data and a radio to send the data to the cloud in real-time. In doing so, these ambient IoT sensors provide real-time monitoring and management of remote assets, resources, and environment to facilitate timely automated decision-making, improve efficiency, and reduce costs.

Billions of easy-to-deploy and low-cost IoT sensors have been implemented in factories, warehouses, retail, supply chains, healthcare, agriculture, buildings, homes, vehicles, etc. IoT market experts predict that the smart sensors industry contains 10s of billions of devices and is growing fast. A high-level summary of some of the data can be found here

To Move Forward, IoT Needs to Move On From the Battery

For such a booming industry, it’s hard to believe IoT could actually be held back by technology. But that’s exactly what’s happening. The IoT industry is being held back by batteries. 

Yes, the tiny little bundles of chemicals that provide the small (but not zero) energy needed to perform the critical functions of sensing, computation, and communication. Batteries eventually die and must be replaced. The cost of replacing batteries is typically many times that of the IoT devices. These batteries must subsequently be disposed of and recycled, exacerbating the problem of keeping spent batteries and their toxic chemicals away from landfills and eventually polluting our environment. 

So which technologies will unshackle IoT devices from battery reliance?

The Many Methods of Ambient IoT Energy Harvesting

Ambient Energy harvesting, the ability to extract energy from the environment, has been presented as a solution to the reliance of IoT devices on batteries. With “ambient IoT” technology, the battery life of the IoT sensors could be extended, and IoT sensors that have no batteries could be realized. Even though ambient energy harvesting can augment a battery and increase its applicable life or reduce its size, the ultimate goal is to build completely batteryless devices.  With this in mind, it is instructive to look at some of the leading technology options and understand what’s feasible. Technology options discussed most frequently include energy harvested through the following mechanisms:

  1. Ambient light
  2. Vibrations
  3. Temperature gradients
  4. Radio Frequency waves (cellular, WiFi, Bluetooth, etc.)

Let’s discuss their suitability for IoT applications.

Motion & Vibration Harvesting

Limits on the energy available and the cost and efficiency of converting it into electricity mean that harvesting human motion and  tiny vibrations through piezoelectricity or other methods and thermal gradients is only appropriate for a few niche use cases. For example, batteryless wireless light switches that harvest mechanical energy from switch activation, or batteryless wrist watches that harvested energy from human movement. For an in-depth technical analysis, refer to this excellent article on vibrational energy harvesters. For those interested in a similar study of thermal energy harvesting, refer to the following article

Solar & Ambient Light

Solar provided roughly 3.4% of the total electric supply in the US in 2022 and is the fastest-growing renewable energy source. We are familiar with calculators, computer keyboards, or TV remotes powered by ambient lighting. Ambient light is undoubtedly attractive in several consumer applications – see the excellent article from Jonna Stern in the Wall Street Journal. 

However, the applicability of harvesting ambient lighting for IoT applications is limited, given that the power density in ambient light is roughly three orders of magnitude (or 1000 times less) lower than solar. Therefore, to meet the energy requirements of most IoT sensors, a large exposed surface area is needed. Furthermore, IoT sensors are often deployed in environments with minimal ambient lighting or where the surface of the IoT sensors is hidden. This implies that while ambient light harvesting can augment or reduce the size of the batteries, it is not feasible to depend on it as the exclusive source of energy and eliminate the batteries.

Ambient RF Harvesting

RF energy due to cellular, WiFi, and Bluetooth is ubiquitous, and it is tempting to believe it can be harvested to power IoT sensors. After all, electronics and antennas to transmit and receive RF signals are already present. However, a back-of-the-envelope calculation (or the use of a path loss calculator) illustrates that the energy that can be harvested from RF communication signals is insufficient to power even the most basic IoT sensors. 

Even though the energy consumption of IoT devices has decreased significantly in recent years, there is simply not enough “ambient” energy to power IoT sensors except for a limited set of applications. 

AirFuel RF

The solution is to consider deploying dedicated energy sources that the IoT devices can harvest. 

RF energy transmitters and harvesters (aka receivers) are particularly attractive, given 

  1. The availability of efficient, small, and cost-effective electronics to convert RF energy into a usable form (typically, DC current)
  2. The small antenna sizes required to harvest energy from RF waves  (typically 900MHz and above)
  3. Their ability to work in diverse environments – factories, warehouses, transport vehicles, retail, homes, hospitals, and others
  4. The ability to provide sufficient energy safely for batteryless IoT sensing for the most popular sensing modalities (temperature, light, humidity, accelerometers, etc.)

Companies like Energous, Atmosic, Williot, Aeterlink, Ossia, and others are doing just that. They are building RF energy transmitters and IoT sensors that operate without batteries. The industry leaders have come together to develop an RF wireless charging industry standard. Recently, a certification program has been instituted to provide the required multi-vendor interoperability. 

AirFuel RF for Ambient IoT

IoT devices are facilitating a smarter and more connected world—so if we can use AirFuel RF wireless power to enable IoT use-cases to reach their full potential, we also unlock our own.

To get started with AirFuel RF for IoT products, learn more about AirFuel RF or become a member of AirFuel Alliance. Members get access to the world’s leading wireless charging standards and development tools so they can accelerate to market with wireless power-enabled products. Have questions? Contact us to talk with an expert.