Battery-Free IoT: Sustainable Connectivity with Ambient IoT

IoT connectivity has made great strides in recent years, with billions of devices now online and tens of billions more to come. But the availability of reliable, resilient connectivity shifts the bottleneck yet again, this time to power and the battery life of massively deployed IoT devices. 

With current technologies, IoT devices can expect battery life of up to ten years in the field, and many of the early waves of IoT deployments will be passing that milestone soon. What if that lifespan could be extended indefinitely?

The battery life of a decade also creates limitations in the scope of deployments, because the more devices deployed, the more replacements needed at the end of that timeframe. What if this timeframe was no longer a concern?

Battery-free IoT devices are emerging as a credible technology for long-term sensor deployment, using energy harvesting techniques to absorb power from ambient sources like solar, radio waves, or even kinetic energy from motion.

What is battery-free IoT?

Whereas IoT devices typically contain a battery to power the onboard sensor and radio, battery-free IoT devices use energy harvesting techniques to draw power from ambient sources like radio waves, solar energy, thermal energy, motion, or mechanical vibrations.

This creates the possibility for low-maintenance devices that could remain in situ for multiple decades. Use cases for now are limited to low energy applications, typically with small data throughput, such as sensors for supply chain and logistics, smart building and lighting, and industrial.

What is the Ambient Internet of Things?

A concept originally coined by 3GPP and adopted by the IEEE and Bluetooth SIG, Ambient IoT refers to an ecosystem of a very large number of devices - heading into the trillions - interconnected as a wireless sensor network using low-cost self-powered nodes.

In many ways, Ambient IoT takes the building blocks created by technologically hamstrung real-world deployments and enables something closer and more authentic to what was ultimately intended by the concept of IoT. Described by Benson Chan, who serves as chair of the US Department of Commerce IoT Advisory Board, as “the original vision for the IoT, which was things interacting with other things".

On a massive scale, Ambient IoT uses highly flexible, inexpensive, low-energy sensors, combined with pervasive connectivity and AI to enable real-time triggers without human intervention.

Whether referred to as battery-free IoT, Ambient IoT, or something else, the concept has far-reaching implications for monitoring food or medicine, supply chains, agriculture, improving carbon accounting, protecting against theft and fraud, and even transportation and smart city initiatives.

How battery-free IoT works

There are a number of techniques that can be used by IoT devices to harvest energy from their surroundings in lieu of a battery.

Light: Harvesting energy from ambient light, both outdoor solar energy and even indoor lighting using photovoltaics.

Kinetic: Converting motion from machinery, vibrations, or any kind of movement into energy.

Thermal: Harnessing heat and temperature differences from the environment.

Radio: Capturing energy from ambient radio waves, such as WiFi, RF, or cellular signals.

Battery-free IoT devices typically make use of a technique known as energy buffering, leveraging small capacitors to store the harvested energy, and operate intermittently. Such devices will be ‘on’ when they have harvested enough energy to perform an action, and then go into a low-power sleep mode when energy is low.

Energy harvesting technologies

Photovoltaic energy harvesting

We’re all familiar with solar panels and cells for harvesting energy from the sun, but indoor photovoltaics represent one of the most promising energy harvesting technologies for IoT applications, capable of generating energy from LED and even fluorescent lighting.

Recent breakthroughs have seen sensitive solar cells reaching 38% power conversion efficiency under typical indoor lighting conditions, making them suitable for powering ultra-low power sensors.​

Radio Frequency (RF) energy harvesting

RF energy harvesting captures ambient electromagnetic waves from cellular, WiFi, Bluetooth, and other wireless transmissions to power devices. This approach is particularly attractive because RF energy already permeates our environment.​

Ambient backscatter technology takes this concept further by enabling devices to communicate using existing RF signals as both power source and communication medium. Trials have demonstrated communication over several feet between devices, with data rates of 1Kbps.​

Piezoelectric energy harvesting

Piezoelectric or kinetic energy harvesting converts mechanical vibrations and motion into electrical energy. These systems are particularly effective in industrial environments where machinery vibrations provide a consistent energy source.

Thermoelectric energy harvesting

Thermoelectric generators (TEGs) convert temperature gradients into electrical energy, making them ideal for applications such as industry and manufacturing, where heat sources are abundant. These systems can generate milliwatts to microwatts of power from temperature differences, which aligns perfectly with the power requirements of IoT sensors.​

Low-power sensors and communication protocols

The main drawback for wireless communication in IoT is that radio signals consume a lot of power. This is why much of the research in the developing area of battery-free IoT is focused on backscatter that reflects ambient radio signals, such as WiFi, from the environment.

Research has shown that backscatter can potentially enable reliable communication over hundreds of meters and even deliver continuous video streaming.

The backscatter approach is applicable to several communication technologies, including WiFi and Bluetooth, as well as numerous novel technologies based on LoRa or LoRaWAN, which operates in unlicensed ISM bands of spectrum, and uses spread spectrum modulation to transmit small data packets over distances of several kilometers at very low power.

For monostatic operation, a reader node serving a particular Ambient IoT device will provide the carrier wave to the AIoT device for signal transmission. For bistatic operation, the carrier wave source for Ambient IoT signal transmission is a different type of node that serves multiple Ambient IoT devices.

Because new access control mechanisms are required for harmonious coexistence of wireless powered communication and backscatter communications, several novel schemes are emerging in battery-free IoT.

• MQTT (MQ Telemetry Transport): A lightweight protocol designed for low-power, low-bandwidth applications.

• Constrained Application Protocol (CoAP): A protocol designed for constrained devices and networks, making it a good fit for low-power IoT scenarios.

• Near Field Communication (NFC): Can be implemented in a battery-free way, powered by the energy from nearby reader devices.

Managing a large, high-density estate of such devices sometimes requires specific software for the reader units and management of Ambient IoT devices such as tags, but the upside is a longer lifespan for devices and reduced overhead from the pain of battery replacement.

Because battery-free and Ambient IoT devices do not have the power or capability to connect directly to the internet over cellular, IoT routers can provide additional benefits in terms of estate management and security and can bring large numbers of devices online by acting as an intermediary to backhaul data.

An IoT router directs data packets to and from IoT devices, and often sports features including additional security features and device management capabilities.

Real-world applications of battery-free IoT

Supply chain and asset tracking

Battery-free tags embedded into raw materials, products, pallets, and containers can provide detailed item-level visibility, chain of custody audit logs, and history throughout logistics networks.​

Retail

Battery-free IoT sensors deployed in retail stores can tackle inventory tracking, freshness monitoring, and shrinkage reduction throughout the entire supply chain. They can also be used for anti-theft and counterfeiting purposes.

Smart buildings

Battery-less switches, monitors, and sensors can enhance automation and reduce maintenance in smart buildings.

Agriculture

Agritech sensors can be deployed to monitor crop conditions in greenhouses and barns, or even on livestock, and still be effective in remote areas.​

Healthcare and wellbeing

Battery-free monitoring sensors can be deployed for patient health and medication storage conditions, benefitting from long-lasting, maintenance-free designs.​

Smart cities

Sensors can be deployed in high-density fogs and meshes around cities, campuses, and municipalities for predictive maintenance, traffic management, and environmental monitoring—leveraging autonomous real-time intelligence.​

Industrial IoT

Smart manufacturing and Industrial IoT provide plenty of opportunities for ambient, energy-harvesting sensors to be deployed. Battery-free sensors could even take the energy they need to trigger an alarm from unusual vibrations in machinery, as part of a predictive maintenance strategy to collect data on equipment status.

Environmental monitoring

IoT sensors are able to feed accurate and real-time data on the environment back into complex analytical models to help organizations understand how they affect the environment and take actions to improve quality of life.

Environmental impact of battery-free IoT devices

Environmentally friendly battery-free IoT devices immediately have a positive impact by significantly reducing the pollution from the millions of discarded batteries used in traditional IoT devices, many of which contain harmful metals.

The higher density of IoT device networks enabled by Ambient IoT also introduces secondary benefits by improving monitoring and measurement capabilities. In terms of measurement and accountability towards targets, IoT enables the continuous collection of real-time data from sensors at sources, including buildings, transportation systems, factories, farms, businesses and utilities.

Challenges in battery-free IoT

The main challenges for battery-free IoT adoption are obvious, in that limited and unpredictable energy availability requires efficient energy harvesting from sources like ambient light or radio waves. But as we see above, significant headway is already being made.

The same is true of challenges around energy storage constraints, even though capacitors have less capacity than conventional batteries, with IoT designs lending themselves well to low-power hardware and software.

The more pressing challenges now are around scalability and standardization, with interoperability issues from novel approaches needing to be overcome to allow for widespread adoption.

Impact and future of battery-free IoT

Battery-free and Ambient IoT has the potential to reshape IoT adoption by making it more sustainable through a significant reduction in battery waste and device replacement.

It could also drive greater density of deployments, potentially taking the number of IoT devices into the trillions, by making devices cheaper and more accessible—embedding IoT into everyday objects at massive scale.

An additional upside of mass deployment of IoT is richer data, driving more efficiencies, and enabling new services and insights across sectors.​