Energy Harvesting for Battery-Free Bluetooth Devices

This page is an entry in our extensive guide to Bluetooth Beacons.

Energy Harvesting for Battery-Free Bluetooth Devices

The Internet of Things (IoT) relies on the ability of network-connected devices to send and receive information for various purposes. In some cases, two-way communication is implemented and end-point devices can perform activities such as controlling equipment on an automated assembly line. In other instances, the IoT device is used to provide real-time information regarding the location, status, or condition of an item in a supply chain.

A common aspect of all IoT devices is that they require an energy source to provide the power necessary for communication. In certain usage scenarios such as monitoring and controlling an assembly line, power sources are freely available for devices by connecting to the facility’s electric grid. When used to track supply chain components or the movement of products such as vaccines or vegetables, access to a power grid is not available. Devices need to use other methods to source electricity. One of those methods is energy harvesting.

What is Energy Harvesting?

Energy harvesting is a process that obtains energy from external sources. Energy harvesting is known by several other names including power harvesting and energy scavenging. Energy harvesting devices typically produce a small amount of energy. The amount of energy generated is enough to meet the minimal power demands of a low-energy electronic device.

Many different types of energy harvesting devices exist and are used in a wide variety of applications. In energy harvesting, power is captured and stored for use in stand-alone devices such as those deployed in wireless networks of sensors used to monitor and track supply chain components.

Examples of energy harvesting technologies include those that generate electricity from solar energy, thermal energy, light energy, and kinetic energy. Piezoelectric energy harvesters can convert motion from the human body into usable electrical power. Radio frequency or RF energy harvesting is a promising field that takes advantage of the radio waves that are generated by mobile phones and other electronic devices.

Energy storage is often done using batteries, which are not always viable for the long-term demands of IoT tracking and monitoring devices. Storing energy in a capacitor makes more sense for powering IoT tracking devices. Capacitors have unlimited charge-discharge cycles which enable them to operate virtually forever without requiring maintenance. These are perfect characteristics for distributed IoT applications like supply chain monitoring and verifying product information.

Energy harvesting systems based on radio frequency energy take advantage of the proliferation of radio transmitters in the world. The number of mobile devices in the world is approaching 16 billion in 2022. These devices offer a tremendous amount of untapped energy available for use. All that’s needed is a method to capture this ambient energy and use it productively.

Wireless energy harvesting (WEH) is becoming a widely used technique for harvesting energy. It’s a method that is easy to deploy with a minimal number of components. The foundation of a WEH is an antenna that picks up RF waves and converts them into stable DC current. This energy can be used to directly power a sensor or can be stored in a capacitor for later use. When energy harvesting devices are sufficiently close to a transmitter, RF energy can power real-time locating systems (RTLS) to track items in the global supply chain.

How IoT Devices Benefit From Energy Harvesting

IoT devices used in supply chain tracking and monitoring need the capacity to handle challenging conditions. IoT devices that rely on battery power cannot always meet these challenges and may prove to be a poor choice when selecting an RTLS solution for the following reasons:

• IoT devices with a finite battery life may run out of power before their intended functionality is completed. Items can sit on shelves for years and still need to be tracked, a challenging task when using expendable batteries.

• Rechargeable batteries will wear down over time and not hold the same amount of energy as capacitors. Eventually, the batteries will fail and need to be replaced.

• Replacing batteries is not a good solution for a tracking solution. It is error prone and expensive to visit and replace batteries on all the devices to maintain the operation of an RTLS. Sending humans to replace batteries defeats the purpose of having an autonomous tracking and monitoring solution.

An embedded energy harvesting system eliminates the potential problems of using batteries. If enough energy can be harvested to power the device, it can operate as a standalone tracking solution that will never run out of power.

Choosing the right type of energy harvesting system is an important consideration when developing an autonomous IoT tracking device. While solar power is plentiful and free, it cannot be used in situations where the devices will not have access to light. Similarly, thermal energy may not be consistently available for the duration of the tracking operation.

The prevalence of wireless technologies that emanate radio frequency waves makes WEH a logical choice for developing robust and versatile IoT devices. RF energy is all around us in most situations and tapping into it offers a virtually limitless source of electrical energy. If this energy is used sparingly when needed, devices using this power source can be used for long-term monitoring and tracking.

Wiliot’s Battery-Free Bluetooth IoT Pixels

Wiliot’s battery-free Bluetooth IoT Pixels are an excellent example of what can be done with the wireless energy harvested from RF waves. The Wiliot battery-free IoT Pixels are postage stamp-sized compute devices that harvest radio waves to power themselves. They are built using an ARM Cortex CPU and are compliant with the latest Bluetooth specifications.

Each Pixel contains an antenna used for power harvesting and data transmission. IoT Pixels are cost-efficient, maintenance-free, and small enough to use on a wide range of products from apparel to vaccine vials.

Wiliot’s battery-free IoT Pixels harvest radio waves from nearby devices with no practical lifetime power limits. They measure 2.8 x 4.4 cm and are 0.2 mm thick. The Pixels are distributed as stickers on reels for easy application, or they can be embedded within the fabric of products and packaging. They provide security with 128-bit AES encryption and authenticity protection. The Pixels work in conjunction withWiliot’s cloud platform to provide manufacturers, retailers and transportation companies with the real-time information they need to track and monitor their products.