As more connected devices enter the market and see wider adoption by an ever increasing number of industries, the Internet of Things (IoT) is rapidly expanding.

Overview of the power densities from various energy sources and average power consumption of electronic devices and systems. (Image Credit: Drayson Technologies)
Smart sensors within manufacturing, production, and energy environments are fuelling this growth, with 25 billion connected “things” expected to be in use by 2020. The IoT is also enjoying significant growth within the consumer space, with sensors for temperature, noise, or air quality helping to construct fully connected “smart homes.” Such connectivity helps to build vast networks that provide rich data for industry verticals and consumers alike. Yet as more devices are manufactured, there is an incremental increase in energy consumption as these billions of devices operate. So how exactly are they being charged?

Currently, the IoT is mainly powered by primary (non-rechargeable) and secondary (rechargeable) batteries, as well as connected devices that are fueled by a wall charger. Furthermore, the energy budget for sensors varies depending on specific device protocols. The IoT market as a whole incorporates a huge number of different devices, all operating in their own specific way and with different energy requirements. The Internet of Things, however, also incorporates low-energy devices in the wearable, beacon, and sensor spaces that do not require substantial amounts of energy to operate. It is for these low-energy IoT devices, in particular, that developments in energy harvesting present a new option in how the devices are charged and operate.

RF’s New Role

Photovoltaic, thermoelectric, and piezoelectric energy harvesting systems have previously been developed as technologies that can power low-energy IoT devices. The tools have their own inherent limitations, such as moving parts, fragility, and most importantly the constant presence of the energy source. Solar energy harvesting, for example, is only operational when there is light.

Electromagnetic energy, specifically radio frequency (RF) waves, however, presents an increasingly attractive option for energy harvesting. RF waves, the foundation upon which modern wireless communications operate, are being generated all around us, at different levels, constantly. There is already an abundance of RF networks in use to broadcast data to relevant receivers: televisions, smartphones, laptops, tablets, and wearables (fitness bands and smart clothing), for example.

Previous attempts to use RF energy to power devices, while successful, have generally required the use of dedicated transmitters. In the 1970s, NASA looked at using large transmitters to transmit power over a specific distance with its space solar power (SSP) research. Harvesting energy from ambient sources, meanwhile, has not been possible.

Now being commercially deployed, the Freevolt™ technology, developed by Drayson Technologies, uses an antenna and associated circuitry (a rectifier and Power Management Module) to harvest ambient radio frequency energy from the carrier waveform of wireless networks, including 2G, 3G, 4G, and Wi-Fi, as well as digital TV broadcast transmissions; RF signals are converted into direct current power.

Freevolt™ applications include motion cameras, smoke alarms, wearables, and beacons. (Image Credit: Drayson Technologies)
The harvester captures the small packets of energy that RF signals are transmitted upon. The antenna receives the RF signal and feeds it to a rectifying circuit; depending on the usage requirements, a Freevolt harvester may be multiband. A multiband capability enables devices to harvest energy from multiple RF sources and at different frequencies. The rectenna harvests energy with a wide angle of absorption, as radio waves naturally arrive at different angles as they reflect off surrounding surfaces. The waves then feed into the Power Management Module, which boosts the DC voltage so that the overall harvested energy becomes usable.

The Power Management Module integrates tracking capabilities, focusing on the high level of energy across a particular spectrum as it constantly changes. The power can then trickle charge energy storage devices, such as batteries or supercapacitors, and operate low-energy devices. Freevolt does not require a dedicated transmitter or modifications to existing RF energy sources, such as Wi-Fi routers.

Commercial Applications

Currently, the first commercial application of the RF technology is the CleanSpace™ Tag, a personal, portable air pollution sensor that uses Freevolt. The CleanSpace Tag constantly measures levels of carbon monoxide in the atmosphere. The Tag has on-board processing power and memory that stores the data on the device and then sends the information to a phone via Bluetooth. By implementing RF energy harvesting technology, the Tag does not have to be charged or have its battery changed.