Energy Harvester Uses RF Waves to Power Air Pollution Sensors

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.

Beacons, wearables, and sensors, in particular, offer application areas that can benefit a wide range of industries. Previously, sensors might require a charging cable, which would limit their placement. RF energy harvesting allows sensors to be located in a variety of environments, including outdoors; with no battery change needed, devices can be hermetically sealed.

In addition, industries can deploy smart sensors that adapt to the scenario in which they are placed. The sensors may operate only when required to do so, to avoid unnecessary energy consumption; they can be powered constantly without the need for a charge cable. A temperature sensor, for example, would no longer need to report data at all times or on a specified schedule. Instead, the device could report data when it exceeds a minimum or maximum temperature threshold. The flexibility saves energy, as the sensor is not reporting at all times, and uses energy from RF waves that would have previously been unused.

Organizations that deploy sensors which operate only when required can enjoy a new form of eco-power, receiving the required data from a device and allowing it to operate only at specified points and operate perpetually. Engineers could also build an array of harvesters by connecting them together, in buildings for example, thereby increasing the total amount of energy harvested. The size can be scaled from one credit-card sized harvester to an entire array of these devices, in a similar way to solar panels.

The Freevolt™ technology and CleanSpace™ Tag. (Image Credit: Drayson Technologies)

As the number of connected devices grows, the opportunities for RF energy harvesting expand. Sensors can be integrated into the fabric of a building, providing temperature, stress, or movement data to architects, as well as monitoring airflow and temperature to validate building design criteria.

Within the wearable sensor sector, rapid developments are driving wider adoption. Just five years ago, wearable sensors were tracking motion and relaying that data back to users. Now, with tools such as the CleanSpace Tag, users track the quality of the air they are breathing.

Looking Ahead

Healthcare is another area that benefits from RF energy harvesting. Experimental sensors can be placed on the skin to enable round-the-clock monitoring of blood flow, wherever a patient goes. Such devices are currently in need of versions that host a self-contained power source. With RF energy harvesting, the devices could be powered without the need to remove them for charging or replacing batteries.

There are also initiatives aimed at helping athletes that could benefit from energy harvesting technology. The Reebok MC10 CHECKLIGHT, a head-impact indicator, for example, measures the force and number of hits an athlete sustains via its wearable sensor. Without the need to change batteries, the device could operate for longer periods, allowing athletes to monitor impacts over time without removing the sensor.

As more developers and companies look to design products with RF energy harvesting technologies that are built in, the IoT could soon operate via perpetual power, reducing time and costs wasted on battery changes and cable charging.

This article was written by Lord Paul Drayson, CEO, Drayson Technologies (London, UK). For more information, visit www.draysontechnologies.com .