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Consider a classic predictive maintenance IoT scenario: You put smart sensors on the wheel bearing casings of all the wheels on a railway car to check for the vibration that presages breakdown in time to prevent disaster. Another: You tag every asset in your hospital with an RFID chip that not only locates the object on a screen display but stores its entire maintenance record.
What might make you think twice about deploying these IoT applications? Powering them. Batteries might make these solutions impractical, difficult or expensive, because these sensors and tags may be placed in remote locations or number in the millions or require surgery to reach.
This is where energy-harvesting technologies, or better, energy scavenging technologies, come into play. This is the capture, storage and reuse of light, vibration or motion, electromagnetic radiation or other energy that otherwise dissipates into the atmosphere. The technology goes back as far as self-winding, battery-free watches. It's gaining momentum now because energy-harvesting technologies are getting more efficient at scavenging miliwatts, and, on the other side, sensors are consuming less energy.
Radio-free wattage energy harvesting for IoT
Bob Hamlin is CTO of Tego Inc., based in Waltham, Mass., which harvests ambient RF energy.
"All FM stations transmit power from antennae at 50 to 100 kilowatts," he noted. "By the time it gets to your FM radio, it's only a few milliwatts. These days those few milliwatts are enough to do all kinds of interesting things with electronic circuits."
The RFID devices Tego makes take the carrier signal of the RFID reader and rectify it into a DC voltage. Tego uses that power -- as little as 4 milliwatts -- to power the processor that is the heart of its RFID chip. Tego's combination RFID chip and antenna add writeable, readable, encryptable data to any kind of asset -- moving intelligence to the very edge of the IoT edge.
Originally, those chips could operate only five or 10 feet from the reader. "These days, traditional passive RFID -- just identification tags -- can work 50 to 100 feet away. These things operate in the microwatts of power," Hamlin said. But Tego's goal isn't stretching the distance between RFID scanner and, say, retail RFID tag, which might just hold 96 bits to identify the make and price of a bathing suit. Instead, it's adding storage and processing workload to the chip. Obviously, it's not doing this to tag bathing suits, but to track and document parts and devices in aerospace, oil and gas exploration, life sciences, and similarly weighty applications.
Tego's roots and wireless protocols are in RFID, but it's also looking at Wi-Fi and other radio transmissions as power sources. "When most people hear IoT, they think of their phone and their laptop," Hamlin said. "We think of that as the first ring on the outside of the network. But further out, there are other rings where devices are no longer plugged into the wall, no longer running Windows or iOS. They're smaller, don't have full-blown OSes, have more dedicated processing and, by their nature, consume much less power." In addition, they may be so remote from power sources that they have to operate "autonomously." Like anemones on the sea floor, they have to sustain themselves on what streams by.
A version of Tego's tags has a serial interface on its chip, suitable for connection to sensors or microprocessors. One client is working on a new highway; installing these tags every 300 feet into pavement being laid across a bridge so they can monitor temperature as the pavement cures, as a step toward improving durability.
Vibration energy harvesting for IoT
ReVibe Energy out of Gothenburg, Sweden, is also serving the predictive maintenance need while focusing on converting vibration into AC current. Its two productized harvesters can be bolted directly to a vibration source and power several sensors via wire. ModelA produces up to 150 milliwatts with a steady vibration frequency of 15 to 100 Hz. ModelD produces up to 40 milliwatts. Like many such harvesting devices, they also store energy for later use.
Its current customers are sensor makers, but it has yet to produce in commercial volumes.
Out of four ways to convert vibration into energy, ReVibe uses electromagnetic induction, said company COO Erik Kling. ReVibe's patented technology improves the efficiency of this method so that more milliwatts are produced for a given weight and cost of harvesting device. As resonant harvesters, ReVibe's products require vibrations of a constant amplitude and dominant frequency.
It's seeing the most interest from railways, aerospace and construction and mining equipment companies. Kling described a pilot study being conducted with Deutsche Bahn (DB), the German national railway. DB's 50,000 track switches are currently fitted with battery-powered wireless sensors that measure their range of motion and upload the data via cellular signal. (Switching problems account for 20% of all DB delays, Kling said.) Their batteries need replacing every two years. ReVibe's harvesters are testing the most heavily trafficked tracks to see if its vibrational recharging energy-harvesting technologies can prolong battery life or even replace them altogether.
Another pilot -- a "textbook" application, Kling said -- is monitoring the temperature of wheel bearings of freight and passenger trains. Perpetuum, a U.K. company in vibration energy-harvesting technologies, has contracts for such applications with U.K. railroads. Kling also mentioned a construction vehicle vendor that wants to use vibration energy to capture sensor data that will enable it to offer customers after-market services. A leasing company wants to attach sensors and data storage that will tell it where its rented vehicles have been and how much they've been used.
Light energy harvesting for IoT
Solar is better known for its panels, an alternative energy source that, like wind, feeds into existing power grids. But on a much smaller scale, photovoltaic (PV) energy is harvested and stored by small autonomous (off-the-grid) devices, using ambient indoor light as well as sunlight.
Wibicom Inc. in Montreal, Canada, has productized a combination PV harvester and antenna, which it offers with a range of sensors. ("Organic" photovoltaic materials -- polymers combined with carbon-chain fullerenes, are a replacement for inorganic, typically silicon-based PV materials, which are less environmentally friendly both in manufacture and disposal.)
Wibicom's ENVIRO, a circular PV harvester and antenna about 5 cm in diameter, can sense and report on environmental data such as temperature, humidity, pressure and acceleration. Its maximum charge, powering Bluetooth LE radio and sensors, is 13 milliwatts in full sun; its data-sending range, with line-of-sight transmission, is over 100 meters. It can work up to two months in the dark on stored energy. Price: around $100. Customers: in pilot stages.
Wibicom's smaller Move harvester -- pictured next to a Canadian two-dollar piece -- is positioned as an advanced, PV-powered beacon and comes with an accelerometer for sensing activity. With a lower milliwattage and price, it can beam out messages to passersby or even power wearable devices.
Mina Danesh, CEO of Wibicom, explained that these communicating PV harvesters "can be connected as a beacon [that might transmit directly to a smartphone] or they can be attached to the internet through a gateway, where a cloud server can collect and analyze the data." They can also receive data or notify a cloud server to send a coupon, say, to a passing smartphone. Wibicom has also developed a WibiSmart mobile app that displays sensed conditions live, and a web version that compiles data over time.
In 2013, Wibicom teamed up with Finnish research and development institute VTT and other companies in a three-year, EU-funded ArtESun project, which demonstrated the product of their research into new organic photovoltaic (OPV) active layer and electrode materials, as well as coating and module interconnection techniques. These efforts are aimed at lower manufacturing cost, higher energy-capture efficiency and softer environmental impact. The project demonstrated an active RFID tag that used a credit-card-sized OPV module and an integrated sensor to report sensed conditions to a RFID reader. The module's integrated energy storage and overvoltage protection could power the tag up to one day during poor light conditions.
A second OPV use case demonstrated the potential for cheap, mass production in the form of a flower-shaped, flexible harvester/antenna module. Produced in a gravure printing process, it powered an antenna and an environmental sensor in a distributed, Bluetooth LE wireless network.
And in a separate proof of concept, Wibicom's partner VTT printed "leaves" that harvest energy from light or wind, and wired them to 3D-printed "trees" that could aggregate the wattage to power more demanding devices. The tree stirred a lot interest and requests to purchase in 2015, said Tapio Ritvonen, VTT research team leader, but the technology is still waiting for commercial production and implementation.
According to French technology market research firm Yole Développement, the energy-harvesting technologies module market is predicted to be worth $227 million by the end of 2017, led by building automation, railway and industrial applications. IoT has given this academic field and its largely European group of tech startups a powerful new raison d'etre and, they hope, the funding and contracts that go with it.
Learn about the batteries available for IoT devices