The IoT has a battery problem. IoT implementations require large numbers of small devices deployed in areas without easy access to mains power. These devices therefore need to be low power and battery powered. But battery-powered devices present challenges. Batteries need to be recharged or replaced regularly, and battery life needs to be monitored to prevent device downtime.
What if there was a way to perpetually power an IoT node device? While it sounds too good to be true, energy harvesting techniques exist today that allow solar, thermal, or RF energy to power a useful IoT node application. A recent product in this category was developed by Tokyo-based Toppan Printing Co. Ltd., and uses NFC energy harvesting to update RFID data and also refresh a low power e-paper display.
With the right harvesting technique and device design, a batteryless approach like this can allow for near-perpetual use. End users also benefit, as the lack of a battery means an end to the cost and logistical challenges of maintaining battery-powered devices.
Wireless Devices Have a Battery Problem
As wireless devices have permeated our lives, batteries have followed suit. Today, the devices we use most often – our smartphones and laptops – are battery powered. We’ve become accustomed to plugging in and charging them every night; a minor tradeoff for the benefits of untethered wireless connectivity.
Just as it has changed the face of consumer electronics, wireless connectivity has also revolutionized industrial devices and enabled the IoT. Wireless connectivity allows sensors and actuators and other industrial IoT devices to be placed in remote locations, and deployed in large numbers without the limitations of networking and power cables.
However, while battery charging and maintenance is trivial for consumer electronics, for industrial markets it provides a bigger challenge. IoT and industrial markets often serve more mission-critical applications where downtime is more serious than losing access to Facebook for the rest of the day. To ensure equipment uptime, battery-powered IoT and industrial devices need to be monitored for battery life, and maintained by regular charging or battery replacement.
Besides the mission-critical aspect, IoT and industrial device deployments often entail far larger numbers of devices. While most of us usually own one, or even two, smartphones or laptops, a typical IoT deployment in a factory may involve dozens or hundreds of individual devices. With more devices to manage, battery maintenance headaches multiply as well.
With its potential to reduce or eliminate dependence on battery power, energy harvesting is well suited to IoT devices. In fact, combining the appropriate energy harvesting approach with low power design can result in devices that can operate near-perpetually.
Achieving the batteryless ideal starts with choosing the right energy harvesting source for the application. While thermal and solar energy seem obvious choices, for many use cases, power production from these sources may be too inconsistent. The ideal energy source is always available when the device is in use.
Low power design is the other half of the zero-power puzzle. Choosing low power components is not enough. The device needs to perform its function within a guaranteed power budget.
RF-based contactless smart cards are a great example of an ideal batteryless device design. These RFID-based devices have a simple memory chip and antenna for both communication and energy harvesting. The device is usually off and consumes no power. When the card is placed in range of an active RF reader/writer device, the card is energized by the RF field, and can be read and/or written to wirelessly.
RF-based energy harvesting makes sense for this application because the smart card only needs power during read/write operations. During those types of operations, an RF reader/writer device will be present and the card can harvest RF energy. By following standards such as RFID or NFC, the smart card can expect a certain guaranteed power budget, simplifying device design.
While RF energy harvesting is most popularly used with smart cards, its potential uses go far beyond contactless payments and authentication. Batteryless thermometers, sensors, and even displays are possible using RF energy harvesting.
Batteryless Display Technology
One of the more interesting low power components suitable for batteryless designs is e-paper. Most famously known as the technology behind the Kindle e-book reader, e-paper is a very low power consumption technology that uses electrophoretically charged ink particles to form an image.
Because of its low power consumption and its unique optical characteristics, e-paper is especially suitable for energy harvesting. Traditional active-matrix LCD displays require a backlight to be visible. E-paper is reflective, (See Figure 1) meaning it works off ambient lighting. LCD displays must constantly refresh the screen just to maintain an image, consuming energy per refresh. E-paper is bistable: no energy is needed to maintain an image, just to update one.
Click image to enlarge
Figure 1: Electrical current used when updating an e-paper display (Source: Pervasive Displays)
Power consumption during screen updates can be quite low, with modern e-paper displays from Pervasive Displays drawing as little as 2 mA during a refresh. All this means that e-paper uses very little power, and the display can be visible – and the device therefore usable – even when power is absent. Its low power consumption and bistable optical characteristics make e-paper an ideal candidate for energy harvesting, by using solar, thermal or RF energy sources.
Toppan’s Zero-Power IoT Device
Though the power limitations of energy harvesting mean it may not be suitable for every use case, it does have the capability to power surprisingly complex applications. Japan’s Toppan Printing Co. Ltd. recently designed a batteryless e-paper display with integrated RFID tag (See Figure 2). This device not only functions as a traditional, machine readable RFID tag, but also can display human readable information on its e-paper display.
The device, which comes in display sizes from 1.44" to 2.70", is less than 7 mm thick and has no battery, working instead completely off RF energy from an NFC reader/writer. Besides 884 bytes of RFID information, its memory can hold three separate images, which can be updated onto its e-paper display. The display and the RFID data are updated through an NFC reader/writer device.
Click image to enlarge
Figure 2: Batteryless EPD (Source: Toppan Printing)
Designed for logistics and warehousing applications, the device can be used to replace traditional paper labels used for asset management, inventory management, or manufacturing. Instead of a plain paper label, its RFID capability makes it machine readable and means goods can be easily tracked automatically as well. Perhaps most importantly, its batteryless operation allows it to be deployed at scale, without having to worry about battery life or maintenance.
The Batteryless IoT
While batteries are a fact of life for our consumer electronics, they don’t always make sense for industrial and IoT applications. In these markets, devices are often deployed in large numbers, and in environments unconducive to frequent maintenance for battery charging or replacing.
Advances in energy harvesting techniques, as well as reductions in power consumption for sensors, actuators, and even displays allow more devices than ever now to be powered purely off of energy harvesting from thermal, solar, or RF energy sources.
E-paper, with its low power consumption and bistable display characteristics, presents a unique opportunity for designers to create new devices for human interaction in industrial settings, which can run without the challenges inherent to battery-driven devices.