Whilst rechargeable (or replaceable) batteries are fine for consumer electronics, when you start thinking about IoT or industrial use, it’s a different story. The scale of the deployment and remote location of the devices mean that operating them all on batteries, however long these may last, isn’t sustainable. The overhead of having to monitor charge levels and then physically intervene would simply cost too much for the solution to be viable.
Instead, energy-harvesting can enable some surprisingly powerful batteryless devices.
Energy-harvesting
There are different ways to harvest energy: solar and thermal are two obvious choices, but factors such as their unpredictability mean they’re not suitable in all situations. If the sun isn’t shining when you need your device to work, it isn’t much use. That’s why harvesting radio frequency (RF) energy is a popular alternative in certain scenarios.
RF energy-harvesting has been around for some time: the contactless bank card in your wallet is a great example. Inside it is a memory chip and an antenna. The latter performs the dual role of communicating with the RF reader/writer and harvesting energy from its RF field. When it comes within range of the reader/writer, the card is energized, meaning its memory chip can be read from and written to.
The contactless smartcard is a relatively simple use of RF energy-harvesting, and while this technique may not be suitable for all IoT applications, it can power some surprisingly sophisticated devices. These need to be designed from the ground up with low power use in mind, blending the right low-power components.
Displays in batteryless IoT devices
One particularly interesting technology for designers of batteryless devices is e-paper, which enables them to incorporate displays, without blowing their power budgets out of the water. Many will have come across e-paper in e-reader devices, such as the Kindle.
E-paper does away with the two biggest consumers of power in traditional liquid crystal displays (LCDs): the backlight and the need to refresh constantly to maintain an image on the screen. Instead, e-paper creates an image using coloured physical ink particles that reflect or absorb ambient light. Once this image is on the screen, it remains visible and uses no further power, until such time as you want to change it. And with a screen update requiring as little as 2mA of current in modern e-paper displays, such as those from Pervasive Displays, it’s clear why the technology is ideal for IoT and industrial applications. These characteristics also mean it can happily work off harvested energy.
The combined batteryless EPD and RFID tag
This is exactly what Toppan Printing in Japan has done with its batteryless e-paper display (EPD) with built-in RFID tag. Aimed at the logistics and warehousing markets, the device enables information to be readable by humans (on the display) and machines (via RFID). There’s a range of screen sizes available (between 1.44 and 2.7 inches) and the device is under 7mm thick. The display gets updated using NFC – which is also where it gets its power from.
And because it’s batteryless, anyone deploying these devices won’t face the overheads associated with monitoring charge levels and replacing or recharging big numbers of batteries.
Consequently, Toppan’s EPD with built-in RFID tag could take the place of paper labels in large-scale asset and inventory management scenarios, for example. This would have the added benefits of the human-readable information (on the display) being editable and the whole thing now being machine-readable (via RFID). The device could also improve on traditional RFID tags, by making key tag data readable by humans at-a-glance, without the need for an additional device.
The batteryless opportunity
So, with a variety of energy harvesting technologies and low-power components – including EPDs – now available, IoT device designers have an incredible opportunity to create devices that can operate pretty much forever, free of the constraints of cabling or batteries. How could energy-harvesting transform your designs?
Author profile:
Scott Soong is CEO of Pervasive Displays
