New-Tech Europe | June 2017

Embedded Solutions Special Edition

Figure 1: This graph shows the current used during an update to an e-paper display (Source: Pervasive Displays)

design process. Smartcards for authentication or contactless payments represent one of the biggest and most high-profile uses of RF energy-harvesting, but the technique could be used in many other scenarios. Sensors, thermometers or even displays can be powered using RF-harvested energy. E-paper: the display technology that doesn’t require a battery Made famous by the Kindle ebook reader, e-paper is a particularly interesting technology for manufacturers of batteryless industrial or IoT devices, because it enables them to incorporate displays into their designs. E-paper uses very little power: where traditional active-matrix LCDs need a power-hungry backlight to make the image visible, e-paper uses electrophoretically charged physical ink particles to create an image, off which ambient light can reflect. Consequently, the content of an

being used. At the same time, the device needs a low-power design – and this goes beyond simply using low-power components. Ultimately, it must be able to operate within a limited power budget. An example of good batteryless device design is the RF-based contactless smartcard. Inside, they contain a memory chip and antenna, which performs the dual purpose of communicating and harvesting energy. Most of the time, the card is ‘off’, and uses no power. But when it comes within the RF field of a reader or writer device, the card is energized, enabling the reader/writer to communicate with it wirelessly. Because the card only needs power to perform read or write operations, RF-based energy harvesting is ideal: there will always be an RF reader/ writer as a source of power. And if designers keep to standards, including NFC or RFID, they know what power budget their card must work within, which simplifies the

It’s a different story when you look at industrial applications and the IoT. Firstly, device downtime may have more serious consequences. Operators of battery-powered networks therefore need to monitor charge levels and periodically recharge or replace batteries to ensure uptime. Secondly, industrial and IoT deployments typically include tens or hundreds of devices. Maintaining this number of batteries represents a major overhead. Energy-harvesting: Ideal for the IoT Energy-harvesting is an ideal way for IoT kit to reduce or even eliminate its reliance on batteries. And by blending this approach with a low- power design, it’s possible to create kit that can run almost perpetually. To achieve this goal, the first step is to select the most appropriate means of harvesting energy for the use case. Solar or thermal may seem obvious choices, but can be inconsistent in their delivery of power. The source of energy needs to be available when the device is

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