Ameya360:Powering E-Paper Displays with NFC Energy Harvesting

　　Based on innovative technology, e-paper displays offer significant advantages over traditional displays. Thanks to their unique characteristics, it is not necessary to continuously power the screen; it is sufficient to supply energy when the content of the displayed page is modified. In this way, significant energy savings are obtained, which, in battery-powered applications, translates into greater autonomy.

　　Additionally, because power consumption is very low, e-paper displays can be powered through energy-harvesting solutions—for example, by converting the RF energy produced by a near-field communication (NFC) transceiver into electricity. Hence, by combining printed e-paper displays with NFC technology, a new range of battery-less products is enabled.

　　In this article, we’ll provide a practical implementation guide on how NFC can be used to power Ynvisible’s e-paper displays.

　　Ynvisible e-paper displays

　　Ynvisible displays are based on an e-paper technology called Electrochromic Display (ECD), which uses organic electrochromic polymers. Unlike other display technologies that emit light, Ynvisible e-paper devices are categorized as reflective displays, meaning they reflect the ambient light instead of using a backlight. The displays are produced on inexpensive plastic (PET) substrates, making the displays thin and flexible.

　　These printed e-paper displays achieve very low power consumption. One square centimeter of active display area requires about 1 mJ to be activated, while the recommended driving voltage is ±1.5 V. That allows Ynvisible’s e-paper displays to achieve the lowest energy consumption on the market for most use cases.

　　Additionally, the displays include an image memory (or image retention), which is a crucial component for applications that don’t require batteries. The average image retention duration for Ynvisible’s standard displays is between five and 15 minutes. A brief refresh pulse may be necessary to retain full contrast after this time period, depending on the use case. The displays are manufactured using roll-to-roll screen-printing and lamination processes. They are non-toxic, ITO-free, and mainly comprised of PET plastic. The plastic substrate and roll-to-roll production means thin, flexible, scalable, and highly cost-effective displays.

　　Ynvisible also offers a segment e-paper display kit, which allows customers to evaluate the ultra-low–power, thin, and flexible segment e-paper displays. Each e-paper display kit (see below figure) comes with different display designs and includes an e-paper display driver with I2C interface with related user manual.

　　Harvesting NFC RF power

　　NFC is a short-range data-exchange technology for electronic devices. An inductive pair between two antennas serves as the basis for the communication. NFC does not require that one of the two communicating devices has built-in power, in contrast to many other communication interfaces. Instead, the power transmitted by an NFC reader/writer (such as a smartphone) is harvested to generate power. Contactless payments are NFC’s most typical use case.

　　To power an Ynvisible e-paper display with energy harvested from an NFC signal, an antenna and a rectifier diode are required. The power from the antenna will be transferred to the display by inductive coupling between the transceiver and the antenna itself. The signal needs to be rectified with a diode because the display requires direct current. If the display content is intended to fade off quickly after activation, the rectifying diode can be connected in parallel with the display.

　　However, if the application requires communicating some data, such as reading an identification code (RFID) or writing data to the device, an NFC chip would be necessary. These chips come in a wide variety of models and vendors, and they each have unique features.

　　They fall into three categories:

　　1.NFC data storage chips. The transceiver can read and/or write data to the chip

　　2.NFC data storage ICs with I2C communication and power output (energy harvesting). These chips can be used to power and/or communicate with an MCU over NFC.

　　3.NFC chips with embedded processor. These chips can be thought of as MCUs with NFC capability, which means they have all of the standard MCU functionalities, plus the potential to be powered and/or communicated with via NFC.

　　Each of the above IC groups requires a different connection scheme to the display. The following are the most common approaches adopted for implementing the display connection:

　　1.Connect in parallel with NFC chip. Following this approach, the NFC chip and the display are connected in parallel. The IC and the display are not directly connected, while the NFC signal powers both the chip and the display. In this scenario, the display will turn on regardless of the transmitted data.

　　2.Power output of the NFC chip. If the chip belongs to the second group, the display can be connected directly to the chip’s power output. Similarly to the previous case, the display will turn on regardless of the transmitted data.

　　3.MCU in between the NFC chip and the display. Using a host controller in between the chip and the MCU is another method applicable to the second group of chips. Due to the MCU’s ability to read the data from the NFC chip, conditional display driving is made possible. If the user has the authority to read the label, this could be handy when the display needs to be turned on.

　　4.Use built-in GPIOs to control the display. This approach is similar to the previous one, but because the MCU capabilities are embedded into the Category 3 NFC chips, no intermediate host controller is needed.

　　The power of NFC

　　NFC has the potential to replace batteries as the main power source in many applications. From a cost, sustainability, and recyclability perspective, batteries often limit the adoption of electronics and printed intelligence in new applications. Target markets for Ynvisible, its partners, and clients include those for medical technology, smart packaging, smart cards, brand protection, and security gadgets.

　　The platform obtained combining NFC and e-paper display technologies can help to create the future of intelligent items, sensors, and other printed electronics.