Copyright is held by the author / owner(s). SIGGRAPH 2011, Vancouver, British Columbia, Canada, August 7 – 11, 2011. ISBN 978-1-4503-0921-9/11/0008

E-Letter: A Paper-based Instant Messaging System Using Selective WirelessPower Transfer

Kening Zhu, Hideaki Nii, Owen Noel Newton Fernando, Adrian David CheokKeio-NUS CUTE Center, National Univeristy of Singapore

Figure 1: E-Letter

1 Introduction

Today as the rapid development of digital technology is turningour society into a paperless one, the traditional letter-writing hasbeen replaced by digital media, such as EMail and Instant Mes-saging. However, research has shown that there are still rich ad-vantages of physical paper in our daily life, and they are hard toattain in the realm of pure software [Hendrix and Eisenberg 2004].For paper-based letter communication, Gregory Davis [Davis 2009]mentioned that unlike electronic communication, the letter engagesthe totality of intellect, the heart, and the senses.

Considering the advantage of paper letter communication, in thispaper we present E-Letter, a paper-based instant messaging system.By wirelessly powering the nichrome wires embedded in the paperto heat up and etch the paper, this system enables users to chat witheach other using paper. The message will display physically on thepaper similar to communicating through letters.

Since the birth of the concept of paper computing, there have beena few researchers focusing on displaying digital information onpaper. The first system closing the gap between paper and digi-tal information spaces was Wellner’s DigitalDesk [Wellner 1993],which ultilized a camera-based tracking system and a projector-based tabletop to interact with paper document and link to the dig-ital service. However, most of the existing works utilized projectorto display message on the paper, which is not really paper display-ing. The information will be removed when the paper is not underthe projection. In addition, it is inconvenient for end users to set upan accurate projection system. Comparing to these existing works,E-Letter can display the digital message permanently on the paperusing electromagnetic power. This provides the missing value oftraditional paper letter to the digital messages.

2 System Overview

The main technical innovation of this system is that the normal pa-per is powered wirelessly through electromagnetic fields with con-trolled frequencies to display different messages. Nichrome wiresare embedded in the paper and heated up wirelessly to generate dif-ferent display patterns. The system can selectively power up differ-ent receiving coils embedded in the paper by controlling the trans-mitting frequency to activate different embedded receivers. Unlikemassive external power connections, this method keeps the intrinsicflexibility of paper interface, enabling users to manipulate the paperfreely.

As shown in Figure 1(a), the transmitter was built with a high poweroutput MOSFET oscillator setup. The LC tank in the system gen-erates the oscillation, and two power MOSFETs amplies the signalto enable the system to transfer energy wirelessly. An array of thecapacitors are respectively controlled by a relay and a switch sodifferent capacitance value can be included at runtime to generate avariety of frequencies, ranging from 200 kHz to 1MHz.

For the receiving coils embedded in the paper in Figure 1(b), weused LC tank to harvest energy at its resonance frequency. The in-ductor coil is made of 0.5mm enameled copper wire in the circularshape with diameter 5cm and 2 turns to match the small resistanceof the nichrome wire. The capacitor and the nichrome wire areattached to the copper coil. Each coil will have a different valueof capacitor attached, thus each will have different resonant fre-quency. Therefore when there are multiple receiving coils with dif-ferent resonant frequencies, we can control the output frequency inthe primary transmitting coil to activate different receiving coils.The receivers are embedded in the paper during the paper-makingprocess.

Finally, we combined this paper powering system with instant mes-saging system. By simply matching the ASCII code of each letterto a 7-digit display, the system heats up the nichorme wires one byone, and displays the incoming message as shown in Figure 1(c).

3 Demonstration Scenario

During the demonstration, audiences can experience the paper-based instant chatting. They can see the messages display on thepaper, reply the messages, hold and read the paper freely, and readand write the letters. The audiences can also take their paper mes-sages back home as souvenir.

References

DAVIS, G. J. 2009. The joys of a handwritten letter. Journal ofAmerican Amateur Press Association, 78, 46 –61.

HENDRIX, S., AND EISENBERG, M. 2004. Computer-assisted en-gineering for children: a pop-up design application. In ICLS ’04:Proceedings of the 6th international conference on Learning sci-ences, International Society of the Learning Sciences, 606–606.

WELLNER, P. 1993. Interacting with paper on the digitaldesk.Commun. ACM 36 (July), 87–96.