The document summarizes different multi-touch screen technologies, including resistive, capacitive, and FTIR (Frustrated Total Internal Reflection) screens. Resistive screens use two conductive layers that are pressed together to detect touch points. Capacitive screens use electrodes to create an electric field and detect disruption when touched. FTIR screens use infrared light and cameras to detect where light paths are interrupted by touch. The document also discusses the history and applications of multi-touch technology, including products from Apple and research by Perceptive Pixel using the FTIR method.

1. MULTI TOUCH TECHNOLOGY
BY: Robert McGrellis

2. SELF INTRODUCTION
 Senior Undergraduate Student at Wright State
University
 Major Field of Study: Electrical Engineering
 Minor: Computer Science

3. OVERVIEW
Introduction of Multi Touch Technology
Scope
Historical Overview
Theory
Multi Touch Screen Designs
Resistive Capacitive Perceptive Pixel
Summary

4. TOPIC INTRODUCTION
 State of the Art Report on Multi Touch Screen
technology
 Technology used in Apple iPhone, iTouch, and in
wall and table displays.
 Jefferson Han founder of Perceptive Pixel

5. SCOPE
 My Research will focus on three techniques
 Resistive
 Capacitive (projective capacitive)
 FTIR (Frustrated Total Internal Reflection method
 Will not cover
 SAW (Surface Acoustic Wave technology)
 Optical Infrared touch screens
 Surface Capacitive touch screens
 Computer Programming aspects

6. HISTORY OF MULTI TOUCH
 1972: PLATO IV Touch Screen Terminal
(Computer-based Education Research Laboratory,
University of Illinois, Urbana-Champain)
Touch screens started to be developed in the
second half of the 1960s.
1982: Flexible Machine Interface (Nimish Mehta ,
University of Toronto).
The first multi-touch screen developed. This screen
is called a resistive touch screen and requires
finger pressure to sense touch.

7. HISTORY OF MULTI TOUCH
 1983 Bell Labs
Bell Labs at Murray Hill published a
comprehensive discussion of touch-
screen based interfaces.
In 1984 Bell Labs engineered a touch
screen that could change images with
more than one hand.
 Fingerworks
a Newark-based company run by
University of Delaware John Elias and
Wayne Westerman
2005: Fingerworks was acquired by
Apple Inc.

8. HISTORY OF MULTI TOUCH
 2005: Jeff Han: consulting research scientist at New York University starts developing Multi
Touch technology
 2006: Perceptive Pixel
Very elegant implementation of a number of techniques and applications on a table format rear
projection surface.
In 2005 Han published a paper on Multi-Touch Sensing through Frustrated Total Internal
Reflection
Formed Perceptive Pixel in 2006 in order to further develop the technology in the private sector
 2007: Apple Inc.
introduced the iPhone, marking the first time multi-touch technology was used on a
phone. The iPhone includes such components as a web browser, music player, video
player, and a cell phone without the use of a hard keypad or stylus.
Following the release of the iPhone, Apple also expanded its use of multi-touch
computing with the new iPod Touch,

9. STANDARD TOUCH SCREENS
 Resistive
two layers of indium tin oxide are printed on a thin sheet of plastic film
with an air gap in between them. The touch location is detected when
finger pressure forces one ITO layer onto the other and the X and Y
coordinates are measured.
 Capacitive
electrodes at corners of the provide a uniform AC voltage field.
When the screen in pressed the field is disrupted. The controller
connected to the touch screen measures the change in current
flowing form each corner and calculates the X and Y coordinates.

10. RESISTIVE TOUCHSCREEN THEORY
 Voltage Divider (Model of Resistive Touch method)
In electronics, a voltage divider is a simple linear circuit that produces an
output voltage (Vout) that is a fraction of its input voltage (Vin). Voltage division
refers to the partitioning of a voltage among the components of the divider.

11. RESISTIVE TOUCH SCREEN
Rx denotes the x-axis resistance of the coating and Ry denotes the y
axis resistance of the coating. When the conductive coating is
pressed against the resistive coating

12. RESISTIVE TOUCH SCREEN
 4-wire technique
Figure 1
Shows the exploded view showing
the layers of a touch screen

13. CAPACITIVE TOUCHSCREEN THEORY
 Capacitive Coupling
the transfer of energy within an electric circuit by
means of the capacitance between circuit nodes.
 Capacitance
a measure of the amount of electric charge stored
(or separated) for a given electric potential.
 Insulator is a material that does not allow the flow
of electric current through them
 Electric field
The space surrounding an electric charge. Exerts
a force on other electrically charged objects. The
concept of an electric field was introduced by
Michael Faraday.

14. CAPACITIVE TOUCH SCREEN
•Uses a single sheet of glass with multiple sheets with
conductive coating.
coated with a material, typically indium tin oxide, that
conducts a continuous electrical current across the
sensor. The sensor therefore exhibits a precisely
controlled field of stored electrons in both the horizontal
and vertical axes - it achieves capacitance.
•An electrode pattern on multiple ITO layers
surrounding the screen produces an AC voltage field
across the coating. When a finger touches the screen a
capacitive coupling effect occurs between your finger
and the screen.
•Detects the position by measuring the distribution of
change in the signals between X and Y electrodes

15. CAPACITIVE TOUCH SCREEN
Mutual capacitance touch-screen contains a grid of sensing
lines and driving lines to determine where the user is
touching.

16. PERCEPTIVE PIXEL
 Jefferson Han founder of Perceptive Pixel Inc
 Demoed display first at TED (Technology
Entertainment Design Conference) Feb 2006
 The displays use infrared light emitting diodes along with an infrared camera to
determine the point of contact. Han envisions large collaborative spaces that will
allow multiple users to work and interact. Perceptive Pixel’s technology is currently
being utilized, in the form of the Multi Touch collaboration wall, by CNN and an
unspecified government contractor
 Building large multi touch screens that can sense up to 20 or more fingers
 Company is doing research to expand the capabilities of multi touch technology
they are developing new applications as you saw in the video clips.
 Getting away from the standard mouse and keyboard computer user input

17. TOTAL INTERNAL REFLECTION
 Total internal reflection is an optical phenomenon that occurs
when a ray of light strikes a medium boundary at an angle larger
than the critical angle with respect to the normal to the surface. If
the refractive index is lower on the other side of the boundary no
light can pass through, so effectively all of the light is reflected. The
critical angle is the angle of incidence above which the total internal
reflection occurs.
•As the angle of incidence increases,
the amount of light transmitted
decreases until total reelection occurs
shown by the blue line

18. FTIR INTERNAL REFLECTION
Frustrated Total
Internal Reflection
•Display surface is 6 mm
piece of clear acrylic with
infared LEDs on the edges
•Light travels predictable
paths within the acrylic,
when uninterrupted
because of total internal
reflection
•When the screen is pressed the light diffuses,
deviates from straight trajectory. This changes
the path of the internal reflection.
•A camera below the acrylic surface captures
the diffusion and sends information to an image
processing software, which translates the
information.

19. SUMMARY
 Many ways to implement Multi Touch Technology
 3 methods for Multi touch
 Resistive
 Capacitive
 FTIR (Frustrated Total Internal Reflection
 Jeff Han, founder of Perceptive Pixel uses the FTIR method. His
research focuses on expanding the capabilities of the Multi Touch
technology

20. CREDITS
 Research
Baker, Bonnie. "Reach out and touch." EDN 52.20 (2007): 24-24.
Fritz, Mark. "Keys to the Kiosk." EMedia 13.4 (Apr. 2000): 28. Academic Search Complete.
EBSCO.17 Feb. 2009
http://search.ebscohost.com/login.aspx?direct=true&db=a9h&AN=3050170&site=ehost-live
Philipp, Hal. "Please Touch! Explore The Evolving World Of Touchscreen Technology Electronic
Design 56.8 (2008): 60-61. “
"How It Works." Popular Mechanics 186.1 (2009): 29-29.
"PRODUCT RESEARCH." Control Engineering 53.4 (2006): 65-65.
"Resistive touchscreens." Machine Design 80.5 (2008): 52-52.
Special thanks to Phil Flynn
•Pictures
www.technologyreview.com
www.apple.com
www.perceptivepixel.com