Touchscreen Technology

TOUCH SCREEN
TECHNOLOGY

Made by:
RITIKA GOLASH

RESISTIVE TOUCHSCREEN
The two sheets are coated with resistive substance, usually a metal
compound called Indium Tin Oxide (ITO). The ITO is thinly and uniformly
sputtered onto both the glass and the PET (Polyethylene terephthalate)
layer. Tiny bumps called spacer dots are then added to the glass
side, on top of the resistive ITO coating, to keep the PET film from
sagging, causing an accidental or false touch.
When the PET film is pressed down, the two resistive surfaces meet.
The position of this meeting (a touch) can be read by a touchscreen
controller circuit.

WORKING:

TOUCHSCREEN TECHNOLOGY

Advantages:
• Most widely used touch technology
• Can be activated by bare finger, gloved hand, or stylus
• Low cost

Disadvantages:
• Top sheet is highly susceptible to scratches, cuts and cigarette burns
• Layer is a flexing mechanical element coated with a conductive
ceramic which wears with every flex
• Transmission typically in 80% to 85%


SURFACE CAPACITIVE TOUCHSCREEN

• Four multi-layer glass.
• The two sides of the glass substrate
are coated with uniform conductive
ITO (indium tin oxide) coating.
• The thickness of 0.0015 millimeter
silicon dioxide hard coating are
coated on the front side of ITO
coating layer.
• There are electrodes on the four
corners for launching electric
current.


WORKING PRINCIPLE
Small amount of voltage is applied to the
electrodes on the four corners. A human
body is an electric conductor, so when
you touch the screen with a finger, a slight
amount of current is drawn, creating a
voltage drop. The current respectively
drifts to the electrodes on the four
corners. Theoretically, the amount of
current that drifts through the four
electrodes should be proportional to the
distance from the touch point to the four
corners.
The controller precisely
calculates the proportion of the current
passed through the four electrodes and
figures out the X/Y coordinate of a touch
point.

Advantages:
• Can be used to register touch on a sensor surface through a glass
window.
• Capacitive touch screen withstand contaminants such as
grease, dirt, water, running liquid, harsh chemicals and can be NEMAsealed.
• The life expectancy is over 225 million mechanical touches.
• Capacitive technology transmits around 90% percent of the light from
the screen.
• Life span of more than more than 50 million touches in one location.
• Technology with fastest touch response time

Disadvantages:
• Limited to 1 resolvable touch point
• Can only register the touch of ungloved fingers or tethered stylus on a
sensors surface.
• Sensitive for electromagnetic interference.
• Severe scratch can affect operation within the damaged area

PROJECTED CAPACITIVE TOUCH:
Projected Capacitive Touch (PCT) technology is a capacitive technology which
permits more accurate and flexible operation, by etching the conductive layer. An
XY array is formed either by etching a single layer to form a grid pattern of
electrodes, or by etching two separate, perpendicular layers of conductive material
with parallel lines or tracks to form the grid (comparable to the pixel grid found in
many LCD displays).


WORKING PRINCIPLE
Applying voltage to the array creates a grid
of capacitors. Bringing a finger or
conductive stylus close to the surface of
the sensor changes the local electrostatic
field. The capacitance change at every
individual point on the grid can be
measured to accurately determine the
touch location. The use of a grid permits a
higher resolution than resistive technology
and also allows multi-touch operation. The
greater resolution of PCT allows operation
without direct contact, such that the
conducting layers can be coated with
further protective insulating layers, and
operate even under screen protectors, or
behind weather and vandal-proof glass.


Advantages:
• Touch
function
operates
through
customer-installed
materials, including vandal-resistant glass up to 18 mm thick.
• Works outdoors-in rain, snow, ice, and dust.
• True flat front surface possible with no bezel.
• Works with fingers, gloved hands or conductive stylus.
• Works even if glass is scratched or broken.

Disadvantages:
• More complex electronics and sensor construction when compared to
other technologies
• Does not have full stylus independence support


SURFACE ACOUSTIC WAVE
With Surface Acoustic Wave (SAW,)
piezoelectric transducers located at
different positions of the screen are
used to turn the waves of mechanical
energy of a touch (vibration) into an
electronic signal. The waves are
spread across the screen by
bouncing off reflector arrays along
the edges of the overlay and are
detected by two "receivers". The
acoustic wave weakens when the
user touches the glass with their
finger, gloved hand or soft stylus.
The coordinates are then determined
by the controller circuitry that
measures the time at which the
amplitude declines.

WORKING:
When the panel is touched, a portion of the wave is absorbed. This change
in the ultrasonic waves registers the position of the touch event and sends
this information to the controller for processing. When sound waves are
transmitted across the surface of the display, the following sequence of
events occurs:
• Each wave is spread across the screen by bouncing off reflector arrays
along the edges of the overlay.
• Two receivers detect the waves.
• When the user touches the glass surface, the user's finger absorbs
some of the energy of the acoustic wave and the controller circuitry
measures the touch location.


Advantages:
• No touch overlay or coating required, so no layers that can be worn.
• No brightness or contrast loss, SAW offers superior image clarity and
high light transmission.
• Screen can be operated by with a finger, gloved hand (cloth, leather, or
rubber), leather or soft stylus. Something hard like a pen doesn't work.
• Durable, scratch-resistant glass surface, continues to work if
scratched.
• Vandalism proof, when protected glass is used.
• Antiglare glass option.
• Very long life span. Tested on more than 50 million touches at a single
location.

Disadvantages:
• The touch screen is not completely sealable, can be affected by large
amounts of dirt, dust, and/or water in the environment.
• Display surface needs to be slightly sunk from its mounting bezel

Acoustic pulse recognition
Acoustic
pulse
recognition
(APR) utilizes one pane of
glass with one transducer in
each corner. When touch
occurs, mechanical energy
(bending waves) radiates from
the touch location and is
detected by the transducers.
The transducers pinpoint the
touch location by generating a
unique sound for that location
on the glass.


WORKING
The acoustic pulse recognition (APR) consists of a glass
overlay with four piezoelectric transducers attached to the back
surface.
The transducers pick up the acoustic wave generated upon a
touch, and convert it to an electronic signal. The signal is then
digitized by the controller and compared to a prerecorded
acoustic profile for every position on the glass. The cursor
position is instantly updated to the touch location.


Advantages:
•
•
•
•
•
•
•
•
•
•
•
•

Optics and durability of pure glass
Works with finger, glove, pen, credit card, fingernail
Resistant to water, dust, grease
No wear-out mechanism
Works even with scratches
Excellent drag performance
Sealable to NEMA 4/IP65 standards
One time factory calibration, no drift
Thin borders—only 5mm
True flat surface
Disadvantages:
Small and large sizes
Palm rejection
• Touchscreen
Mounting
Essential
• Not a True Multi-Touch


is

OPTICAL TOUCH
Optical touch is the technique of
using infrared (IR) LED lighting to
irradiate a sensing area. Intersecting
the area reflects back the IR light to
camera to detect fingers. Via precise
calculation, system will get the
coordinates of the fingers caught by
camera. This technique is very
suitable for large scale touch
displays. With this technology, the
accuracy and system speed is
perfect, and multi touch function is
also available.

WORKING
Working in concert, optical sensors
located around the perimeter of the screen
track the movement of any object close to
the surface by detecting the interruption of
an infra-red light source. The light is
emitted in a plane across the surface of
the screen and can be either active (infrared LED) or passive (special reflective
surfaces). At the heart of the system is a
printed circuit controller board that
receives signals from the optical sensors.
Its software then compensates for optical
distortions and triangulates the position of
the touching object with extreme accuracy.


Advantages:
• 100% light transmission (not an overlay)
• Accurate
• Can be retro-fitted to any existing large format LCD or Plasma
display
• Can be used with finger, gloved hand or stylus
• Requires only one calibration
• Plug and play - no software drivers

Disadvantages:
•
•
•
•

Susceptible to “Ghosting” (Motion blur)
Can Be Affected by Direct Sunlight
Frame increases overall depth of monitor
Cannot be fitted to plasma and LCD displays with
integrated speakers


INFRARED TOUCH
Infrared technology relies on the interruption of
an IR light grid in front of the display screen. The
touch frame or opto-matrix frame contains a row
of IR-light emitting diodes (LEDs) and photo
transistors, each mounted on two opposite sides
to create a grid of invisible infrared light. The
frame assembly is comprised of PCBs on which
the opto electronics are mounted and are
concealed behind a IR-transparent bezel which
shields the opto’s from the operating
environment whilst allowing the IR beams to
pass through. When touching the screen one or
more of the beams are obstructed resulting in an
X and a Y coordinate being sent to the control
electronics to indicate the exact touch point.


Advantages:
•
•
•

100% light transmission since no overlay covering the display screen (protected
glass is optional).
Almost all kinds of stylus materials can be used in Infrared Touch Screen.
Infrared is the earliest and most reliable touch screen technology, due to the
improvement of LED materials. The lifetime of Infrared Touch Screen is much
longer and more stable in operation.

Disadvantages:
•
•
•
•
•

Low resolution
Exhibits worst parallax problem of all technologies for CRT use since light
beams do not follow curvature of CRT faceplate
May cause unintended activation of target prior to finger contact with CRT
caused by IR light beam location above surface of CRT
Pressure hose down may cause unwanted target selection
Dust, oil or grease buildup on frame that impedes light beam may cause
malfunction


DISPERSIVE SIGNAL TECHNOLOGY
Dispersive
Signal
Technology, specifically developed for
interactive digital signage
applications, sets new large-format
touch standards for fast, accurate
repeatable
touch
response.
In
addition,
Dispersive
Signal
Technology’s operation is unaffected
by contaminants, static objects or
other touches on the touch screen.
Other key
characteristics
of
this
patented
technology
are
exceptional
optics, ease of integration, and input
flexibility.


WORKING


• Dispersive
Signal
Technology
determines a “touch point” by
measuring the mechanical energy
(bending waves) within a substrate
created by a finger or stylus touching
the surface of the glass.
• When the touch implement impacts the
screen, bending waves are induced that
radiate away from the touch location.
• As the wave travels outwards, the
signal spreads out over time due to the
phenomena of dispersion. Piezoelectric
sensors positioned in the corners on the
backside of the glass convert this
smeared mechanical impulse into an
electrical signal.
• The distance from each sensor
determines the extent to which the
signal is dispersed. The further away
the “touch point” is from the sensor, the
more the signal is smeared.

Advantages and Disadvantages:
• Because the bending wave travels within the glass
substrate, objects or hands resting on the screen or onscreen contaminants do not affect the bending wave and
therefore, do not affect the performance of the
touchscreen.
• 3M
DST
can
be
activated
by
bare
finger, fingernail, stylus, and pen or basically anything
that create the bending wave in the glass Substrate.
• A downside is that after the initial touch, the system
cannot detect a motionless finger.


MULTI-TOUCH
In computing, multi-touch refers
to a touch sensing surface's
(track pad or touchscreen) ability
to recognize the presence of two
or more points of contact with the
surface.
This
plural-point
awareness is often used to
implement advanced functionality
such as pinch to zoom or
activating predefined programs.


Multi-touch
has
been
implemented in several
different ways, depending
on the size and type of
interface. The most popular
form
are
mobile
devices,
tablets,
touchtables and walls. Both
touch-tables and touch walls
project an image through
acrylic or glass, and then
back-light the image with
LEDs.


TYPES:
• Capacitive Technologies:
• Surface Capacitive Technology or Near Field Imaging
(NFI)
• Projected Capacitive Touch (PCT)
• Mutual capacitance
• Self-capacitance
• In-cell: Capacitive

• Resistive Technologies:
• Analog Resistive
• Digital Resistive or In-Cell: Resistive

• Wave Technologies:
• Surface Acoustic Wave (SAW)
• Bending Wave Touch (BWT)
• Dispersive Signal Touch (DST)
• Acoustic Pulse Recognition (APR)


• Optical Technologies:
• Optical Imaging or Infrared technology
• Rear Diffused Illumination (DI)
• Infrared Grid Technology (opto-matrix) or
Digital Waveguide Touch (DWT)™ or
Infrared Optical Waveguide
• Frustrated

Total

Internal

Reflection

(FTIR)
• Diffused Surface Illumination (DSI)
• Laser Light Plane (LLP)
• In-Cell: Optical

• Force-Sensing Touch Technology

The upcoming in-cell and on-cell technologies

WHAT ARE THESE TECHNOLOGIES?
• Manufacturers of touch screen devices usually use three layer.
• This is because LCD manufacturers produce the LCD panel, touch
sensor manufacturers produce the touch screen layer and glass
manufacturers (such as Corning) produce the protective outer glass.
• But instead we can actually move the touch technology onto the outer
glass layer. This is called on-cell or G2.
• We can also choose to put the touch sensors into the actual display
panel. This is called in-cell. Both layers are perfectly suited for the touch
electrodes.


WHY WE NEED THEM?
• With both in-cell and out-cell technologies, the thickness of
smartphones, tablets etc. considerably reduces.
• With both on-cell and in-cell we can expect better color saturation
as light has to pass through fewer layers.
• Depending on the implementation it can even make touch
feedback more accurate.
• And lastly, on-cell and in-cell makes it feel like we are actually
touching our phone’s display instead of an outer glass layer.


Touchscreen Technology

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