II. CAPACITIVE TOUCH:
It has two coatings as well.
Conductive lower
coating (Indium-Tin-Oxide)
No top coating, only rigid protective cover
Finger serves as
second conducting layer
Ohm’s Law relates current to voltage in DC circuit in the
form of V = iR
Capacitive touch screen uses Alternating Current (AC).
The current is continuous across the ITO surface, remember Sinusoidal waves from lab.
Impedance is equivalent to resistor in AC circuit implies, V
= iZ; where Z = (1/JwC)
And, J = sqrt(-1) w= 2pF where F = Freq.
C = Capacitance = (erA)/d
Human body achieves capacitance and conducts current.
Touch Event implies, Voltage drop at the point of touching.
Thus affecting the strength of current, across the ITO
surface.
Also, Voltage gradient across surface.
Conductive ITO surface allows for continuous current across
the surface.
Electronic circuits located underneath ITO surface measure
the resulting distortion in the sine waves produced by voltage drop as a result
of the touch event.
III. SURFACE ACOUSTIC WAVE:
Based upon emission and absorption of sound waves
Materials used are:
Transducers
One glass screen
Reflectors
Sensors
Two transducers are placed along the X and Y axes and
generate sound waves.
The waves propagate across the glass and are reflected back
to the sensors.
When screen touched, a portion of the wave is reflected back
to the sensors immediately.
The sensor is able to tell if the wave has been disturbed by
a touch event at any instant, and can locate it accordingly.
How do the sensors tell?
Waves travel at the speed of sound, Speed of Sound = 343 m/s
Based on the time it takes for the wave to return to the
source, the sensor can tell if it was disturbed or not.
If it was, based on the time it takes to get back to the
source, the sensor can calculate the distance.
These calculations will generate (X,Y) coordinates
Benefits
100% clarity because of the lack of metallic layers in the
screen
Able to interact with the use of multiple mediums like
Stylus, finger, glove etc
Negatives
Screen can become contaminated and cease to operate
correctly.
IV. INFRARED:
An infrared touchscreen uses an array of X-Y infrared LED
and photodetector pairs around the edges of the screen to detect a disruption
in the pattern of LED beams. These LED beams cross each other in vertical and
horizontal patterns. This helps the sensors pick up the exact location of the
touch. A major benefit of such a system is that it can detect essentially any
input including a finger, gloved finger, stylus or pen. Unlike capacitive
touchscreens, infrared touchscreens do not require any patterning on the glass
which increases durability and optical clarity of the overall system. Infrared
touchscreens are sensitive to dirt/dust that can interfere with the IR beams,
and suffer from parallax in curved surfaces and accidental press when the user
hovers his/her finger over the screen while searching for the item to be
selected.
V. OPTICAL IMAGING:
This is a relatively modern development in touchscreen
technology, in which two or more image sensors are placed around the edges
(mostly the corners) of the screen. Infrared back lights are placed in the
camera's field of view on the other side of the screen. A touch shows up as a shadow
and each pair of cameras can then be pinpointed to locate the touch or even
measure the size of the touching object (see visual hull). This technology is
growing in popularity, due to its scalability, versatility, and affordability,
especially for larger units.
VI. DISPERSIVE SIGNAL TECHNOLOGY:
Introduced in 2002 by 3M,
this system uses sensors to detect the piezoelectricity in the glass that
occurs due to a touch. Complex algorithms then interpret this information and
provide the actual location of the touch. The technology claims to be
unaffected by dust and other outside elements, including scratches. Since there
is no need for additional elements on screen, it also claims to provide
excellent optical clarity. Also, since mechanical vibrations are used to detect
a touch event, any object can be used to generate these events, including
fingers and stylus. A downside is that after the initial touch the system
cannot detect a motionless finger.
VII. ACOUSTIC PULSE RECOGNITION:
In this system, introduced by Tyco International's Elo division in 2006, the key to the invention
is that a touch at each position on the glass generates a unique sound. Four
tiny transducers attached to the edges of the touchscreen glass pick up the
sound of the touch. The sound is then digitized by the controller and compared
to a list of prerecorded sounds for every position on the glass. The cursor
position is instantly updated to the touch location. APR is designed to ignore
extraneous and ambient sounds, since they do not match a stored sound profile.
APR differs from other attempts to recognize the position of touch with
transducers or microphones, in using a simple table lookup method rather than
requiring powerful and expensive signal processing hardware to attempt to calculate
the touch location without any references. The touchscreen itself is made of
ordinary glass, giving it good durability and optical clarity. It is usually
able to function with scratches and dust on the screen with good accuracy. The
technology is also well suited to displays that are physically larger. Similar
to the dispersive signal technology system, after the initial touch, a
motionless finger cannot be detected. However, for the same reason, the touch
recognition is not disrupted by any resting objects.
CURRENT USES:
Kiosks: ATMs, Self Checkout Counters, Airport Check-in, etc.
PDAs
Tablet PCs
Mobile
Phones or rather Smart-Phones
Handheld Gaming Consoles
Different Methods of
determining X-Y position of the finger.
A person working on Smartphone.
Boy playing Jigsaw Puzzles on HP
touch-smart.
Here's a video of a Surface acoustic Wave technology.
