Frustrated Total Internal Reflection based Touch Screen

1. NITISH RANJAN
Branch- ETC

2. Principal of Working
The main principal of working
is Total Internal Reflection.
A clear acrylic sheet is used as the
touch surface.
Explanation:- Since both side of acrylic
sheet have air or vacuum so TIR takes
place between the surface.
If any object say finger is placed on
the surface of acrylic sheet then the
medium changes there and reflection
is said to be frustrated there causing
light to escape from the surface
This escaped light falls on the camera
underling the acrylic sheet and
camera registers the image into it.

3. Camera consists of CCD
sensor (for Analog
cameras) or CMOS sensor
(for digital cameras)
We basically use IR light
source which is invisible
to human eye but it is
visible to cameras.
After recording the image, camera sends
information to the Microprocessor or
Microcontroller (if any) or Software for further
processing and action.
3

4. Software first analyze the user
input and after some correction
(such as changing threshold or
intensity or dpi etc.) produces a
clear output on the screen.
Surface Capture via Detector
Using concept of Image Processing
software also knows that at which point
the user is touching the screen or acrylic
sheet.
Thus it can then easily work as Multi-
Touch for different applications.
Digitized View

5. Optical Fingerprint scanner uses FTIR
technique for capturing and storing
image of fingerprint.
Since it uses Light rays for capturing
image of fingerprint, it is more
accurate than Capacitive scanner.

6. Now a days technology has developed
such an extent that we can use our
Working Tables (made up of Glass) as
display screen.
If these display screen will be touch
sensitive then we can also give instructions
to it by single or multiple touch.
This type of Multi-Touch table can be
constructed using the same concept of
FTIR.
Instruction is manipulated and preformed on
the basis of Image Processing technique in
which co-ordinates of touch point is
registered and software performs required
action on the basis of programming/coding
done to it.

7. It Requires significant space behind touch surface for
proper position of camera.
Since it uses concept of refractive index so it might
not register input with Gloves in hand or sometimes
even dry skin also.
Water or Sweat on the surface can also produce FTIR effect

8. Thanks