Specifications

14
In order to select the touch technology
that best fits your needs, it is important to
take a brief look at how each technology
functions. There are six basic types of
touch technology: capacitive overlay,
guided acoustic wave, resistive overlay,
scanning infrared, near field imaging, and
surface acoustic wave. Each type of touch
technology has attributes that are desirable
for specific applications.
All types of touch systems are
attached to a display unit, whether a
terminal, CRT, flat panel display, static
graphic, or combination of flat panel
display and static graphic. The differences
between the technologies lie largely in the
way the touch is detected and the method
used to process the touch data.
The following sections give a short
introduction to the types of touch
technologies available today.
Capacitive Overlay
Capacitive overlay technology uses a
glass overlay with a thin metallic coating
over the surface of the display screen. The
user must touch the overlay with a
conductive stylus, such as a finger, to
activate the system. Touching the overlay
surface causes a capacitive coupling with
the voltage field, drawing a minute amount
of current to the point of contact. The
current flow from each corner is
proportional to the distance to the finger
and the ratios of these flows are measured
by the controller and used to locate the
touch.
Section 3. Types of Touch Technologies