This is the entrance to the room or
hallway where the installation will be fixed. The detection whether
the cell phone is present in the pocket of the person or not will be
determined after the person enters in the room. This will be based on
the pulse induction (PI).
Typical PI systems use a coil of wire on one side of the arch as the
transmitter and receiver. This technology sends powerful, short bursts
(pulses) of current through the coil of wire. Each pulse generates a
brief magnetic field. When the pulse ends, the magnetic field reverses
polarity and collapses very suddenly, resulting in a sharp electrical
spike. This spike lasts a few microseconds (millionths of a second)
and causes another current to run through the coil. This subsequent
current is called the reflected pulse and lasts only about 30
microseconds. Another pulse is then sent and the process repeats. A
typical PI-based metal detector sends about 100 pulses per second, but
the number can vary greatly based on the manufacturer and model,
ranging from about 25 pulses per second to over 1,000.
If a wireless device passes through this
mechanism, the pulse creates an opposite magnetic field in the object.
When the pulse's magnetic field collapses, causing the reflected pulse,
the magnetic field of the object makes it take longer for the reflected
pulse to completely disappear. This process works something like echoes:
If you yell in a room with only a few hard surfaces, you probably hear
only a very brief echo, or you may not hear one at all. But if you yell
into a room with a lot of hard surfaces, the echo lasts longer. In a PI
metal detector, the magnetic fields from target objects add their
"echo" to the reflected pulse, making it last a fraction
longer than it would without them.
A sampling circuit in the metal detector
is set to monitor the length of the reflected pulse. By comparing it to
the expected length, the circuit can determine if another magnetic field
has caused the reflected pulse to take longer to decay. If the decay of
the reflected pulse takes more than a few microseconds longer than
normal, there is probably a metal object interfering with it.
In FDMA Each
Phone has a different frequency that can be used to group together the
presence of same kind of grouped together phones under beam of one kind of
This is the view of the magnetic
sensing devices installed in the floor of the space to be designed for
this kind of installation. The floor of the room looks like installed
worked up for the installation purposes.
The Detection mechanism to be
installed the floor
For getting the bird's eye view
of the details of the Cell Phone and technology behind it look here.