An electronic cigarette (or "e-cigarette") is an alternative
to smoked tobacco products, such as cigarettes, cigars, or pipes. It
is a battery-powered device that provides inhaled doses of nicotine
by delivering a vaporized propylene glycol/nicotine solution. In addition
to nicotine delivery, this vapor also provides a flavor and physical
sensation similar to that of inhaled tobacco smoke, while no tobacco,
smoke, or combustion is actually involved in its operation.
The electronic cigarette usually takes the form of some manner of elongated
tube, though many are designed to resemble the outward appearance of
real smoking products, like cigarettes, cigars, and pipes. A common
design is also the "pen-style", so named for its visual resemblance
to a ballpoint pen.

A disassembled cigarette-shaped electronic cigarette.
A. LED light cover
B. battery (also houses circuitry)
C. atomizer
D. cartridge.
When a user inhales through the device, air flow is detected by a sensor,
which activates a heating element that vaporizes a nicotine solution
stored in the mouthpiece.It
is this vapor that is inhaled by the user. An LED on the opposite end
of the device is also activated during inhalation, which serves as an
indicator of use, and also to simulate the glow of actual burning tobacco.
Components
While electronic cigarettes take many forms, they each generally employ
the same basic components: a mouthpiece, a heating element, a rechargeable
battery, and various electronic circuits. A number of disposable electronic
cigarettes have been developed, including products by Gamucci Ltd and
Ruyan.
Mouthpiece ("cartridge")




The mouthpiece is a small disposable plastic cup affixed to the end
of the tube. Inside, the piece contains an absorbent material that is
moistened with a flavored propylene glycol/nicotine liquid solution.
The mouthpiece is referred to in the industry as a "cartridge".
When the liquid in the cartridge has been depleted, it can either be
refilled by the user, or replaced with another pre-filled cartridge.
Heating element ("atomizer")



The heating element serves to vaporize the liquid in the mouthpiece so that it can be inhaled. This component is referred to in the industry as an "atomizer".
Most electronic cigarettes employ a lithium-ion rechargeable battery
to power the heating element. Battery life varies depending on the battery
type and size, frequency of use, and operating environment. Many different
battery charger types are available, such as wall outlet, car, and USB.
The battery is generally the largest component of an electronic cigarette.
Electronic cigarettes require an electronic airflow sensor. Various
other electronic circuits are usually employed as well, such as a timed
cutoff switch to prevent overheating, and an LED to signal activation
of the device. An orange-colored light is often chosen for its visual
resemblance to actual burning tobacco in the front of the cigarette.
While some larger electronic cigarette models employ an independently replaceable
standard-size battery cell, many models are too small to house a standard-size
cell and instead require a proprietary component made by the electronic
cigarette manufacturer. For those models, the battery and electronic
components are housed within a single replaceable part, which is generally
referred to in the industry simply as the "battery" — even though
it actually contains many other components as well.
Nicotine solution

Liquid nicotine solution, or "eLiquid" for electronic cigarettes is
available in a variety of different flavors and nicotine concentrations.
Nicotine concentrations range from high doses (to mimic the content
of regular cigarettes) to midrange and low doses (that mimic the nicotine
content of "light" and "ultralight" cigarettes). Solutions are also
available without any nicotine or without propylene glycol at all.