An electronic cigarette, also known as an e-cigarette or personal vaporizer, is a battery-powered device that provides inhaled doses of nicotine by way of a vaporized solution. It is an alternative to smoked tobacco products, such as cigarettes, cigars, or pipes. In addition to purported 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.

An 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. Another common design is the "pen-style", so named for its visual resemblance to a ballpoint pen. Most electronic cigarettes are reusable devices with replaceable and refillable parts. A number of disposable electronic cigarettes have also been developed.

What is an 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". Some models combine an atomizer and pre-filled cartridge into one disposable component referred to as a "cartomizer".

How does the battery work?

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 chargers. The battery is generally the largest component of an electronic cigarette.

Some electronic cigarettes employ an electronic airflow sensor to automatically activate the heating element upon inhalation, while other models require the user to press a button while inhaling. Various other electronic circuits are usually employed as well, such as a timed cutoff switch to prevent overheating and a colored LED to signal activation of the device.

Traditionally, electronic cigarettes have utilized an electronic means of activation. This involved the use of small tactile switches, vacuum switches and the related wiring and electronics necessary to run them. Users soon discovered these could be unreliable. With the advent of "mods", several manufacturer's have created all mechanical electronic cigarettes that eliminate the use of any wiring, solder or electronics in an effort to improve switch reliability.

While some larger electronic cigarette models employ a user-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 still generally referred to in the industry simply as the "battery".

What is e-liquid/nicotine liquid?

Nicotine solutions sold separately for use in refillable cartridges are sometimes referred to as "e-liquid" or "e-juice", and commonly contain some amount of flavoring, with several different flavors available. They consist of nicotine dissolved in propylene glycol (PG) and/or glycerin (glycerol). Both PG and glycerin are common food additives.

Solutions are also available in differing nicotine concentrations, to let the user decide the amount of nicotine to be taken in. Concentrations range from low and midrange doses (6-8mg/ml and 10-14mg/ml respectively), to high and extra-high doses (16-18mg/ml and 20-54mg/ml respectively). The concentration ratings are often printed at the e-liquid bottle or cartridge, although the standard notation "mg/ml" often gets abbreviated to just "mg". Solutions are also available that contain no nicotine at all.

Source: http://en.wikipedia.org/wiki/Electronic_cigarette