In its most basic sense, an emitter is simply a device which discharges a type of signal or other medium. This can include light, sound, odor, taste or something else that impacts one of the senses. Generally, an emitter can be found on electronic devices or beacons in a way that users utilize the signal as an identifiable factor. Emitters are designed to give a user some sort of information about the function of a device or as a warning to avoid a certain material or area.
One of the most common uses for an emitter is in devices such as the cathode of a vacuum tube or an anode in another type of instrument. A vacuum tube produces electrons through the processes of either thermionic or electron field emission. Thermionic emission involves the transfer of electrons caused by heat, while electron field emission discharges electrons caused by factors from electromagnetic fields. In an anode, solid surface ions are transferred from one location to another, creating an emission.
Perhaps the most prevalent form of emitters on electronic devices are positioned on devices such as video cassette recorders (VCR) to emulate the controls of a remote device. These infrared light emitting diode (LED) controls are connected to the device and interact with external television components to mimic the patterns created by remote controls. This allows the VCR to be used to record programs automatically when chosen from the television signal itself. Features like an infrared LED are common on advanced forms of media technology.
One traditional example of an emitter uses basic technology that has existed for centuries, namely sirens and light projection. Lighthouses act as beacons positioned along shorelines of lakes, seas and oceans. They are designed to prevent ships from crashing into reefs or beaching where the water meets the land. Although modern lighthouses use emitter technology involving radio frequencies, traditional examples used light beacons and loud sirens to warn off the boats.
Although it is used for a vastly different purpose, the horticulture industry also uses the concept of an emitter to perform irrigation. In the process of drip irrigation, small amounts of water is slowly discharged onto roots or in the soil of vegetation. This dripper is commonly known as the emitter and uses a piping system to transmit the water. Usually, the flow rate of the water is less than four gallons (16 liters) per hour to be considered emission in drip irrigation.