A sensor node is also known as a mote (mostly in North America). This sensor node in a wireless sensor network is capable of performing some processing, gathering of sensory information and communicating with other connected nodes in the network. It must be clearly understood that a mote is a node but a node is not always a mote. Although wireless sensor nodes have existed for decades and used for applications as diverse as earthquake measurements to even warfare, the latest development of small sensor nodes dates back to the 1998 Smartdust project and the NASA Sensor Webs Project. One of the objectives of the Smart dust project was to create autonomous sensing and communication within a cubic millimeter of space. Though this project ended early on, it led to many more research projects. They include major research centers in Berkeley NEST  and CENS . The researchers involved in these projects came up with the term mote to refer to a sensor node. The equivalent term in the NASA Sensor Webs Project for a physical sensor node is pod, although the sensor node in a Sensor Web can be another Sensor Web itself. Physical sensor nodes have been able to increase their capability in conjunction with Moore's Law. The footprint of the chip contains more complex microcontrollers and these microcontrollers are also lower powered. Thus, for the same footprint of the node, more silicon capability can be now packed into it. Nowadays, motes or nodes focus on providing the longest wireless range upto dozens of km, with lowest energy consumption and the easiest development process for the user.
Figure1.1: A typical example of sensor node
1.2 Sensor architecture:
Sensors in wireless sensor networks have the following basic architecture:
Figure 1.2: Basic components of a wireless sensor node.
A sensor node consists of basically the components shown in the figure above. The main components of a sensor are radio transceiver or optical as the communication unit, sensor as the sensing unit, a micro-controller for the processing unit and battery or solsr cells as the power unit. Several sensors may be present in the hardware device in the sensing unit. This device produces measurable response to change which acts as an Interface between motes to the environment. Theses measurable changes are sound, motion, vibration, temperature, pollutants or the pressures in environmental conditions. There are mainly two kinds of sensor used in the network. First, is the normal sensor node deployed to accuraately sense the phenomena. The second is a gateway node that interfaces sensor network to the external world so that the sensed data could reach the user. Hence the whole mechanism of wireless sensor networks works on this principle. Many types of sensor exist now-a-days such as magnetometer, accelerometer, light and others but the types of sensor being used in a sensor node will depend on the application for which it is being deployed. The processing unit in...