SENSORS

 SENSORS:-

Sensors are the device which is used for the two following purpose:-

1.senses or detects any change in the ambient condition of change in the state of another device

2.records or conveys the information about the change in a certain manner.

The specific input could be any one of the followings :

light

heat

motion

moisture

pressure

any one of the great number of other environmental phenomena.

After the sensing or detection,the output which is generally a signal converted to the human-readable display at the sensor location or transmitted electronically over a network for reading or further processing.

Wireless sensor network (WSN):-

The group of spatially dispersed and dedicated sensor is referred to as Wireless sensor network (WSN). The main activities of this sensor in the WSN are monitoring, recording the physical conditions of environment and organizing the collected data at a central location. Next question is what does the WSN measure? The response to the query is an environmental condition like temperature, sound, pollution levels, humidity, wind speed and direction, pressure, etc. It is interesting to know that WSNs were designed initially to facilitate military operations. But in due course time, the scope of its application extended to include health, traffic, and many other consumers and the industrial areas. There is practically no limit on the number of sensor nodes in a WSN, it can vary from few hundreds to the thousands. Typically a radio transceiver along with the antenna, also a microcontroller, an interfacing electronic circuit, and an energy source like battery constitute sensor node

RF WIRELESS SENSORS:-

In practical life, there are two disadvantages for battery usage in wireless sensor and they are firstly the need of battery limits the application space and secondly the initial and recurring cost is increased. In some cases, the temptation comes for using traditional wired sensors.

A unique solution to this practical problem is offered by RF (Radio Frequency ) energy harvesting. RF energy harvesting facilitates the implementation of a battery and the super capacitor-free wireless sensing node with the 24-hour operation. The consumption is fewμW in sleep mode and hundreds μW in active mode for most of the commonly used wireless sensor.

The main advantage of RF harvesting is that it is available all hours of the day and night. For a solar harvesting node, it is clear that IN daytime the energy is generated from some. But what happens when the sun is not there? To respond to the query we can state that there must be a battery or super capacitor (large charge storage device), to deal with the blackout period in which the energy source is unavailable. The RF harvesting node typically does not need to stores much energy as there is no chance of occurring during the blackout period.