Sensors in the natural world include those which equip us with our five senses: sight, hearing, smell, taste, and touch. These convert the various and diverse inputs to electrochemical signals that can be used to inform or control the living organism. In a similar way, in man-made devices, sensors are also used to measure various stimuli. However, because of the broad range of potential inputs and outputs, the accepted definition of a sensor is refined. In this definition, all devices that convert input energy into output energy are referred to as transducers, and sensors form a small subset of the group as defined below: 'A sensor is a transducer that receives an input signal or stimulus and responds with an electrical signal bearing a known relationship to the input' (Fraden 2003). Systems of sensors and transducers are constructed for a variety of applications, including surveillance, imaging, mapping, and target tracking. In some cases, the sensors provide their own source of illumination and are referred to as active sensors. Passive sensors, on the other hand, do not provide illumination and depend on variations of natural conditions for detection.

Chapter Contents:

• 1.1 Introduction
• 1.1.1 Active Sensors
• 1.1.2 Passive Sensors
• 1.2 A Brief History of Sensing
• 1.2.1 Sonar
• 1.2.2 Radar
• 1.2.3 Lidar
• 1.3 Passive Infrared Sensing
• 1.4 Sensor Systems
• 1.5 Frequency Band Allocations for the Electromagnetic Spectrum
• 1.6 Frequency Band Allocations for the Acoustic Spectrum
• 1.7 References

Inspec keywords: transducers; sensors

Other keywords: sight; electrical signal; target tracking; hearing; imaging; touch; passive sensors; living organism; transducers; taste; mapping; smell; illumination source; surveillance; man-made devices; active sensors; electrochemical signals

Subjects: Sensing devices and transducers