The word “sensor” is derived from the Latin term “sensus,” which means sense, perception, or observation. Numerous modern definitions for the term sensor have been proposed which accentuate different aspects of sensing. These include the following definitions, which have been selected for the specific purpose of this book:

• A sensor is a device which receives and responds to a stimulus [69]. • A sensor is a device that measures a physical or chemical quantity and converts it into

a signal that can be read by an observer or by modern electronic instruments.