A transducer is a device that converts one form of energy to another. Energy types include (but are not limited to): electrical, mechanical, electromagnetic (including light),chemical, acoustic, and thermal energy. Usually a transducer converts a signal in one form of energy to a signal in another[1] (for example, a loudspeaker driver converts anelectric signal to sound), but any variable attenuation of energy may serve as input; for example, the light reflecting off the landscape, although it is not a signal, conveys information that image sensors, one form of transducer, can convert. A sensor is a transducer whose purpose is to sense (i.e. detect) some characteristic of its environs; it is used to detect a parameter in one form and report it in another form of energy, often an electrical signal. For example, a pressure sensor might detect pressure (a mechanical form of energy) and convert it to electrical signal for display at a remote gauge. Transducers are widely used in measuring instruments.
An actuator is a transducer that accepts energy and produces the kinetic energy of movement (action). The energy supplied to an actuator might be electrical or mechanical (pneumatic, hydraulic, etc.). An electric motor and a hydraulic cylinder are both actuators, converting electrical energy and fluid power into motion for different purposes.
Combination transducers have both functions; they both detect and create action. The most common example is an antenna, a transducer of radio waves that can transmit,receive, or both (transceiver). Another example is the typical ultrasonic transducer, which switches back and forth many times a second between acting as an actuator to produce ultrasonic waves, and acting as a sensor to detect ultrasonic waves. Rotating a DC electric motor's rotor will produce electricity, and voice-coil speakers can also act asmicrophones.
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