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A transducer is a device that converts one form of energy to another form of energy. 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 (for example, a loudspeaker converts an electric 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 a transducer can convert (which is what image sensors, one form of transducer, do). A sensor is a transducer whose purpose is to sense (that is, to detect) some characteristic of its environs. A sensor 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 as microphones.
- Antenna – converts propagating electromagnetic waves to and from conducted electrical signals
- Magnetic cartridge – converts relative physical motion to and from electrical signals
- Tape head, Disk read-and-write head – converts magnetic fields on a magnetic medium to and from electrical signals
- Hall effect sensor – converts a magnetic field level into an electrical signal
- Electromechanical (electromechanical output devices are generically called actuators):
- Electroactive polymers
- Microelectromechanical systems
- Rotary motor, linear motor
- Vibration powered generator
- Potentiometer when used for measuring position
- Linear variable differential transformer or Rotary variable differential transformer
- Load cell – converts force to mV/V electrical signal using strain gauge
- Strain gauge
- String potentiometer
- Air flow sensor
- Tactile sensor
- Loudspeaker, earphone – converts electrical signals into sound (amplified signal → magnetic field → motion → air pressure)
- Microphone – converts sound into an electrical signal (air pressure → motion of conductor/coil → magnetic field → electrical signal)
- Pickup (music technology) – converts motion of metal strings into an electrical signal (magnetism → electrical signal)
- Tactile transducer – converts electrical signal into vibration ( electrical signal → vibration)
- Piezoelectric crystal – converts deformations of solid-state crystals (vibrations) to and from electrical signals
- Geophone – converts a ground movement (displacement) into voltage (vibrations → motion of conductor/coil → magnetic field → signal)
- Gramophone pickup – (air pressure → motion → magnetic field → electrical signal)
- Hydrophone – converts changes in water pressure into an electrical signal
- Sonar transponder (water pressure → motion of conductor/coil → magnetic field → electrical signal)
- Ultrasonic transceiver, transmitting ultrasound (transduced from electricity) as well as receiving it after sound reflection from target objects, availing for imaging of those objects.
- Electro-optical (Photoelectric):
- Fluorescent lamp – converts electrical power into incoherent light
- Incandescent lamp – converts electrical power into incoherent light
- Light-emitting diode – converts electrical power into incoherent light
- Laser Diode – converts electrical power into coherent light
- Photodiode, photoresistor, phototransistor, photomultiplier – converts changing light levels into electrical signals
- Photodetector or photoresistor or light dependent resistor (LDR) – converts changes in light levels into changes in electrical resistance
- Cathode ray tube (CRT) – converts electrical signals into visual signals
- Agarwal, Anant. Foundations of Analog and Digital Electronic Circuits.Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, 2005, p. 43.
- Agarwal, Anant. Foundations of Analog and Digital Electronic Circuits.Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, 2005, p. 43