A transducer is a device that converts one type of energy to another. The conversion can be to/from electrical, electro-mechanical, electromagnetic, photonic, photovoltaic, or any other form of energy. While the term transducer commonly implies use as a sensor/detector, any device which converts energy can be considered a transducer.

[edit] Types

Transducers may be categorized by application: Sensor, actuator, or combination.

A sensor is used to detect a parameter in one form and report it in another form of energy (usually an electrical and/or digital signal). For example, a pressure sensor] might detect pressure (a mechanical form of energy) and convert it to electricity for display at a remote gauge.

An actuator accepts energy and produces movement (action). The energy supplied to an actuator might be electrical or mechanical (pneumatic, hydraulic, etc.). An electric motor and a loudspeaker are both transducers, converting electrical energy into motion for different purposes.

Combination transducers have both functions -- they both detect and create action. For example, a typical ultrasonic transducer 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.

[edit] Applications

• Electromagnetic:
  • Antenna - converts electromagnetic waves into electric current and vice versa.
  • Cathode ray tube (CRT) - converts electrical signals into visual form
  • Fluorescent lamp, light bulb - converts electrical power into visible light
  • Magnetic cartridge - converts motion into electrical form
  • Photodetector or Photoresistor (LDR) - converts changes in light levels into resistance changes
  • Tape head - converts changing magnetic fields into electrical form
  • Hall effect sensor - converts a magnetic field level into electrical form only.

• Electrochemical:
  • pH probes
  • Electro-galvanic fuel cell
  • Hydrogen sensor
• Electromechanical (electromechanical output devices are generically called actuators):
  • Electroactive polymers
  • Galvanometer
  • MEMS
  • Rotary motor, linear motor
  • Vibration powered generator
  • Potentiometer when used for measuring position
  • Load cell converts force to mV/V electrical signal using strain gauge
  • Accelerometer
  • Strain gauge
  • String Potentiometer
  • Air flow sensor

• Electroacoustic:
  • 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 → signal)
  • Pick up (music technology) - converts motion of metal strings into an electrical signal (magnetism → electricity (signal))
  • Tactile transducer - converts solid-state vibrations into electrical signal (vibration → ? → signal)
  • Piezoelectric crystal - converts solid-state electrical moduluations into an electrical signal (vibration → ? → signal)
  • Geophone - convert a ground movement (displacement) into voltage - (vibrations → motion of conductor/coil → magnetic field → signal)
  • Gramophone pick-up - (air pressure → motion → magnetic field → signal)
  • Hydrophone - converts changes in water pressure into an electrical form
  • Sonar transponder (water pressure → motion of conductor/coil → magnetic field → signal)

• Photoelectric:
  • Laser diode, light-emitting diode - convert electrical power into forms of light
  • Photodiode, photoresistor, phototransistor, photomultiplier tube - converts changing light levels into electrical form

• Electrostatic:
  • Electrometer

• Thermoelectric:
  • RTD Resistance Temperature Detector
  • Thermocouple
  • Peltier cooler
  • Thermistor (includes PTC resistor and NTC resistor)

• Radioacoustic:
  • Geiger-Müller tube used for measuring radioactivity.
  • Receiver (radio)

[edit] See also