Transducer

                      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.

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 actuators, 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.

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 or light dependent resistor (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
• Microelectromechanical systems
• 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
• Tactile 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)
• Pickup (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 modulations into an electrical signal (vibration → electrical current → signal)
• Geophone – converts a ground movement (displacement) into voltage (vibrations → motion of conductor/coil → magnetic field → signal)
• Gramophone pickup – (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:xxfhm
• Laser diode, light-emitting diode – converts electrical power into forms of light
• Photodiode, photoresistor, phototransistor, photomultiplier tube – converts changing light levels into electrical form

Electrostatic:

• Electrometer

Thermoelectric:

• Resistance temperature detector (RTD)
• Thermocouple
• Peltier cooler
• Thermistor (includes PTC resistor and NTC resistor)

Radioacoustic:

• Geiger–Müller tube – used for measuring radioactivity
• Receiver (radio)