Transducer Definition

A transducer is a device, usually electrical, electronic, electro-mechanical, electromagnetic, photonic, or photovoltaic that converts one type of energy or physical attribute to another for various purposes including measurement or information transfer (for example, pressure sensors).
The term transducer is commonly used in two senses; the sensor, used to detect a parameter in one form and report it in another (usually an electrical or digital signal), and the audio loudspeaker, which converts electrical voltage variations representing music or speech, to mechanical cone vibration and hence vibrates air molecules creating sound.
Types of transducers
• Electromagnetic:
o Antenna - converts electromagnetic waves into electric current and vice versa.
o Cathode ray tube (CRT) - converts electrical signals into visual form
o Fluorescent lamp, - converts electrical power into visible light
o Magnetic cartridge - converts motion into electrical form
o Pick up (music technology)- converts motion into electrical form
o Photodetector or Photoresistor (LDR) - converts changes in light levels into resistance changes
o Tape head - converts changing magnetic fields into electrical form
o Hall effect sensor - converts a magnetic field level into electrical form only.
• Electrochemical:
o pH probes
o Electro-galvanic fuel cell
• Electromechanical (electromechanical output devices are generically called actuators):
o Electroactive polymers
o Galvanometer
o Rotary motor, linear motor
o Vibration powered generator
o Potentiometer when used for measuring position
o Load cell converts force to mV/V electrical signal using strain gauge
o Accelerometer
o Strain gauge
o Air flow sensor
• Electroacoustic:
o Geophone - convert a ground movement (displacement) into voltage
o Gramophone pick-up
o Hydrophone - converts changes in water pressure into an electrical form
o - converts changes in electrical signals into acoustic form
o Microphone - converts changes in air pressure into an electrical signal
o Piezoelectric crystal - converts pressure changes into electrical form (and electrical signals into acoustic/mechanical form)
o Tactile transducer
• Photoelectric:
o Laser diode, light-emitting diode- convert electrical power into forms of light
o Photodiode, photoresistor, tube - converts changing light levels into electrical form
• Electrostatic:
o Electrometer
• Thermoelectric:
o Resistance Temperature Detector
o Thermocouple
o Thermistor (includes PTC resistor and NTC resistor)
• Radioacoustic:
o used for measuring radioactivity.
o Receiver (radio)