The term transducer deals with the subject of energy conversion. Transducer devices whether electrical, electronic, electro-mechanical, electromagnetic, photonic, or photovoltaic are designed and constructed to convert a particular type of energy to another. The purposes of the conversion may vary from measurement to information transfer, for example a pressure sensor.
Another example, the conversion of electrical voltage variations representing music or speech to mechanical cone vibrations, which vibrate air molecules to create acoustic energy. This conversion of signals from one form to another takes place in a viable system model transducer device known as an audio speaker.
Electromagnetic transducer devices include antennas where the conversion of electromagnetic waves into electric current and vice versa takes place, cathode ray tubes or CRT that convert electrical signals into visual forms, fluorescent lamps and light bulbs that convert electrical power into visible light, magnetic cartridges or converters of motion into electrical forms, photocells or light-dependent resistors or LDR that convert changes in light levels into resistance changes, tape heads used for the conversion of changing magnetic fields into electrical forms, and hall effect sensors used to convert magnetic field levels into electrical forms.
Electrochemical transducers include pH probes and electro-galvanic fuel cells. Electromechanical or electromechanical output devices commonly known as actuators include electro-active polymers, galvanometers, MEMS, rotary or linear motors, vibration powered generators, potentiometers, load cells, accelerometers, strain gauges, switches, string potentiometers, and air flow sensors.
Electro-acoustic transducers include geophones that convert ground movement or displacement into voltage, gramophone pick-ups, hydrophones or converters of water pressure into an electrical forms, loudspeakers and earphones, microphones, piezoelectric crystals that convert pressure changes into electrical forms, and tactile transducers.