Transducers are devices that convert energy from one form to another. Common examples include microphones, speakers, thermometers, position and pressure sensors, and antennas. Although not generally considered a transducer, photovoltaic cells, LEDs (light emitting diodes) and even ordinary light bulbs are transducers.
Efficiency is an important consideration for any sensor. Transducer efficiency is defined as the ratio of desired form of power output to total power input. Mathematically, if P represents the total power input and Q represents the desired form of power output, the efficiency E, which is the ratio between 0 and 1, is given by:
E = Q / P
If E% represents the percentage efficiency, then:
E% = 100Q / P
No sensor is 100% efficient; there will always be some power lost during the conversion. This loss usually manifests itself in the form of heat. Some antennas are close to 100% efficiency. A well-designed antenna that provides 100 watts of radio frequency (RF) power radiates 80 or 90 watts in the form of an electromagnetic field. Several watts of heat are dissipated in the antenna conductor, the feeder conductor and the dielectric, as well as the object close to the antenna. The worst efficiency transducer is an incandescent lamp. A 100-watt bulb emits only a few watts in visible light. Most of the energy is dissipated as heat; there is a small amount of radiation in the UV spectrum.