Sensors as Information Transducers
  This chapter reviews the mechanisms by which sensors gather information from the physical world and transform it into the electronic signals that are used in today's information and control systems. It introduces a new methodology for describing sensing mechanisms based on the process of information flow and applies it to the broad spectrum of sensors, instruments and data input devices in current use. We identify four distinct elemental transduction processes: energy conversion, energy dispersion, energy modulation and modulation of a material property. We posit that these four mechanisms form a complete set for describing information transduction in sensing systems. 
J. David zook and Norbert Schroeder