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The application of the physical properties of liquids and gases as a fluid to perform logic operations that control other mechanical systems is called fluidics. Hydraulics and pneumatics, respectively, starting from the Industrial Revolution that began around the late 1700s, provided a foundation. Subsequent study on the dynamics of fluids — liquids in particular — developed into a theoretical model of predictive behavior. This gave engineers a framework from which to conceive switches and other logic circuits which became the forerunners of modern electronics. Although digital circuits dominate the world today, fluidic processors remain in critical use.
Fluidics is not to be confused with the compression or expansion of liquids and gases as a hydraulic or pneumatic power source. Instead, the flow of a fluid is conceived as a medium capable of changing its character, carrying this information and transmitting it to other flows. The core functioning of a fluidic device has no moving parts.
The first set of assumptions about fluid dynamics is the Newtonian physics of classical mechanics. To this is added the variables of velocity, pressure, density and temperature as functions of space and time. An additional law is especially important — the “continuum assumption,” that the flow characteristics of a fluid can be described without accounting for the known fact that fluids are composed of discreet molecular particles. Both theoretical and empirical physicists continue to expand computational understanding of viscosity, turbulence and other peculiar features of a fluid in motion. Engineers have followed with increasingly sophisticated fluidic devices.
Fluidics technology did not have a full opportunity to mature. The first logic circuits, including an amplifier and a diode, were invented in the early 1960s. Concurrently, the same concepts of signal amplification and transmission were realized employing a flow of electrons, and the invention of the solid state transistor ushered in a digital revolution.
The physical flow of a fluid, of course, cannot match the speed of an electron. A fluidic signal processor typically has an operating speed of just a few kilohertz. Unlike an electron, however, the mass flow of a liquid or gas is unaffected by electromagnetic or ionic interferences. Fluidics therefore remain necessary for the control of some failure-intolerant systems, such as military avionics. Fluidics have also developed into effective processors of analog data because of the nature of fluids to flow as a wave.
One of the major challenges of fluidics is that the principles of fluid dynamics are apparently different according to scale. To be sure, climatologists have yet to fully understand how massively large bodies of water or currents of air behave. Likewise, scientists have discovered that fluids behave very differently when studied at the scale of nanotechnology. Future study and application of the latter, called nano-fluidics, pose the possibility of significantly faster and more complex circuitry, including multiple gate arrays for parallel processing.