Fluidics, orfluidic logic, is the use of afluid to performanalog ordigital operations similar to those performed withelectronics.
The physical basis of fluidics ispneumatics andhydraulics, based on the theoretical foundation offluid dynamics. The termfluidics is normally used when devices have nomoving parts, so ordinary hydraulic components such ashydraulic cylinders and spool valves are not considered or referred to as fluidic devices.
A jet of fluid can be deflected by a weaker jet striking it at the side. This providesnonlinearamplification, similar to thetransistor used in electronic digital logic. It is used mostly in environments where electronic digital logic would be unreliable, as in systems exposed to high levels ofelectromagnetic interference orionizing radiation.
Nanotechnology considers fluidics as one of its instruments. In this domain, effects such as fluid–solid and fluid–fluid interface forces are often highly significant. Fluidics have also been used for military applications.
In 1920, Nikola Tesla patented a valvular conduit orTesla valve that works as a fluidic diode. It was a leaky diode, i.e. the reverse flow is non-zero for any applied pressure difference. Tesla's valve also had non-linear response, as its diodicity had frequency dependence. It could be used in fluid circuits, such as a full-wave rectifier, to convert AC to DC.[1] In 1957, Billy M. Horton of theHarry Diamond Laboratories (which later became a part of theArmy Research Laboratory) first came up with the idea for the fluidic amplifier when he realized that he could redirect the direction of flue gases using a smallbellows.[2] He proposed a theory on stream interaction, stating that one can achieve amplification by deflecting a stream of fluid with a different stream of fluid. In 1959, Horton and his associates, Dr. R. E. Bowles and Ray Warren, constructed a family of working vortex amplifiers out of soap, linoleum, and wood.[3] Their published result caught the attention of several major industries and created a surge of interest in applying fluidics (then called fluid amplification) to sophisticated control systems, which lasted throughout the 1960s.[4][5] Horton is credited for developing the first fluid amplifier control device and launching the field of fluidics.[6] In 1961, Horton, Warren, and Bowles were among the 27 recipients to receive the first Army Research and Development Achievement Award for developing the fluid amplifier control device.[7]
Logic gates can be built that use water instead of electricity to power the gating function. These are reliant on being positioned in one orientation to perform correctly. An OR gate is simply two pipes being merged, and a NOT gate (inverter) consists of "A" deflecting a supply stream to produce Ā. The AND and XOR gates are sketched in the diagram. An inverter could also be implemented with the XOR gate, as A XOR 1 = Ā.[8]
Another kind of fluidic logic isbubble logic. Bubble logic gates conserve the number of bits entering and exiting the device, because bubbles are neither produced nor destroyed in the logic operation, analogous tobilliard-ball computer gates.[9]
In a fluidic amplifier, a fluid supply, which may be air, water, orhydraulic fluid, enters at the bottom. Pressure applied to the control ports C1 or C2 deflects the stream, so that it exits via either port O1 or O2. The stream entering the control ports may be much weaker than the stream being deflected, so the device hasgain.
This basic device can be used to construct other fluidic logic elements, as well fluidic oscillators that can be used in analogous way asflip flops.[10] Simple systems of digital logic can thus be built.
Fluidic amplifiers typically have bandwidths in the lowkilohertz range, so systems built from them are quite slow compared to electronic devices.
The fluidictriode, anamplification device that uses afluid to convey thesignal, has been invented, as have fluid diodes, a fluid oscillator and a variety of hydraulic "circuits," including one that has no electronic counterpart.[11]
TheMONIAC Computer built in 1949 was a fluid-basedanalogue computer used for teaching economic principles as it could recreate complex simulations that digital computers could not at the time. Twelve to fourteen were built and acquired by businesses and teaching establishments.
The FLODAC Computer was built in 1964 as a proof of concept fluid-baseddigital computer.[12]
Fluidic components appear in some hydraulic and pneumatic systems, including some automotiveautomatic transmissions. As electronicdigital logic has become more accepted in industrial control, the role of fluidics in industrial control has declined.
In the consumer market, fluidically controlled products are increasing in both popularity and presence, installed in items ranging from toy spray guns through shower heads and hot tub jets; all provide oscillating or pulsating streams of air or water. Logic-enabled textiles for applications inwearable technology has also been researched.[13]
Fluid logic can be used to create avalve with no moving parts such as in someanaesthetic machines.[14]
Fluidic oscillators were used in the design of pressure-triggered,3D printable, emergency ventilators for theCOVID-19 pandemic.[15][16][17]
Fluidic amplifiers are used to generate ultrasound for non-destructive testing by quickly switching pressurized air from one outlet to another.[18]
A fluidic sound ampliflication system has been demonstrated in a synagogue, where regular electronic sound amplification can not be used for religious reasons.[19][20]
Fluidic injection is being researched for use inaircraft to control direction, in two ways:circulation control andthrust vectoring. In both, larger more complex mechanical parts are replaced by fluidic systems, in which larger forces in fluids are diverted by smaller jets or flows of fluid intermittently, to change the direction of vehicles. In circulation control, near the trailing edges of wings,aircraft flight control systems such asailerons,elevators,elevons,flaps, andflaperons are replaced by openings, usually rows of holes, or elongated slots, which emit fluid flows.[21][22][23] Inthrust vectoring, injet engine nozzles, swiveling parts are replaced by openings which inject fluid flows into jets.[24] Such systems divert thrust via fluid effects. Tests show that air forced into a jet engine exhaust stream can deflect thrust up to 15 degrees.[24] In such uses, fluidics is desirable for lower: mass, cost (up to 50% less), drag (up to 15% less during use),inertia (for faster, stronger control response), complexity (mechanically simpler, fewer or no moving parts or surfaces, less maintenance), andradar cross section forstealth.[25][26] This will likely be used in manyunmanned aerial vehicles (UAVs), 6th generationfighter aircraft, andships.
As of 2023[update], at least two countries are known to be researching fluidic control. In Britain,BAE Systems has tested two fluidically controlled unmanned aircraft, one starting in 2010 namedDemon,[27][28] and another starting in 2017 named MAGMA, with theUniversity of Manchester.[29] In the United States, theDefense Advanced Research Projects Agency (DARPA) program namedControl of Revolutionary Aircraft with Novel Effectors (CRANE) seeks "... to design, build, and flight test a novel X-plane that incorporates active flow control (AFC) as a primary design consideration. ... In 2023, the aircraft received its official designation as X-65."[30][31] In winter 2024, construction began, atBoeing subsidiaryAurora Flight Sciences.[32] In summer 2025, flight testing is to start.[32]
Octobot, a 2016proof of conceptsoft-bodiedautonomous robot containing amicrofluidiclogic circuit, has been developed by researchers atHarvard University'sWyss Institute for Biologically Inspired Engineering.[33]
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