The physical basis of fluidics is pneumatics and hydraulics, based on the theoretical foundation of fluid dynamics. The term fluidics is normally used when devices have no moving parts, so ordinary hydraulic components such as hydraulic cylinders and spool valves are not considered or referred to as fluidic devices. The 1960s saw the application of fluidics to sophisticated control systems, with the introduction of the fluidic amplifier.
A jet of fluid can be deflected by a weaker jet striking it at the side. This provides nonlinear amplification, similar to the transistor 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 of electromagnetic interference or ionizing 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.
The basic concept of the fluidic amplifier is shown here. A fluid supply, which may be air, water, or hydraulic 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 has gain.
Given this basic device, flip flops and other fluidic logic elements can be constructed. Simple systems of digital logic can thus be built.
Fluidic amplifiers typically have bandwidths in the low kilohertz range, so systems built from them are quite slow compared to electronic devices.
Although much studied in the laboratory they have few practical applications. Many expect them to be key elements of nanotechnology.
The Fluidic Triode was invented in 1962 by Murray O. Meetze, Jr., a high school student in Heath Springs, S.C. He also built a fluid diode, a fluid oscillator and a variety of hydraulic "circuits," including one that has no electronic counterpart. As a result he was invited to the National Science Fair, held this year at the Seattle Century 21 Exposition. There his project won an award.
- (Scientific American, Aug. 1962)
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, a NOT gate consists of "A" deflecting a supply stream to produce Ā. An inverter could also be implemented with the XOR gate, as A XOR 1 = Ā. 
Bubble logic is another kind of fluidic logic. Bubble logic gates conserve the number of bits entering and exiting the device, since bubbles are neither produced nor destroyed in the logic operation, analogous to billiard-ball computer gates. 
The MONIAC Computer built in 1949 was a fluid-based analogue computer used for teaching economic principles as it could recreate complex simulations that digital computers could not. Twelve to fourteen were built and acquired by businesses and teaching establishments.
Fluidic components appear in some hydraulic and pneumatic systems, including some automotive automatic transmissions. As digital 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 streams of air and/or water.
Fluidic injection is being researched for use in aircraft to control direction, in two ways: circulation control and thrust 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 as ailerons, elevators, elevons, flaps and flaperons are replaced by slots which emit fluid flows.
In thrust vectoring, in jet engine nozzles, swiveling parts are replaced by slots which inject fluid flows into jets. 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.
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), and radar cross section for stealth. This will likely be used in many unmanned aerial vehicles (UAVs), 6th generation fighter aircraft, and ships.
- A four-bit Adder made using fluidic logic
- Manu Prakash. "Bubble Logic". MIT 2007.
- P John (2010). "The flapless air vehicle integrated industrial research (FLAVIIR) programme in aeronautical engineering". Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering (London: Mechanical Engineering Publications) 224 (4): 355–363. doi:10.1243/09544100JAERO580. ISSN 0954-4100.
- "Showcase UAV Demonstrates Flapless Flight". BAE Systems. 2010. Retrieved 2010-12-22.
- "Demon UAV jets into history by flying without flaps". Metro.co.uk (London: Associated Newspapers Limited). 28 September 2010.
- P. J. Yagle, D. N. Miller, K. B. Ginn, J. W. Hamstra (2001). "Demonstration of Fluidic Throat Skewing for Thrust Vectoring in Structurally Fixed Nozzles". Journal of Engineering for Gas Turbines and Power 123 (3): 502–508. doi:10.1115/1.1361109.
- Forbes T., Brown (1967). Advances in Fluidics. The American Society of Mechanical Engineers.
- Hydraulic Machines Lal J. Metropolitan Book
- A Guide to Fluidics A. Conway ISBN 9780444196019
- Fluidics: Components and Circuits Foster, Kenneth John Wiley & Sons （1970）ISBN 9780471267706
- Scanned article available online from Google Books: Popular Science June 1967, Fluidics: How They've Taught A Stream of Air to Think pp. 118–121,196.197, illustrating several switch designs and discussing applications