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You have probably heard about the mechanical computers built before the electronic age. But did you know that computers and ‘circuits’ based on fluid flows have been built and used since the late 50s? You’ve probably used one; until recently, most automatic transmissions used oil-pressure logic to select gears. And now “microfluidics” brings more options for logic and analog signal processing. Fluid logic, Fluidics and Microfluidics F Ordinary hydraulic devices such as luid logic, known as “fluidics”, “fluidic oscillators”. Electrical or elechydraulic cylinders are not considered was a concept that came about tronic implementation of these same to be fluidic devices. during the late 1950s and was functions would be expensive, comThe initial motivation for developheavily researched in the 60s and 70s. plicated and require electrical wiring. ing these devices was due to the Cold Like electronics, these devices have no Certain windscreen washer nozzles War. There was pressure between the moving parts; they use fluids (liquids generate a moving spray pattern using West and the Soviet Bloc to produce deor gases) to perform similar functions fluidic effects; “flapless” aircraft convices that were resistant to the effects to the electrons in electronics. trol systems also use fluidics. of electromagnetic pulses and raTypically, the fluid moves through diation from nuclear explosions. channels etched or machined in Fluidics offered a solution to a solid block of material, such as this problem (see Figs.2-5). metal or plastic. Later, these devices were The functions provided can adopted for more peaceful uses be analog or digital in nature. due to their robustness, in apFor example, a fluidic device plications such as industrial could provide amplification automation. (analog) or perform boolean But with the rapid developlogic operations (digital). ment of military and civilianDevices that incorporate grade electronics that could fluidics and also use moving withstand the effects of nuclear parts, such as valves or elecwar and the rigours of industry, tronics, are known as hybrid they became mostly obsolete systems. some time in the 1970s, and few As mentioned above, the people know of them today. example you’re most likely Fluidics is considered to have to be familiar with is an austarted in what is now known as the tomatic transmission; the conArmy Research Laboratory in Marytrolling ‘valve body’ is a hybrid land, USA. device – see Fig.1. Fig.1: the valve body from an automotive automatic In 1957, Billy M. Horton inOther examples of fluidic transmission. The numerous passages that are filled with vented the fluidic amplifier devices in widespread use totransmission fluid work as a fluidic computer, to make day are devices that provide decisions as to when or if to shift gear and to direct fluid, (then called fluid amplification). pulsating streams of water, as via valves, into the appropriate clutch pack or band In 1959, Horton and colused in some shower heads servo. Newer automatic transmissions are controlled by leagues R. E. Bowles and Ray and hot tub jets which employ a computer using solenoids in the valve body. 14 Silicon Chip Australia’s electronics magazine siliconchip.com.au By Dr David Maddison Wyss Institute of Harvard University’s “lung on a chip” which mimics the mechanical and biochemical behaviours of a human lung. It is intended to replace animals in drug and toxin testing and other lung-related research. See the video titled “Wyss Institute Human Lung-on-a-Chip” at: https://vimeo.com/22999280 Warren developed a range of such devices, and this attracted widespread industrial and military interest. There are earlier patents on fluidic amplifiers from the 1930s and 1940s, but these attracted little attention at the time. The development of fluidic systems peaked in the 1960s and 1970s, and NASA produced a list shown of systems that had been successfully imple- Fig.2: a fluidic ‘integrated circuit’ logic device (stepper motor actuator) for a nuclear rocket motor from a 1972 NASA document. Fluidics was chosen for this device as it was to be placed next to the nuclear fuel in a high radiation and heat area. siliconchip.com.au mented as of 1972 – see Table 1. Compared to electronic devices of the time, fluidic devices were slow and operated at no more than a few kilohertz. They were smaller than equivalent electromechanical components such as solenoids and relays, but much larger than electronic equivalents. In practice, no more than three fluidic elements could be connected in a Fig.3: an exploded view of the stepper motor actuator shown in Fig.2. Australia’s electronics magazine chain, but they were very robust compared to electronics of that era. Apart from some niche applications for traditional fluidics, which are described below, there has in recent times (since the 1980s) been a revival of interest in fluidics. But interest is now in a different area, known as “microfluidics”. Microfluidics is mostly used in biotechnology, but also in some other areas. It involves the manipulation of tiny Fig.4: details of one of the fluidic components of the integrated logic circuit – a pulse conditioner – shown in Figs.2 & 3. August 2019  15 Most fluidic amplifying or control devices have four basic elements: a supply port, an output port, a control port and an interaction region (see Fig.6). In terms of a vacuum tube equivalent, these elements would be, in order, the cathode, plate, grid and the interelectrode region. With greater device complexity, there may be more ports. The behaviour of the fluidic device is governed by the types of fluid dynamic phenomena that occur in the interaction region. The three main types of effects that occur are: 1) Jet interaction, where an unconstrained stream of fluid (the supply jet) is influenced by a control flow which moderates it. 2) Surface interaction, where the supply jet interacts with a surface. This includes the Coandå effect, which refers to the tendency of a stream of fluid near a surface to attach to that surface and to remain in contact with it, even though the direction of the surface is different from the initial flow of the stream. 3) Vortex flow, in which a vortex, or tendency to form one, influences the device function. Fig.7(a) shows an example of a logic device that uses jet interaction. It is an AND/XOR logic gate. The output of an AND gate is high (on) if both inputs are high (on) while the output of an XOR gate is high (on) if one input is high (on) and the other is low (off). The first picture shows the device with no fluid. At the top there are two channels; one is for the supply and the other may be considered the control channel. In the middle, there is a “bucket” which forms the AND gate. It collects (or doesn’t collect) streams of fluid and has its own output connection. At the bottom of the device, there is another output to collect (or not) a stream of fluid, and this is the XOR gate output. Fig.7(b) shows how, with fluid applied to one of the inputs but not both, it can pass through to the output at the bottom, giving the correct result for an XOR gate. But as shown in Fig.7(c), if both input streams contain fluid, the two streams collide and the fluid is col- (b) (c) Fig.6: an idealised representation of the basic parts of a fluidic device. The output of the device is dependent upon what happens in the interaction region. Source: NASA. Fig.5: a close-up of the power amplifier plate, “Power amplifier D” from the NASA fluidic integrated circuit (Figs.2-4). Note the scale. amounts of liquid, typically in the picolitre (10-12l) to microlitre (10-6l) range. To visualise a picolitre, it is the volume of a cube measuring just 0.01mm on each side! Examples of microfluidic devices include “labs on a chip”, DNA microarrays, inkjet printer heads and some micropropulsion devices for miniature spacecraft. Basic principles of fluidics Fluidics utilises the interaction of gas or liquid streams in appropriately etched or otherwise shaped constraining structures. These can provide sensing, computing, amplifying and controlling functions, generally without moving parts. These devices are therefore simple, robust and reliable. (a) Fig.7: a fluidic logic AND/XOR logic gate, using jet interaction. If one of the input streams contains fluid but not the other, that fluid flows out the bottom. But if both streams contain fluid, they collide and collect in the upper bucket, and exit through the separate hose. Source: Paulo Blikstein. 16 Silicon Chip Australia’s electronics magazine siliconchip.com.au ¦P = 0 Fig.9: a wall attachment fluidic amplifier. Source: J.W. Joyce and R.N. Gottron, US Army, HDL-SR-77-6. Fig.10 (above): a microchannel fluidic diode (note the scale). The diode element is the chain of triangular channels. The direction of highest flow resistance is from right to left, which may seem counter-intuitive. Nikola Tesla patented a similar device called the Tesla valve in 1920. Source: Graydon Yoder et al, Oak Ridge National Laboratory, ORNL/TM-2011/425. ¦P = 0 Fig.8: a jet deflection fluidic proportional amplifier. Source: J.W. Joyce and R.N. Gottron, US Army, HDL-SR-77-6. lected in the AND bucket and flows through the upper output tube, giving the correct result for an AND gate. Examples of devices which use surface interaction (fluidic thrust vectoring) and vortex flow (spray nozzles, flow rate metering and massage chair control) are given below. Fluidic element examples As mentioned above, fluidic elements can perform analog or digital functions. Here are some examples of both, but note that this is only a small subset of the fluidic designs which exist. A jet deflection fluidic proportional amplifier is an analog device in which a supply jet is diverted from one output port to another, depending on the flow coming from one of the control ports. Fig.11 (right): various fluidic logic (digital) device schematics showing the valve, logical and electrical equivalents for each, as used in fluidic digital logic modules from the 1960s and 1970s by Bowles Fluidics Corporation. These were used in industrial assembly lines and by the US Navy for boiler control. Source: Bowles Fluidics Corporation, now known as dlhBowles. siliconchip.com.au Australia’s electronics magazine August 2019  17 sistance thermometers and shielded thermocouples. A fluidic oscillator temperature sensor works by supplying fluid with a varying pressure of fixed amplitude and frequency to a sensor tube. Temperature changes in this tube cause a varying phase shift in the pressure wave passing through this tube, and a fluidic phase discriminator measures the resulting phase shift and produces a signal proportional to the sensor tube temperature. Fluidic flight controls Fig.12: the channel pattern for a divide-by-ten fluidic computer component, as featured in Scientific American, December 1964. It produces one output pulse for every ten input pulses. The circuit contains ten logic elements arranged in pairs, with two on the right and three on the left. Each element has an input stream (sausage shape), an output (a small circle attached to a short, straight channel), four control jets (tear-drop shapes) and four vents (large circles). With no flow to the control ports, the supply port provides an equal flow to both output ports, but with a flow from one control port, it produces a proportional difference in the flow to the output ports – see Fig.8. A wall attachment fluidic amplifier, like the jet deflection amplifier, has a supply port, control ports, output ports and vents but is a digital, bistable device. When a control port stream impinges on the supply stream, the stream remains directed to one of the out- Fig.14: a comparison of airflow control on an aircraft with conventional flaps and one with fluidic control. The airflow is deflected the same in both but with fluidic control, this is done by the injection of additional air into the top of the trailing edge, which tends to follow the profile of that curved surface (due to the Coandå effect), causing deflection of the main air flow. Source: FLAVIIR project. 18 Silicon Chip Fig.13: the fluidic oscillator based temperature sensor mounted on top of the vertical fin of an X-15 hypersonic aircraft. put ports, even if the control port is switched off. That’s because the stream is attached to one of the device’s walls due to the Coandå effect (Fig.9). Fig.10 shows how a microfluidic diode is formed, while Fig.11 gives various examples of different digital logic circuits implemented using fluidics. Fig.12 shows a fluidic divide-by-10 counter implemented as a single, complex channel in a solid block of material. The result is quite aesthetically pleasing. Fluidic oscillators A fluidic oscillator is another important type of fluidic device. Fluidic oscillator temperature sensing devices were used on the X-15 rocket-powered research aircraft, as they can cope with the extremely high temperatures experienced during flight at speeds up to Mach 6.7 (7,274km/h) – see Fig.13. This was beyond the capability of re- The BAE Systems “Demon” is an experimental unmanned aerial vehicle (UAV) with a wingspan of 2.5m, first flown in 2010. It uses fluidic flight controls, based on surface interaction and the Coandå effect, instead of conventional thrust-vectoring and flaps such as elevators and ailerons – see Figs.14, 15 & 16. In addition to the fluidic controls, it also has conventional flaps that are presumably used as a backup system, as they are not necessary for flight control. The elimination of flaps and conventional thrust vectoring results in much less mechanical complexity and hence greater reliability, and probably lower cost too. The absence of moveable control surfaces on aircraft with fluidic controls also enables the aircraft shape to be optimised for a lower radar signature, and therefore improved stealth capabilities. See the video titled “Cranfield/BAE Systems Demon UAV’s flapless flight” at: siliconchip.com.au/link/aarr Australian innovation Australian inventor Dr Duncan Fig.15: this shows how fluidic thrust vectoring works. There is a primary flow from the jet exhaust, as with a conventional arrangement, but then there is an additional secondary flow. Depending upon the location of the secondary flow, it causes the primary flow to be deflected up, down or sideways. Source: FLAVIIR project. Australia’s electronics magazine siliconchip.com.au One of the first mentions of fluidics or pure fluid amplifier circuits (PFAs, as they were then known) from Science and Mechanics magazine of June 1960. This was the first page of the article. It notes that “Almost everything that has been done so far in the Army laboratory can be done in the home workshop”. siliconchip.com.au Australia’s electronics magazine August 2019  19 www.baesystems.com An auxiliary power unit provides compresed air to circulation control devices in the wings of the craft. SOURCE: BAE Systems The management of compressed air throughout the aircraft is controlled by DEMON’s onboard computer. The trailing edge of each wing has slots from which jets of air can be expelled. These jets replace the need for the elevators or ailerons found in traditional aircraft. BACKGROUND The demonstrator aircraft, which weighs approx. 90kgs and has a wingspan of 2.5m, undertook the first 'flapless' flight ever to be allowed by the UK Civil Aviation Authority on 17 September 2010. Jets of air expelled from the bottom wing slots curl upward (this has the effect of lowering the wing). Because it is designed to fly with no conventional elevators or ailerons, getting its pitch and roll control from technologies which rely on blown air, it requires much fewer moving parts, making it a lot easier to maintain and repair. DEMON can fly parts of its mission by itself but, as it is currently an experimental vehicle, is not fully autonomous unlike, for example, BAE Systems’ MANTIS. It was developed by BAE Systems and Craneld University in the UK. It incorporates fluidic flight controls developed at Cranfield and Manchester Universities and flight control algorithms developed at Leicester University and Imperial College. ENGINE: TITAN 390 N WINGSPAN: 2.5 METRES WEIGHT: 90 KILOGRAMS BODY: CARBON FIBRE COMPOSITE Jets of air expelled from the top wing slots curl downward (this has the effect of lifting the wing). The primary jet stream flows from the fluidic thrust vectoring nozzle. Secondary jets, either above or below the primary jet, can lift or lower the direction of the main thrust. Fig.16: the fluidic thrust-vectoring system on the BAE Systems “Demon” experimental UAV, first flown in 2010. Fluidic controls result in much less mechanical complexity and improved reliability as well as better stealth (low radar signature), as the shape of the aircraft can be optimised without moveable flaps. The primary thrust (jet exhaust) is vectored by fluidic control; conventional trailing-edge wing flaps are also replaced by fluidic controls. Campbell invented an anaesthetic machine in 1973 that employed fluidic controls, including the Coandå effect. This machine became extremely popular in Australia and New Zealand. Vortex flow-based fluidics As mentioned earlier, fluidic devices based on vortex flow include certain shower heads, windscreen washer nozzles, flow rate meters and a switching device to alternately fill and empty bladders in a massage chair (Fig.17). A windscreen washer nozzle may seem a humble application for fluidics, but such a nozzle containing a fluidic oscillator (like some shower heads – see Fig.18) has the capability of sweeping up and down and from side to side with no moving parts (see Figs.19, 20 & 21). The leader in this field is dlhBOWLES (https://dlhbowles.com/). They report the following benefits from their nozzle: * Cleans 62-70% faster * Uses 65-74% less fluid to clean * Allows for 53-65 more cleanings per bottle fill Fig.18 (left): diagram from 1989 European Patent EP0319594A1 for a “Fluidic oscillator with resonant inertance and dynamic compliance circuit”. This can be used in a pulsating shower head or other pulsating water jet device, and has no moving parts. Sub-figs.5-9 show the flow pattern in the device while Sub-fig.10 shows the pattern of jets from such a device with multiple outlets. Sub-fig.11 shows a means to adjust the device. Fig.17: a diagram of a fluidic oscillator with no moving parts from US patent 6,916,300 for a seat massager from dlhBOWLES, Inc. An air source is supplied at the bottom (16) and is alternately directed to the supply lines to bladders in the chair connected to 26 and 28. The air from the bladders is alternately vented at vents 39a and 39b. 20 Silicon Chip * Pre-wets an area 19-23 times larger * Holds spray position better at all road speeds * Greatly improved visibility and driver safety * Dramatically reduced smearing, streaking * Significantly reduces wiper blade wear For more information, see the video titled “FLUIDICS - FULL SPEED, FLUENT VIEW & SLOW MOTION” at: siliconchip.com.au/link/aars There is no mention of which cars use these nozzles, but one web reference states that Nissan vehicles have Australia’s electronics magazine siliconchip.com.au Fig.19: a fluidic windscreen spray nozzle from Bowles Fluidics Corporation illustrating different oscillatory spray motions, all achieved without moving parts. had them since 2004 and they are also available as aftermarket accessories for certain cars. dlhBOWLES makes over 40 million fluidic oscillator spray nozzles per year, of various types and has over 230 patents in the area. The same company makes the fluidic oscillator for a massage chair that alternately fills and empties two bladders mentioned earlier (Fig.17). Fluidic flow measurement Sontex (https://sontex.ch/en/) have a range of meters to measure flow rates of fluid in heating systems. They utilise a fluidic oscillator which has a frequency dependant upon its flow rate. A piezoelectric sensor measures the frequency of oscillation in the fluidic oscillator, and thus the flow rate is determined with no moving parts – see Figs.22 & 23. See also the video titled “Sontex Superstatic 749 Fluidic Oscillator Heat Meter” at: siliconchip.com.au/link/aart Fluidic computers MONIAC (Monetary National Income Analog Computer) was also known as the Phillips Hydraulic Computer and the Financephalograph. It was invented by New Zealander Bill Phillips in 1949 and is generally regarded as a fluidic computer. It is a water-based computer that uses fluidic logic and was initially designed as an educational tool, but was found to be a useful economic modelling device as digital com- Fig.21: the flow pattern inside a fluidic cleaning nozzle from automotive technology company Continental (siliconchip.com. au/link/aaru), which manufactures fluidic nozzles to clean automotive headlights, cameras and LIDAR sensors. siliconchip.com.au Fig.20: the spray pattern from the Bowles fluidic windscreen washer nozzle. A conventional nozzle would produce a single stream of fluid. puters at that time were not widely available. It was also used for military purposes. Twelve to fourteen of these machines were built, and there is a working one on display at the Reserve Bank of New Zealand and another at Cambridge University in the UK (see Fig.26). There is also a non-working one on display at the University of Melbourne. Various economic parameters such as the amount of money in the treasury, health and education expenditure, taxation and tax rates, savings, investment income, import expenditure and export income could be input via valve adjustments, and accumulated funds were represented by the amount of fluid within tanks. Results could be recorded on a mechanical plotter. While MONIAC is generally regarded as a fluidic device, it did have some mechanical components, so it was not a fluidic device in the purest interpretation of the term, but a hybrid system. See the videos titled “Making Money Flow: The MONIAC” (siliconchip.com.au/link/aarv), “Moniac Economic Analog Computer” (siliconchip.com.au/link/aask) and “Matletik Fig.22: the Sontex Superstatic 749 flow rate meter, utilising fluidic oscillation and a piezoelectric sensor for reliable measurement without moving parts. Australia’s electronics magazine August 2019  21 Table 1: 1972 NASA list of fluidic systems in commercial use • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • Automatic turret lathe sequencing Automatic sealing of random-sized boxes Measurement and control of frost buildup on refrigerator coils Punch press work positioning Photographic film winding control Gauging for automatic grinding machines Candy box filling machine control Scale control for weighing explosives Sewing machine trimming knife actuation Controlling a semiautomatic crimping machine Controlling paper making machinery Automatic punching machine operation Sewage pumping station liquid level control Soft drink bottle casing Thread, wire, or rod diameter measurement Bow thruster for boat or ship Breathing assist device Automatic boiler control Non-contact position measurement or proximity switching Counter systems (predetermining and cumulative) Disk memories for computers Automated paint spraying Alphanumeric displays Leak testing of automobile gasoline tanks Pallet loading of different size boxes and conveyor control Newspaper materials handling machine controls Ordnance round assembly tolerance inspection Machining and assembly control of live mortar rounds Inspection/classification of automotive pollution control valves Liquid drum filling monitoring and control Scrap metal baler control Metal tapping machine control Steam turbine governor Gas turbine or jet engine overspeed limiter Broken tool detector Moving belt edge guide control Bin level control for liquid, powder, and small parts Environmental control in large buildings Industrial air motor governors Life test cycling of heart pump check valves Automatic cold saw cutting-angle setting Monitoring and control of vacuum in tyre making equipment Filter bag cleaning controls in tyre making equipment Paper splice detection for paper coating machinery Lip-seal inspection using moving-part logic Life test cycling of postage meters Coil winding machinery controls Acid vaporiser controls for textile processing Irrigation channel switching Fluidic lawn sprinklers Tachometers for diesel motor ships Transistor lead bender 22 Silicon Chip Fig.23: a video screen grab of a Sontex meter showing details of its fluidic oscillator, with simulated fluid flow via computational fluid dynamics. The stream switches between the two lobes seen in the centre and the frequency at which this happens is proportional to the flow rate. Moniac Simulation” (siliconchip.com.au/link/aarw). You can experiment with a virtual MONIAC at: siliconchip.com.au/link/aarx (note: the Flash plug-in is required in your web browser). Another simulator is available at the AnyLogic Cloud at the following link, which does not require Adobe Flash: siliconchip.com.au/link/aary Microfluidics Microfluidics takes the earlier work on fluidics and dramatically reduces the scale, operating at sub-millimetre sizes. It introduces a whole new range of possibilities, not only because of the reduced scale, but because fluids behave differently at micro scales than they do at macro scales. To be considered microfluidics, at least one dimension of the fluid has to be in the micron or tens of microns range (one micron is one-thousandth of a millimetre). A microfluidic device might be in the form of a ‘chip’, or it might utilise a microfluidic effect in another type of device such as the Australian Vortex Fluidics Device, discussed later. At the tiny dimensions used in microfluidics, several different fluid behaviours are introduced which can be utilised in these devices. One is that the flow of fluids is no longer typically turbulent but rather, laminar (see Fig.24) and therefore fluids do not flow or mix with other fluids in the traditional sense. This “clean” flow allows for precise control of fluids such as their movement and their mixing (or not mixing). For example, two streams of different fluid can exist sideby-side, or a bubble of one type of fluid can exist inside a medium of a different type. Books on fluidics Today, there is not much readily available information on fluidics, but two books of interest are “Fluid Logic Controls and Industrial Automation” by D. Bouteille (Wiley, 1973) and “Fluidics: Components and circuits” by K. Foster and G.A. Parker (Wiley-Interscience, 1970). Australia’s electronics magazine siliconchip.com.au Fig.24: turbulent and laminar flow. Laminar flow is what almost always occurs in microfluidic devices. Microfluidic chip devices are often made from glass, silicon or a silicone polymer or other diverse materials, with channels etched or moulded into the device. “Inputs” and “outputs” from the device to the outside world are made with fine tubes; for example. a syringe needle can be used in prototypes. A typical experimental device might consist of something like a glass microscope slide as a base with a silicone polymer on top that has the channels moulded into it. Photolithography can be used to produce the desired pattern, similarly to how conventional microchips are made. See Fig.25 for details of the basic fabrication process. Fluids are pumped from the external environment into the microfluidic device, where they undergo the desired process(es) and are then removed from the device. The processes undertaken might include mixing, sorting, or a chemical or biochemical reaction. Apart from actions caused by the mixing and arrangement of channels in the device, materials used in the device’s fabrication may be chemically or biochemically reactive and participate in the desired reaction within the device. So-called ‘droplet fluidics’, with a bubble of one type of fluid inside a different media is becoming an important part of microfluidics for performing or controlling certain types of chemical or biochemical reactions (see Figs.27-30). Once droplets are formed, they can be collected and used, or two different types of droplets can be merged for effective mixing (not possible at a larger scale). Individual droplets can also be sorted or separated according to some pasiliconchip.com.au Fig.25 (right): the fabrication of a basic microfluidic device. First, a ‘master’ is made using photolithography with the inverse of the desired shape, then the silicone polymer (PDMS plastic) is poured onto this and cured. This is then peeled from the master and it is attached to a glass substrate, and access ports added. Source: A. San-Miguel & H. Lu, Creative Commons Attribution-Share Alike 3.0 Unported license. Fig.26: a MONIAC fluidic logic computer at the Science Museum, London. Credit: Wikimedia user Kulmalukko (Creative Commons Attribution-Share Alike 3.0 Unported license). Australia’s electronics magazine August 2019  23 Fig.27: a microfluidic chip scheme to generate droplets, a common operation. In this case, a reagent is injected from the top and oil is injected from the sides to generate an emulsion of reagent droplets within oil. Note how the reagent stream is ‘pinched’ and broken off as it goes through the restriction. This is called “flow focusing”. The width of the reagent channel might be 20 microns or so, and the emulsion containing channel might be 100 microns (0.1mm). Source: On-Chip Biotechnologies Co Ltd, Japan. rameter such as colour. Another thing that can be done with droplets is to put individual biological cells inside them. There are numerous applications for microfluidics, such as biological cell sorting (Fig.30), digital microfluidics to move droplets around on a chip such as the OpenDrop (Fig.32) or microfluidic transistors (Fig.33) and a soft robot-like “Octobot” that uses a microfluidic logic controller (Fig.34) – see the video titled “Octobot: A Soft, Autonomous Robot” at: siliconchip.com.au/link/aarz Other biological uses for microfluidics include creating artificial lungs (as shown on page 15) and testing liver function. There are even microfluidic devices printed on paper with the help of a specialised inkjet printer and others too numerous to detail here, beyond these few Fig.28: a variety of methods of microfluidic droplet formation, as used in “droplet fluidics” mentioned in the text: a) crossflow, b) co-flow, c) flow-focusing, d) step emulsification, e) microchannel emulsification; and f) membrane emulsification. The coloured fluid patterns reveal the process of droplet formation. Source: P. Zhu & L. Wang, Creative Commons Attribution-ShareAlike 3.0 Unported license. 24 Silicon Chip Australia’s electronics magazine siliconchip.com.au Fluidics projects that you can try at home You can make a computer similar to the MONIAC fluidic computer described in the main text using drinking straws, water bottles and some other pieces. See the video titled “A 3-bit hydropneumatic” at siliconchip.com.au/link/aas0 Author “dAcid” has described pneumatic logic gates made with simple tools on the Instructables website, at: siliconchip.com.au/ link/aas1 (see Fig.a). Fig.a: a simple pneumatic logic gate, as described by author “dAcid”. Note that CNC equipment is required for this. You might be able to get access to such equipment at your local Makerspace if you don’t have any. Google the terms “makerspace” and the name of your town or city and find one that has appropriate equipment. Author “novelchip” on Instructables has described vacuum-powered fluidic ink “LEDs” and circuits at: http://siliconchip.com.au/link/aas2 (see Figs.b, c & d). Fig.b: “LED” indicator devices implemented using fluidics. The devices on the bottom row fluoresce under UV light. Also see the videos at: siliconchip.com.au/link/ aas3 and siliconchip.com. au/link/aas4 Once again, note that CNC equipment is required to make these devices. OpenDrop (siliconchip.com.au/link/aas5) is an open-source hardware and software project that is a “desktop digital biology laboratory”. Fig.c: a fluidic integrated circuit (a hex inverter) by author “novelchip”, alongside its electronic equivalent, the Texas Instruments SN74S04N. In this case, the fluidic version is not much bigger than the electronic one. Quoting directly from their website, “OpenDrop is a new design for an open source digital microfluidics platform for research purposes. The device uses modern electro-wetting technology to control small droplets of liquids.” “Potential applications are lab on a chip devices for automating processes of digital biology. However, the present design should also open the technology to other field and allow experimentation to find new applications. Including the field of art, music, games and education.” Liquid droplets are moved around the device under an electric field of up to 300V AC or DC. For some current OpenDrop projects, see: siliconchip.com. au/link/aas6 siliconchip.com.au Fig.d: details of the fluidic hex inverter integrated circuit shown in Fig.42, taken from the Instructables web page. For videos about how liquid drops are manipulated in the device, see the video titled “OpenDrop Liquid Reservoirs” at: siliconchip. com.au/link/aas7 and “Control Software for OpenDrop V3 Digital Microfluidics Platform” at: siliconchip.com.au/link/aas8 There is a Russian YouTube video titled “Binary pneumatic adder from paper” at: siliconchip.com.au/link/aas9 and an associated description in Russian, at: siliconchip.com.au/link/aasa by author Aliaksei Zholner (see fig.e). You can use Google to translate the text into English. The logic devices are made from paper, so no special equipment whatsoever is needed (except a stream of air; the author uses a balloon). The author does not use the term “fluidic”, although that is the operating principle of the constructed devices. Logic elements AND, OR, XOR gates and a transistor are made. It is a very clever digital fluidic computer. If you have a 3D printer, you can go to www.thingiverse.com and search using the term “fluidic” to find some fluidic devices you can print. There is a good discussion of some of the challenges in making a home-built fluidic computer at: siliconchip.com.au/link/aasb but there is no indication as to whether the author ever built this computer. There are some interesting ideas there if you want to build your own! One of many companies selling microfluidics components Fig.e: an element of is the microfluidic ChipShop the paper-based fluidic (siliconchip.com.au/link/aasc), computer. although there are others. Fig.f shows some of the materials available for experimenters. Fig.f: a microfluidics starter kit from the microfluidic ChipShop that comes with a frame to hold chips, connectors, two straight channel chips with four channels (200 microns square), two straight channel chips with four channels (100 microns square), one straight channel chip with 16 channels (1000 x 200 microns), H-shaped channel chip, droplet generator chip, PCR (polymerase chain reaction) chips and 120 microlitre rhombic chamber chip. Australia’s electronics magazine August 2019  25 Fig.29: one possible microfluidic scheme for merging two droplets. The direction of motion is left to right and top to bottom. representative examples. More Australian innovation A fluidic device has been invented by researchers at Flinders University in South Australia, in the University’s Institute for Nanoscale Science and Technology. It is called the Vortex Fluidics Device or VFD. The VFD works by delivering reagents to a rapidly rotating tube in which a thin (250 micron or 0.25mm thick) film is produced, which results in intense mixing. Demonstrated applications include protein folding and unfolding. Famously, it was used to “unboil an egg” (see siliconchip.com.au/link/aasd). It can also be used for biodiesel production at room temperature without solvents; pharmaceutical synthesis with continuous flow and high yield; mesoporous silica production at room temperature; plasma processing with a plasma in contact with a thin film; and various applications in synthetic organic chemistry, including making the anaesthetic lidocaine with much less waste than normal, plus many other applications. The technology has already been commercialised. Flinders Partners, the commercial arm for Flinders University, launched Vortex Fluidic Technologies (siliconchip.com. au/link/aase) in July 2015, to help commercialise the VFD. 2D Fluidics Pty Ltd (www.2dfluidics.com) was formed in 2018 through a collaboration between ASX-listed First Graphene Ltd and Flinders University. Fig.30: microfluidics biological cell sorting. The cells are probed with a laser and those determined to be separated are pushed into a reservoir. Source: On-Chip Biotechnologies Co Ltd, Japan. 2D Fluidics produces electronics-grade graphene and specific length carbon nanotubes without harsh or toxic chemicals, for research and commercial purposes, plus sells VFD devices. For videos about the VFD, see: * “Introducing the Vortex Fluidic Device” at: siliconchip.com.au/link/aasf * “Fluid Dynamics Within the Vortex Fluidic Device” at: siliconchip.com.au/link/aasg * “Droplet Dynamics Within the Vortex Fluidic Device” at: siliconchip.com.au/link/aash * “ABC News 24 - Ig Nobel prize winner Raston cracks SC global anaesthetic” at: siliconchip.com.au/link/aasi Fig.32: a microfluidic logic and motor circuit (top) along with the electronic equivalent (bottom) for Octobot. This is said to be the world’s first autonomous soft robot. Fig.31: the OpenDrop v3 is a digital microfluidics development board, shown with a bottle of reagent and a micropipette. This is available for a base price of €695 (AU$1120) at the time of going to press. The blue liquid drops can be seen in the large gridded area, and the location for the next move (as directed by software) is shown in the OLED screen at upper right. 26 Silicon Chip Fig.33: a microfluidic transistor, as might be used in a microfluidic logic device. Australia’s electronics magazine Fig.34: Wyss Institute of Harvard University’s 3D printed Octobot, powered by microfluidic logic and motor. siliconchip.com.au