Liquid Jets as Logic-ComputingFluid-User-Interfaces

Audrey Ziwei Hu, University of Toronto - ziwei.hu@mail.utoronto.caRyan Janzen, University of Toronto - ryan.janzen@mail.utoronto.ca

Max Hao Lu, University of Toronto - hao.lv@mail.utoronto.caSteve Mann, Stanford University - mann@eyetap.org

ABSTRACT

We present a fluid user interface that functions as a logic-computing input/output device, based on touching smalljets of water. Tactile interaction occurs in two directions:(1) from the human to the device, where minute motionsof the finger through fluid flow are sensed by a computer;(2) from the device to the human, where water pressure (orflow) is controlled by computer and sensed by the finger.Tactile feedback occurs due to a fluid pressure-to-proximityrelationship. This human-in-the-loop system was used as amultisensory teaching tool, to demonstrate logic gates andflip flops, demonstrating the elementary logic operations ofdigital electronics via liquid flow rather than via the flowof electricity. Fuzzy logic could be demonstrated by smoothvariations in fluid flow control. Applications also includedgame development and tactile communication-at-a-distance,where we implemented a first-mover-advantage game, basedon pushing virtual packets of water over virtual pipes fasterthan the speed of sound, through electronic packets thatencoded the exact finger expressions created in the fluid flowin each jet.

CCS CONCEPTS

• Human-centered computing → Haptic devices; Sound-based input / output ;

KEYWORDS

Fluid User Interface; Fluid-User-Interface; Fluid UI; FUI;Signal Processing; Multisensory Interaction; Fluid Dynamics;Fluid Mechanics; Turbulence; Hydraulophone; Poly-Synapse;Polysynapse; Water Jets; Flow Sensing

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ThematicWorkshops’17, October 23–27, 2017, Mountain View, CA,USA

© 2017 Copyright held by the owner/author(s). Publication rightslicensed to Association for Computing Machinery.ACM ISBN 978-1-4503-5416-5/17/10. . . $15.00https://doi.org/10.1145/3126686.3126765

1 INTRODUCTION

Liquids have been used as an interactive medium in varioushuman-machine interfaces, configured as either droplets [1],jets [10] [4], horizontal liquid surfaces using waves and opticalreflection [7] [13], vertical planar surfaces that are falling froma linear nozzle [3], or volumetric liquids which are interactedwith in bulk via turbulent or laminar flow in a vessel [10].These liquid configurations allow a human user to controlsystems by tactile interaction, and they can also displaydata [15] [4] [5].

To translate the touched-liquid phenomena into simplecomputer control inputs, turbulent/acoustic detection algo-rithms [3] can search for signature patterns in the liquidsmotion, using a sensor (such as a sound pickup) placed di-rectly in the fluid. As well, computer-vision algorithms caninterpret the liquid flow [7] [9], although this only works incertain configurations with specialized lighting.

The hydraulophone is a water-based musical instrumentcomprising a row of water jets, touched by the users fin-ger [10] [4] [9]. Sound is produced by vibrations of waterinside the instrument, in response to the fingers touching thewater jets. The sound responds to the absement, displacementand velocity of the fingers [10]. See Fig 1 for an example of ahydraulophone. By touching, blocking, or pushing against awater jet, water flow is diverted inside the instrument intothe sounding-producing mechanism corresponding to thatjet [10]. The hydraulophone can also be generalized beyondmusical instruments, more broadly as a fluid-user-interface(FUI) giving continuous control from an infinite space offinger positions touching a water jet—continuous both in thetime domain and in the amplitude domain [10].

Hydraulophones involve two key aspects: (1) sound produc-tion based on liquid vibration; and (2) a user-interface modal-ity with fingers coupled to liquid flow. For (1), turbulenceand vibrations are initiated in liquids such as water,when itis confined in pipes and flow chambers to overcome the highacoustic impedance of liquids [8]. As a user-interface (2), thehydraulophone is expressive beyond the capabilities of othermusical instruments, since it can be played with polyphonicembouchure—continuous control over each note, for each noteseparately and simultaneously [6]. To accurately detect fingermotion, we devised a system which used machine learning toidentify turbulence signatures in water flow [3].

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Figure 1: Example of a fluid user-interface: water jets form a medium for tactile interaction and control, andin this case the jets were arranged with a piano/organ layout, and are linked to internal sounding pipes toform a musical instrument: a hydraulophone.

Previous researchers [11] [12] have created containmentvessels inside which logical phenomena can be observed influid flow, whereas this study creates an actual user-interfaceto demonstrate logic operations in response to human touch,and to demonstrate more complex gaming and communica-tion applications of fluid-user-interfaces.

2 INPUT-OUTPUTFLUID-USER-INTERFACE

To create a fluid jet system as a combined input-output device,the flow must be simultaneously controlled and sensed in amanner in which the controlling and sensing do not conflict— namely, (1) that oscillation from a controlled actuator isnot significantly picked up by the flow sensor, or that it canbe distinguished from salient signals from the finger; and (2)that the controlled flow allows the sensing process to proceed,except for when the flow is completely absent (no jet).

Rather than merely using a flow-switch sensor, we builta number of fluid interfaces based around high-sample-rateanalog signal detection, to represent time-varying propertiesof the flow. Acoustic waves were sensed using a hydrophone(underwater microphone), and turbulent phenomena weresensed with narrow-port localized pressure sensors with awideband frequency response.

The overall system consists of piping and sensing systems,as in Fig. 2. The diagram in this example illustrates a T-configuration of the sensing piping, wherein a finger blockingthe jet causes exhaust flow whose turbulent and acousticcontent are sensed. However, later in this paper, we employa simpler, straight-through pipe configuration: The flow inletis simply a pipe leading to the jet outlet, via a sensingmechanism partway along the pipe. In this latter case, a fingerblocking the jet causes the opposite reaction in the sensedflow – a decrease in flow, below what would normally occurbased on the pump speed. Fig. 2 also shows interconnects toother FUI units in the case of an interactive jet array.

Fig. 3 illustrates the flow of information in one single fluiduser interface jet system, in a feedback loop.

3 INTERACTIVE WATER JETS,EXHIBITING LOGIC COMPUTINGPHENOMENA

We built a FUI device having two water jets, with twoindividually-controllable pumps feeding the two water jets.The device also included a detection circuit to sense the ac-tion of a finger on the jet. The finger acted outside the jetoutlet, touching the jet itself, whereas the detection processwas built inside the device.

The pump controller was first programmed to obey thefollowing logic:

𝑃𝐴 = 𝐷𝐵 + 𝑃𝐵 (1)

𝑃𝐵 = 𝐷𝐴 + 𝑃𝐴 (2)

The + sign indicates a logic OR operation, and 𝑥 indicatesa NOT operation. Each pump (e.g. 𝑃𝐴 or 𝑃𝐵) turned onwhenever the the opposite jet experienced a water diversion(e.g. 𝐷𝐴 or 𝐷𝐵) due to finger blockage, or as long as theopposite pump was off. The fluid piping was set up in a Tconfiguration for each jet (like most hydraulophones) with aninlet, outlet and diversion, so that water from a pump (e.g.𝑃𝐴) normally sprayed out a jet, except when blocked by afinger (e.g. 𝐹𝐴). Whenever both the pump was on (e.g. 𝑃𝐴)and the finger was blocking (e.g. 𝐹𝐴), then diverted waterwas detected (e.g. 𝐷𝐴). This is represented logically with thelogic AND operation (∙):

𝐷𝐴 = 𝑃𝐴 ∙ 𝐹𝐴 (3)

𝐷𝐵 = 𝑃𝐵 ∙ 𝐹𝐵 (4)

As a result, we can use elementary logic-based algebra toevaluate these expressions:

𝑃𝐴 = (𝑃𝐵 ∙ 𝐹𝐵) + 𝑃𝐵 = (𝑃𝐵 ∙ 𝐹𝐵) = 𝑃𝐵 + 𝐹𝐵 (5)

𝑃𝐵 = (𝑃𝐴 ∙ 𝐹𝐴) + 𝑃𝐴 = (𝑃𝐴 ∙ 𝐹𝐴) = 𝑃𝐴 + 𝐹𝐴 (6)

The result is an interesting behavior of cross-effects betweenthe two jets and pumps. Indeed, (5) and (6) exactly de-scribe the behavior of a flip-flop operation in digital circuits.Specifically, it represents an SR latch, as shown in Fig. 4.

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FLOW STATEACTUATOR

HYDRAULOPHONICINLET

HYDRAULOPHONICTURBULENT/ACOUSTICFEATURE-EXTRACTION PROCESSOR

JET OUTLETCHANNEL

HYDR. SOUNDING PIPE

TRANSDUCER:SOUND PICKUP

FLUID VALVEE.G. COANDA SWITCH

FLOW STATEBIFURCATIONREGION

COANDAAMPLIFICATIONREGION

FLOW PATH FORSTANDBY & BLOCKED STATES

EXHAUST RECIRC.WATER OUTLET

PRE-COANDALAMINARIZER

INCOMING FLOW

BIDIRECTIONAL USER-INTERACTION:CONTROLLING WATER FLOW,WHILE FEELING TURBULENCE ON FINGER

MACHINELEARNING SYSTEM:USER-INPUTPROCESSOR

JET OUTLETINSTALLATION SURFACECOVERING COMPONENTS

JET STATECONTROLLERFORINTERACTIVEPATTERNS

COMMUNICATIONLINK BETWEENWATER JETS

CONTROL SIGNALTO LOCAL ACTUATORWATER INLET

Figure 2: Fluid user-interface array components: flow configuration and electronic configuration. In this casewe illustrate an electronic flow control mechanism via a coanda switch. An alternate method is by directcontrol of a pump, which feeds water into the inlet at the bottom of the diagram.

Turbulent/Acoustic Analysis

User-InputInterpreter

Jet State Controller

FluidJet

Transducer:AcousticPickup

or FlowfieldSensor

FluidObstruction

Fluid SupplyActuator

(Valve or Pump)

Human FingerInteraction

TactileFeedback

Figure 3: Signal flow (as opposed to fluid flow), or more precisely, the directionality of cause and effect, inone single element of a fluid-user-interface (FUI). These components form one single autonomous unit, withone fluid jet, and sensing and control components.

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Figure 4: A fundamental unit of logic memory stor-age, as illustrated from the world of digital electron-ics: SR Latch. The output signals 𝑄 and 𝑄 representthe pump power for each jet: 𝑃𝐴 and 𝑃𝐵. The inputsignals 𝑆 and 𝑅 represent the finger motion on eachjet: 𝐹𝐴 and 𝐹𝐵. Note that the equations derived ear-lier express one of many slight variants of the basicSR latch, having different NOT operations, but thesame topology.

We therefore made a fluid-user-interface which exhibitsthe behavior of a fundamental logic circuit building-block,exhibited to the fingertips.

We also experimented with fuzzy logic in water jets, bydetecting a smooth gradation of the amount of finger blockage.Each water jet was designed as an autonomous unit (Fig. 3),sensing fluid-flow restriction from the finger, and thereforefunctioning as a restrictometer [4]. In this case, a gradualincrease in finger pressure on the water led to gradual changesin logic outputs (i.e. fuzzy logic).

4 IMPLEMENTATION OF LOGIC JETUSER-INTERFACE

This section describes a low-cost implementation that can beset up for experimentation without the need for sophisticatedequipment. We describe a method to save on flow-sensingcomponents by using low-cost fountain pumps for dual pur-poses, with a simple auxiliary electronic circuit.

4.1 Hardware architecture

From the perspective of the jet as an input device, we detectchanges in water flow by sensing electrical power demandedby each pump, due to a relationship between kinetic energyimparted to the water and the water flow rate. The electricalpower is sensed using a current-sensing resistor configuration.A power resistor is connected in series with each pump, totransform the current flow into a varying voltage. The changein current is slight, according to the pump’s impeller speed inresponse to the change in water flow. A ceramic power resistorshould be chosen with resistance which is approximately1/100th the pump resistance, to allow a sufficiently-widevoltage swing to be detected by analog-to-digital conversion,while ensuring the normal functionality of the pump andavoiding unnecessary energy loss on the power resistor.

From the perspective of the jet as an output device, weinitially used conventional relays to control the pump power.We then also deployed solid-state relays with pulse widthmodulation for smoothly-varying control, for fuzzy logic.

With the intention of seeking a low-cost method that doesnot require sophisticated equipment, we used two ordinarydesk fountains with internal pumps. Because ordinary deskfountains are originally designed for decoration without theconsideration of signal processing, the pump wires contain agood deal of electrical noise during operation, and the changeof electric flow is modest when blocking the pump completely.Simple filter circuits were required to reduce the effect ofthe noise. We observed that finger blockage on the jet outletresults in a slight decrease in pump current, compared tounobstructed pumping. Monitoring the change of electricityflow allows the circuit to identify whether and to what degreethe jet is obstructed.

For simplified setup and prototyping, an Arduino Unoboard served as the analog-to-digital converter and proces-sor. The Arduino Uno contains a 5V regulator, along withmultiple analog input pins, several digital output pins, amicro-controller and LEDs. This ready-to-use board allowsus to sense and control voltages from multiple sources simul-taneously in real time.

Fig 6 shows the hardware circuit of each fluid jet module.We added a filter consisting of a large resistor, a diode and asmall capacitor before the signal going into the Arduino toprevent voltage spikes, and minimize the signal noise whilemaintaining the accuracy of the voltage.

4.2 Software architecture: feedbackbetween multiple fountains

With two ordinary desk fountains as shown in Fig. 5, theprocessor could get the real-time voltage from both analoginputs and determine the output signal for the two relayssimultaneously. Water flow can be determined from the analoginputs through calibration of the circuit and scaling with thepump’s power curve.

Conditioning the signal inputs is provided both by thehardware filters, as well as in software, with moving averagefilters [2] for signal inputs and a self-updating threshold forstatus determination. By adding a buffer for input signals,the moving average filter continuously updates the average ofthe input values over a certain length, therefore preventingthe effect of sudden noises in the circuit.

Each of the fountains is equipped with both the hardwareand software mentioned above, making the signals jointlyavailable in real time.

5 APPLICATIONS OF THELOGIC-BASED FLUID INTERFACE

We implemented several modes of signal processing logicbased on this user interface, which enabled a series of edu-cational games. The first game is a finger-operated desktopversion of “First Mover Advantage”, which senses the block-age on either one pump and starts the other pump/jet while

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Figure 5: Experimental version of a logic-computing fluid interface.

Figure 6: Electronic configuration of one logical wa-ter jet.

turning off the current pump/jet. By adding a clock signal,we also created several logic gates including a T flip-flop, SRflip-flop and JK flip-flop as shown in Tables 1, 2, 3, and 4.

A second game is called ”WOIP” (”Water Over InternetProtocol”). Two participants can engage in tactile communication-at-a-distance, based on pushing virtual packets of water overvirtual pipes faster than the speed of sound, through elec-tronic packets that encoded the exact finger expressionscreated in the fluid flow in each jet.

This interactive interface can serve as a teaching tool forstudents to control signals and observe results immediately,by physical interaction in a continuous input space, with acontinuum of recirculating fluid. Furthermore, the systemengages multiple senses (touch, vision, hearing). Multisensoryexposure has previously been shown to facilitate memorycompared to unisensory exposure [14].

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Table 1: Truth table for fluid-jets as a T flip-flop.

Inputs Outputs

FingerTouch A

FingerTouch B

Pump A Pump B

Blocked X On Toggle

Unblocked X On NoChange

(X = ”Don’t care”)

Table 2: Truth table for fluid-jets as an SR flip-flop

Inputs Outputs

FingerTouch A

FingerTouch B

Pump Anext state

Pump Bnext state

Unblocked Unblocked NoChange

NoChange

Unblocked Blocked On Off

Blocked Unblocked Off On

Blocked Blocked On On

Table 3: Truth table for fluid-jets as a JK flip-flop

Inputs Outputs

ClockSignal

FingerTouch A

FingerTouch B

PumpA nextstate

PumpB nextstate

Rising

Edge

Unblocked Unblocked NoChange

NoChange

Unblocked Blocked Toggle OnBlocked Unblocked On ToggleBlocked Blocked On On

NoRisingEdge

X X Remain Remain

(X = ”Don’t care”)

Table 4: Animated interaction version of a JK flip-flop

Inputs Outputs

ClockSignal

FingerTouch A

FingerTouch B

PumpA nextstate

PumpB nextstate

Rising

Edge

Unblocked Blocked Toggle OnBlocked Unblocked On ToggleBlocked Blocked On On

Blocked BlockedOff Off

Delay 1 secondOn On

NoRisingEdge

X X Remain Remain

6 FLOW-BASED LOGIC, IN A“POLY-SYNAPSE”HYDRAULOPHONE

A hydraulophone with chorded fingerings was built by authorR. Janzen, exhibiting multi-level logic operations. The multi-level operations have as their input the space of all discretecombinations of jets blocked with fingers (finger chords), aswell as the amount of finger pressure applied to each jet.Blocking or touching jets causes water to be diverted insidethe instrument into sounding chambers. Thus, finger actionon the jets affects the final sound in terms of frequency,amplitude, and other characteristics of the water resonance.

This device is pictured in Fig. 7.The instrument operates based on coupled behaviour be-

tween different water jets. When jets are touched or blocked,their exhaust flows (similar to the exhaust flow shown inFig. 2 for one jet) are merged together inside “synapses” —pipe networks which combine the flow in specific ratios toachieve carefully adjusted tunings, for different musical notescorresponding to different chorded finger combinations. Thecombined water flow is fed into acoustic sounding pipes.

Figure 8 shows a piping diagram for one of the synapses.The combinatoric adjustments allow multi-level logic opera-tions create specific acoustic frequencies depending on logicalcombinations of jets that are blocked by the fingers.

Importantly, the combinatoric adjustments are not likelogic gates in the sense of information flowing in one direc-tion from input to output. Rather, in this case, informationflows in both directions in each pipe, and a matrix algebrarelationship exists from the various flow constrictions andthe final physical flow realized in the circuit. To tune thisinstrument to achieve an array of musical notes for differentfingerings, this algebraic operation is reversed to optimizethe tuning of the restriction (resistance) valves.

Besides the logical-algebraic operation on the combinationsof jets that are blocked, subtler variations are possible withsub-jet resolution. Fine motions in the fingers also createexpression in the sound such as vibrato and tremolo, throughslight movements of less than 1mm when applying pressureto the water jet as it emerges from the outlet. One playingtechnique is to pivot the fingers on the edges of jet outlets inorder to transform muscle motion with leverage into smallermovements of the fingertip, to precisely change the forceapplied against the water flow.

In one implemetation, the alpha and beta synapses werejointly connected for coarse and fine effects on pitch, respec-tively. Touching or blocking jets on the alpha synapse withvarying amounts of pressure caused the pitch to jump upor down by P5 steps (perfect-5th), similarly to the tuningof strings on a violin. Playing the beta synapse jets causedsmall incremental steps in the pitch, analogously to playingdifferent notes on the same violin string. Fingering charts areshown in Tables 6 and 6.

Sound samples and images of this device can be found at:

http://eyetap.org/hydraulophone/research/polysynapse

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Figure 7: Poly-synapse hydraulophone, with multi-level logic operations, to create specific acoustic frequenciesdepending on logical combinations of jets that are blocked by the fingers.

Table 5: Fingering chart for the poly-synapse hy-draulophone, in a joint alpha-beta configuration.Each water jet is played by blocking the water flowwith one finger.

Alpha Synapse position

Primary Secondary Tertiary

BetaSynapseposition

Open jet 4 jet 5 jets 4,5Stepped jets 2,4 jets 2,5 jets

(2),4,5Bistepped jets 1,4 jets 1,5 jets

(1),4,5Penultimate jets

1,2,3,4jets1,2,(3),5

jets(1),(2),4,5

Table 6: Fingering chart showing tuned frequenciesas musical notes.

Alpha Synapse position

Primary Secondary Tertiary

BetaSynapseposition

Open F C G’Stepped G♭ D♭ A♭’Bistepped A♭ E♭ B♭’Penultimate B♭ F’ C’

7 CONCLUSION

Fluid user interfaces were created to demonstrate elementarylogic operations of digital electronics via liquid flow ratherthan via the flow of electricity. In particular, the liquid logicphenomena were shown in user-interfaces, where human touchof water jets creates logical processing inside of pipes andflow chambers, to demonstrate elementary logic gates, andto control other phenomena including sound.

A fluid user-interface was designed, with bidirectionalinput-output fluid jets: jets that are both a display anda user input medium. Fluid information is transformed intoelectronic information, and vice versa. This interface wascreated as a low-cost reproducible design, taking advantageof pumps themselves as sensors. Applications include multi-media interfaces, game development, and education on basiclogic processing with tactile interaction.

In addition, water-based logic and multi-level algebraicprocessing were demonstrated by building a new musicalinstrument: the poly-synapse hydraulophone. This instru-ment has water jets that are blocked by human fingers indifferent combinations, to generate underwater resonanceat different frequencies. Fluid dynamics effectively performcomputational operations by combining information fromeach jet.

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1

2

3

FlushingInlineVolume

Atmosphere

AmbientPressure atInstrumentOutlets

Typical0.5m ~ 1mHead

Double-Ambientator inopen-ended instrument body

Flow-EnabledAmbientator

Manifold

Pump Filter

Pump battery

Phantom Powerfor Pickups

UnderwaterSound PickupsXLR Out

Jet Outletscorresponding to Beta Synapse

HydraulophonicAcoustic Resonator(sealed fluid cavity module)

Beta SynapseFlow Channel

Manifold Supplyto other jets

Synapse Back-Flow / Forward FlowCombinatoricAdjustments

Manifold Supplyto other jets

Drain for Cleaning

Figure 8: Poly-synapse hydraulophone: fluid circuit diagram, representing one subset of the instrument’sjets. Resistors represent fluid resistance, and inductors represent fluid inductance (flow inertia). This usesan analogy with electrical current representing flow rate, and electrical voltage representing pressure. Wateris pumped, filtered, pressure-stabilized in a manifold, and distributed to T-fittings at the water jet outlets.Touching or blocking a water jet causes water to be diverted out the side discharge of the T-fitting, where itis combined in the synapse flow channel, with some backflow into other jets through the tuned combinatoricadjustments. Finally, the flow enters into a resonant chamber, where the resulting sound can be heard directlyand/or picked up by an underwater sound pickup (hydrophone). Ambientators, which are designed to couplepiping to the average ambient flow conditions in surrounding water without allowing fingers to block the flowor change the pressure, are affixed to the fluid exhaust discharge and a fluid reference port.

REFERENCES[1] Mary Beth Griggs. June 10, 2015. This Computer

Runs On Water Droplets And Magnets. (June 10,2015). http://www.popsci.com/new-computer-operates-water-droplets-and-magnets.

[2] Forester W. Isen. 2008. DSP for MATLAB and LabVIEW III:Digital Filter Design (Synthesis Lectures on Signal Processing).Morgan & Claypool.

[3] Ryan Janzen and Steve Mann. 2007. Arrays of water jets asuser interfaces: Detection and estimation of flow by listeningto turbulence signatures using hydrophones. In Proceedings ofthe 15th annual ACM international conference on Multimedia,September 24-29, Augsburg, Germany. 505–8.

[4] Steve Mann. 2005. flUId streams: fountains that are keyboardswith nozzle spray as keys that give rich tactile feedback and aremore expressive and more fun than plastic keys. In Proceedings ofthe 13th annual ACM international conference on Multimedia.ACM, 181–190.

[5] Steve Mann, Michael Georgas, and Ryan Janzen. 2006. Water Jetsas Pixels: Water Fountains as Both Sensors and Displays. In Proc.8th IEEE International Symposium on Multimedia (ISM’06).766–772. Digital Object Identifier 10.1109/ISM.2006.158.

[6] Steve Mann and Ryan Janzen. 2009. Polyphonic Embouchure onan Intricately Expressive Musical Keyboard formed by an Array ofWater Jets. In Proc. International Computer Music Conference(ICMC), August 16-21, 2009, Montreal. 545–8.

[7] Steve Mann, Ryan Janzen, and Jason Huang. 2011. ”WaterTouch”:An Aquatic Interactive Multimedia Sensory Table Based on TotalInternal Reflection in Water. In Proc. of the 19th ACM Interna-tional Conference on Multimedia (MM ’11). ACM, New York,NY, USA, 925–928. https://doi.org/10.1145/2072298.2071904

[8] Steve Mann, Ryan Janzen, Jason Huang, Matthew Kelly,Jimmy Lei Ba, and Alexander Chen. 2011. User-Interfaces Basedon the Water-Hammer Effect. In Proc. Tangible and EmbeddedInteraction (TEI 2011). 1–8.

[9] Steve Mann, Ryan Janzen, Raymond Lo, and James Fung. 2007.Non-electrophonic cyborg instruments: Playing on everyday thingsas if the whole world were one giant musical instrument. In Pro-ceedings of the 15th annual ACM international conference onMultimedia, September 24-29, Augsburg, Germany. 932–941.

[10] S Mann, R Janzen, and M Post. 2006. Hydraulophone designconsiderations: Absement, displacement, and velocity-sensitivemusic keyboard in which each key is a water jet. In Proc. ACMInternational Conference on Multimedia, October 23-27, SantaBarbara, USA. 519–528.

[11] Ninad Mehendale, Rajesh Patil, and Deborshi Chakraborty. 2015.Logic Gate Simulation for Fluidic Computers. In Proceedings ofthe 2015 COMSOL Conference.

[12] Horton Billy Mitchusson. 1961. Fluid logic components. (March 171961). US Patent 3,107,850 A.

[13] Hendrik Richter, Felix Manke, and Moriel Seror. 2013. LiquiTouch:Liquid As a Medium for Versatile Tactile Feedback on TouchSurfaces. In Proceedings of the 7th International Conference onTangible, Embedded and Embodied Interaction (TEI ’13). ACM,New York, NY, USA, 315–318. https://doi.org/10.1145/2460625.2460678

[14] Ladan Shams and Aaron R. Seitz. 2008. Benefits of multisensorylearning. Trends in Cognitive Sciences 12, 11 (2008), 411 – 417.https://doi.org/10.1016/j.tics.2008.07.006

[15] Koert van Mensvoort. 2005. Datafountain: Money trans-lated to water. Online documentation by the inventor,http://www.koert.com/work/datafountain/.

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