Hello everyone
My name is Yutaka Tokuda from University of Sussex.
I’d like to present Flowcuits Crafting Tangible and Interactive
Electrical Components with Liquid Metal Circuits.
This is a joint work with Deepak Ranjan Sahoo and
Matt Jones at Swansea University, Sriram Subramanian at
UCL, and Anusha Withana from The University of Sydney.
DIY tangible computing toolkits have changed learning
experience in electronics more playful and creative with
interactive engagement.
However, it is still hard to craft DIY electronic components
and playfully learn electronics principles
for instance, it is difficult to interactively and visually
explore the law of resistivity
and two plate capacitor model with the same DIY method.
Researchers investigated DIY methods to build
various analog electronic components
with high conductive liquid metal.
For example, Wu et al. used liquid metal to create
3D printed passive components,
and Nagels et al. demonstrated various flexible sensors
by sealing liquid metal circuit with silicone.
Meanwhile, other studies showed the usability of fluidics
to make tunable electronics and interactive materials.
As examples, Gerrad et al., utilized the flow of
conductive liquid as dynamical switch
and Mor et al., explored various fluidic mechanisms
to build analog fluidic sensors and displays.
In this paper, we introduce Flowcuits, which is a DIY toolkit
to build interactive electronic components
with liquid metal fluidics.
Flowcuits uses analogy of conductive liquid flow and
electronic current for playful learning basic electronic components.
For instance, we can easily build and explore a tunable
capacitor by controlling liquid metal flow.
As a design concept,
Flowcuits follows Tangible Visual Electrical analogy,
where tangible inputs are directly reflected
in both visual and electrical change as the outputs.
Let me explain this with examples.
This image shows dynamical liquid switch
composed of sealed liquid metal in a reservoir,
transparent liquid channel,
and LED as electrical output.
To explore switching mechanism of electronic circuits,
we can press liquid metal to deform and visually probe
the electrical contact with an open LED circuit.
Likewise, we can demonstrate electrical state changes
by adding another reservoir along the channel.
Conductive liquid metal droplet moves to another reservoir
by giving pressure
and works like a binary switch to turn on multiple LEDs.
Furthermore,
we can interactively explore electronics principles
with visually tunable liquid electronic components.
For example, we can build tunable resistor
with high conductive liquid metal
and low conductive ionic solution
and demonstrate the law of resistivity
by adjusting the liquid volume ratio.
Next, let me explain Flowcuits Workflow.
There are three main steps.
The first step is design and preparation of
3D printed stamps and molding material.
Flowcuits uses familiar stamping process
to design liquid electronic components.
The second step is fabrication processes of liquid
electronic components. There are three hands-on processes
imprinting substrates, sealing imprinted liquid channel,
and infusing conductive liquid.
The last step is tangible interaction to probe the
functionality of the fabricated liquid electronic components.
Let me start from design and preparation step.
To design Flowcuits stamp,
there are three types of elements:
namely, Fluid Elements, Fluid I/O, and Electrical I/O.
Fluid elements design liquid channel, reservoir, resistor,
and capacitor.
Fluid I/O imprints Fluid ports for infusion/drain process.
Electrical I/O designs wiring terminals
to probe electrical changes.
Design of Fluid Elements requires to model fluid properties,
such as pressure and hydraulic resistance
, as well as electrical properties.
We created Flowcuits stamp 3D CAD toolkit which informs
these values from stamp geometry and liquid parameters
and provides Graphical User Interface to tune
and assemble template stamp elements.
The toolkit can export the designed stamp as a STL file
to 3D print for the following imprinting process.
To help manual imprinting, we optionally provide
a stamp holder and stamp support pillars
to control imprinting depth.
As a molding substrate of Flowcuits, we use Blu Tack,
which is commonly available pressure sensitive adhesive silicone.
Blu Tack works like a clay to imprint fine textures,
and very sticky to a tape.
We wet Blu Tack to reduce adhesiveness
and place it between shims,
then use a clay roller machine to make even surface
with a specific thickness.
Next, I will move on to the fabrication step.
Since Blu Tack is very adhesive to a 3D printed stamp,
we must coat the surface with fine powders
such as corn starch before imprinting.
We can restore the Blu Tack adhesiveness
by cleaning the surface with water.
If imprinting fails, we can recycle Blu Tack
through a clay roller machine
The next process is sealing the imprinted channel
with a tape and prepare a Fluid I/O terminal for infusion.
After placing a washer as a gasket at the terminal,
we seal the imprinted area with a transparent duct tape.
We use a soldering iron to open the terminal,
then glue magnet rings on the top.
The sealed component is easily cut out with a hobby knife.
Fabrication process is completed
by infusing a conductive liquid through a Fluid I/O terminal.
A custom magnetic tube adapter is designed to
quickly attach and detach a tube to a Fluid I/O terminal.
We use a Tygon tubing for smooth fluid flow.
As conductive liquids,
we tested highly conductive EGaIn liquid metal and
low conductive sodium hydroxide solution,
which also works as a lubricant of liquid metal
by preventing the oxidation.
Finally, we discuss the robustness of tangible interaction.
The robustness to tangible interaction
depends on substrate material.
We found Blu Tack likely yields above a force of 50 N
which is regular finger pressure force.
To enhance the elasticity, we mixed a Blu Tack with
thermoplastic elastomer, Oyumaru,
and gained significant improvement of yielding strength
with a trade-off of adhesiveness.
Let me introduce interactive applications.
Utilizing elastic deformation of liquid metal
with surface tension,
we can craft a dynamical liquid push-button switch
by imprinting a set of a reservoir and a channel.
Likewise, toggle switch is easily made
by imprinting a second reservoir for liquid metal relocation.
We can apply these fluid switching mechanisms
to design various digital logic gates.
Analog electronic component is another application.
We can create variable resistor
by infusing different volume of two conductive liquids.
As the law of resistivity simulates, resistance decreases
proportionally to the volume of high conductive liquid metal.
We can also design a variable capacitor
by controlling liquid metal flow between ITO electrodes.
We found linear increase of capacitance
with respect to liquid metal area
as the equation for a parallel plate capacitor says.
We can also use force-sensitive liquid deformation
as pressure sensor after calibration.
As limitation, maximum fabrication size depends on
the clay roller size, which is around A4 paper size.
Considering robustness,
1 mm to 2 mm square liquid channel is recommended
with larger depth.
Although liquid metal is safe,
sodium hydroxide solution is caustic
and better to dilute for safety.
In conclusion, we proposed Flowcuits, a DIY toolkit
to craft electrical components with liquid metals.
We explored Tangible Visual Electrical Analogy for
playful learning electronics principle.
We technically evaluated Flowcuits concept with applications.
That's all my presentation.
Thank you for your attention.