Thanks, Alex, for the nice introduction.
On behalf of my co-authors, Joan Sol Roo, Tobias Kraus,
and Jurgen Steimle, I will present soft inkjet circuits,
a rapid approach for fabrication of soft circuits
using a commodity inkjet printer.
This work is done in collaboration between HCI,
lab at Saarlan University, and the material science
lab at the Leibniz Institute for New Materials,
both located on the same campus in Saarbrucken, Germany.
Soft interfaces-- soft interactive devices
are becoming increasingly popular,
as they offer unique features and can be seamlessly embedded
in demanding physical contexts.
Moving beyond flexible only devices,
a wide array of soft interfaces have been explored.
These devices typically include conformal skin-worn interfaces,
stretchable objects, e-textile, and shape-changing devices.
Despite the increasing popularity
of these soft interactive devices,
their fabrication remains complex and time-consuming,
as they commonly require either extensive manual work, such as
for screen printing and silicone casting, or expert knowledge
and dedicated equipment.
And hence, these approaches are hard to implement
for rapid fabrication.
Instead of these manual or slow approaches,
what if you just simply inkjet print these devices?
Well, this is exactly what people in material science
are working on, fabricating these interfaces
by inkjet printing.
However, for this, they are using
expensive research-grade printers instead.
And these printers are expensive, complex to operate,
and slow to print.
Therefore, this approach didn't make into the HCI DIY
community.
In contrast, pioneering work by Kawahara, et al,
demonstrated how rapid inkjet printing
can empower the HCI community.
Their approach enabled printing custom flexible circuits
within minutes using an inexpensive desktop inkjet
printer, which has facilitated prototyping
of interfaces for research in various domains.
However, their approach is limited
to a single ink and few substrate materials,
and not compatible with stretchable textile
or ultra-thin devices.
Here, we present the first systematic approach
for rapid fabrication of multi-material soft circuits
on a commodity inkjet printer.
Our techniques support a wide set of soft-based substrate
materials, such that they are stretchable, ultra-thin,
compatible with textile, and reshapable.
Our techniques also support multi-material printing
of a wide variety of functional inks,
including conductive inks and isolating inks
along with graphical inks.
First, let me give you an overview of our approach.
We first start by creating a digital design of the circuit.
Any 2D graphic tool can be used.
Then we print the design using a commodity inkjet printer.
After curing, the circuit undergoes a heat curing step.
Then we edit electronic components in connection
using common approaches, for example,
Z-tape, sewing, or soldering.
This pipeline enables easy and rapid fabrication
of multi-material soft circuits and can easily
be replicated by using commonly available tools.
Out of these four steps, I will focus on printing
in this talk, which is the major challenge in enabling
this pipeline.
In printing, we contribute in four categories.
We provide useful guidelines for appropriate printer selection.
We introduce the simultaneous usage
of multiple inks in one printer.
We extended the set of substrate material
from flexible-only films to soft and stretchable materials.
At last, we presented DIY techniques
to enhance the compatibility between these inks
and substrates.
I won't go into the details of the printer selection.
However, I do want to highlight that we
did an extensive exploration of printers
and identified the requirements.
This allowed us to recommend two suitable motors out
of a large variety of commodity inkjet printers available.
Details are in the paper.
Now that we have selected a printer, let's look
at how to select inks for multi-ink, multi-functional
printing.
For this, we first select our functional inks
and then we combine them into a single printer
to print multi-material circuits.
The first crucial step of ink selection
is to identify which inks are printable on our selected
printer.
Well, this is not a trivial task,
given the large number of available inks,
and that we might want to select multiple inks
with different functionality.
As a solution, we propose to use a systematic approach developed
in material science as a tool for HCI researcher and makers
to select printable inks in a feasible manner,
improving the common trial-and-error-based
selection.
The main idea is to predict the inkjet printability
based on three ink properties, which
are commonly available in the data sheet of the inks
and the nozzle diameter of the printer.
The printability is then expressed
by Fromm number Z. Here is the equation to calculate it
based on four known values.
I'm not going to bore you with the details of this equation.
What's more important is how to interpret the result.
For printability, Z should be in the range.
From 1 to 10 is highlighted in this graph.
Values outside this range are not printable.
This systematic approach allows us-- gives us
the ability to select printable inks to demonstrate
our approach.
In addition to graphical inks, we selected three functional
inks; silver for high conductivity,
PEDOT:PSS for high stretchability,
and PVP is an insulating ink.
Based on our selection process, we
can easily identify a set of inks
with desired functional properties.
This, in turn, enables our multi-material approach
that combines multiple inks into a single printer.
This approach leverages the feature of commodity inkjet
printers, that they use different cartridges
for each color channel, and that each cartridge has
its own individual printing head, which
means that we can combine multiple inks
into a single printer using these separate heads.
And so we did combine our selected functional inks
into a single printer.
For instance, in this setup, we put
isolating PVP ink into color cartridges,
and silver into the black cartridge of the printer.
We then printed isolating PVP ink on top of silver
to have exposed electrodes and isolated circuitry.
Similarly, we can even combine conductive inks
with graphic inks to print circuits
with art layer in a single pass.
We can even combine all functional inks
in a single printer.
This gives us the largest flexibility
for combining functional inks.
For instance, here, we printed silver with PEDOT:PSS
in a single pass to have circuits that combines
the complementary benefits of silver-based and polymeric
conductors.
Now that we systematically select the inks
and combine them, for multi-ink, multi-functional printing,
let me talk about the soft substrate materials.
One of our main contributions is that we extended
the set of substrate materials from those predominantly used
substrates such as PET foils and photo paper to soft materials.
We have explored a broad set of materials
that exhibit the mechanical properties of soft substrates,
such as they are stretchable, ultra-thin,
compatible with textile, and reshapable.
I will show some example later.
Now I have talked about inks in substrates,
as a last important point, we need
to consider the interaction between these two.
There is basically some combination
of inks and substrate-caused issue,
and are thus, not printable.
To address these issues, we present
DIY approaches and conducted a series of evaluation
to make inks compatible with the substrates.
I will not go into the details of methods here.
You can find those in the paper.
The thing I want to highlight, however,
is the result, which is that using the DIY approaches,
we successfully printed all inks presented
above on each substrate.
This is the visual.
This is visualized in the summary image of the printed
traces of highly conductive silver and intrinsically
stretchable PEDOT:PSS on all four selected substrates.
The image shows that we can print with fine features.
And the indicated values shows that we
achieve a good level of conductivity
for all inks and all substrates.
With that, I have explained our main contribution
in printing, which in turn, allows us to realize
our fabrication pipeline.
Last, I want to show you four application examples that
demonstrate the versatile capabilities of all approaches
for rapid prototyping.
The first example demonstrates the rapid fabrication
of a stretchable input device.
We fabricated this device by printing four resistive strain
sensors on stretchable TPU substrates.
The sensors are designed in a metrics layout,
which allows to detect deformation input,
as shown in this video.
The total fabrication process took less than 10 minutes,
which shows the ease of use of our approach
for rapid prototyping.
Our second example demonstrated rapid fabrication
of soft interactive e-textile using a transfer approach.
It also demonstrated the ease of fabricating a design featuring
a full colored art layer with integrated circuit traces.
First, color and silver inks are printed in a single pass
onto the transfer substrate and then transferred
by simply ironing the design onto the fabric.
Conventional electronic components
is used for e-textile applications can then be added
by sewing with conductive yarn.
Fabrication took about 8 minutes in this case,
and the result nicely demonstrated
that integration of the printed soft circuits with the textile.
With our third example, we demonstrate rapid fabrication
of interfaces even closer to the body.
We present the first electronic skin
tattoo fabricated using a simple desktop inkjet printer.
Our approach allows us to rapidly fabricate
these ultra-thin devices while prior work relied
on time-consuming processes like screen printing.
In this example, we realize skin-mounted interfaces
for continuous measurement of electrothermal activity.
For this, we leveraged our multi-material printing
capabilities to create skin-exposed electrode.
We first bring two electrodes with connecting traces
onto tattoo paper, and then print additional layer of PVP
to isolate traces while leaving the electrodes exposed.
Our last example demonstrates the versatility of our approach
by printing onto a shape-changeable thermal
plastic material.
We fabricated an interactive body accessory
that featured custom designed artwork in circuits,
and is moldable into our desired shape.
We first print the graphic in circuits--
circuit design onto thermoplastic films in a single
pass using silver and color ink.
We then molded the bracelet into their desired curve shape
by heating it.
Last, we soldered electronic components directly
onto the printed circuit.
As a result, we fabricated an interactive wearable device
with custom shape, visual appearance, and electronics
within 10 minutes.
In summary, our example demonstrated
the versatile capabilities of our approach
for rapid prototyping of soft circuits.
I invite everyone to come to see these fabricated
prototypes at our demo right after this talk.
In summary, I have presented to you soft inkjet circuits,
the first approach for rapid fabrication of soft circuit
using a commodity inkjet printer.
It supports inkjet printing of circuits,
that they are stretchable, ultra-thin, high resolution,
and integrated with a wide variety of materials
for prototyping.
It supports multi-material functional printing
on a desktop printer for realizing
multi-material devices, including
conductive and isolated inks.
And with this, I conclude my presentation.
Thank you for your attention, and I
am happy to take questions.
[APPLAUSE]
Great collection of work.
So my question is, do you need to cure the ink
after printing each layer?
So you mentioned about the multi-layer circuit.
But my question is, do you really
need to cure each layer after printing?
No, we only need drying, not the curing after step.
After each step, the curing is good,
but only drying is enough, just to let the solvent evaporate.
So I'd like to, more detailly, know the thinking process.
So you printed the first layer and then dried it?
Yes.
Then print the second layer and dried it.
Yes.
So how long will it take?
Depends on the substrate.
For example, for some substrate, like the textile transfer one,
it absorb inks really quickly, so you don't need to wait.
For TPU, you you probably need more waiting
because it doesn't absorb the ink quickly.
Yeah, because--
Or, you can use like a mild heater or a heat gun
to quickly dry it.
Yeah, because one of the biggest benefits of the inkjet--
the inkjet circuit is its sintering-free process.
So is there any possibility of this process
to achieve a sintering-free?
That's a good question.
But here, the heating is actually
giving us the leverage to use multiple materials because we
only need heat.
For that approach, I guess, they're
limited by the substrate.
Thank you.
OK, thank you.
Any other questions?
So I was wondering also, in terms of--
so a lot of these designs are thin, small,
but it's hard to ignore the cables that
are run out from the circuit.
So have you looked at using backscatter or enabling
antennas, or sort of remote powering of these circuits?
Would that be compatible with this fabrication?
I guess that's one of our future--
we mention it in the paper in future works,
that currently, it is-- for integration, we use the wiring.
But later, for the wireless connection, maybe the antennas,
that can be another one of the directions
to use these interfaces.
Yeah.
OK, thanks.
Any other questions?
OK, let's thank the author again.
[APPLAUSE]