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Interconnection & Double Layer for Flexible Electronic Circuit with Instant Inkjet Circuits
• A rapid prototyping tool for printing circuits– At low-cost
• < a few hundred dollars
– Off-the-shelf
• Using a home inkjet printer and ink available in the market
– Fast
• < a few minutes
Instant Inkjet Circuits
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RFIDPCB
Touch Sensor
Capacitive Sensor
Figure 8. Operating pr inciple of an inter-digitated capacitivesensor.
Figure 9. A plush toy instrumented with an instant inkjet pr inted ca-pacitive sensor r ibbon.
can be readily integrated with flat, curved or even flexiblesurfaces. Theprinted sensor electrode can beused to detect aslight change of permittivity near its surface; this signal canbe easily read by off-the-shelf microcontrollers such as Ar-duino. In our prototype, we attached the sensing ribbon tothe inside of the skin of a stuffed toy, see Figure 9. Sincethe capacitance of each strip can be read independently us-ing multiple microcontroller I/O pins, it is possible to detectthe exact touch location, causing the toy to react differentlydepending on the how the user touches it during interactions.
Capacitive sensing for liquid level detection
Figure 10 shows another example application based on aribbon-shaped inter-digitated sensing sticker. A laminate-coated sensor strip isattached to theinsideof adrinking glass.The flexibility of the ribbon allows it to fit to the curved sur-face of the glass. Its capacitance is measured using an Ar-duino nano and the Arudino CapSense Library. The graphin Figure 10 shows a very good correlation between mea-sured capacitance and liquid level, and for comparison theprinted sensor is much more accurate than the RFID-basedsystem presented in [3]. Since the sensor ribbon is insulatedby a laminate coating, it will not contaminate the liquid in theglass (or vice-versa). The manufacturing cost of one sensorribbon is no more than a few cents while the Arduino-basedcapacitance reader costs a few tens of dollars.
Printed Antennas
An antenna is an electronic component that converts electri-cal energy into electromagnetic radiation in the form of radiowaves and vice-versa. The simplest antennas consist of onlyan arrangement of metallic conductors, and in this case theconductivity, permittivity and shapeof theantennahasahugebearing on its performance.
0"
0.5"
1"
1.5"
2"
0" 50" 100"
Figure 10. A laminate-coated inter-digitated capacitive r ibbon is at-tached inside a dr inking glass. The r ibbon is connected to the digitalI /O of Arduino nano in order to measure the capacitance which is pro-por tional to the liquid level
Figure 11. University logo is modified as915MHz UHF band antenna. RFID chip isattached using conductive epoxy.
15#
20#
25#
30#
35#
50# 75# 100#125#
Power&(dBm)&
Range&(cm)&
Minimum&Power&Level&to&Read&Tag&
Figure 12. Per formanceof custom pr inted RFIDtag.
A 915MHz band dipoleantennawasdesigned based on auni-versity logo using the CST Studio microwave simulator. Thedimensions of the antenna are such that it fitsonto astandardsized business card. The antenna impedance was matchedto that of a standard RFID chip to support direct attachmentto the antenna terminals using conductive epoxy. Figure 11shows thefinal antenna design, which isacombination of theuniversity logo and a functional UHF folded dipole antenna.Figure 12 showstheperformance of theassembled RFID tag,which was comparable to that of a commercial low-profileUHF RFID tags. This result demonstrates that our instantinkjet printing process is suitable for prototyping RF struc-tures such as antennas.
Time domain reflectometry
Wimmer et al. did not suggest the use of inkjet printing theirwork on time domain reflectrometry for sensing interaction[21], but we have successfully implemented this techniqueusing an inkjet printed transmission line, see Figure 13. Weused a Hilbert curve as the basis of the stripline pair whichmakes up the transmission line. This is a fractal space-fillingcurve that gives a fairly good mapping between 1D and 2Dspace that preserves locality, which means that the patternoffers consistent touch resolution in the x and y directions.
DISCUSSION
Additional practical issues
Throughout the course of this work we have been pleasantlysurprised how well the inkjet process has worked. Of course,anumber of issueshavecometo light. Asalready mentioned,
Moisture Sensor
Instant Inkjet Circuits• Only Single Layered Circuits
• Difficult to route complex circuits
LED Matrix
Tunable Coil9
Hide Wiring10/16/2015 UbiComp ‘15
Instant Inkjet Circuits• Only Single Layered Circuits
• Difficult to route complex circuits
LED Matrix
Tunable Coil10
Hide Wiring
Needs • Double and Multilayered Circuits• Interconnection between layers
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Related Works
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Related Works
Stapler
Electro-plate
12
Conductive Adhesive
[Kisiel, et al., 2002]
Laser Cutter
[Falat, et al., 2011]
Rivet
[Anderson, et al., 2014]10/16/2015 UbiComp ‘15
Related Works
13
Conductive Adhesive
Laser Cutter Stapler Rivet
Footprint Small Small Large Large
Positioning Flexible Flexible Not Flexible Flexible
Energy Medium Huge Low Low
Time Long Long Short Medium
Durability Stable Stable Not Stable Not Stable
Danger Low High Low Low
Needs• Small Footprint• Flexible Positioning• Low Power Consumption
• Short Time• Durable• Not Dangerous
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Proposal
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Proposal – Idea
• Use double sided paper• Via hole to make interconnection• Drill Bits – Hole Punchers – Felting Needles
• Diameter: 0.2mm ~ 1mm• Drill hole• Fill silver ink
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Proposal – How Does It Work?
16
Paper LayerResin Coated
Layer
Micro-porousLayer
Structure of Double Sided Paper
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Coating develops silver particle to bulk metal
17
Paper LayerResin Coated
Layer
Micro-porousLayer
Structure of Double Sided PaperWith Via-Hole
Proposal – How Does It Work?
No coating layer inside the hole
Is it? NO
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Paper LayerResin Coated
Layer
Micro-porousLayer
Structure of Double Sided PaperWith Via-Hole
Proposal – How Does It Work?
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Paper LayerResin Coated
Layer
Micro-porousLayer
Material Entanglement
Structure of Double Sided PaperWith Via-Hole
Proposal – How Does It Work?Sintering-free
Immediately Conductive
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Experiment
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Experiment – Preparation
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Hole Opener
Drill Bit Hole Puncher Felting Needle
22
Experiment – Preparation
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Substrate & Silver Nanoparticle Ink
From Mitsubishi Paper Mills• Double Side Photo paper• Silver Ink NBSIJ-MU01
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Experiment – Preparation
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Environment
• Environment vs. Conductivity
• Temperature: 20ºC
• Humidity: 20% ~ 30%
• Humidifier: create 100% humidity box
24
Experiment – Conduction
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How to fill silver ink? – 3 options
• AgIC silver ink brush
• Epson Inkjet Printer• Open source driver Gutenprint
(widely applicable)• Control overprinting• “Print Density” (1 – 8)
• Print Density > 2• dirty sample• Use Print Density 1 & 2