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Prined wireless sensor technology
In collaboration with Precisia (Ann Arbor, US), TagMaster (Kista, Sweden), Bofors Defence (Karlskoga, Sweden) and SCA Research
Extremely low cost wireless technology - RFID
• Two different technologies– Silicon based printed RFID
• Intelligence in Silicon• Printed sensors and antennas
– Fully printed RFID tags• Polymer based intelligence...• Printed sensors and antennas
– Where will it be used?• Polymer is always competing at cost levels
where silicon cannot reach (estimated below 5 cent per tag)
Self Assembly
• Alien Technology FSA (Fluidic Self Assembly)
• Revolutionazing technology with the capacity to produce 2 billion chip attachments per year in one machine – The total need when RFID is
fully adopted for logistics is approximately 20 billion tags
• Enabling technology for 5 cent silicon tags
Problems to resolve• Applied research
– Robustness of RFID systems• Evaluation in real life use• Customization of tag solutions for various situations• Hybridization with printed sensor function
• Fundamental research– Key components by printing
• Efficient rectifier• Efficient frequency modulator• Stability in logic functions
First study of carbon nanotube ink
- Nanotubes deluted in acid deposited with different cleaning procedures deposited on silicon wafer
- Electrical characterization
- AFM, SEM analysis
- First try directly on paper
- better deposition but problematic to form thin enought layers
IV-characteristics of nano-network (transistor action demonstrated)
Antennae robustness
• Different aspects of RFID antennae robustness– Reliability in manufacturing (inks and chip
packaging)– Damages during tag life time– Performance degradation due to tag
environmentAre there antenna structures that are more robust than others?
If so, how much better are they?
Are there antenna structures that are more robust than others?
If so, how much better are they?
Manufacturing
• Printed antennas– Uniformity of ink layers
• More or less under control, parameter stability of conducting inks may still provide difficulties
– Variations in substrate material• Still a problem in multilayer
antennae solutions– Feed point tolerances
• An increasingly difficult issue as chip dimensions are reduced
Cost versus robustness
• Narrow sections should be avoided in order to obtain a robust antennae
• However, wider sections demands more ink which increases cost
– In high volume production a trade of between these two constraints would provide an efficient solution
Costs for 900 MHz tag antenna
1.97.75Wide Bowtie
0.41.7Narrow Bowtie
0.020.05Dipole
Estimated cost of Printed
Antenna (cents)
Estimated cost of Copper Antenna (cents)
Figures from
Precisia, LLC (USA)
Radiation Efficiency Vs.Conductor Thickness
Bow-tie antenna Wire-approximation of Bow-tie antenna.
Reading distance degradation due to the environment
• Power loss due to impedance miss-match and reduction in radiation efficiency of antenna
0 50 100 1500
0.2
0.4
0.6
0.8
1
Distance between conductor and antennae [mm]
Perc
ent o
f max
pow
er to
ID c
hip
Matchedcondition
Patch antennas may solve the problem
• Micro-strip antenna with at least two conducting layers
• Sensitivity towards top side• Not sensitive to background material
Conducting patch
Dielectriclayer
Conducting ground plane
Losses in patch antennas
0 0.02 0.04 0.060
0.2
0.4
0.6
0.8
1
Loss tangent
Rad
iatio
n ef
ficie
ncy
104
106
108
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
Conductivity [S/m]
Rad
iatio
n ef
ficie
ncy
Paper substratePlastic
substrate
Microwave substrate
Conductive inks
Copper
Radiation losses calculated using the cavity model (in good agreement with FDTD simulations)
Lossy antennas in RFID systems
• Passive– Reduction of reading
distance as
• Semi-passive– Reduction of reading
distance as
lossless
lossPassive G
G=γ
41
⎟⎟⎠
⎞⎜⎜⎝
⎛=−
lossless
losspassiveSemi G
Gγ
0 0.5 10
0.2
0.4
0.6
0.8
1
Gloss/Glossless
Rea
ding
dis
tanc
e re
duct
ion γ
PassiveSemi-passive
50% loss gives 71% reading distance for passive system and 84% reading distance for a semi-passive systems
50% loss gives 71% reading distance for passive system and 84% reading distance for a semi-passive systems
Example• TagMaster semi-active RFID tag
– Patch antennae on microwave substrate– Reading range of 4-8 m (measurement)– Maximum reading distance up to 12 meters
• Paper version of TagMaster semi-active RFID tag– Silver ink (σ=5 x 105 S/m) patch antennae
on paper board substrate (loss tangent 0.05) and on plastic substrate (loss tangent 0.004)
• Semi-active tags can be designed using printed batteries
Measured phase modulation in Silver Ink patch on PELD plastics
Smith Chart for Znorm=R+jXX=1.5X=1
X=0.5
X=-1.5X=-1
X=-0.5
R=0 R=1R=0.5
1 1.5 2 2.5 3-20
0
20
40
60
80
Frequency [GHz]
Pha
se d
iffer
ence
[Deg
rees
]
Fig. A. Impedance in Smith diagram for high and low signal from ID chip
Fig. B. Phase modulation as a function of frequency
Peak for 2.45GHz
Stability Silver ink on PELD
2.35 2.4 2.45 2.5 2.55
-5
0
5
10
15
20
25
Frequency [GHz]
Pha
se m
odul
atio
n [D
egre
es]
Smallestsize
Largest size
Less chance for failure for the larger structuresLess chance for failure for the larger structures
Simple demonstrator setup
• Direct measurment on sensor in box – Wet textile in bottom of
plastic box– Moisture sensor 2 cm
from plastic cover of wet textile
– Measurement starts when box is covered with plastic seal
Printed sensor
– Four layer electronic ink structure
– Substrate• News paper
materials as moisture absorbant layer
Printed moisture sensor
0 20 40 60 80 100 120 1400
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
0.5
Time [min]
Sen
sor
sign
al [V
]
Sensor put in box with wet textil at the bottom (sensor is not in contact with wet part)
Box opened
Time constants:
- 28 min for moisture to build up in box and to penetrate paper media in sensor
- 13 min for energy process to be turned off
- Fast drop in signal when moisture leaves the box
- Strong drying of paper media in open air
Threshold control
• Two sensors design for different threshold
• Hysteresis due to termodynamic effect in the cellulosa – Provides
latch function for alarms
Cool chain control
• Frozen sensor concept– Water is preloaded into sensor before
freezing down the box– Sensor cell provides a low level signal with no
current driving capability when frozen– As soon as the sensor is put out in room
temperature it respond (within a few minutes)– Action Activated Tag concept is possible
• The package take action when needed
Typical signal from sensor
0 50 100 150 200 2500
0.2
0.4
0.6
0.8
1
1.2
1.4
Time [s]
Sen
sor
sign
al [V
]
Signal is unstable and weak in frozen condition
Full signal 1.2V with power driving capability
The sensor design include water absorbent layer to assist in moisture preloading
Could be directly attached to semi-passive RFID
- passive for control of system and active to be able to take action by itself (AAT concept)
Other applications for semi-passive RFID tag solutions
• The semi-active configuration is very interesting in combination with sensor functionality (logging)
• Research on printed sensors at the Mid-Sweden University
– Smart diaper demonstrator (health care safety alarm)
• Spin-of company Sensible Solution Sweden– Touch sensitive large area paper displays
• Interactive paper displays• Commercial spin-of from master student project• Further developed by AddMarkable
Technologies
SenseSoft –printed sensor element in smart diaper