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