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Design of RFID Tags for the Real World

(and how to test you got it right)

Ian J Forster

Clive P Hohberger

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Tag requirements

In designing a tag for the ‘real world’ we have to start somewhere with...

The REQUIREMENT

AT BESTA well researched detailed

description of exactly what is needed, where it will work, on what,

when…

AT WORSTOn napkins…

Summarised as two key

parameters:Cost and

Performance

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Inlay cost and performance drivers

Inlay Cost drivers

• Area of silicon

• Cost of chip

• Cost of antenna

• Assembly technique

• Test methodology

• Quality of roll

• Wafer yield – chips

• Volume

• +

But… its like pushing on Jell-O, all parameters interact

Inlay Performance drivers

• Process size used

• Parasitic effects

• Antenna Conductivity

• Assembly technique

• Antenna size

• Target product range

• +

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The blob of Jell-O

With cost and performance,everything affects everything else

Can I ever say ‘YES’ or ‘NO’… without a ‘BUT’?

Smaller Chip

Higher assembly

cost

Lower threshold sensitivity

Lower cost antenna to achieve a

given performance

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OK, now what?

• The key is making the right trade-offs in cost and performance to be “good enough”

• Robust antenna designs can be made which work well over a wide range of applications

• We’ll talk about one such design later.

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Transponders are perfect in free space

• Nothing is physically there to distort their field or detune their antennas

• Reader is so far away that it interacts with the transponder only through the RF signal (“far field”, typically a few wavelengths away– UHF wavelength ~0.34m, so 3 meters is far field)

• In the free space and far field, the tag acts like the spec sheet says

• Then some idiot goes and slaps it on a carton…

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RF properties of things…

• What’s in YOUR carton?

100%RF Reflecting

100% RF Absorbing

100% RF Transparent

● Canned hams

● Potato chips in foil bags

● Jars of pickles

● Bottled water

● Bubble wrap

● Dried foods

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Real products in cartons

• Alien squiggle transponder, horizontally polarized• Measured distance at which good read rate drops to 50%

Product in carton Product Packaging Distance Comment(product as purchased) inches

Air none 75Cheerios Cardboard box 70 weak absorberPennzoil 10w40 HDPE bottle 65 weak absorberTortilla chips Aluminized plastic bag 50 foil bag scatters RFRoot beer (24 pk) 12 oz aluminum cans 45 best if tag vertical in gapGatorade Plastic bottle 41 electrolytes absorb RF energyLiquid Tide HDPE bottle 35 electrolytes absorb RF energyCat litter Cardboard box 35 clay is good passive RF absorberIvory Soap plastic/paper wrapped 25 soap is good RF absorberPantene Shampoo HDPE bottle 21 soap + electrolytesCascade Foil covered paper box 15 Foil capacitance detunes antenna

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We’re not in free space any more, Toto..

‘Real World’ influences

Conductors

Dielectrics

‘Mixtures’

Results in changes in:Antenna bandwidth

Operating FrequencyImpedance Match

Antenna Efficiency…

=

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And its worse than that…

‘Real World’ Products have a 3D shape

T T

T T

C

C

Layer of corrugatedcardboard

Pack of canned goods

Antenna position dramatically changes electrical environment

tag is operating in

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Still worse…

Connectivity between conductive objects matter

T TC

Layer of corrugatedcardboard

Pack of canned goods

Electrically isolated when

pack is bent, in contact at other

times

So, shape, materials, connectivity all interact with mounting position to determine how well

a deployed label works

And we can’t design a different antenna for each situation…

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Special antenna technology approach

Avery’s Carton Content Insensitive Technology

‘Near field interaction of specific elements in the antenna design re-tunes the far field response’

H field Interaction

E field Interaction

E field Interaction

When placed 1.7mm away from a set of cans the operating frequency changes by >100MHz

When placed 1.7mm away from a set of cans the operating frequency changes by <10MHzIN BOTH CHIP CENTRE AND CHIP GAP

Carton Contents Insensitive (CCI) technology is intended to reduce the number of different designs we need to cope with a diverse range of products

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Special antenna technology approach

• Avery’s CCI Technology allows a single tag design to work on a larger group of products

• Works well with metal objects, conductive liquids are a challenge but progress is being made

• More difficult to design than a tag specifically tuned for one position and one product

• More difficult to test

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Avery’s testing systems for real world products

PRIMARY SYSTEMS

SECONDARY SYSTEMS

TERTIARY SYSTEMS

TEST CUBE SYSTEM

HIGH SPEED INLINE TEST

CONVERTER TEST SYSTEMS

APPLICATION TEST SYSTEMS

SWEET SPOT TESTER

END USER TEST SYSTEMS

Cal

ibra

tion

and

trace

abilit

y

mai

ntai

ned

betw

een

all l

evel

s RESPONSE TEST

SYSTEM

PRIMARY SYSTEMS

SECONDARY SYSTEMS

TERTIARY SYSTEMS

PRIMARY SYSTEMS

SECONDARY SYSTEMS

TERTIARY SYSTEMS

TEST CUBE SYSTEM

HIGH SPEED INLINE TEST

CONVERTER TEST SYSTEMS

APPLICATION TEST SYSTEMS

SWEET SPOT TESTER

END USER TEST SYSTEMS

Cal

ibra

tion

and

trace

abilit

y

mai

ntai

ned

betw

een

all l

evel

s RESPONSE TEST

SYSTEM

• Provides optimal trade-off between

– Accuracy– Cost– Speed– Flexibility

• Ensures repeatability & traceability to National Standards through

– Calibration routines– Test RFID devices– Defined procedures

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Avery primary response testing system

VECTOR SIGNAL GENERATOR

REAL TIME SPECTRUM ANALYZER

DEVICE UNDER TEST

LOW DIELECTICSUPPORT

CONTROL AND DISPLAY SYSTEM

ROTATOR MOTOR

COMPACT ANECHOIC CHAMBER

IMPORTANT!Does NOT use a reader

Test Distance

Establishes a ‘Baseline’ for all other test systems

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Zebra primary response testing system

• Built in a G-TEM horn antenna with anechoic foam in bottom

• Uniform field in 6x6x6 inch volume• 3-axis motion stepping tests 3-D

transponder response field

• Uses calibrated UHF reader with PC-controlled step attenuators to measure transponder sensitivity

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Avery tag testing on real world products

Secondary Reader Based System Calibrated To Primary System

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Avery “sweet spot” tag position testing

READER SYSTEM AND DISPLAY

COAXIAL CABLENEAR FIELD COUPLER

TEST TAG

COMPLIANT FOAM POLYSTYRENE BLOCK

Tertiary Reader Based System Calibrated To Primary System via secondary system

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Can I test my own cartons?

• Some simple test procedures are in Annex C of: Proposed Guidelines for the Use of RFID-Enabled Labels in Military Logistics: Recommendations for Revision of MIL-STD-129

• Written by the AIM RFID Experts Group

• Free from AIM at: https://www.aimglobal.org/estore/ProductDetails.aspx?productID=241

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19 mm (0,75 in) minimumfrom either vertical edge

25 mm (1 in) minfrom natural bottom

430 mm (17 in) maxfrom natural bottom25 mm (1 in) min

from top

Target area for RFID transponder

DoD recommended smart label placement

• Problem: Where is the best spot to put the label in the allowed target area?

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Reader threshold power test

• Start in the center• Test same tag at different points on case at a fixed distance from a reader with

programmable power• Find relative reader power to activate tag at each position• Find position or region requiring minimum power• Put label there!

DJ

L+6

F-3

G+1

H0dB

J-2

K-1

Mno

E-1

C-1

D-3

B+1

A+2

N+2

P0

Q+1

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Thanks!

Questions?