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ISELINSTITUTO SUPERIOR DE ENGENHARIA DE LISBOA SERVIÇO DE DOCUMENTAÇÃO E PUBLICAÇÕES

Wireless Magnetic Based Sensor System For Vehicles Classification

Pierre Ghislain1, Duarte Carona1, António Serrador1, P.aulo Jorge1, Pedro Ferreira1 and Jorge Lopes2

ID-25

CONFERENCE ON ELECTRONICS, TELECOMMUNICATIONS AND COMPUTERS NOVEMBER 24-25, 2011, ISEL, LISBON, PORTUGAL

1ISEL-ADEETC,Lisbon Portugal, 2Brisa, Auto-estradas de Portugal, Portugal

Outline

• Introduction, Motivation and Objectives

• State of the Art

• Solution

• Implementation

• Results

• Conclusions

• Acknowledgments

INTRODUCTION,

MOTIVATION AND

OBJECTIVES

Introduction

• Needs to monitor traffic

• Traffic Jam

• Accidents

• Weather condition

• Illegal U-Turn, entry in exit lane

• Control Service Level Agreements

• Determine vehicle class stats

• Real time to take actions

• 365 days 24 hours service

• Must be very robust and resilient

Motivation

• Present systems

• Sensible to weather conditions

• Very expensive

• Heavy intervention in the lane

• Energy intensive

• Limited use to strategic points

• New sensors

• Much more smaller

• Green Energy

• Use wireless

• Easy to install and maintain

Objectives

Design of a device:

• Traffic counter

• Vehicle Classification

• Real time data

• Many year autonomy

• Wireless, no cables

• As small as possible

• Easy to install

• Low maintenance

• Resilient to weather conditions

• Green energy harvest

STATE OF THE ART

Wireless data communication • IEEE 802.15.4 PHY and Datalink

• Low rate

• Low cost

• Short distance

• Power efficient

• Piconet capability

• Coexistence w/ 802.11b 802.15.3

• ZigBee

• NetWork OSI layer protocol

• Auto configuration

• Association

• Data routing up to the Coordinator

• Define many appliance profiles

AMR, Anisotropic Magnetic Resistance

• Sensing of Magnetic Fluctuations

• Permalloy films

• Magnetic permittivity > 1000

• Magnetization axe low resistance

• Sense 0,5% of ∆EMF

• Purely resistive, 4 MHz bandwidth

• Relative low power

• Require periodic Set/Reset

Energy harvest – Green sensors

• Low power devices

• DC-DC optimization

• Solar energy Cells

• None rechargeable Battery

• Rechargeable battery

• Hypercondensator

THE SOLUTION

The Architecture

Architectures

• No optimization

• Interrupt give by the AMR

• Interrupt + duty cycle on AMR

• CPU Master – full duty cycle

Estimated consumption

50 mA

20 mA

6 mA

< 1 mA

Consumption model

Expected less than 6 mA of consumption

Solar Panel surface estimation model Pr : expectable solar radiation for the worse place and month [Wh/m2/day];

rtrc : conversion yield due to the temperature, reflection and DC-DC electronic conversion;

Rdir e Rind : distribution of the direct and indirect radiation percentage during the day;

rh : conversion yield due to the horizontal position of the device;

rj : conversion yield due to the windows of the sensor;

fo : conversion yield due to the due to the shadow created by the passing over vehicles;

fc : conversion yield due to the solar cells;

Pc : receivable power which corresponded to Pr less all the losses [Wh/m2/day];

Pn : necessary power calculated via the consumption model of the device [Wh] ;

S : minimal surface of solar cells in [m2].

(1)

(2)

IMPLEMENTATION

CPU Master

Solar Panel

Battery

Controler

AMR sensor

Diferencial OpAmp

µP

Rádio Interface IEEE 802.15.4

ZigBee

Set / Reset

Power Suply

Command

Analogic signal

Legend

VCC 3.3 V

Design of the firmware

EMF

Send wireless Signature

Signature digitalization

Detection of the vehicle

Speed estimation

RESULTS

Communication distance

Distance Emission Reception PER

[m] [dBm] [dBm] [%]

1 -3 -55 0

10 -3 -58 0

25 -3 -78 0

75 -3 -94 55

ZigBee + IEEE 805.15.4 give an excellent response for short range

Soil attenuation

Distance Obstacle Emission Reception Per

[m] [dBm] [dBm] [%]

0,4 soil -3 -52 0,0

12 soil +

asphalt +

los

-3 -98 98,5

4 -97 9,0

30 4 -96 11,5

Soil attenuation is unsustainable. The sensor can’t be burry.

Material attenuation

Material Thickness Attenuation

[cm] [dB]

Acrylic 2 2

Glass 2 4

Asphalt 10 11

Microwave attenuation of asphalt is surprisingly lower

Coordinator must be positioned the highest possible

Coordinator antenna Inclination

Link budget

Item Attenuation Unit

Emissor -3 dBm

Antenna of the sensor device 0 dBi

Acrylic window reinforced of 2 cm -4 dB

Inclination loss, 10 meter distance -18 dB

Free space attenuation -63 dB

Coordinator ‘s Antenna 10 dBi

Total -78 dBm

Receptor sensibility -97 dBm

Power reserve -19 dBm

Vehicle signature, 1 mag. axe

0

0,5

1

1,5

2

2,5

3

0 20 40 60 80 100 120 140

Ou

tpu

t te

nsio

n a

fter

the O

pA

mp

[V

]

Samples

Assinatura CMTsignature EMF

Detection of EMF and complete magnetic signature capture is achieved

Vehicle signature, 2 mag. axes

Samples

Ou

tpu

t te

nsio

n a

fte

r th

e O

pA

mp [V

]

The sensor can digitalize 2 magnetic axe but energy saving is lower

Parallel

Lateral

Nom

POWER_SAVE mode

Measured consumption in detection state: Less than 1 mA

92%

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

180 x 10 90 x 10 90 x 5 45 x 5 20 x 5

Po

wer

sav

ing

perc

en

tag

e

Maximum velocity x samples number per vehicle meter

Normal

POWER_SAVING

CONCLUSIONS

Conclusions

• The power consumption can be lower than 1 mA

• The algorithms of the firmware perform nicely

• The sensor network operates well

• Results shows the importance of Set/Reset

• Two options are proposed to the sponsor:

• The design of a simple and cheap sensor solution to

count and classify vehicles

• The design of a high precision sensor equipment to

be included in an array of sensor s to design a vehicle

magnetic scanner.

Proposed Integrated Sensor Device

Proposed Integrated Coordinator Device

ACKNOWLEDGMENT

Acknowledgment

• A special thank to

• Prof. António Serrador, thesis orienteer

• Eng.º Duarte Carona, thesis co-orienteer

• Eng.º Jorge Lopes, Brisa Inovation representative

• Thanks also to my colleagues

• Mário Lopes, Filipe Palhinha, Pedro Ferreira for the

availability and the teamwork's.

OBRIGADO – THANK YOU Pierre Ghislain