the underground m system mems sensors · the underground m3 system progress update: april 2007 mems...

The Underground M3 SystemProgress Update: April 2007

MEMs Sensors

Department of Engineering, University of Cambridge

James Ransley, Gary Choy, Ashwin Seshia, Kenichi SogaDepartment of Engineering, Trumpington Street, Cambridge, CB2 1PZ

Overview

Attempts to measure Gary’s devices (initial prototypes)

Tronics Device design

Board Design for Bonded Chip Measurements

Progress with Mote interface etc.

Conclusions & Future Directions

Tronics Device Design

Attempts to measure Gary’s Devices

•Devices are definitely released – movement can be seen.

•Issues with maximum DC voltage – chip fails when a voltage of approximately 30V is applied – issue with grounding…

•The parasitic capacitance will probably mean that these devices cannot be measured. To confirm for certain, need to measure the device bonded up in a chip carrier.

Board Design for Bonded Chips

Circuit Simulations

-100

-80

-60

-40

-20

0

20

-92.5

-92

-91.5

-91

-90.5

-90

-89.5

104 105 106 107

Am

plitu

de (d

B)

Phase ( o)Frequency (Hz)

10fF

100fF

1pF

Gary’s Device assuming Q=2000 (vacuum conditions – vacuum chamber about to come online)

Tronics Device assuming Q=370 (a low estimate for the Q of these vacuum packaged devices…)

-100

-80

-60

-40

-20

0

103 104 105

Am

plitu

de (d

B)

Frequency (Hz)

-180-90

090

180

103 104 105

Phas

e (o )

Frequency (Hz)

10fF

100fF

1pF

Mote Interface

SCA103T-D04Inclinomter

5V Buried ZenerVotlage Reference:LT1236AIN8-5or similar withFET amplifier

Power in

Analog out 1

Analog out 2

Channel 1

Channel 2

Power in Reference in

3-10V DC to DCconverter

16 Bit A-D converter:LTC2489I or similar

YSI 44006thermistorto be supplied

Chip resistor10k 0.02%

Photoresistordigikey PDV-P7002or similar

Chip resistor10k 0.02%

PW1 (30)

ADC 6 (37)

PW2 (31)

ADC 5 (38)

Analog ground(1)

PW3 (32)

I2C Data (22)

I2C Clock (21)

I2C Data

I2C Clock

Analog ground(1 or 51)

51 p

in F

emal

e bo

ard

to b

oard

con

nect

orD

igik

ey P

art

H10

408C

T-N

D

Crossbow MicaZ MotesSensor Board Design

Initial attempts at looking at MicaZmote interfaces:

•Analog voltage measurement demonstrated

•Working on an A-D and digital interface

0

500

1000

1500

2000

2500

3000

0 15 30

Vol

tage

(mV

)

Time (minutes)

Conclusions & Further Work

Gary’s devices may not be measurable – will try once more with new board and vacuum setup when operational.

Tronics devices will arrive at the end of April – these should be much easier to measure and to work with because of wafer level vacuum packaging.

Initial experiments with interfaces to motes performed, eventually this will help with interfacing strain sensors with the motes.

Vacuum measurement facility and custom measuring board will be operational soon.

Underground M3, Barcelona, Apr 2007IMM Bologna

Underground M3 periodic meeting (6Underground M3 periodic meeting (6thth month)month)

IMM BolognaIMM Bologna

Institute of Microelectronics and Microsystems (IMM) Bologna Unit

A. Roncaglia

1


2

• Strain sensors: design and modelling of resonant DETFs.

• Process flow for sensors’ fabrication.

• Development of basic process steps: spacers technology, anti-stiction, DRIE etching, polysilicon interconnections.

• Conclusions – next actions.

OUTLINE


3

DETF electrical model

v1 v2

GND

d0


4

Process simulation - 1


5

Process simulation - 2


6

Development of basic process steps

• Surface micromachining with sacrificial oxide and anti-stiction procedure.

• Spacer technology for gap reduction

• Optimized DRIE recipe for anisotropic silicon micro-machining.

• Realization of heavily doped polysilicon interconnections on high steps.


7

STICTION on MEMS Materials

• The phenomenon is meanly due to the attractive interfacial forces induced by capillarity, van der Waals and electrostatic forces

• The stiction can occur during fabrication (release stiction) or during application (in-use stiction).

• Permanent adhesion of suspended structures on a substrate when the surfaces contact each other


Thin films on siliconDry etchingWet etching Residual water dropsCapillary forcesStiction

8

The problem of stiction


9

Anti-stiction procedure

E. Forsén, Z.J. Davis, M. Dong, S.G. Nilsson, L. Montelius, A. Boisen, “Dry release of suspended nanostructures”, Microelectronic Engineering, 73-74 (2004), pp. 487-490

Sacrificial oxide etching (BOE)

Deionized water rinse (no sample drying)

Acetone immersion

Add photoresist until saturation

Sample spinning for excess resist removal

Soft bake

Complete resist removal with oxygen plasma


Thin filmsDry etchingWet etchingWater rinseAcetone rinseAcetone rinseAcetone rinseAcetone rinseAcetone rinsePhotoresistDry release (O2 plasma)

10

Anti-stiction process


11

Anti-stiction test: process 1


12

Anti-stiction test 1

1100 oC - 60 min.920 oC

1100 oC - 60 min1000 oC

AnnealingPREDEP (POCl3)

Polysilicon doping and annealing conditions

Mask details


13

Anti-stiction test 1 – released structures

Released polysilicon

Sacrificial oxideSi bulk

Stuck structure

Released structure


14

Anti-stiction test 1: effect on narrow poly beams

With no anti-stiction

With anti-stiction


15

Anti-stiction test 1: effect on wide structuresWith no anti-stiction

With no anti-stiction

With anti-stiction

With anti-stiction


16

Anti-stiction test 2: process flow

Yao-Joe Yang, Wen-Cheng Kuo, “A novel fabrication method for suspended high-aspect-ratio microstructures”, J. Micromech. Microeng 15 (2005), pp. 2184-2193.Noel C. MacDonald, “SCREAM MicroElectroMechanical Systems”, Microelectronic Engineering 32 (1996), pp. 49-73


17

Anti-stiction test: iso etching (SF6 plasma)

Mask detailsIsotropic etching (2 mins)

CVD oxide

Silicon


18

Anti-stiction test: iso etching (SF6 plasma)


19

Anti-stiction test 2: released single-crystal silicon beams

No stiction observed on single-crystal silicon ! → anti stictionnot applied


Spacers technology: process flow

20


Spacer technology: results

21


Process parameters1800 W

60 W (LF)

10 °C

300 sccm

150 sccm

7/2

Source power

Substrate Power

Temperature

SF6

C4F8

Cycle

Optimized DRIE Recipe

22


Polysilicon connections on high steps

23


Polysilicon Interconnections: results

24


25

Conclusions

• Surface micromachining/anti-stiction ok

• Spacer technology ok

• DRIE silicon micromachining ok

• Polysilicon interconnections ok

• Mask design/modeling ongoing

MEMS Inclinometer

The University of Cambridge(The University of Tokyo)

Taro Uchimura

MEMS Inclinometer SCA103/100TMEMS inclinometer: SCA103T-D04 (VTI Technologies)

Direction: 1-Axis (2-Axis in 1 direction); Range: -0.26 to 0.26 g (-15 to 15 degree); BW = 8-28 HzSensitivity: 16 volt/g; Resolution: 0.0013 degree (analog I/F at 10 Hz), Sensitivity: 6554 LSB /g; Resolution: 0.009 degree (digital SPI I/F)Output Noise Density: 0.0004 degree/√Hz at DC to 100 HzPower supply: 5 volt x 4 - 5 mA; Price: 36GBP (2 pcs)

High resolution

Small package(12 pin DIP IC size)

Low power consumption

Low Price

Moving electrode

Sensitivedirection

Fixed electrode

Capacitance is measured

Possible mechanisms:

0. 023mg, 4.68 arcsec -> (0.37V)

MEMS Inclinometer SCA103/100T(cf:) SCA3000-D01/D02Direction: 3-Axis;Range: -2 to 2 g (360 degree); BW = 45 HzSensitivity: 1333 LSB /g; Resolution: 0.75mg = 0.04degree (digital SPI/I2C I/F)Noise: 3 mg RMSPower supply: 2.35-3.6 volt x 0.48-0.65 mA; Price: 15 GBP (2 pcs)

(cf:) ADXL202E *** installed in MTS310 ***Direction: 2-Axis; Range: -2 to 2 g (360 degree); BW = 6000 HzSensitivity: 11% /g (Digital Duty Cycle I/F),

167mV/g (analog I/F, at Vcc = 3V), 312mV/g (analog I/F, at Vcc = 5V)Noise: 0.2 mg/√Hz RMS (max: 1 mg/√Hz RMS)Power supply: 3.0-5.25 volt x 0.60 mA (max: 1mA); Price: 34.5 or 28.5 GBP (2 pcs)

(cf.) Schaevitz Accustar P/N 02111002-000)Range: = ±60deg, Sensitivity: 0.001deg Pow.= ±9V x 6mA, 100GBP)

(cf) Digital Q Tilt 200 (OYO) : Servo-type inclinometerSensitivity: < 10 sec = 0.0028 deg = 0.05 mg

(cf) Inclinometers for seismology: Sensitiity = 1μg ← Higher by three order.

MEMS Inclinometer SCA103/100T

SCA103T

GND

+5V

MICAz

Power control

ADC(16bit)

Battery

I2C

Analogoutput

SPI(Digital output)

Power supply monitor

Possible connection between SCA103T and MOTESupported by MDA300 or original design

SPI interface is alreadyused for MICAz system

GND

+3VBattery

Fiber Optics strain measurement

MEMS inclinometer

15m

MEMS Inclinometer for Slope (London)

SCA100T-D01( Direction: 2D,

Sens.= 0.0025deg, Range = ±30deg, Pow.= +5V x 5mA, 8100yen)

MEMS inclinometer

15m


MEMS Inclinometer for Slope (Tokyo)

傾斜

土壌水分

MEMS inclinometer

Volumetric water content meter

MEMS Inclinometer for Slope (Tokyo)(1) Displacement: Inclinometer (VTI Technology, SCA100T-D01) MEMS

(Sens.= 0.0025deg, Range = ±30deg, Pow.= +5V x 5mA, 8100yen)(2) Water condition: Volumetric water contents (DECAGON ECH2O EC-5)

(Accu.=0.003m3/m3, Range ～ 0-100%, Pow.= 3V x 10mA, 15000yen)(3) Wireless data transfer: (Nippo Electronics, PL2130B: Not changed)

and, Cell Phone network (KDDI, JAPAN). Long distance data transfer.(4) Power supply: 4 x AA alkaline batteries, (> 1 year)(5) CPU: TI, MSP430-F169 (Pow.= 3V x 330mA at active, 2mA at sleep, 8000yen with test board)(6) Backup Memory: SD/MMC memory(7) Cost of parts: 40000 yen (170GBP) / point < 1/10 of similar system in market

Inclinometer

CPU Wireless data transfer unit

Power unitInclinometer

Water content meter


Wireless data transfer

Soil moisture sensor

InternetEasy installation : (< 30 mins work)

(with Public Work Research Institute : Tsukuba, Japan）

25cm

0

1

2

3

4

5

6

7

8

9500 9700時間(分)

変位

（mm

）

10:00:00

9:15:00

降雨開始時刻9:00:00

10:45:00

ユニット2

ユニット1

崩壊(下部）10:54:00

崩壊（上部）12:10:00

ユニットの足元が滑る

ユニットが前に転倒する

ユニットの足元が滑って転倒した

10:27:00

Incl

inom

eter

s (m

m/2

00m

m)

Inclinometers detected abnormal behaviorsmore than 30 minutes before failure.

Elapsed time (min) Failure at lower part

Failure at upper part

Rainfall started(15 mm/hr)

Upper sensor unit

Lowersensor unit

Unit leaned forward

Unit leaned backward

Unit leaned backward


TEST 2005

250000 255000 260000 265000 270000 275000-10

-5

0

5

10

15

20

25

30

35

40

ユニット４

ユニット３

ユニット２

時間(秒)

変位(mm)

ユニット１

降雨開始

下部にクラック

転倒

崩壊まで約30分

予兆無く転倒

周囲のクラックとともに変化

下部崩壊

But the behaviours before failure are not Always the same……

MEMS Inclinometer for Slope (Tokyo)In

clin

omet

ers

(mm

/200

mm

)

Elapsed time (min)

Failure at lower part

Rainfall started(15 mm/hr)

Leanedwith cracking

Lower unit

Crack atlower part

Leaning forward

Sudden move

30mins

Upper unit

Middle unit

Middle unit

TEST 2006

Stability of sensor output

18000 18600 19200 19800 20400 21000 21600 22200 22800 23400 24000

1.242

1.244

1.246

1.248

1.250 0.001 V = 0.00025 g = 0.014 deg(Voltage is 1/2 of sensor output)

Test: 061227Inclinometer is on with ADC for 10 times x 50 ms before data transfer every 30 sec.0.1µF capacitor for inclinometer VoutX.No LED flushing.Data transfer for every 30 sec.Vbat = C alkalyne x 4 cells.

Inclinometer X Vout(with 0.1µ F capacitor)拡大図

Time (s)

Incl

inom

eter

(vol

t)

F

0 21600 43200 64800 86400 108000 129600 151200 172800

1.244

1.246

1.248

1.250

1.252

1.254

1.256

1.258

1.260

1.262

1.264

1.266

1.268

1.270

Inclinometer X Vout(with 0.1µF capacitor)0.001 V = 0.00025 g = 0.014 deg(Voltage is 1/2 of sensor output)


Start at 19:35

Time (s)

Incl

inom

eter

(vol

t)

F

End at 07:40

0 21600 43200 64800 86400 108000 129600 151200 172800

6

8

10

12

14

16

18Open windows

Heater off.OutingCooking


Time (s)

Tem

pera

ture

(C)

EStart at 19:35 on 26 Dec 06

End at 07:40

Heater on

Return home,Cooking

Stir room air

Close windows,Heater on.

Thank you

OBJECTIVESMitigation of rainfall-induced slope failures- There are countless number of potential landslides in Japan.- However, most of them are relatively small-scale landslides on the surface. (Large slide with circular slip surface are rare.)→We cannot pay for each of small potential slopes.

Low-cost, simple warning system is needed.→ Then, local residents can install them as self-defense activities.

Low-cost systems are also acceptable in developing countries.

http://upload.wikimedia.org/wikipedia/commons/2/22/Southern_Leyte_mudslide_2006_pic01.jpgHuge scale landslide (2006.2 Leyte, Philippines)

Small scale landslide (2005.9 Kagoshima, JAPAN)

METHODS# Screening of minimum measuring points:

(1) Displacement and (2) Water condition at the Toe of Slopes.

# Simple and low-cost measuring devices:(1) Displacement:

Extensometer Inclinometer MEMS Inclinometer

(2) Water condition:Suction Volumetric water contents

# Wireless system:(3) Data transfer: Wired Wireless (short distance)

Wireless (cell phone network)

(4) Power supply: Wired Battery drive(low power devices, power saving control)

●Orense, Farooq, Towhata et al.(The University of Tokyo：～2003）

METHODS (screening of measurement)

0

5

10降雨による模型斜面崩壊実験

変位cm

法尻部の変位地表

深さ5cm

0.0

0.25

0.50含水率

斜面中の　水分含有率

飽和度90%相当

0.0

4.0

8.0

0 1000 2000 3000 4000 500

間隙水圧

kPa

降雨時間（秒）

斜面中の　間隙水圧

Artificial rainfall tests on slope models

High water content, and slow displacementat the toe of slope can be a signal of failure.

P. W

. P.

(kPa

)W

ater

vo

lum

e (%

)D

ispl

acem

ent

(mm

)

At slope toe Surface

Inside

Sr = 90 %

Pore water pressure

Elapsed time (sec)

METHODS (extensometer inclinometer)【Observation of displacement】(1) Extensometers

Absolute displacement can be measured （some mm/hour order）.But, very hard and expensive to install and to maintain it.

(One end of extensometer wire is fixed to an immobile point far from the point to be observed.)

(2) Inclinometer ← BETTER CHOICEThe absolute value of displacement can not be observed.But, easy to install and maintain. (Just installing the sensor at the point to be observed.)

Immobilepoint

Point to be observed

Extensometer’s wireInclinometer

【Observation of soil moisture】(1) Measurement of suction

(Mechanical parameter which affects the slope stability.)

(2) Soil moisture sensor （Volumetric water content） ← BETTER CHOICE(Indirect parameter to evaluate the slope stability.But, low-cost, stable, and maintenance free.

Suction sensor


Pore water pressure sensorceramic cap

Inner part must be filled with no-gas-containing water

METHODS (suction water contents)

PROTOTYPE in 2005(1) Displacement: Inclinometer (Schaevitz Accustar P/N 02111002-000)

(Sens.= 0.001deg, Range = ±60deg, Pow.= ±9V x 6mA, 24000yen)(2) Water condition: Volumetric water contents (DECAGON ECH2O EC-10)

(Accu.=0.03m3/m3, Range ～ 0-100%, Pow.～ 3V x 3mA, 20000yen)(3) Wireless data transfer: (Nippo Electronics, PL2130B)

(2.4GHz, 57.6kbps, Pow.= 3V x 23mA at active, 0.3-10µA at sleep, communication distance ～70m, 12000yen)

(4) Power supply: Wired (Power save management was not achieved.)(5) CPU: Microchip/Akizuki, AKI-PIC877 (Pow.= 5V x 600µA, 1700yen)(6) Cost of parts: 60000 yen (260GBP) / point < 1/10 of similar system in market

CPU

Wireless data transfer unit

Inclinometer

PROTOTYPE in 2005

Easy installation : (< 30 mins work)

Data is sent wirelessly

25cm


Inclinometer &Micro conputer

Wireless data transfeunit

ROADMAP in 2006, and after2006～ Now working in Tokyo. : (More low-cost, low power, small devices)(1) Displacement: Inclinometer (VTI Technology, SCA100T-D01) MEMS

(Sens.= 0.003deg, Range = ±30deg, Pow.= +5V x 6mA, 8100yen)(2) Water condition: Volumetric water contents (DECAGON ECH2O EC-5)

(Accu.=0.003m3/m3, Range ～ 0-100%, Pow.= 3V x 10mA, 15000yen)(3) Wireless data transfer: (Nippo Electronics, PL2130B: Not changed)

and, Cell Phone network (KDDI, JAPAN). Long distance data transfer.(4) Power supply: Battery drive (> 1 year with 4 x AA alkaline batteries)

Full wireless is achieved.(5) CPU: TI, MSP430-F169

(Pow.= 3V x 330µA at active, 2µA at sleep, 20000yen with development board)(6) Backup Memory: SD/MMC memory(7) Cost of parts: 60000 yen (260GBP) / point < 1/10 of similar system in market

2007～(3) Wireless data transfer: Nippo Electronics will modify PL2130B.

(Lower frequency 430MHz Lower power consumption, longer communication distance ～300m)

(5) CPU: Special board is designed. Only CPU chip (1500yen) is needed.preparing for mass production.

VERIFICATION (with prototype 2005version)

(with Public Work Research Institute : Tsukuba, Japan）

20cm

20cm

25cm

25cm

80cm

Artificial rainfall tests on 1 m-height models of embankment are conducted to verify the workability of sensor unit. (15 mm/hr)

Thanks to Mr. MORI’s lab.


10

15

20

25

30

9600 9650 9700 9750 9800 9850

時間（分）

体積含水比

(

%

)

降雨開始時刻9:00:00

10:54:00崩壊（下部）

12:10:00崩壊（上部）

ユニット1

ユニット2

Soil moisture meter also responsed, but it is sensitive to the position of installation.

Failure at lower part

Failure at upper partRainfall started

(15 mm/hr)

Upper sensor unit

Lowersensor unit

Vol

umet

ric w

ater

con

tent

(%)

Elapsed time (min)


Verification test on large-scale slope model(3m height)

Erosion started from the toe, then gradually moved toward the top of the slope

(Cooperation: Public Work Research Institute : Tsukuba, Japan）


5.5 6.0 6.5 7.0

0

2

4

6

8

10

(レンジオーバー)

CH 7 まで侵食

CH 8 まで侵食

CH 9 まで侵食

CH10 まで侵食

CH7CH8

CH9

Time = 0: 2006/3/30 16:30:00

Time (day)

Rel

ativ

e di

spla

cem

ent (

mm

) Cli3 Cli5 Cli9 Cli10

CH10

The inclinometers detected abnormal changes before the erosion proceeded the place of sensor unit. But, their trend of behaviors are case-by-case.

Rainfall started

Eroded to Ch10 Eroded to Ch7

Eroded to Ch8

Eroded to Ch9

OTHER TASKS・Empirical & theoretical background:

Data accumulation for long-term at various places, andTheoretical understanding of the mechanism of the inclination on slope surface.

A logic to translate the data from inclinometer to conventional extensometeris needed.

・Installation and operation:Technical matters:

Which slopes should be observed?Where on the slope the sensor unit should be installed?Durability and reliability for long period of time should be verified.

Management:Who will install and operate the disaster mitigation system?Who will pay for the cost?

・Further options for hardware:Power supply （Battery Solar cell? More advanced “Power Harvest”??)Data Transfer （Short wireless & Cellular phone Satellite communication?? ）More intelligent control of communication?? (like IMOTE)Other usage: Useful as a universal data logging system by replacing the sensors. Development of new sensors: (ex. MEMS for suction measurement??)

The Underground M3 SystemProgress Update: April 2007

Power Harvesting

Department of Engineering, University of Cambridge

James Ransley, Gary Choy, Ashwin Seshia, Kenichi SogaDepartment of Engineering, Trumpington Street, Cambridge, CB2 1PZ

Overview

Mote Power Consumption.

Available Power Sources in the tunnels.

Discussion of each available source.

Summary, conclusions and further work.

How much power do we need?Crossbow MicaZ

Cycle Duration/mins 30 Battery Capacity/mA-hr 3000 Battery voltage 30.5

Radio Receive Radio TransmitLogger Write Logger Read

Current /µA Time /hr



Processor 8000 0.01 0 0 8 0.49 167.84 503.52Radio 8000 0.0075 12000 0.0025 2 0.49 181.96 545.88Logger 15000 0 4000 0 2 0.5 2 6Sensor Board 5000 0.01 0 0 5 0.49 104.9 314.7

TOTAL 456.7 1370.1Battery Life /months 8.99

Mean Power /µW

Operation 1 Operation 2 Sleep Mean Current /µW

0

5

10

15

20

0 10 20 30 40 50 603A-h

Bat

tery

Life

time

(mon

ths)

Mean Cycle Time (minutes)

0

2

4

6

8

10

12

14

0 10 20 30 40 50 60Po

wer

Con

sum

ptio

n (m

W)

Mean Cycle Time (minutes)

Power sources Available in Underground TunnelsLights – on in engineering hours.

Rail/Sleeper Deflection as a result of weight of the train.

Ambient vibrations from passing train.

Wind/Pressure difference as train travels down tunnel

Electromagnetic radiation produced by current spike from live rail as train passes

Temperature gradients?

Rails/rail pads warm after passing train?

Note that for a given power source the ‘duty cycle’ as well as the power available is important – what counts is the average power harvested.

Electromagnetic Power Harvesting

•London underground is operated from a DC live rail.

•Current spikes of 100’s of Amps over 10s occur when a train passes.

•Mean field density of only approximately 6mT through cm sized yoke.

•Harvestable power ~10µW from a 20cm long section while a train is passing.

•Situation is even worse if the rails have a high permeability (like iron!) – which is likely the case.

Light Harvesting & Related

•Existing product - Heliomote

•100 mWcm-2 (directed toward sun)

•100 μWcm-2 (illuminated office)

•London Underground – Probably Much Less!

•May be useful in over ground sections…

Solar Panels:

•Replace Bulb with a socket splitter – take power from one output and put second bulb in a second output.

•Are there any Health and Safety issues?

•Would need at least some wiring for locations away from tunnel edge.

Peter’s Solution:

Wind/Pressure Differences

Priya – UT Arlington

•Piezoelectric wind harvesting 100 μWcm-2

•With small turbines piezoelectric generators are apparently more efficient (18% efficiency) than electromagnetic generators (1% efficiency).

•NSF grant holder – possibility of collaboration?

Holmes – Imperial

•Miniature MEMs wind turbine: 1Wcm-2.

•Requires 30 litres/min air flow & 8 bar pressure difference.

•Unlikely to be able to create an 8 bar pressure difference…

Kinetic Energy of air at 30mph = 1.7Wcm-2

Temperature Gradients

•Thermoelectric effect employs temperature gradients to generate a voltage and hence a current.

•Seiko thermic watch on left is powered by temperature difference of between 1 and 3oC

• Thermo life generator with ∆T=5K: 60 μWcm-2.

•Probably not practical for our application – no large areas of significant temperature difference all year round…

Rail/Sleeper DeflectionParadiso MIT:

•Electromagnetic ‘heel strike power harvester.

•7W potentially available from walking, 100’s of mW demonstrated.

•Piezoelectric version also made (more comfortable!).

Railway equivalent:

•Rail deflects through 1mm with a force of 20kN every time an axel passes – this represents 20J per axel – approx 200J per train.

•With 1 train every 10 minutes on average this represents 0.3W – lots of power – again 100’s of mW

•Disadvantage: wiring would be needed from the rail to the location of the mote…

Vibrational Harvesting

Existing Porducts: Perpetuum Harvesters

•Enclosed unit that harvests power from ambient vibrations.

•May be possible to operate using ambient vibrations caused by passing trains – so in principle could operate all around the tunnel & be integrated with motes.

•mWcm-3 reported at 100Hz.

•Perpetuum existing product: 10mW power from a 55mm diameter by 55mm height device at vibration amplitudes of 400µm.

•Already have some contact with Perpetuum.

•Work is ongoing to develop a similar device in Cambridge with a more extended frequency range.

Summary

Y130µW0.091.5mW50 ×50Thermoelectric‡

Y600mW0.096.7W?Rail Deflection

0.09

0.09

0.13

0.13

0.09

Duty Cycle*

0.88mW

130mW

Unlimited

«300µW

0.9µW

Net Power

10mW

1.6W

Unlimited

«2.5mW

10µW

OperatingPower

55×55

50 ×50

NA

50 ×50

200×150×10

Device Size (dimensions mm)

NVibrational

NWind Based Device †

YLight Socket Splitter

NSolar Panels

YElectromagnetic Harvester

Wiring to Mote?

Device

*assuming trains passing for 30s every on average every 5 minutes during running times† assuming 18% efficiency and 10mph wind speed at tunnel edge ‡assuming ∆T=5K

Conclusions and Further Work

Three routes to proceed identified:

•Wind

•Vibrations

•Semi-wired via light sockets

James to work on vibrations.

Light socket option to be investigated in collaboration with infrastructure owners.

Wind – pursued in collaboration with others?

the underground m system mems sensors · the underground m3 system progress update: april 2007 mems...

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