Přesné magnetické snímače a jejich aplikace

I N V EST I C E D O ROZ VOJ E V Z D Ě LÁVÁ N Í

Přesné magnetické snímače a jejich aplikace Pavel Ripka Czech Technical University, Prague, Czech Republic

Tato prezentace je spolufinancována Evropským sociálním fondem a státním rozpočtem České republiky. 25.6.2010

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Obsah přednášky • Rozsah měřených polí • Typy magnetických senzorů • Základní principy a nové trendy: – Polovodičové senzory – XMR – Fluxgate – Resonanční senzory – Indukční cívky …. 25.6.2010

INVESTICE DO ROZVOJE VZDĚLÁVÁNÍ

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Motivation: applications The Earth’s field: total 50 µT, horizontal 20 µT • Compass – 1 deg ~ 350 nT ... makes 17 m error in 1 km – 0.1 deg ~ 35 nT – gimballing error

• UXO location – 155 mm projectile 1.5 m deep ... 10 to 50 nT – bomb 6 m deep ... 1 to 5 nT 1 nT in 50 000 nT ~ 20 ppm 25.6.2010


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Typical daily variations of the Earth’s field

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Magnetic sensors: basic types • Magnetic field sensors – semiconductor – ferromagnetic – other (optical, resonant, SQUID…)

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Magnetic field sensors Scalar Measure the size of B (“total field B”)

B = Bx2 + B y2 + Bz2 only resonant sensors

Vector Measure the projection of B into the sensitive axis • single-axis • tri-axial most magnetic sensors

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Tri-axial sensors: compass

X (forward)

Bx

α By

Horizontal component Y (right)

Bz Earth’s Field vector B Z (down) α = Azimuth or Heading

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Magnetic field sensors: DC and AC

AC

DC

Measure only changing field: induction coils

dΦ d = − ( NAB ) Vi = − dt dt

Measure DC and AC fields

most magnetic sensors

Vi .. Induced voltage Φ .. Magnetic flux A .. Coil area N .. Number of turns 25.6.2010


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Basic sensor specifications • • • • • •

FS range, linearity, hysteresis TC (“tempco”) of sensitivity Offset, offset tempco and long-term stability Perming (= null change after magnetic shock) Crossfield sensitivity Noise – PSD , rms or p-p value

• Resistance against environment – temperature, humidity, vibrations 25.6.2010


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Types of magnetic field sensors • Semiconductor sensors (Hall, …) • Ferromagnetic magnetoresistors (AMR, GMR, …) – – – – –

Resonant magnetometers (Proton, Cesium, ...) SQUIDs (LTS + HTS) Induction coils, rotating coils Optical (Fibre optic, ... ) Fluxgate

• Other principles (GMI, magnetoelastic, …)

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Magnetic field magnitudes 100 T 10 T 2T 0.5 T 0.1 T 10 mT 50 µT 1 µT 10 fT

Pulse field Superconducting magnet Electromagnet Surface of strong perm. magnet (NdFeB) Surface of cheap magnet (ferrite) Power cable Earth’s field Vehicle Human brain

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Range fT

pT

µT

nT

mT

T

Induction Coils Fluxgate SQUID

Resonant Hall Magnetoresistors Magnetooptical

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Basic rules Dipole field (from small objects) B ∼ 1/r3 Long iron pipe B ∼ 1/r2 Long straight current conductor B ∼ 1/r

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Semiconductor magnetic sensors • Hall – integrated – GaAs, Si, (Ge) – non-plate: vertical, cylindrical

• Semiconductor magnetoresistors • Exotic (magnetotransistors, magnetodiodes, rotating current domain, ...)

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Permalloy Flux concentrators

Used for Hall and MR Increase sensitivity Possible problems: • TC of sensitivity • perming • linearity Cylindrical Hall device with integrated magnetic flux concentrators (Sentron AG) 25.6.2010


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InSb Hall element with ferrite field concentrator

(Asahi Kasei Electronic HW series). 25.6.2010


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Magnetic force lines of field concentrators for a thin-film Hall sensor

(FEM simulation) - courtesy of Asahi Kasei Electronic 25.6.2010


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Semiconductor Magnetoresistors

2%/°C www.murata.com

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AMR: anisotropic magnetoresistance

HY

• Permalloy thin film strip deposited on a silicon wafer magnetized in x direction • HY rotates magnetisation M → R changes by 2%-3%

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AMR: linearisation Bad idea:

Shifting the working point by bias field

Good idea:

Barber-pole Al bars deflect the current by 450 (Honeywell)

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AMR bridge sensor

Philips KMZ Full bridge made of meandered resistors with barber-pole strips 25.6.2010


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Noise of AMR

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Noise of AMR

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AMR: flipping P.F. +

-

Unwanted change of strip permanent magnetization may distort the sensor characteristic. Periodical saturation of the permalloy strips is the cure

Characteristics of Philips KMZ 10 after positive [+] and negative [-] flip P.F. is characteristics for periodicalflipping 25.6.2010


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AMR: flipping

Flipping: + decreases offset + reduces perming + increases sensitivity - increases power consumption Honeywell AMR sensor with integrated flat flipping coil

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KMZ 51 – virgin accuracy

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Flipped + compensated KMZ 51 - overall accuracy Linearity error [ppm FS]

Linearity error of flipped & compensated AMR magnetometer 80 60 40 20 0 -400

-300

-200

-100

0

100

200

300

400

-20 -40 -60 -80 Magnetic flux density [uT]

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KMZ 51 - overview • no flipping: – Linearity and hysteresis: +/- 1 % FS (+/- 300uT) – Tempco. OFFSET –90 nT/K – Tempco. SENSITIVITY –585 ppm/K

• flipping & feedback: – Linearity and hysteresis: +/- 40ppm FS (+/-300uT) – Tempco. OFFSET approx. 2.1 nT/K – Tempco. SENSITIVITY approx. 20ppm/K + noise: 5 nT/sqrHz @ 1Hz

no statistics! 25.6.2010


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HMC 1001

Flipping OFF 7000 6000 5000

Offset (nT)

4000

Hx

3000 2000 1000

Hz Hy

0 -18

-8

-1000

2

12

22

Temperature (°) 25.6.2010


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HMC 1001

flipping ON 100 Hz

0

Offset (nT)

-20

-10

-100 -200

0

10

20

30

40

50

Hx

-300 -400 -500

Hy

-600 -700 Temperature (°C) 25.6.2010


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HMC 1001 – offset drift nT/ 50 OC

x

y

z

No flipping

7 000

3 500

3 700

flipped

250

200

50

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AMR vs. Hall and fluxgate Hall with field concentarors

AMR

AMR

(KMZ 51)

flipped+feedback

fluxgate

linear range

5 mT

300 µT

300 µT

0. 5 mT

size

6 mm

6 mm

6 mm

30 mm

linearity

0.1 < 0.2 %

1%

40 ppm

1 ppm

sensitivity TC

200 ppm/K

600

20

30

offset@250C

50 µT

< 10 µT

< 1 µT

5 nT

offset TC

600 nT/K

100 nT/K

2 nT/K

0.1 nT/K

resolution

1 µT

10 nT(1 nT)

10 nT

100 pT

perming, hyst.

1 µT (?)

300 nT

10 nT

< 1 nT

BW

100 kHz

100 kHz

100 Hz

1 kHz

power cons.

55 mW

30 mW

100mW

150 mW

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GMR: Giant Magnetoresistance I

B

Spin - dependent scaterring: Resistance of two thin ferromagnetic layers separated by a thin nonmagnetic conducting layer can be altered by changing the moments of the ferromagnetic layers from parallel to antiparallel. 25.6.2010


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Common GMR structures

technology developed for reading heads

A: Spin valve B: Sandwich C: Multilayer 25.6.2010


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GMR sandwich

0.74 0.735 0.73

voltage (V)

0.725 0.72

0.715 0.71 0.705 0.7 -50

-40

-30

-20 -10 0 10 20 applie d fie ld (Oe )

30

40

50

Sensitive, but not good for linear sensors

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GMR: spin valve 2750

13

Resistance (Ω)

Resistance (Ohms)

12

11

10

2700

2650

9

2600 08 -200

-100

-30 0

100

200

Angle (Degrees)

Angular response Unpinned soft layer rotates with external field

-20

-10

0

10

20

30

Applied Field (mTesla)

Large field response hard layer may be demagnetized

If saturated, responds only to field direction, not value 25.6.2010


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SDT (spin-dependent tunelling) magnetoresistor

source: Mark Tondra, NVE A cross section of the SDT structure. The vertical scale is exaggerated so the thicknesses are visible. The lateral dimensions of the tunnel junctions range from 0.1 µm to 1000 µm. 25.6.2010


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SDT (spin-dependent tunelling) magnetoresistor 1600

HARD LAYER 1550 SOFT LAYER

Junction Resistance

JMR = R(high) - R(low) R(low) = 21 %

1500

1450

1400

1350

HARD LAYER

RA = 362 kΩ−µm2 Area = 274 µm2

SOFT LAYER

Hpin = 175 Oe Hc = 9 Oe

1300 -40

-30

-20

-10

0

10

20

30

40

Applied Magnetic Field (Oe)

The magnitude of the SDT magnetoresistance can be greater than 40% source: Mark Tondra, compared to ~10% for spin valves. NVE

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Biased SDT sensor 68

1172

1122 64 62

1072

60

Output (mV/V)

Resistance (kΩ)

66

1022 58 56 -0.8

972 -0.6

-0.4

-0.2

0

0.2

0.4


A common magnetic tool for getting a linear response from almost any material is to incorporate a feedback coil and measure the current in this coil that is required to keep the sensor’s output at a certain value. source: M. Tondra, NVE 25.6.2010


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GMR bridge sensor GMR resistors configured as a Wheatstone bridge sensor (NVE) • •

R2, R3 are shielded R1, R4: field is concentrated by approx. D1/D2

250

Still has nonlinear

40 150 30 100 20 50

(NVE)

0 -2.5

Output (mV/V)

unlike AMR bridge

Voltage (mV)

response

50 200

10 0 -1.5

-0.5

0.5

1.5

2.5


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Advantages of magnetoresistors Compared to Hall sensors: • high sensitivity – for position sensors: magnet may be cheaper or smaller or airgap higher – for magnetic field sensors: higher accuracy

• no piezo effect • higher operational temperatures

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GMI Giant magnetoimpedance effect Based on Z ~ δ ~ μ ~ B, Works on MHz frequencies Problems: perming temperature dependence (30nT/K) even response (need bias)

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GMI curve GMI (%)

250

200 Decreasing H Increasing H

150

100

50 -50

-30

-10

10

30 H(A/m) 50

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Temperature drift Impedance and resistance dependence on temperature

5.79

22

5.78

21

5.77

|Z| (Ω)

23

RDC (Ω)

5.8

20

-0.005 %/ºC Rdc |Z|

5.76

19

5.75

18 -25

0

25

50

temp (°C) 75

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Double-core GMI

resulting characteristics 25.6.2010


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Fluxgate sensors Most sensitive room-temperature magnetic sensors Based on non-linear magnetization characteristics of ferromagnetic core. Measure up to 1 mT with 100 pT resolution Classical fluxgates: precise, but expensive (CTU Prague) 25.6.2010


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Fluxgate principle • Ferromagnetic core - non-linear B-H • Excitation and sensing coil • Core is periodically saturated by Iexc, µ drops to 1 twice each period • Measured B0 causes 2nd harmonics in Vind

Vind Iexc(t)

µ(t)

B(t)

Bo

N

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B(Φ)

Φ

Fluxgate principle

H

Hexc

a)

Vi

Hm

t

Φ

t

Vi

B(Φ)

• In absence of external field, magnetisation is symmetrical • External measured field causes assymetry – detected in induced voltage

t

H Hexc+H0

t b)

Vi

t Hm

t

H0

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Basic types of fluxgate

• Double core suppresses first harmonics 25.6.2010


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Orthogonal Fluxgate

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Fluxgate magnetometer

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Parameters of fluxgate sensors Parameter

Top

Standard 30 μT / nT

Sensitivity Range

10 mT

200 μT

Linearity error

10 ppm

100 ppm

Tempco of sensitivity

10 ppm / 0C

50 ppm / 0C

Crossfield error for 50 μT field

< 1 nT

5 nT

Temp. offset drift

50 pT / 0C

0.2 nT / 0C

Perming after 10 mT shock

< 1 nT

< 5 nT

Noise (rms 50 mHz..10 Hz)

5 pT

100 pT

Long-term offset stability

2 nT/year

5 nT/8 hours

Bandwidth

10 kHz

20 Hz

Temp. range

-60 ..+2000C

-20 ..+70 0C

Power consumprion

1 mW

100 mW

Size

2 mm

30 mm

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Low-noise fluxgate sensor

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Temperature offset drift of Oersted sensor

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Offset recovery after temperature shock

offset change (nT)

10 5 0 -5 -10 0

1000

2000

3000 time (s)

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Sensitivity tempco

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Crossfield effect

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Micro-fluxgate sensors (in development) • flat coils • electrodeposited core or amorphous strips • electronics on chip • cheap • resolution still higher than MR

Shizuoka University 25.6.2010


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Flat coils Core

B0

Flat coils

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Two-axial sensor with flat coils

B0x

B0y

pair of cores for x axis

Vix Bexc

Bexc

x-axis pick-up coils excitation coil Uind y Bexc

Bexc

y x Iexc

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Microfluxgate sensor with symmetrical core

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Microfluxgate: Large field characteristics

Vout [mV]

20

15

Iexc 10

waveform - SIN, fexc = 1MHz 5

0 -3000

-2000

-1000

0 -5

1000

2000

B [uT]

3000

Iexc=30mA Iexc=50mA

-10

Iexc=80mA Iexc=100mA

-15

Iexc=120mA Iexc=140mA Iexc=160mA

-20

Iexc=180mA

-25

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Hysteresis and perming of the single-core sensor in the 400 mT range Uout [V]

12

waveform - SIN fexc=1MHz Iexc=180mA

D 10 8 6 4

C

2

A 0 -400

-300

-200

-100

0

E

100

200

-2 -4 -6

300

400

B [uT] 1- initial curve after -6mT shock I after +6mT shock

-8

after -6mT shock II

-10

B -12

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Uout [mV]

Hysteresis and perming of the sensor with double-sided core waveform - SIN fexc=1MHz Iexc=200mAp-p

Z 8

3

X -500

-400

-300

-200

-100

0

100

200

300

-2

-7

400

500

B [µT]

1- initial curve after -6mT shock (first)

Y

-12

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Present limitation of microfluxgate: 80 nT p-p noise

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Resonance sensors • Proton magnetometer (NMR – Nuclear Magnetic Resonance) • Overhauser • Optically pumped – Cesium All resonance magnetometers are scalar

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Proton magnetometer • based on precession frequency of proton ω = γB 42 MHz/T ... 42 mHz/nT • usually free precession after polarization switched off • absolut precission • sensitive to gradient and EMC • slow (1 sec) • requires 10 ml to 500 ml volume – difficult miniaturization

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Overhauser magnetometer Variation of proton magnetometer Based on dynamic nuclear polarization: from electrons to protons 0.1 nT resolution 0.5 nT absolute accuracy Resistant to field gradients and EMC

source: GEM 25.6.2010


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Optically pumped magnetometers • Cesium, Potassium, Helium • Based on ESR (electron spin resonance) or Zeeman splitting • highest resolution: 7Hz/nT • Requires lamp + RF source

source: GEM

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Optically pumped magnetometers

Potassium (GEM) • •

0.2 nT absolute accuracy 7 pT resolutin @ 10 Hz sampling

Cesium (Geometrics) •

1 nT heading error

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Precise fluxgate magnetometers

O.V.Nielsen, J.R.Petersen, F.Primdahl, P.Brauer, B.Hernando, A.Fernandez, J.M.G.Merayo, P.Ripka: Development, construction and analysis of the 'Orsted' fluxgate magnetometer Meas. Sci. Technol. 6 (1995), 1099-1115. P. Ripka, F. Primdahl, O.V. Nielsen, J.R. Petersen, A.Ranta: AC magnetic field measurement using the fluxgate, Sensors and Actuators A, 46-47 (1995), pp. 307-311 25.6.2010


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Testing and calibration • • • •

Precise coil systems + current sources Shieldings Non-magnetic thermostats Large non-magnetic facilities

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Shieldings and calibration coils

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Resources • www.nve.com (GMR) • www.Sentron.ch (vertical Hall) •

www.ssec.honeywell.com/magnetic/ (AMR)

• www. Micronas.com (Hall) • www.Infineon.com (Siemens: Hall, GMR) •

www.semiconductors.Philips.com/automotive/sensors_discretes (AMR)

• www.Geometrics.com (resonant magnetometers) • measure.feld.cvut.cz/groups/maglab (fluxgate) • P. Ripka (ed.): Magnetic sensors and Magnetometers Artech, 2001,www.artechouse.com • Tumanski S, Thin ﬁlm magnetoresistive sensors, IOP (2001) ISBN 075030702 • Popovic, R.S., Hall Effect Devices, Bristol: Adam Hilger, 1991. 25.6.2010


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OSTATNÍ APLIKACE

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Applications: Metal detectors

Finding small objects: mines, coins, golden nuggets.. portable instruments… similar to NDT Finding large and deep objects: scanning, sensor fields … -> geophysical methods, image analysis, recognition 25.6.2010


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Testing fields of European Comission in Ispra, Italy

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Gauss laboratory, Ispra

Sensor footprint 25.6.2010


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ERW – explosive remnants of war • Mines and Booby traps – AP pressure mines – Tripwire activated AP mines – AT mines – often protected by AP • Active magnetic methods (AC metal detectors) – eddy currents • GPR • Sniffing of explosive

• Small UXO (unexploded ordnance): projectiles, sub-munition, … • Deeply burried ERW – mainly bombs • Active AC magnetic methods • Passive magnetic methods: DC magnetometers – up to 5 m 25.6.2010


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PMN antipersonnel mine

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Small fragmentation bomb (sub-munition)

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Humanitarian demining • HD: all explosive items must be removed or destroyed to a recorded depth. • military demining: under time pressure, small losses acceptable

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Metal detectors: working principles • Pulsed induction – – – – –

Ebinger 420GC Guartel MD8 Minelab F1A4 and F3 Schiebel AN19 (PSS12) Vallon 1620 and VMH2.

• Continuous wave – CEIA MIL D1 – Foerster Minex 2FD – Ebinger 420SC

• (DC)Magnetometers: fluxgate, Cesium 25.6.2010


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Pulsed induction detectors 1-coil-systems, measurements in TD 10-5s - 10-3s.

370 μs pulse width 225 Hz repetition freq. 25.6.2010


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Ground compensation

soil signal decays after 20 μs Advanced methods: processing multiple samples and/or using excitation pulses of different lengths. 25.6.2010


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Continuous wave detector

2 or 3 coils: compensation of the primary field with differencial receiver-coils or bucking coils Förster Minex 2FD 4500

Sorce: Jörn Lange, Institute for Geophysics & Meteorology, Cologne

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Basic principle Transmitter (0)

M02

V2 Receiver (2)

I0

M01

R

M12

L

Target (2)

I1

M 01 R − j ωL I 1 = − jω I 0 = − jωM 01 2 I 2 2 0 R + j ωL R +ω L

R − jωL V2 (ω ) = − jωM 12 I1 = ω M 12 M 01 2 I 2 2 0 R +ω L 2

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Basic principle V2 (ω ) = − jωM 12 I 1 = ω M 12 M 01 2

R − j ωL I 2 2 2 0 R +ω L

Response function

F = V2 (ω ) / ω = ωM 12 M 01

ωL

Where

α=

and

α = σµωa 2

R

 jα  R − j ωL  I = β  2 2 2 0 R +ω L  1 + jα 

is response parameter for “first order object”

for metal sphere of diameter a

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Response function

ideal response

12” shell Chilaka 2004

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If the receiver is set up to reject signals of a certain phase the soil signal in this case will be ignored. Even better ground compensation can be achieved by using two or more frequencies. 25.6.2010


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Continuous wave detector 2 400 Hz + 19 200 Hz.

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Magnetic and conductive soils Many places Susceptibility 10-6 to 10-3 … ferrites and other Conductivity .. Salt water “Difficult soils” Bosnia, Laos, … Frequency dependent susceptibility - mainly due to superparamagnetic nanoparticles 25.6.2010


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Soil characterisation in time domain

0.1 0.0001

0.00001

PK2

0.01

1/x

0.001

1.5

1/x

1.1

1/x

0.0001

Neel theory of superparamagnetic isolated particles: 1/t time response

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Soil characterisation in frequency domain

k [10e-5 SI]

PJ1 250

200

150 100 mA

100

Bartington

50

0 0.1

1

10

100

1000 f [kHz]

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Frequency-domain versus time-domain

• Time-domain detectors always use pulsed field excitation. • Frequency-domain detectors: usually continuous wave fields

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Static and dynamic modes ‘dynamic mode’ detectors: the alarm turns off after a few seconds • can help when working in the presence of constant background disturbance, such as alongside a metal rail or fence or when attempting to locate a small AP mine in the vicinity of a large metal-cased AT mine. • Requires experienced operator • Dynamic: Guartel MD8, Minelab F1A4 and Vallon detectors • Selectable Static-dynamic: Ebinger 421GC

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Single versus double-D (differential, gradient) receive coils can also be used beside rails and metal fences

CEIA MIL D1 Foerster Minex 2FD Guartel MD8 detectors. 25.6.2010


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Size of the coil • Small objects – small coil • Deep objects – large coil Typical diameters: Demining detector: 20 cm UXO detector: 1 m 25.6.2010


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Large-loop detector

Ebinger UPEX 740 M Geonix EM61 25.6.2010


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CEIA UXO detector

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Finding large and/or deep objects • AC methods: require artificial source: big coils, 100 A sensing coils: up to 10 kg

Can detect conducting objects • DC methods: use Earth’s field Can detect only ferromagnetic objects

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DC methods UXO location – 155 mm projectile 1.5 m deep ... 10 to 50 nT – bomb 6 m deep ... 1 to 5 nT 1 nT in 50 000 nT ~ 20 ppm

Vectorial sensors: angular stability 0.001 deg ~ 0.35 nT 25.6.2010


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DC Magnetometers Vectorial: • Fluxgate – Ebinger Magnex – Foerster Ferex – Schiebel Dimads (3-axis)

Scalar: • Optically pumped: Cesium vapour • Proton, Overhauser 25.6.2010


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Why fluxgate and not Hall, AMR, GMR, SDT, GMI.. Classical fluxgates: big and expensive (CTU Prague)

Fluxgates: most precise magnetic sensors Based on non-linear magnetization characteristics of ferromagnetic core. Measure up to 1 mT with 100 pT resolution (10 pT) 10 ppm linearity

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Ebinger Magnex

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Gradiometer suppresses interferences t [hod] 0

1

2

3

4

5

6

20 nT B1

B2

20 nT/m

Grad

16.2.1999

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Foerster Ferex

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Work nice in Europe, problems in Singapore

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Fluxgate object locator DIMADS Schiebel Austria, sensors from Czech Technical University

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Geometrics Cesium magnetometer

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Geometrics Multi-Sensor Towed Array Detection System (MTADS 8 Cesium magnetometers (3) modified Geonics EM-61 time domain electromagnetic (TDEM) sensors

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Other explosive remnants of war detection methods • • • • • •

Ground-penetrating radar (GPR) Electrical impedance tomography X-ray backscatter detection Infrared and multi-spectral detection Acoustic detection Detecting explosives

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Explosive detecting dogs (EDDs) A: to run dogs over the suspect area, B: to take air sample filters in a suspect area and present the filters to dogs later. Also rats and insects (bees, vasps)

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Ground-penetrating radar (GPR) – dielectric contrast necessary (not plastic mines in dry sand) – short-wavelength radar waves needed to find small mines (over 800 MHz frequency) do not penetrate wet soil very well. – Good for metal objects New mine detectors: Eddy currents + GPR

Primary: Detect small metal objects

To reduce the response to clutter

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GPR imaging system

Noggin 1000 (Sensors and Software Inc.

http://www.sensoft.ca)

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Dual technology detectors

AN/PSS-14 : dual technology, audio output CyTerra Corp. (radar part) http://www.cyterra.com and MineLab (metal detector part) Also Vallon VMR-1 25.6.2010


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APPLICATIONS

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Applications II • Detection and recognition of vehicles (incl. submersible)

• Detection frames and other sensors for border security • Magnetic labels and anti-theft system • Navigation systems • Magnetic tracking • Distance measurement • Distributed sensors and sensor areas 25.6.2010


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Detection and recognition of vehicles Vehicles can be identified usig magnetic signature The same technology is used for detection of ferromagnetic bodies

Magnetic field of Skoda car measured by 3-axis CTU fluxgate under the road surface 25.6.2010


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Detection frames and other sensors for border security

Eddy-current technollogy – multi-pulse Multi-zone Ceia, Vallon, …

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Magnetic labels and anti-theft system

Sensormatic/ Tyco Fire & Security

Magnetoelastic labels www.vacuumschmelze.de

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Aplication: Compass

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Fluxgate compass: 0.05 deg accuracy

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Micro-fluxgate sensors (in development) • flat coils • electrodeposited core or amorphous strips • electronics on chip • cheap • resolution still higher than MR

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AMR Compass: Honeywell Magnetic compass + inclinometers

X (forward) Bx

Hnorth

α

Y

= backup for GPS

(right)

By

Hearth

Bz Z (down) α = Azimuth or Heading

x

φ

pitch

Com

pas s

Forward Level

y z

θ Right roll

Level

Honeywell 3-axis AMR magnetometer with digital output

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AMR Compass: Our experimental system

AMR modules with HMC100X, HMC102X, KMZ51

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AMR compass system

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AMR compass system

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Obstacles in compass application • • • •

Crossfield sensitivity Orthogonality of XYZ sensors Horizontality (knowledge of tilt) Angular deviations: g sensors B sensors reference directions

• Offset, perming, temperature drifts of sensors

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Crossfield error - simulation Azimuth Error due to CrossAxis

Azimuth Error (deg)

3

a .B V= BS + BC

2 1 0 -1 0

90

180

270

360

-2 -3 Azimuth (deg)

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Crossfield error: possible solutions • Feedback compensation – power consumption – limited bandwidth – precision?

• Numerical corrections – is the formula precise? – how precisely we know Bs?

a .B V= BS + BC

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Azimuth residual error (deg)

Crossfield error after numerical correction effect of bad estimate of Bs (model) 0,15

V=

0,1

a .B BS + BC

0,64 0,72 0,76 0,88

0,05 0 0

90

180

270

360

-0,05 Azimuth (deg) -0,1 -0,15

HMC 1002

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Error due to non-orthogonality

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Error due to non-horizontality Synth. Data: Mag Pitch 0 Roll 0..5 not corrected 15

Pitch 0 Roll 0 Pitch 0 Roll 1 Pitch 0 Roll 2 Pitch 0 Roll 5

Azimuth Diff [deg]

10 5 0 0

45

90

135

180

225

270

315

360

-5 -10 -15 Azimuth Ref [deg]

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Angular deviations

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A: rotation in roll … accelerometers Gx before and after correction (rotation in roll)

-36

0

5

10

15

Gx[mg]

-38 -40 -42 -44 -46 -48 -50 sample (roll)

Gx before correction Gx after correction

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A: rotation in roll … magnetic sensors

Azimuth [°]

Azimuth before and after correction (rotation in roll) 90 89 88 87 86 85 84 83 82 81 0

5

10 sample (roll)

Azimuth before correction 15 20 Azimuth after correction

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Total error

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Total error

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Magnetic tracking – moving sensors

Translation Range : 3 m x 3 m Static Accuracy Position: 1.5 cm RMS Static Accuracy Orientation: 1.0° RMS

/www.ascension-tech.com/

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Magnetic tracking – moving marker

Hashi et al, 2004) 25.6.2010


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Magnetic tracking – moving marker

Hashi et al, 2004) 25.6.2010


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Dipole source

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Distance measurement

Distance - Induced Voltage 160 140

Uind [microV]

120 100 80 60 40 20 0 0

2

4

6

8

10

12

14

Distance [cm]

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Distance measurement in vivo

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References • P. Ripka (ed.): Magnetic sensors and Magnetometers Artech, 2001,www.artechouse.com • Guelle, D., Smith, A., Lewis, A., and T. Bloodworth (2003): Metal Detector Handbook for Humanitarian Demining European Communities 2003, ISBN 92-894-6236-1Fulltext available at http://serac.jrc.it/publications/pdf/metal_detector_handbook.pdf • J. Dirscherl, C. Bruschini: Metal Detectors Catalogue 2005 Geneva International Centre for Humanitarian Demining, ISBN 2-88487-009-1 Available at www.gichd.ch

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Přesné magnetické snímače a jejich aplikace

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