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Dual-Band Search Coil Magnetometer (SCM)
for RPWI consortium : concept & design report.
(September 19, 2010)
LPP (Laboratory of Plasma Physics)
L2E (Laboratory of Electronic and Electromagnetism)
& University of Kanazawa
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OUTLINE
1)
2)
3)
4)
5)
Team organization
Overview
Heritage
Sensors : principle & design
Preamplifier : principle, ASIC design and
results
6) SCM performances, mass & power
consumption budget
7) Open questions
8) Conclusion
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TEAM ORGANIZATION
Institute
Role
P. Canu
Scientist
T. Chust
Scientist
Y. Zouganelis
Scientist
D. Alison
LPP
SCM tests & EGSE
C. Coillot
SCM technical manager
P. Leroy
ASIC design & SC design support
G. Sou
(+ Ph.D student:
A. Rhouni)
M. Ozaki
S. Yagitani
L2E
U. Kanazawa
ASIC design
Science, SCM design support and
EMC support
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OUTLINE
1)
2)
3)
4)
5)
6)
7)
8)
Team organization
Overview
Sensors : principle & design
Preamplifier : principle, ASIC design and
results
Heritage
SCM performances, mass & power
consumption budget
Open questions
Conclusion
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OVERVIEW
DB-SCM is a part of RPWI.
DB-SCM will measure weak
magnetic field (up to few
fT/sqrt(Hz)) in frequency range =>
divided in LF1 [0.1Hz;4kHz] and
LF2 [1kHz; 20kHz] .
X =>200mm
It consists in:
-Tri-axis dual band search-coil
sensors mounted on a boom,
-2 Low noise & low power
consumption
preamplifier
per
sensor (1 for LF1 and 1 for LF2)
mounted close to the sensors.
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OVERVIEW : SCIENTIFIC OBJECTIVES
Study the electrodynamics of the Jovian system:
•
Determine the wave electric & magnetic fields (KAW, ICW, Whistler waves …) in
the magnetosphere of Jupiter (“rotator” theme)
•
Characterize the interaction of the flowing Jovian magnetosphere with the
Galilean moons (“binary system” theme)
“High-frequency” electromagnetic wave processes:
- Reconnection / large-scale instability (both Jupiter’s & Ganymede’s magnetospheres)
- Particle acceleration and heating (both electrons & ions)
- Energy transfer (wave-particle interaction, mode coupling, turbulence)
- Mass loading (ion pick-up)
Frequency bandwidth: 0.1 Hz - 20 kHz.
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OUTLINE
1)
2)
3)
4)
5)
Team organization
Overview
Heritage
Sensors : principle & design
Preamplifier : principle, ASIC design and
results
6) SCM performances, mass & power
consumption budget
7) Open questions
8) Conclusion
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Heritage
The search coil magnetometer (SCM) is part
of a long line of LPP (formerly CETP and
CRPE) SCMs, developed for major space
missions, including: Ulysses, Galileo,
Cassini, Cluster, more recently THEMIS and
currently for Bepi-colombo and MMS.
Example of Themis sensors (17cm length),
tri-axis structure (560gr) and preamplifier
(200gr and 100mW):
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Heritage
LF-SC
Bepicolombo Heritage:
Mast axis
LF-SC
Bracket
Collaboration between University of
Kanazawa and LPP.
DB-SC
Tri-axis structure mounted on a 4.6m
comprising 2 low frequency search-coil
and one dual-band search-coil (1Hz up to
640kHz).
Spacecraft spin axis
Preamplifier combines 2 low frequency
preamplifier for LF sensors and one 3D
preamplifier for the dual band sensor
(70gr, 200mW) using components
qualified up to 70kRad.
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OUTLINE
1)
2)
3)
4)
5)
Team organization
Overview
Heritage
Sensors : principle & design
Preamplifier : principle, ASIC design and
results
6) SCM performances, mass & power
consumption budget
7) Open questions
8) Conclusion
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Sensors : search-coil (SC) principle
Search-coil: N turns wounded around a high permeability
magnetic core.
Magnetic core « amplifies » external magnetic field. Magnetic
amplification µapp depends on µr and shape of the core.
Winding :Flux variation (Bout*S) induces a voltage
proportional to number of turns (N):
e  N
d
with    B dS
dt
e( j )   jN1Sµapp Bout
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Sensors : search-coil (SC) principle
Search-coil: N turns wounded around a high permeability
magnetic core.
Magnetic core « amplifies » external magnetic field. Magnetic
amplification µapp depends on µr and shape of the core.
Winding :Flux variation (Bout*S) induces a voltage
proportional to number of turns (N):
e  N
d
with    B dS
dt
e( j )   jN1Sµapp Bout
Electrokinetic's representation : Search-coil behaves like a source voltage “e” applied
on a RLC circuit :
N1*S*µapp
L1
d/dt
1
R1
2
7.5H
Bout
e
1k
Vout
C1
55p
0
Natural resonance of the sensor reduces
dynamic and frequency range.
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Sensors : search-coil (SC) principle
Search-coil behavior using a feedback-flux
Winding voltage is amplified (Vout) : Vout  G0Vin
Output generates a current such as:
I  I CR 
Bout--- Direct amplification
--- Feedback flux
Vout G0Vin

R
R
Current generates a mutual-flux inside magnetic core :
1  N1 B  µapp  S  L1 I1  M 21I
Vin 
 j ( N1S  µapp  B  M 21I )
(1  L1C1 2 )  jR1C1
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Sensors : search-coil (SC) principle
Search-coil behavior using a feedback-flux
Winding voltage is amplified (Vout) : Vout  G0Vin
Output generates a current such as:
I  I CR 
Bout--- Direct amplification
--- Feedback flux
Vout G0Vin

R
R
Current generates a mutual-flux inside magnetic core :
1  N1 B  µapp  S  L1 I1  M 21I
Vin 
 j ( N1S  µapp  B  M 21I )
(1  L1C1 2 )  jR1C1
By combining : I  G0Vin R and Vout  G0Vin
we deduce :
N1S  µapp  RCR
 G0 jN1S  µapp 
Vout


M
M 21
B
(1  L1C1 2 )  j ( R1C1  21 G0 )
RCR
Go=
100
Resonance is flattened.
On flat part, gain is independent from temperature variation
Frequency range remains limited by the resonance
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Sensors : dual-band SC principle
Extension of the magnetic field measurement at frequencies beyond 10kHz :
LF2 (alone) : 400 turns winding
LF2 winding
LF2 (400turns)+LF1 (10000 turns)
LF1 winding
LF2 winding
LF2
LF1+LF2
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Sensors : dual-band SC principle
Extension of the magnetic field measurement at frequencies beyond 10kHz :
LF2 (alone) : 400 turns winding
LF2 (400turns)+LF1 (10000 turns)
LF1 winding
LF2 winding
LF2 winding
LF2
LF1+LF2
What happens ? Current through the LF1 winding:
N1*S*µapp
L1
d/dt
1
2
7.5H
Bext
I1
e
R1
1k
C1
55p
Vout
I1 
0
 N1 BSµ app j
1
R1  jL1 
jC1
I1  
N1BSµapp
L1
Expression of I is replaced inside equation of flux
2  N 2 B  µapp  S  L2 I 2  M12 I1
2  N 2 Bµapp S  L2 I 2  M 12
N1 Bµapp S
 ( N 2  N 2 ) Bµapp S  L2 I 2
L1
2  L2 I 2
magnetic field can not be measured
with a second winding after the
resonance of the first one.
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Sensors : dual-band SC principle
Principle of the mutual reducer to extend frequency bandwidth
Mutual reducer consists in an added cylinder of magnetic material.
The flux from the self-induction is diverted through the mutual reducer
Flux seen under a path
from magnetic core to
LF2 winding :
LF1winding
LF
winding
HF winding
LF2-bis
winding
(E-6) Weber
6
5
4
3
Mutual reducer
Magnetic core
2
1
mm
0
0
Mutual flux seen by LF2 winding is notably reduced.
2,5
5
7,5
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Sensors : dual-band SC principle
Behavior of dual-band sensor using a mutual reducer:
LF2-bis : 400 turns winding + LF1(10000 turns) + mutual reducer
LF1
LF2-bis
LF1winding
LF
winding
HF winding
LF2-bis
winding
Mutual reducer
Magnetic core
Transfer function of the LF2 on a LF1 winding is possible by using a “mutual
reducer”
Frequency range can be extended up to MHz
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Sensors : dual-band design for EJSM
Dual-band search-coil design for Bepi-Colombo (MMO-PWI):
Ketron Peek tube
+ copper sheet for ES shielding
LF & MF windings
+potting inside the tube
+ Ferrite mutual reducer
Machined magnetic core
Length=112mm,
Diameter=16mm
Ketron Peek tube
+ copper sheet for ES shielding
LF & MF windings
+potting inside the tube
+ Ferrite mutual reducer
Machined magnetic core
 EJSM dual-band sensor is designed to improve the sensitivity between 2 kHz and
20 kHz, with no loss of sensitivity at lower frequencies and little extra mass.
 EJSM
sensor is designed to permit to manage very close resonances between LF1
Length=112mm,
and Diameter=16mm
LF2 (improvement from BepiColombo design)
EJSM sensor will be longer than Bepicolombo sensor to permit to reach lower
sensitivity (20cm for EJSM instead of 10cm for Bepicolombo)
Low temperature ferromagnetic material are under study
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OUTLINE
1)
2)
3)
4)
5)
Team organization
Overview
Heritage
Sensors : principle & design
Preamplifier : principle, ASIC design and
results
6) SCM performances, mass & power
consumption budget
7) Open questions
8) Conclusion
20
Preamplifier: principle, ASIC design and results
Synoptic of the search-coil preamplifier:
Preamplifier required two
stages:
First stage must achieve high
gain, low input noise and
manage the flux feedback,
-
Second stage must have high
gain, low power consumption
and filtering abilities.
-
LF1 ASIC Preamplifier specifications:
 Input noise: 4 nV/√Hz @ 10 Hz
 Gain: 83 dB
 Power consumption: < BEPICOLOMBO
preamplifier (40mW)
 (ASIC + Search-coil) NEMI: 0.6 pT/√Hz
@10 Hz
LF2 ASIC Preamplifier specifications:
 Input noise: 1.5 nV/√Hz @ 1 kHz
 Gain: 83 dB
 Power consumption: < 40mW
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Preamplifier: principle, ASIC design and results
MP3
MP2
MP7
MP4
MP10
Vcc = 3 V
MP0
R2
MP1
MP5
MP8 R5
MP6
MP9
gnd
Vout
Vss = -3 V
R0
R1
Vin
C2
R6
MN0
MN1
R4
C1
CL
MN2
MN3
MN4
MN5
MN6
R3
A1
A2
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Preamplifier: principle, ASIC design and results
The preamplifier has been fabricated in CMOS
0.35 µm four metal technology :
1) Low power consumption :
12mW
2) Design of rad tolerant
transistors using guard rings
Low noise preamplifier ASIC for LF1 is under
pre-environmental tests:
1. Tested under radiation dose (Cobalt
60) up to 150kRad
2. Thermal tests has to be done
Low noise preamplifier ASIC for LF2 is under
design.
Microphtograph of 2.2 x 2.3 mm
chip containing one amplifier
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Preamplifier: principle, ASIC design and results
Measured transfer function
of the LF1 ASIC amplifier :
Gain is close to design : 83dB
Low cut-off frequency is
>60kHz
Measured input voltage noise
spectrum : comparison
between MMS/Bepicolombo
preamplifier and ASIC
preamplifier for EJSM :
Input noise is 3.5nV/sqrt(Hz)
@1kHz
-
Input noise @10Hz is close to
the objective (4nT/sqrt(Hz)).
-
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Preamplifier: principle, ASIC design and results
LF1 ASIC preamplifier + MMS search coil (10cm length)
Transfer function and Noise Equivalent Magnetic Induction of
EJSM ASIC combined to a 10 cm search coil (MMS design).
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Preamplifier: principle, ASIC design and results
LF1 ASIC preamplifier tested in Radiation (facilities test at Louvain la
Neuve) up to 300kRad
Current available datas goes up to 150kRad on 10 samples.
Ability of the current ASIC design to withstand severe
Radiation environment is partially proofed.
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OUTLINE
1)
2)
3)
4)
5)
Team organization
Overview
Heritage
Sensors : principle & design
Preamplifier : principle, ASIC design and
results
6) SCM performances, mass & power
consumption budget
7) Open questions
8) Conclusion
27
SCM Performances: design goal for RPWI
EJSM Dual-Band Search Coils (DB-SC) in red.
Design hypotesis : preamplifier located close to the sensor… possibly
inserted inside the hollow of the ferromagnetic core.
Noise Magnetic Induction (fT/sqrt(Hz))
1,E+05
1,E+04
Bepi-Colombo
1,E+03
1,E+02
Cluster
1,E+01
Galileo
1,E+00
1,E+00
1,E+01
1,E+02
1,E+03
Frequency (Hz)
1,E+04
1,E+05
1,E+06
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SCM Performances: mass/power budget
Optimized design using
20 cm Dual-Band
Search Coil sensors
(a) 1 mm Al thickness is
assumed
(b) In case of PA mounted
on the boom
(c) +/-5V is assumed.
Number of DB-SC sensors
3
Bandwidth
0.1 Hz to 4 kHz (LF1 band)
1 kHz to 20 kHz (LF2 band)
Sensitivity
8 pT/√Hz @ 1 Hz
0.6 pT/√Hz @ 10 Hz
0.06 pT/√Hz @ 100 Hz
10 fT/√Hz @ 1 kHz
4.5 fT/√Hz @ 10 kHz
Mass (DB-SC + PA(a))
< 700 g (+ cables ~85 g/m)(b)
Power (under +/-5V)
240 mW (c)
Length
20 cm
Location
boom (3.75 m from S/C)
Electrical interface
6 analog signals to LFR
Heritage: Ulysses (ESA/NASA), Galileo & Cassini (NASA), Cluster (ESA),
THEMIS (NASA). Current fabrication: MMS (NASA), Bepi Colombo (ESA/JAXA)
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OUTLINE
1)
2)
3)
4)
5)
Team organization
Overview
Heritage
Sensors : principle & design
Preamplifier : principle, ASIC design and
results
6) SCM performances, mass & power
consumption budget
7) Open questions
8) Conclusion
30
OPEN QUESTIONS & REQUIREMENTS
Environment :
– Maximum intensity of Jovian magnetic field seen by EJSM ? What are the
radiations at sensor location ?
– What is the expected temperature range for sensors ? And electronic ?
Calibration signal for SCM is TBD.
Telemetry is TBD (sampling rate, dynamic, rate, mode.. 12 bits could be sufficient).
EMC cleanliness: disturbances from other experiments should not exceed the
magnetic field measured by SCM… EJSM plan to be filled by SCM… What is the
policy for receiver : differential or grounded ?
Available voltage supplies : preferred is Analog +/-5V
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OPEN QUESTIONS & REQUIREMENTS
Accomodation of tri-axis sensor on MLA boom/MAG boom ?
Option 1 : SCM alone on a boom (as for CLUSTER, DSP, THEMIS and
Bepicolombo…)
Option 2 : SCM on MLA boom:
Requirement 1: SCM should be as far as possible from spacecraft (>3m),
for THEMIS it was 1m and signal is noisy and requires cleaning to be
analyzed.
Requirement 2: SCM to MLA minimum distance has to be validated
Option 3 : SCM on MAG boom :
Requirement 1: If MAG is digital… SCM disturbances will be prohibitive
Requirement 2: Interference measurement has to be done
Requirement 3:Excitation lines of Fluxgate has to be extremely stable in
frequency and amplitude.. The two frequencies excitation should be as
close as possible.
Accomodation of preamplifier, 2 options :
Option 1: Preamplifier located close to the sensor (lower capacitance but
stronger environment : thermal and radiation)
Will depend on shielding efficiency of sensor and temperature !
Option 2 :Preamplifier on the spacecraft (higher capacitance and worst
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sensitivity)
CONCLUSION
Dual band search-coil has been designed for EJSM.
Dual Band Search-coil prototype manufacturing has started => expected
before AO.
Ferromagnetic material for low temperature are under investigation (in
collaboration with LPC2E)
A low noise, low frequency ASIC preamplifier adapted for LF1 [0.1Hz-4kHz]
part of EJSM search coil magnetometer has been designed, fabricated,
tested (electrical & radiations tests) and validated.
A second ASIC more adapted to LF2 [1kHz-20kHz] (lower background noise
but higher low frequency noise) has been designed and will be fabricated
before December 2011 and fully tested before AO.
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THANK YOU !
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100kHz Search Coil: conception pour haute sensibilité
Optimized design using
50 cm Search Coil sensor
Number of SC sensors
1
Bandwidth
10 kHz to 600 kHz (MF band)
Sensitivity
0.3 fT/√Hz @ 30 kHz
0.12 fT/√Hz @ 100 kHz
0.3 fT/√Hz @ 300 kHz
0.6 fT/√Hz @ 600 kHz
Mass (SC + PA(a))
< 350 g (+ cables ~40 g/m )(b)
Power
40 mW
Length
50 cm
Location
boom ( > 5 m away from S/C)
Electrical interface
1 analog signal to MFR
(a) 1 mm Al thickness (box: ~7 g)
(b) PA mounted on the boom
Heritage: Ulysses (ESA/NASA), Galileo & Cassini (NASA), Cluster (ESA),
THEMIS (NASA). Current fabrication: MMS (NASA), Bepi Colombo (ESA/JAXA)
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