Fakultät Elektrotechnik und Informationstechnik, Elektrotechnisches Institut, Elektrische Maschinen und Antriebe
Flux Based Control and Monitoring of Active Magnetic
Bearings Using Ultra-Thin and Flexible Bismuth Hall Sensors
Falk Bahr1, Michael Melzer2, Denys Makarov2, Daniil Karnaushenko2, Oliver G. Schmidt2, and Wilfried Hofmann1
1 Technische
Universität Dresden, Elektrotechnisches Institut, 01062 Dresden, Germany
2 Institute for Integrative Nanoschiences (IIN), IFW Dresden, Helmholtzstraße 20, 01069 Dresden, Germany
Motivation: Ultra-thin and flexible Hall sensors for electrical machines and drives
Magnetic flux based control approach[1]
Envisioned applications of ultra-thin flexible Hall sensors providing flux feedback
Task: Measurement of the flux density of up to 2.3 T in
narrow air gaps between stator and rotor (< 0.5 mm) is crucial
Improvement of the dynamic performance of
high precision machining tools

Enhancement of stiffness, damping and rotor
positioning accuracy of AMBs

Flux density measurement
instead of position feedback

Angular encoding systems
for rotor position detection

Manufacturing the combustion engine pistons
and high quality optical components

Pumping systems: cost
reduction and miniaturization

Monitoring magnetic field
and rotor unbalance
Aim: Ultra-thin and flexible Hall sensors have to be developed
Statorpole
500 µm
< 200 µm sensor
thickness
Tomography of a commercial Hall sensor (TUD)
< 500 µm
air gap
Oerlikon Leybold
MECOS Traxler AG
Statorpole
Ultra-thin flexible Bismuth Hall sensors
bearingstore.com

Commercially available flexible PCB providing
4 contacts for Hall element
Flex PCB

Schematics of the Hall sensor cross-section
(left) Confocal 3D image of the Bismuth sensor
element. (right) Integration of the sensors at
the stator pole of a magnetic bearing system
4 nm
145 µm
•
•
•
Optimization of Hall sensitivity
by tuning Bismuth thickness
Temperature stability in the
industrial temperature range
Performance upon bending for
typical machinery radii

Encapsulation of the sensor element with a
polymeric overcoat[5]
The flexible sensors are mounted on the
curved surface of a stator pole of the AMB




[2]
AMB
9.00
8.75
8.50
Flux based control: Bismuth Hall
Flux based control: GaAs Hall
Conventional current control
125
100
75
0
50
100
time in ms
150
200
Prototype
Single-axis AMB (electro-magnet and magnetically painted ball)
Flux density measurement with prototype Bismuth Hall element
Implemented linear cascaded position and flux control loops
Achieved improved dynamic performance using flux based control
xref
-
position Bδref
controller
-
flux density
controller
i1ref
-
current u1 magnetic x
controller
bearing
i1 Bδ
Levitating ball setup
Radius of curvature of the pole: 22 mm
PARAMETER
Sensor
dimensions
Electrical
parameters
Other
parameters
Monitoring a two-axes radial
Bending performance
Active sensor area
Bismuth film thickness
Total height
Supply current
Hall responsivity
Sensor resolution
Signal-to-noise ratio
Temperature range (tested)
Temperature coefficient
Max bending radius
[3]
AMB
AMB demonstration setup

Single sided two-axes AMB setup with
asynchronous motor; Air gap of 500 µm

Homopolar bias magnetization 0.9 T and
hetoropolar control magnetization


Two stators each with four stator poles
Nominal force of the radial bearing: 460 N
Value
Integrated flexible Hall sensor
1x1 mm²
2 µm
150 µm
10 mA
≈0.2 V/(A·T)
25 mT
32 dB
0 to 80 °C
-0.35 mV/(A·T·K)
2 mm

Bismuth Hall effect sensors on commercial
flexible printed circuit board (PCB)


Total thickness is 150 µm including cabling

Real-time flux density monitoring realized
Conclusions




position
sensor
xmeas*
Deposition of Bismuth film with a thickness
from 20 nm up to 3 µm[4]
Temperature dependence
Measuring the application relevant
sensor parameters:
fmag
flux density
sensor
Bmeas*
Characterization of the flexible Bismuth Hall sensor elements

x
Bmeas
fG
Electrical contacting is acomplished directly
during the deposition of the metal film

imeas
signal amplifier
2 µm


i
Φ
PWM
xmeas
Cr
Fahrrad-ro.de
Med. Universität Wien
controller
Flexible Bismuth Hall sensors
Thickness dependence
4QC
(H-bridge)
Deposition of Chromium
(layer 4 nm thick)
Bi
integratedsoft.com
Flux based control of single-axis
Fabrication of the Hall elements[2,3]

Buildaroo.com
position in mm
Rotor
Sportrider.com
flux density in mT
Issue: Conventional rigid Hall sensors are too thick
Monitoring performance of
eMotors and generators
Universitätsspital Zürich
Requirement: Magnetic field sensors have to be mounted on
the curved surface of the stator pole in the air gap
Magnetic bearings without
position measurement
Achieved magnetic field resolution after
amplification: 25 mT (at supply curent 10 mA)
References
Ultra-thin (150 µm) and flexible Bismuth Hall sensors are fabricated and characterized
Integration of flexible sensors onto the curved stator pole is successfully realized
[1] H. Bleuler et al., New Concepts for cost-effective Magnetic Bearing Control, Automatica 30, 871 (1995).
[2] F. Bahr et al., Flux Based Control of AMBs Using Integrated Ultra-Thin Flexible Bismuth Hall Sensors, Proceedings of
the 13th International Symposium on Magnetic Bearings - ISMB 13, Arlington, USA, 2012.
Flux based control and monitoring of a single- and two-axes AMB is demonstrated
[3] F. Bahr et al., Permanent Magnet Bias AMB Using Integrated Hall Sensor Based Air Gap Flux Density Feedback,
Proceedings of the 1st Brazilian Workshop on Magnetic Bearings, Rio de Janeiro, Brazil, 2013.
Angular encoding of the rotor position of an eBike was shown using the flexible sensors
[5] M. Melzer et al., Stretchable Magnetoelectronics, Nano Lett. 11, 2522 (2011).
Contact
Falk Bahr
E-Mail: falk.bahr@tu-dresden.de
Phone: +49 (351) 463-35052
Helmholtzstr. 9, 01069 Dresden
This work is funded in part via:
[4] R. Koseva et al., Bismuth Hall probes: Preparation, properties and application, Thin Solid Films 518, 4847 (2010)