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Title:
:
applications of magnetic fluids for inertial sensors .
Type:
:
Mechanics .
Journal of Magnetism and Magnetic Materials 20 (1999) 380}384 Applications of magnetic fluids for inertial sensors
} ( )
M.I.
M.i
Piso Institute of Space Science } GRL, 220 Iuliu Maniu Blvd., 77538 Bucharest, Romania
BlvdIuliu Maniu GRL }
Bucharest
Received 2 June 1998;
received in revised form 10 October 1998
Abstract .
One of the significant application of magnetic fluids technology is given by inertial and gravity sensors.
엥
some of the present and coming achievements in the research, development and applications of various inertial sensors are
summarized.
the paper presents some results, developed mainly by GRL Bucharest, in particular for applications in acceleration and gravity
gradient sensors.
GRL Bucharest
( 1999 Elsevier Science B.V .
B.VElsevier (
All rights reserved.
Keywords:
:
Magnetic fluids;
Sensors;
Gravity
1.
General
Magnetic fluids (MFs) over various opportunities to build several classes of sensors for mechanical, electromagnetic and aero and
hydrodynamic measurements .
( MFs )
In particular, the use of MFs in accelerometer design and construction is favored, because of some magneto fluidic fulfillments of the
necessary accelerometer elements:
MFs
: 䥐 1
mass suspension, elastic constant, inertial mass, proportional damping, magnetofluidic levitation servoloop [4].
䑛
] servoloop [
Several types of accelerometers and inclinometers were achieved, their field of application extending from oilrig survey to basic
research.
Sensitivities in the range from 10 10 to 100 m s 2 , frequency domains from static to several 103 Hz and precision up to 16 bit
were obtained [3, 4].
S m
] [ Hz
A presentation of the various types of acceleration sensors with magnetofluidic media, arranged on the combinations between the
different types of inertial mass and mechanoelectric transducer, is given in Table 1 [4].
] [
A main characteristic that distinguishes this class of sensors is the significant response to quasistatic and low frequency inertial and
gravity variations, a difficult task for most of the common sensors.
quasistatic
Relevant performance could be attained in the end of high sensitivity and linearity measurements, the inertial magnetic fluid sensors
providing smaller sizes and costs at equivalent performance.
䤢
For advanced applications as terrestrial tides and seismic monitoring, geophysical surveys, inertial guidance, those sensors are
competitive in performance with the superconducting devices.
ꤪ
䤢
𗨢
Both linear and angular movement could be sensed by magnetic fluid aided sensors or even by some intrinsic effects of the
magnetofluidic material.
Most of the presented types of sensor could be miniaturized.
Fields as robotics and aerospace technology may constitute a proper end in which inertial sensors could be applied, especially for
guidance, attitude control, tethered components control, motion movement and monitoring.
A relatively large number of applications, covering almost all the principles of sensors described in 0304-8853/99/$ } see front
matter ( 1999 Elsevier Science B.V.
}
B.VElsevier ( -//$
All rights reserved.
PII:
: Pii
S 0 3 0 4 - 8 8 5 3 ( 9 9 ) 0 0 1 6 4 - XTable 1 Types of MF inertial sensors.
MF XTable ( ) S
Combinations of inertial mass mechanoelectric transducer.
Inertial mass transducer inductive passive inductive parametric capacitive .
엨 엨
Conductive Hall effect.
()
Dielectric MF with magnetic compliance .
㮑 MF
Conductive MF with magnetic compliance
㮑 MF
MF composite with conductive inclusions .
MF composite with dielectric inclusions.
Permanent magnet conductor .
Permanent magnet dielectric
Nonmagnet conductor .
Nonmagnet dielectric
MF segment, dielectric .
MF segment, conductive
Table 1, were designed and tested by the Gravitational Researches Laboratory in Bucharest during 1983-1997.
- Bucharest 쟗
Some particular present and coming achievements in the research, development and applications of such inertial sensors [5}11] are
summarized in the sequel.
] } [
2.
Low frequency accelerometer
the accelerometer has been initially designed for a wide range measurements of general motion and slope.
荤
A rst accurate prototype has been manufactured in order to be employed in the process of calibration of sea and land gravimeters,
providing a sensitivity of 0.2 arcsec/bit (16 bits output).
rst
arcsec/bit ) .
(
Given the long-term stability of the magnetic fluid device, experimented during several years of operation, another prototype has
been developed for performing horizontal acceleration measurements for seismic noise monitoring.
𗨢
A description is given in Fig. 1, representing an axial section of the cylindrical symmetric transducer.
the inertial mass is cylindrical, made of aluminum.
the static elastic element is a thin aluminum 5056 rod, calculated in such a manner that its mechanical compliance contributes with
a factor of three to the equivalent gravitational rigidity of a wire pendulum of the same length.
the inertial mass is immersed in a magnetic fluid, which ensures at the same time active positioning by means of magnetic levitation
and the adjustment of Fig. 1.
Two-axis accelerometer .
the fluid damping.
the position of the mass is transduced by means of four quarter-cylindrical electrode plates.
quarter-cylindrical transduced
Each plate includes a high permeability ferromagnetic core and an electromagnet.
the system is sealed and included in a cylindrical tank that also provides the magnetic screening.
𗨢
the basic parameters of the sensor are the following:
:
horizontal two-axis measurements of the M.I.
M.I
Piso / Journal of Magnetism and Magnetic Materials 201 (1999) 380}384 381
} ( ) /
Table 1 .
Types of MF inertial sensors.
MF
Combinations of inertial mass/mechanoelectric transducer
mass/mechanoelectric
Inertial massCtransducer Inductive passive Inductive parametric Capacitive Conductive Hall effect
massctransducer
()
Dielectric MF with magnetic compliance .
㮑 MF
Conductive MF with magnetic compliance.
㮑 MF
MF composite with conductive inclusions .
MF composite with dielectric inclusions
Permanent magnet conductor .
Permanent magnet dielectric.
Nonmagnet coductor .
coductor
Nonmagnet dielectric
MF segment, dielectric .
MF segment, conductive
Table 1, were designed and tested by the Gravitational .
Researches Laboratory in Bucharest during 1983-1997.
- Bucharest 쟗
Some particular present and coming achievements in the research, development and applications of such inertial sensors [5}11] are
summarized in the sequel.
] } [
2.
Low frequency accelerometer
the accelerometer has been initially designed for a wide range measurements of general motion and slope.
荤
A rst accurate prototype has been manufactured in order to be employed in the process of calibration of sea and land gravimeters,
providing a sensitivity of 0.2 arcsec/bit (16 bits output).
rst
arcsec/bit ) .
(
Given the long-term stability of the magnetic fluid device, experimented during several years of operation, another prototype has
been developed for performing horizontal acceleration measurements for seismic noise monitoring.
𗨢
A description is given in Fig. 1, representing an axial section of the cylindrical symmetric transducer.
the inertial mass is cylindrical, made of aluminum.
the static elastic element is a thin aluminum 5056 rod, calculated in such a manner that its mechanical compliance contributes with
a factor of three to the equivalent gravitational rigidity of a wire pendulum of the same length.
the inertial mass is immersed in a magnetic fluid, which ensures at the same time active positioning by means of magnetic levitation
and the adjustment of Fig. 1.
Two-axis accelerometer .
the fluid damping.
the position of the mass is transduced by means of four quarter-cylindrical electrode plates.
quarter-cylindrical transduced
Each plate includes a high permeability ferromagnetic core and an electromagnet .
the system is sealed and included in a cylindrical tank that also provides the magnetic screening.
𗨢
the basic parameters of the sensor are the following:
:
horizontal two-axis measurements of the M.I.
M.I
Piso / Journal of Magnetism and Magnetic Materials 201 (1999) 380}384 381
} ( ) /
Fig. 2.
Response for the LF accelerometer
acceleration and slope, sensitivity from 10 6 up to 10 9 m s 2 per bit, relative small dimensions (160 mm in diameter and 180
mm height with the electronic system and the magnetic screening).
S m
ꗤ mm 줢 mm )
(
the system is active for both static and dynamical measurements .
𗨢
In the dynamical mode, a typical acceleration versus output signal response function is given in Fig. 2
3.
Three-axis miniature accelerometer the small dimensions sensor is a 15 mm edge cube containing a three rectangular axis shaped
magnetic fluid column, con ned by annular permanent magnets and controlled by a number of six coils (two per each axis).
mm
ned
( ) 㗯
the principle of the sensor is presented in Fig. 3.
the grey colored three-axis shape represents a contiguous liquid mass.
the transducers are passive (induction) or parametric.
( )
the response acceleration versus output signal for one axis is given in Fig. 4.
the demonstration unit is tested for automotive, robotics and aerospace inertial guidance applications.
𗨢
4.
Gravitational gradiometer
Gravitational gradiometers are very sensitive devices measuring the differences in the gravitational intensity for distances of the order
of meters or less.
𗨢
ꑨ
they are widely needed in geophysical surveys, but their field of application could extend from generic Fig. 3.
Three-axis accelerometer .
Fig. 4.
Response for the miniature accelerometer .
detection of masses to deep space missions.
the principle of such a gravitational gradiometer, depicted in Fig. 5, resides on the measurement of the relative movement of the two
systems of masses produced by the differential forces induced by the gravitational gradient.
𗨢
A prototype of a gravitational gradiometer employing magnetic fluids developed by GRL is presented in Fig. 6, which depicts an
exploded view of the system.
ꗩ GRL
𗨢
the four masses are realized by the two crossed aluminum elements (2), plunged in a magnetic fluid, levitated by means of the
permanent magnets (4) and centered by the magnet (5).
) ( 쟗
) (
( (
the differential distances between the four emerged 382 M.I.
M.I ꑨ
Piso / Journal of Magnetism and Magnetic Materials 201 (1999) 380}384
} ( ) /
Fig. 5.
Principle of a gravitational gradiometer
Fig. 6.
Gravitational gradiometer with magnetic fluids
gaps between the two elements are measured by means of electrical methods by means of the electrodes (6) and monitored by
levitation through magnetic fields produced in four coils included in the electrodes (not represented).
) (
( (
the performances of the distance transducers are dramatically increased when a high permitivity magnetofluidic composite is utilized
as dielectric media.
ꑨ
餬
Preliminary tests performed with a octanole based magnetic liquid containing as inclusions aluminum quasispherical particles with
diameters of 2}5 lm have proven a sensitivity of 10 9 m s 2 /m.
octanole
} 쑓
/m S m ()
5.
Conclusions and trends
Magnetic fluids over the possibility to develop almost all types of sensors necessary for motion measurement, widely necessary in the
present trend towards an informational society.
餯
it seems that inertial sensors using magnetic fluid properties may have a future among the conventional ones, in particular for
applications that request extremes:
: ꤯ ones
either low cost, or high linearity and sensitivity .
their main feature consists in the significant linear response to quasistatical and low frequency inertial and gravity variations, with
applications to inertia guidance, geodynamics, basic research, aerospace technology, robotics and automotive industry
quasistatical
Future developments may end success either in high performance accelerometers comparable with the superconducting devices for
space applications or in miniature sensors for acceleration and gyration for standard motion control.
𗨢
Microminiature magnetic fluid sensors integrated in the systems are possible to be achieved by means of the outstanding physical
and chemical properties of the magnetic fluids composites.
𗨢
Acknowledgements .
the magnetic fluids employed in sensors and experiments were developed and manufactured by the Institute of Complex Fluids from
Timis7oara.
Timis7oara
M.I.
M.i
Piso / Journal of Magnetism and Magnetic Materials 201 (1999) 380}384 383
} ( ) /
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