U.S. patent application number 11/033513 was filed with the patent office on 2007-01-04 for magnetofluidic accelerometer with partial filling of cavity with magnetic fluid.
This patent application is currently assigned to Innalabs Technologies, Inc.. Invention is credited to Alexander G. Pristup, Yuri I. Romanov.
Application Number | 20070000324 11/033513 |
Document ID | / |
Family ID | 35544099 |
Filed Date | 2007-01-04 |
United States Patent
Application |
20070000324 |
Kind Code |
A9 |
Pristup; Alexander G. ; et
al. |
January 4, 2007 |
Magnetofluidic accelerometer with partial filling of cavity with
magnetic fluid
Abstract
A sensor includes a housing and a magnetic fluid within the
housing that incompletely fills the housing. An inertial body is in
contact with the magnetic fluid. Displacement of the inertial body
relative to the magnetic fluid is indicative of acceleration on the
housing. The acceleration includes linear and/or angular
acceleration. The inertial body can be an air bubble, or a
dissimilar liquid. A plurality of magnets are mounted on the
housing, wherein the magnetic fluid is positioned in droplets
between the magnets and the inertial body. The magnetic fluid can
be a single droplet between each magnet and the inertial body, or
multiple droplets between each magnet and the inertial body. The
remaining volume in the housing can be filled with a non-magnetic
fluid.
Inventors: |
Pristup; Alexander G.;
(Novosibirsk, RU) ; Romanov; Yuri I.;
(Novosibirsk, RU) |
Correspondence
Address: |
BARDMESSER LAW GROUP, P.C.
910 17TH STREET, N.W.
SUITE 800
WASHINGTON
DC
20006
US
|
Assignee: |
Innalabs Technologies, Inc.
|
Prior
Publication: |
|
Document Identifier |
Publication Date |
|
US 20060059991 A1 |
March 23, 2006 |
|
|
Family ID: |
35544099 |
Appl. No.: |
11/033513 |
Filed: |
January 12, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10980791 |
Nov 4, 2004 |
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11033513 |
Jan 12, 2005 |
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11006567 |
Dec 8, 2004 |
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11033513 |
Jan 12, 2005 |
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10992289 |
Nov 19, 2004 |
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11033513 |
Jan 12, 2005 |
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11010329 |
Dec 14, 2004 |
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11033513 |
Jan 12, 2005 |
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10836186 |
May 3, 2004 |
6985134 |
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11033513 |
Jan 12, 2005 |
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10209197 |
Aug 1, 2002 |
6731268 |
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10836186 |
May 3, 2004 |
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09511831 |
Feb 24, 2000 |
6466200 |
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10209197 |
Aug 1, 2002 |
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60616849 |
Oct 8, 2004 |
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60614415 |
Sep 30, 2004 |
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60613723 |
Sep 29, 2004 |
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60612227 |
Sep 23, 2004 |
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Current U.S.
Class: |
73/514.39 |
Current CPC
Class: |
G01P 15/11 20130101;
G01P 1/023 20130101; G01P 15/105 20130101; G01P 15/18 20130101;
G01P 15/0888 20130101 |
Class at
Publication: |
073/514.39 |
International
Class: |
G01P 3/44 20060101
G01P003/44 |
Claims
1. A sensor comprising: a housing; a magnetic fluid within the
housing, the magnetic fluid incompletely filling the housing; and
an inertial body in contact with the magnetic fluid, wherein
displacement of the inertial body relative to the magnetic fluid is
indicative of acceleration on the housing.
2. The sensor of claim 1, wherein the acceleration includes linear
acceleration.
3. The sensor of claim 1, wherein the acceleration includes angular
acceleration.
4. The sensor of claim 1, wherein the inertial body is an air
bubble.
5. The sensor of claim 1, wherein the inertial body is a liquid
drop of a liquid dissimilar to the magnetic liquid.
6. The sensor of claim 1, further comprising a plurality of magnets
mounted on the housing, wherein the magnetic fluid is positioned in
droplets between the magnets and the inertial body.
7. The sensor of claim 6, wherein magnetic fluid comprises a single
droplet between each magnet and the inertial body.
8. The sensor of claim 6, wherein magnetic fluid comprises a
plurality of droplets between each magnet and the inertial
body.
9. The sensor of claim 1, wherein the remaining volume in the
housing is filled with a non-magnetic fluid.
10. A sensor comprising: a magnetic fluid arranged in droplets
generally around an inertial body; and a second fluid different
from the magnetic fluid arranged generally between the magnetic
fluid and the inertial body, wherein displacement of the inertial
body is indicative of acceleration of the sensor.
11. The sensor of claim 10, wherein the inertial body is an air
bubble.
12. The sensor of claim 10, wherein the inertial body is a liquid
drop of a liquid dissimilar to the magnetic liquid.
13. The sensor of claim 10, further comprising a housing, and a
plurality of magnets mounted on the housing, wherein the droplets
are between the magnets and the inertial body.
14. The sensor of claim 13, wherein the magnetic fluid comprises a
single droplet between each magnet and the inertial body.
15. The sensor of claim 13, wherein the magnetic fluid comprises a
plurality of droplets between each magnet and the inertial
body.
16. A sensor comprising: an inertial body; a plurality of droplets
of magnetic fluid holding the inertial body in suspension; and a
plurality of magnetic poles maintaining the droplets of the
magnetic fluid in place, wherein displacement of the inertial body
relative to the magnetic fluid is indicative of acceleration on the
sensor.
17. A method for measuring acceleration comprising: suspending an
inertial body using droplets of magnetic fluid; measuring a
position of the inertial body in response to a force applied to the
inertial body; and calculating acceleration based on the
displacement.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation-in-part of U.S. patent
application Ser. No. 10/980,791, entitled MAGNETOFLUIDIC
ACCELEROMETER WITH ACTIVE SUSPENSION, filed Nov. 4, 2004, a
continuation-in-part of U.S. patent application Ser. No.
11/006,567, entitled MAGNETOFLUIDIC ACCELEROMETER WITH NON-MAGNETIC
FILM ON DRIVE MAGNETS, filed Dec. 8, 2004, a continuation-in-part
of U.S. patent application Ser. No. 10/992,289, entitled
ACCELEROMETER WITH REAL-TIME CALIBRATION, filed Nov. 19, 2004, a
continuation-in-part of U.S. patent application Ser. No.
11/010,329, entitled HOUSING FOR AN ACCELEROMETER USING
MAGNETOFLUIDIC EFFECT, filed Dec. 14, 2004, all of which are
incorporated by reference herein in their entirety.
[0002] This application claims the benefit of U.S. Provisional
Patent Application No. 60/616,849, entitled MAGNETOFLUIDIC
ACCELEROMETER AND USE OF MAGNETOFLUIDICS FOR OPTICAL COMPONENT
JITTER COMPENSATION, Inventors: SUPRUN et al., filed: Oct. 8, 2004;
U.S. Provisional Patent Application No. 60/614,415, entitled METHOD
OF CALCULATING LINEAR AND ANGULAR ACCELERATION IN A MAGNETOFLUIDIC
ACCELEROMETER WITH AN INERTIAL BODY, Inventors: ROMANOV et al.,
filed: Sep. 30, 2004; U.S. Provisional Patent Application No.
60/613,723, entitled IMPROVED ACCELEROMETER USING MAGNETOFLUIDIC
EFFECT, Inventors: SIMONENKO et al., filed: Sep. 29, 2004; and U.S.
Provisional Patent Application No. 60/612,227, entitled METHOD OF
SUPPRESSION OF ZERO BIAS DRIFT IN ACCELERATION SENSOR, Inventor:
Yuri I, ROMANOV, filed: Sep. 23, 2004; which are all incorporated
by reference herein in their entirety.
[0003] This application is related to U.S. patent application Ser.
No. 10/836,624, filed May 3, 2004; U.S. patent application Ser. No.
10/836,186, filed May 3, 2004; U.S. patent application Ser. No.
10/422,170, filed May 21, 2003; U.S. patent application Ser. No.
10/209,197, filed Aug. 1, 2002, now U.S. Pat. No. 6,731,268; U.S.
patent application Ser. No. 09/511,831, filed Feb. 24, 2000, now
U.S. Pat. No. 6,466,200; and Russian patent application
No.99122838, filed Nov. 3, 1999, which are all incorporated by
reference herein in their entirety.
BACKGROUND OF THE INVENTION
[0004] 1. Field of the Invention
[0005] The present invention is related to magnetofluidic
acceleration sensors.
[0006] 2. Background Art
[0007] Magnetofluidic accelerometers are generally known and
described in, e.g., U.S. patent application Ser. No. 10/836,624,
filed May 3, 2004, U.S. patent application Ser. No. 10/836,186,
filed May 3, 2004, U.S. patent application Ser. No. 10/422,170,
filed May 21, 2003, U.S. patent application Ser. No. 10/209,197,
filed Aug. 1, 2002 (now U.S. Pat. No. 6,731,268), U.S. patent
application Ser. No. 09/511,831, filed Feb. 24, 2000 (now U.S. Pat.
No. 6,466,200), and Russian patent application No. 99122838, filed
Nov. 3, 1999 that utilize magnetofluidic principles and an inertial
body suspended in a magnetic fluid, to measure acceleration. Such
an accelerometer often includes a sensor casing (sensor housing, or
"vessel"), which is filled with magnetic fluid. An inertial body
(inertial object) is suspended in the magnetic fluid. The
accelerometer usually includes a number of drive coils (power
coils) generating a magnetic field in the magnetic fluid, and a
number of measuring coils to detect changes in the magnetic field
due to relative motion of the inertial body.
[0008] When the power coils are energized and generate a magnetic
field, the magnetic fluid attempts to position itself as close to
the power coils as possible. This, in effect, results in suspending
the inertial body in the approximate geometric center of the
housing. When a force is applied to the accelerometer (or to
whatever device the accelerometer is mounted on), so as to cause
angular or linear acceleration, the inertial body attempts to
remain in place. The inertial body therefore "presses" against the
magnetic fluid, disturbing it and changing the distribution of the
magnetic fields inside the magnetic fluid. This change in the
magnetic field distribution is sensed by the measuring coils, and
is then converted electronically to values of linear and angular
acceleration. Knowing linear and angular acceleration, it is then
possible, through straightforward mathematical operations, to
calculate linear and angular velocity, and, if necessary, linear
and angular position. Phrased another way, the accelerometer
provides information about six degrees of freedom--three linear
degrees of freedom (x, y, z), and three angular (or rotational)
degrees of freedom (angular acceleration .omega.'.sub.x,
.omega.'.sub.y, .omega.'.sub.z about the axes x, y, z).
[0009] Generally, the precise characteristics of the acceleration
sensor are highly dependent on the geometry of the housing, the
inertial body, the arrangements of the magnets, the properties of
the magnetic fluid, etc. For a designer, as wide a range as
possible of various sensor parameters is desirable. Such parameters
include, e.g., dynamic range, sensitivity, response time, physical
dimensions, cost, drift, susceptibility to environmental factors,
etc. One of the factors that effects the performance of the sensor
is hydrodynamic resistance, which results from the inertial body
trying to move against the magnetic fluid. Generally, the magnetic
fluid is a relatively viscous fluid, and the larger the area of the
inertial body in contact with the magnetic fluid, the greater the
hydrodynamic resistance. Higher hydrodynamic resistance therefore
leads to a lower frequency response.
[0010] Accordingly, there is a need in the art for a way to reduce
hydrodynamic resistance in a magnetofluidic accelerometer.
BRIEF SUMMARY OF THE INVENTION
[0011] The present invention relates to a magnetofluidic
accelerometer with partial filling of the cavity with magnetic
fluid that substantially obviates one or more of the issues
associated with known accelerometers.
[0012] More particularly, in an exemplary embodiment of the present
invention, a sensor includes a housing and a magnetic fluid within
the housing that incompletely fills the housing. An inertial body
is in contact with the magnetic fluid. Displacement of the inertial
body relative to the magnetic fluid is indicative of acceleration
on the housing. The acceleration includes linear and/or angular
acceleration. The inertial body can be an air bubble, or a
dissimilar liquid. A plurality of magnets are mounted on the
housing, wherein the magnetic fluid is positioned in droplets
between the magnets and the inertial body. The magnetic fluid can
be a single droplet between each magnet and the inertial body, or
multiple droplets between each magnet and the inertial body. The
remaining volume in the housing can be filled with a non-magnetic
fluid.
[0013] In another aspect, a sensor includes a magnetic fluid
arranged in droplets generally around an inertial body. A second
fluid, different from the magnetic fluid, is arranged generally
between the magnetic fluid and the inertial body. Displacement of
the inertial body relative to the magnetic fluid is indicative of
acceleration on the sensor.
[0014] In another aspect, a sensor includes an inertial body, and a
plurality of droplets of magnetic fluid holding the inertial body
in suspension. A plurality of magnetic poles maintain the droplets
of the magnetic fluid in contact with the inertial body.
Displacement of the inertial body relative to the magnetic fluid is
indicative of acceleration on the sensor.
[0015] In another aspect, a method for measuring acceleration
includes suspending an inertial body using droplets of magnetic
fluid; measuring a position of the inertial body in response to a
force applied to the inertial body; [0016] and calculating
acceleration based on the displacement.
[0017] In another aspect, a method for measuring acceleration
includes suspending an inertial body using droplets of magnetic
fluid; generating a magnetic field within the magnetic fluid;
modulating the magnetic field to counteract a change in position of
the inertial body relative to the droplets of magnetic fluid due to
acceleration; and calculating the acceleration based on the
modulation.
[0018] Additional features and advantages of the invention will be
set forth in the description that follows, and in part will be
apparent from the description, or may be learned by practice of the
invention. The advantages of the invention will be realized and
attained by the structure particularly pointed out in the written
description and claims hereof as well as the appended drawings.
[0019] It is to be understood that both the foregoing general
description and the following detailed description are exemplary
and explanatory and are intended to provide further explanation of
the invention as claimed.
BRIEF DESCRIPTION OF THE FIGURES
[0020] The accompanying drawings, which are included to provide a
further understanding of the invention and are incorporated in and
constitute a part of this specification, illustrate embodiments of
the invention and together with the description serve to explain
the principles of the invention. In the drawings:
[0021] FIG. 1 illustrates an isometric three-dimensional view of an
assembled magneto fluidic acceleration sensor of the present
invention.
[0022] FIG. 2 illustrates a side view of the sensor with one of the
drive magnet assemblies removed.
[0023] FIG. 3 illustrates a partial cutaway view showing the
arrangements of the drive magnet coils and the sensing coils.
[0024] FIG. 4 illustrates an exploded side view of the sensor.
[0025] FIG. 5 illustrates a three-dimensional isometric view of the
sensor of FIG. 4, but viewed from a different angle.
[0026] FIG. 6 illustrates one embodiment of the invention that uses
a single droplet of magnetic fluid for each drive magnet
assembly.
[0027] FIG. 7 illustrates an alternative embodiment, where multiple
droplets of magnetic fluid are used for each drive magnet
assembly.
DETAILED DESCRIPTION OF THE INVENTION
[0028] Reference will now be made in detail to embodiments of the
present invention, examples of which are illustrated in the
accompanying drawings.
[0029] FIGS. 1-5 illustrate an exemplary embodiment of a
magnetofluidic acceleration sensor of the present invention. The
general principles of operation of the magnetofluidic sensor are
described in U.S. Pat. No. 6,466,200, which is incorporated herein
by reference. The sensor's behavior is generally described by a set
of non-linear partial differential equations, see U.S. Provisional
Patent Application No. 60/614,415, to which this application claims
priority.
[0030] In particular, FIG. 1 illustrates an isometric
three-dimensional view of an assembled acceleration sensor. FIG. 2
illustrates a side view of the acceleration sensor with one of the
drive magnet casings removed. Note the inertial body in the
center.
[0031] FIG. 3 illustrates a partial cutaway view showing the
arrangements of the drive magnet coils and the sensing coils. FIG.
4 illustrates an exploded side view of the sensor, showing the
housing, magnetic fluid inside the housing, and the inertial body
surrounded by the magnetic fluid. FIG. 5 illustrates a
three-dimensional isometric view of what is shown in FIG. 4, but
viewed from a different angle.
[0032] Further with reference to FIG. 1, the accelerometer 102,
shown in FIG. 1 in assembled form, includes a housing 104, and a
number of drive magnet assemblies 106A-106E, each of which is
connected to a power source using corresponding wires 110A-110E.
Note that in this view, only five drive magnet assemblies 106 are
shown, but see FIG. 4, where a sixth drive magnet assembly
(designated 106F) is also illustrated.
[0033] FIG. 2 illustrates the sensor 102 of FIG. 1, with one of the
drive magnet assemblies removed. With the drive magnet assembly
106C removed, an inertial body 202 is visible in an approximate
geometric center of the housing 104. The magnetic fluid 204 fills
the remainder of the available volume within the housing. Note that
the magnetic fluid itself is not actually drawn in the figure for
clarity, although most such fluids are black in color and have an
"oily" feel to them.
[0034] FIG. 3 illustrates a partial cutaway view, showing the
sensor 102. Only some of the components are labeled in FIG. 3 for
clarity. Shown in FIG. 3 are four drive coils (or drive magnets)
302A, 302B, 302E and 302D, collectively referred to as drive
magnets 302 (the remaining two drive magnets are not shown in this
figure). The drive magnets 302 are also sometimes referred to as
suspension magnets, power magnets, or suspension coils (if
electromagnets are used).
[0035] In one embodiment, each such drive magnet assembly 106 has
two sensing coils, designated by 306 and 308 (in FIG. 3, 306A,
308A, 306B, 308B, 306E, 308E, 306E, 308E). The sensing coils 306,
308 are also sometimes referred to as "sensing magnets", or
"measuring coils." Note further that in order to measure both
linear and angular acceleration, two sensing coils per side of the
"cube" are necessary. If only a single sensing coil were to be
positioned in a center of each side of the "cube," measuring
angular acceleration would be impossible. As a less preferred
alternative, it is possible to use only one sensing coil per side
of the cube, but to displace it off center. However, the
mathematical analysis becomes considerably more complex in this
case.
[0036] FIGS. 4 and 5 illustrate "exploded" views of the sensor 102,
showing the same structure from two different angles. In
particular, shown in FIGS. 4 and 5 is an exploded view of one of
the drive magnet assembly 106D. As shown in the figures, the drive
magnet assembly 106D includes a casing 402, a rear cap 404, the
drive coil 302D, two sensing coils 306D and 308D, magnet cores 406
(one for each sensing coil 306D and 308D), and a drive magnet core
408. In an alternative embodiment, the cores 406 and 408 can be
manufactured as a single common piece (in essence, as a single
"transformer core").
[0037] In this embodiment, the sensing coils 306D and 308D are
located inside the drive coil 302D, and the rear cap 404 holds the
drive coil 302D and the sensing coils 306D and 308D in place in the
drive coil assembly 106D.
[0038] The drive magnets 302 are used to keep the inertial body 202
suspended in an approximate geometric center of the housing 104.
The sensing coils 306, 308 measure the changes in the magnetic flux
within the housing 104. The magnetic fluid 204 attempts to flow to
locations where the magnetic field is strongest. This results in a
repulsive force against the inertial body 202, which is usually
either non-magnetic, or partly magnetic (i.e., less magnetic than
the magnetic fluid 204).
[0039] The magnetic fluid 203 is highly magnetic, and is attracted
to the drive magnets 302. Therefore, by trying to be as close to
the drive magnets 302 as possible, the magnetic fluid in effect
"pushes out," or repels, the inertial body 202 away from the drive
magnets 302. In the case where all the drive magnets 302 are
substantially identical, or where all the drive magnets 302 exert a
substantially identical force, and the drive magnets 302 are
arranged symmetrically about the inertial body 202, the inertial
body 202 will tend to be in the geometric center of the housing
104. This effect may be thought of as a repulsive magnetic effect
(even though, in reality, the inertial body 202 is not affected by
the drive magnets 302 directly, but indirectly, through the
magnetic fluid 204).
[0040] One example of the magnetic fluid 204 is kerosene with iron
oxide (Fe.sub.3O.sub.4) particles dissolved in the kerosene. The
magnetic fluid 204 is a colloidal suspension. Typical diameter of
the Fe.sub.3O.sub.4 particles is on the order of 10-20 nanometers
(or smaller). The Fe.sub.3O.sub.4 particles are generally spherical
in shape, and act as the magnetic dipoles when the magnetic field
is applied.
[0041] More generally, the magnetic fluid 204 can use other
ferromagnetic metals, such as cobalt, gadolinium, nickel,
dysprosium and iron, their oxides, e.g., Fe.sub.3O.sub.4,
FeO.sub.2, Fe.sub.2O.sub.3, as well as such magnetic compounds as
manganese zinc ferrite (Zn.sub.xMn.sub.1-xFe.sub.2O.sub.4), cobalt
ferrites, or other ferromagnetic alloys, oxides and ferrites. Also,
water or oil can be used as the base liquid, in addition to
kerosene.
[0042] FIG. 6 illustrates one embodiment of the present invention.
Shown in FIG. 6 is the sensor illustrated in FIGS. 1-5, in
cross-sectional view, with droplets of magnetic fluid used to
suspend the inertial body 202. Only some of the elements are
labeled in FIG. 6 for clarity. As shown in FIG. 6, for each drive
magnet assembly 106, a single droplet (labeled 620A, 620D, 620E and
620B in FIG. 6, with four of the six droplets illustrated in the
figure). Also, in FIG. 6, the cavity, or "empty space" in which the
inertial body 202 is located, is designated by 622. Other than the
droplets 620 and the inertial body 202, the cavity 622 can be
filled with air or some other gas. Alternatively, the remainder of
the volume of the cavity 622 can be filled with a second liquid
(not shown). The second liquid is preferably non-magnetic, and such
that it does not readily mix with the magnetic fluid. Note further
that the second liquid, which is dissimilar to the magnetic fluid,
can itself be used as an inertial body, rather than a "solid"
inertial body shown in FIG. 202. Also, an air bubble can be used as
an inertial body (in other words, essentially, the inertial body
202 shown in FIG. 6 is removed, and the sensing coils sense the
"sloshing" of the droplets 620.
[0043] Note also that the droplets 620 would have approximately the
shape shown in FIG. 6 only when the magnetic field is applied from
the drive magnets 302. In the absence of a magnetic field, all the
magnetic fluid 204 would "pool" in one of the corners of the cavity
622. It is generally preferred to use either a permanent magnet as
the drive magnet 302, or a combination of permanent and
electromagnets as the drive magnets 302, particularly for assembly
purposes, so as to avoid the possibility of pooling of the magnetic
fluid 204, and ensuring that the droplets 620 are formed as
shown.
[0044] Note also that the magnetic fluid 204 can be a relatively
expensive component of the overall sensor 102. Thus, reducing the
amount of magnetic fluid 204 used in the sensor 102 is desirable
from a cost standpoint. Also, as discussed above, the hydrodynamic
resistance depends on the area of contact between the inertial body
202 and the magnetic fluid 204. If the magnetic fluid 204 is
arranged in the form of droplets 620, the contact area between the
magnetic fluid 204 and the inertial body 202 is reduced, improving
the frequency response of the sensor 102.
[0045] FIG. 7 illustrates another embodiment of the invention,
where instead of a single droplet 620, multiple droplets for each
drive magnet assembly 106 are used. These droplets are
correspondingly labeled 626A, 624A, 626B, 624B, etc. in FIG. 7.
Although two droplets per drive magnet assembly 106 are shown in
FIG. 7, more such droplets, for example, three or four, may be used
for each drive magnet assembly 106, depending on the desired
characteristics, the arrangement of the drive magnets 302 and the
magnetic field distribution generated by the drive magnets 302. As
with FIG. 6, the remaining volume in the cavity 622 can be filled
with air, gas, a second liquid, etc.
[0046] Having thus described an embodiment of the invention, it
should be apparent to those skilled in the art that certain
advantages of the described method and apparatus have been
achieved. It should also be appreciated that various modifications,
adaptations, and alternative embodiments thereof may be made within
the scope and spirit of the present invention. The invention is
further defined by the following claims.
* * * * *