Note: Descriptions are shown in the official language in which they were submitted.
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AN APPARATUS FOR GENERATING POWER RESPONSIVE TO MECHANICAL
VIBRATION
STATEMENT OF GOVERNMENT INTEREST
The invention described herein may be manufactured and used by or for the
Government
of the United States of America for Governmental purpose without the payment
of any royalties
thereon or therefore.
FEDERALLY-SPONSORED RESEARCH AND DEVELOPMENT
This application is assigned to the United States Government and is available
for
licensing for commercial purposes. No license is necessary when used for
Governmental
purposes. Licensing and technical inquiries should be directed to the Office
of Patent Counsel,
Space and Naval Warfare Systems Center, San Diego, Code 20012, San Diego,
Calif., 92152;
telephone (619)553-3001, facsimile (619)553-3821. Reference Navy Case # 99735.
BACKGROUND OF THE INVENTION
There is a growing interest in the field of miniature sensors in applications
such as
medical implants and embedded sensors in buildings. One of the projected goals
for micro-
electro-mechanical systems (MEMS) technology is to develop low-cost and high-
performance
distributed sensor systems for medical, automotive, manufacturing, robotics,
and household
applications. One area that has received little attention is how to
effectively supply the required
electrical power to such sensor elements. Many applications require the
sensors to be completely
embedded in a structure with no physical connection to the outside world.
Ideally, the elements
of these distributed systems have their own integrated power supplies to
reduce problems related
to interconnection, electronic noise and control system complexity. Efforts
are underway to
develop integrated chemically-based power supplies with MEMS devices. Chemical
power
supply (battery) technology is well-developed for such applications but, where
shelf life or
replacement accessibility is a limiting factor, chemical power supplies may
not be suitable for
the application. Another approach to supplying power to such systems is to
include a renewable
power supply within the sensor element, thereby making them self-powered
microsystems.
Renewable power supplies convert energy harvested from an existing energy
source
within the environment into electrical energy. The preferred source of energy
depends on the
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application. Some possible energy sources include optical energy from ambient
light such as
sunlight, theimal energy harvested across a temperature gradient, volume flow
energy harvested
across a liquid or gas pressure gradient, and mechanical energy harvested from
motion and
vibration. Of these sources, light and theimal energy have already been
exploited for use in
micro-power supplies. However, there are many applications where there is an
insufficient
amount of light or theimal energy such as in medical implants. Therefore,
practitioners in the art
have proposed many different power supplies that generate electricity from
ambient mechanical
energy. Ambient mechanical vibrations inherent in the environment, from the
movement of our
bodies to the hum of a computer, can provide a constant power density of 10 to
50 W/cc.
Several practitioners have proposed rudimentary vibration-based power
generators at the
University of Sheffield [C.B. Williams, R.B. Yates, "Analysis of a micro-
electric generator for
micro-systems," 8th Intl. Conf. on Solid-State Sens. & Actuators, Stockholm,
Sweden, 25-
29Jun1995, 87-B4, pp. 369-72] and Massachusetts Institute of Technology [Scott
Meninger, Jose
Oscar Mur-Miranda, Rajeevan Amirtharajah, Anantha P. Chandrakasan, and Jeffrey
H. Lang,
"Vibration-to-Electric Energy Conversion," IEEE Trans. on VLSI Systems Vol. 9,
No. 1, pp. 64-
76, Feb 2001] for example. Meninger, et al. describe a micro-generator that
harvests vibrational
energy by accumulating the voltage created by vibration-induced changes in a
variable capacitor.
Others have recently improved on the earlier efforts. For example, Ching et
al. [Neil N.H.
Ching, H.Y Wong, Wen J. Li, Philip H.W. Leong, and Zhiyu Wen, "A laser-micro-
machined
multi-modal resonating power transducer for wireless sensing systems," Sensors
and Actuators
A. Physical, Vol. 97-98, pp.685-690, 2002.] describe a micromachined generator
with enough
power to drive an off-the-shelf circuit. For this work, Ching et al. prefer
micromachining
methods to build their vibration-induced power generator because the methods
afford precise
control of the mechanical resonance necessary for generator efficiency, and
batch fabricability
for low-cost mass production of commercially viable generators. Similarly,
Williams et al. later
describe [C.B. Williams, C. Shearwood, M.A. Harradine, P.H. Mellor, T.S. Birch
and R.B.
Yates, "Development of an electromagnetic micro-generator," IEE Proc. -
Circuits Devices Syst.,
Vol. 148, No. 6, pp. 337-342, Dec 2001] a simple inertial generator built
according to their
earlier theoretical analysis that is also fabricated by means of
micromachining. Other examples
include the laser-micro-machined electromagnetic generator described by Li et
al. [Wen J. Li,
Terry C.H. Ho, Gordon M.H. Chan, Philip H.W. Leong and Hui Yung Wong,
"Infrared Signal
Transmission by a Laser-Micro-machined Vibration-Induced Power Generator,"
Proc. 43rd IEEE
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Midwest Symp. on Circuits and Systems, Lansing MI, 08-11Aug2000, pp236-9],
which provides
2VDC power sufficient to send 140ms pulse trains every minute when subjected
to 250 micron
vibrations in the 64-120 Hz region.
In U.S. Patent No. 6,127,812, Ghezzo et al. describe an energy extractor that
includes a
capacitor that experiences capacitance and voltage changes in response to
movement of a
capacitor plate or of a dielectric material. In one embodiment, a third plate
is positioned between
first and second plates to create two capacitors of varying capacitances. In
another embodiment,
one capacitor plate is attached by flexible arms which permit movement across
another capacitor
plate. The above capacitors can be used singularly or with one or more other
capacitors and are
rectified either individually or in a cascaded arrangement for supplying power
to a rechargeable
energy source. The above capacitors can be fabricated on a substrate along
with supporting
electronics such as diodes. Ghezzo et al. employ varying capacitance and
neither consider nor
suggest any solution the problem of fabricating an electromagnetic micro-
generator.
In U.S. Patent No. 6,722,206 B2, Takeda describes a force sensing device
having an
element of magnetic material mounted to a substrate such that another magneto-
electrical
material element is subjected to the magnetic field generated by the magnetic
member. A
movable member is mounted for oscillation in response to vibration and such
oscillation changes
the magnetic field experienced by the magneto-electrical material, which in
turn changes an
electrical property of the magneto-electrical material. Takeda neither
considers nor suggests any
solution to the problem of fabricating an electromagnetic micro-generator.
Despite the efforts of several practitioners in the art, there still exists a
need in the art for
an electromagnetic micro-generator suitable for inexpensive fabrication in
volume at the MEMS
scale that can generate power sufficient for operating today's microchips. The
electromagnetic
devices known in the art all generally employ a single magnetic mass which
oscillates on a
spring element to change the magnetic flux at a nearby stationary coil. These
devices are thereby
limited in power output capacity by the limited mass of the single magnet, the
limited room for a
number of coils in the flux field of the single magnet and the limited flux
slope available at the
coils because of the single magnetic pole exposed thereto. These unresolved
problems and
deficiencies are clearly felt in the art and are solved by this invention in
the manner described
below.
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SUMMARY OF THE INVENTION
A vibrational energy harvesting apparatus is disclosed herein that comprises a
substrate
with a plurality of integral compliant regions, at least two ferromagnetic
masses, and a coil.
Each ferromagnetic mass is coupled to a corresponding one or more of the
integral compliant
regions such that at least one of the ferromagnetic masses moves with respect
to the substrate
responsive to substrate acceleration. Each ferromagnetic mass has an inner
magnetic pole
disposed such that the inner magnetic poles are separated from one another by
a flux gap. The
magnetic polarity of each inner magnetic pole is similar to the magnetic
polarity of the inner
magnetic pole on the opposing side of the flux gap. The inner magnetic poles
form a steep flux
gradient region in the flux gap. The coil is coupled to the substrate and
disposed within the steep
flux gradient region where it is exposed to a changing magnetic flux arising
from motion of at
least one of the ferromagnetic masses with respect to the substrate.
In an alternate embodiment of the energy harvesting apparatus described above,
the two
ferromagnetic masses may be rigidly coupled to one another and disposed to
move
synchronously.
In another alternate embodiment of the energy harvesting apparatus described
above, the
coupled ferromagnetic masses may be configured to move linearly with respect
to the substrate
responsive to substrate acceleration.
In another alternate embodiment of the energy harvesting apparatus described
above,
conductors may be coupled to the coil for conducting electrical current
flowing in response to the
changing magnetic flux.
In another alternate embodiment of the energy harvesting apparatus described
above, the
coil may comprise a plurality of independent coils coupled to the substrate
and disposed within
the flux gap where the plurality of independent coils are exposed to the
changing magnetic flux.
In another alternate embodiment of the energy harvesting apparatus described
above, the
coil may be disposed within the flux gap and outside of a volume defined by
perimeters of the
coupled ferromagnetic masses.
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In another alternate embodiment of the energy harvesting apparatus described
above, the
coil may be disposed within the flux gap and outside of a volume defined by
perimeters of the
coupled ferromagnetic masses.
The vibrational energy harvesting apparatus may be constructed as a micro-
electro-
mechanical system (MEMS) power generator comprising: a substrate having a
plurality of
integral compliant regions; at least one monolithic micro-generator, a coil,
and conductors. In
this embodiment, each monolithic micro-generator comprises at least two
ferromagnetic masses.
Each ferromagnetic mass may be coupled to a corresponding one or more of the
integral
compliant regions such that at least one of the ferromagnetic masses moves
with respect to the
substrate responsive to substrate acceleration. Each ferromagnetic mass has an
inner magnetic
pole disposed such that the inner magnetic poles of the ferromagnetic masses
are of the same
magnetic polarity and are separated from one another by a flux gap. The inner
magnetic poles
form a steep flux gradient region in the flux gap. The coil is coupled to the
substrate and
disposed within the flux gap where it is exposed to a changing magnetic flux
arising from motion
of at least one of the ferromagnetic masses with respect to the substrate. The
conductors are
coupled to each micro-generator coil for conducting electrical current flowing
in response to the
magnetic flux changes.
In one aspect, there is provided a vibrational energy harvesting apparatus
comprising: a
substrate having a plurality of integral compliant regions; two ferromagnetic
masses each
coupled to a corresponding one or more of the integral compliant regions such
that at least one of
the ferromagnetic masses moves with respect to the substrate responsive to
substrate
acceleration, each ferromagnetic mass having an inner magnetic pole disposed
such that the inner
magnetic poles are separated from one another by a flux gap, wherein the
magnetic polarity of
each inner magnetic pole is similar to the magnetic polarity of the inner
magnetic pole on the
opposing side of the flux gap; wherein the ferromagnetic masses are disposed
so as to form a
steep flux gradient region in the flux gap; and a coil coupled to the
substrate and disposed within
the steep flux gradient region where it is exposed to a changing magnetic flux
arising from
motion of at least one of the ferromagnetic masses with respect to the
substrate.
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In another aspect, there is provided a micro-electro-mechanical system (MEMS)
power
generator comprising: a substrate having a plurality of integral compliant
regions; at least one
monolithic micro-generator, each monolithic micro-generator comprising: at
least two
ferromagnetic masses each coupled to a corresponding one or more of the
integral compliant
regions such that at least one of the ferromagnetic masses moves with respect
to the substrate
responsive to substrate acceleration, each ferromagnetic mass having an inner
magnetic pole
disposed such that the inner magnetic poles of the ferromagnetic masses are of
the same
magnetic polarity and are separated from one another by a flux gap, wherein
the inner magnetic
poles form a steep flux gradient region in the flux gap; and a coil coupled to
the substrate and
disposed within the steep flux gradient region where it is exposed to a
changing magnetic flux
arising from motion of at least one of the ferromagnetic masses with respect
to the substrate; and
conductors coupled to each micro-generator coil for conducting electrical
current flowing in
response to the magnetic flux changes.
In another aspect, there is provided an energy harvesting apparatus
comprising: a
substrate having a plurality of integral compliant regions; at least two
ferromagnetic masses each
coupled to a corresponding one or more of the integral compliant regions such
that at least one of
the ferromagnetic masses moves with respect to the substrate responsive to
substrate
acceleration, each ferromagnetic mass having an inner magnetic pole disposed
such that the inner
magnetic poles are separated from one another by a flux gap, wherein the
magnetic polarity of
each inner magnetic pole is similar to the magnetic polarity of the inner
magnetic pole on the
opposing side of the flux gap; a coil coupled to the substrate and disposed
within the flux gap
where it is exposed to a changing magnetic flux arising from motion of at
least one of the
ferromagnetic masses with respect to the substrate; and conductors coupled to
the coil for
conducting electrical current flowing in response to the changing magnetic
flux.
In another aspect, there is provided a micro-electro-mechanical system (MEMS)
power
generator comprising: a substrate having a plurality of integral compliant
regions; at least one
monolithic micro-generator, each monolithic micro-generator comprising: at
least two
ferromagnetic masses each coupled to a corresponding one or more of the
integral compliant
regions such that at least one of the ferromagnetic masses moves with respect
to the substrate
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responsive to substrate acceleration, each ferromagnetic mass having an inner
magnetic pole
disposed such that the inner magnetic poles of the ferromagnetic masses are of
the same
magnetic polarity and are separated from one another by a flux gap, and a coil
coupled to the
substrate and disposed within the flux gap where it is exposed to a changing
magnetic flux
arising from motion of at least one of the ferromagnetic masses with respect
to the substrate; and
conductors coupled to each micro-generator coil for conducting electrical
current flowing in
response to the magnetic flux changes.
In another aspect, there is provided an energy harvester comprising: a
substrate having a
plurality of integral compliant regions; two ferromagnetic masses each coupled
to one or more of
the integral compliant regions such that at least one of the ferromagnetic
masses moves linearly
with respect to the substrate responsive to substrate acceleration, each
ferromagnetic mass
having an inner magnetic pole disposed such that the inner magnetic poles of
the ferromagnetic
masses are separated from one another by a flux gap, wherein the magnetic
polarity of each inner
magnetic pole is similar to the magnetic polarity of the inner magnetic pole
on the opposing side
of the flux gap and the inner magnetic poles form a steep flux gradient region
in the flux gap; a
coil coupled to the substrate and disposed within the flux gap where it is
exposed to a changing
magnetic flux arising from motion of the ferromagnetic masses with respect to
the substrate; and
conductors coupled to the coil for conducting electrical current flowing in
response to the
changing magnetic flux.
BRIEF DESCRIPTION OF THE DRAWINGS
For a more complete understanding of this invention, reference is now made to
the
following detailed description of the embodiments as illustrated in the
accompanying drawing, in
which like reference designations represent like features throughout the
several views.
Fig. 1 is a schematic diagram illustrating a damped mass-spring model
representative of
the micro-generator system of this invention.
Fig. 2 illustrates the theoretical relationship between coil voltage, flux
density and
relative displacement according to classical electromagnetic theory for the
model of Fig. 1.
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Fig. 3 is a diagram illustrating an edge view of several different coil/flux
configurations
available for use in the micro-generator system of this invention.
Fig. 4 is a diagram illustrating an edge perspective of an exemplary
embodiment of the
micro-generator of this invention.
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Fig. 5 is a diagram illustrating an edge perspective of an exemplary
embodiment of the
micro-electro-mechanical system (MEMS) power generator system of this
invention.
Fig. 6, comprising Figs. 6(a)-(d), is a diagram illustrating an edge view of
an exemplary
magnet layer fabrication process of this invention.
Fig. 7, comprising Figs. 7(a)-(e), is a diagram illustrating an edge view of
an exemplary
magnet layer fabrication process of this invention.
Fig. 8 is a diagram illustrating a facial view of the exemplary magnet layer
embodiments
of Figs. 6 and 7.
Fig. 9, comprising Figs. 9(a)-(d), is a diagram illustrating an edge view of
an exemplary
coil layer fabrication process of this invention.
Fig. 10 illustrates a facial view of the exemplary coil layer embodiment of
Fig. 9.
Fig. 11, comprising Figs. 11(a)-(c), is a diagram illustrating an edge view of
a first
exemplary micro-generator fabrication process of this invention using the
magnet layer
embodiment of Fig. 6.
Fig. 12, comprising Figs. 12(a)-(b), is a diagram illustrating an edge view of
a second
exemplary micro-generator fabrication process of this invention using the
magnet layer
embodiment of Fig. 7.
DETAILED DESCRIPTION OF EMBODIMENTS
Fig. 1 is a schematic diagram illustrating a damped mass-spring model
representative of
the micro-generator system of this invention. Both electrical and mechanical
damping must be
considered in analyzing and optimizing the design for particular ambient
vibration spectra.
Referring to Fig. 1, for time t, a mass m, a spring constant k, an electrical
damping factor be, a
mechanical damping factor bin, and a displacement function z(t), the power P
available from the
coil current may be expressed as shown in Eqn. 1:
P Jo Fdv =Jb dv
1 =b vdv =¨bev2 =-1¨be.;2
0 e [Eqn.
11
7 2 -
Conservation of energy leads to Eqn. 2:
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[Eqn. 21
Laplacian transformation and the substitution of variables can be shown to
provide the following
Eqns. 3-10:
¨ins2Y
Z = ___________________________________ 2
[Egli- 31
flLS
= 2m4.0).
Let:
[Eqns. 4]
bm = 2rg.oin
where 032 = k I rn
f'
CO
Thus, 1 1 n
= 1,2
[Eqn. 51
A4, 4õ)iffl +1 ____________________________________
0)õ icon
ra, 'N3
2 t"
in4.conco co
and 1P1 n
¨2
[Eqn. 61
co
CO
2(4. + 1 ¨ ¨
CO CO
t tr
3 2
2
Or //kW nti4../1
[Eqn. 7]
I = ________________________________ &)2 40)(4.
where A = oi2Y
This is a non-linear problem and, because of the nonlinear nature of the
reaction force
from the coil current, the system resonance may be optimized with reference to
Eqn. 7 for a
given application without undue experimentation. In general, the inventors
have discovered that
a higher electrical damping &improves power output performance at frequencies
below the
mechanical resonant frequencyfi= 27con of the system.
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Fig. 2 is a chart illustrating the expected coil voltage, flux density and
relative
displacement for various electrical and mechanical assumptions. The
acceleration is assumed to
be a constant 1.0 m/sec2over the entire frequency range, B..= 1 Tesla, k 1
N/m, velocity = 50
min/sec, mass = 1 mg, and x = 1 mm. The inventors have conducted both
experimental and
theoretical tests and have found that the predictions disclosed in Fig. 2
agree well with
experimental measurements implemented on a larger physical scale.
A macro-scale version of the energy harvesting device was fabricated to verify
the
expected voltage output per coil. The experimental setup consisted of a one
Tesla magnet
measuring one inch in diameter and 3/16 inches in thickness. It was attached 5
to a spring with
sufficient spring force to result in a displacement of 2.5 mm under
accelerations of 1.0 m/s2at a
frequency of 20 Hz. The number of turns in the coil was varied sequentially
from 5 to 40 in
increments of 5 and voltage output measurements were made for each
configuration. It was
observed that the voltage generated per turn of the coil was very close to the
expected value of 1
mV/turn using the simple one-dimensional (1-D) model described above.
A detailed analysis was performed by modeling the magnetic flux density in two
dimensions and summing the total flux density normal to the surface of the
coil. The input was
once again assumed to be a 20 Hz sinusoidal input at 1.0 m/s2. At each time
step, the velocity,
displacement from the coil to the magnet and total magnetic flux density
normal to the surface
were calculated. The results of this detailed analysis confirmed the simple 1-
D calculations and
the macro-scale experimental observations of 1 mV/turn.
Fig. 3 is a diagram illustrating an edge view of several different coil/flux
configurations.
In Fig. 3, a coil 20 is disposed at a flux gap 22 formed by the two magnetic
masses 24 and 26. In
Figs. 3(a) and 3(b), a "steep" flux gradient region is formed in flux gap 22
by virtue of the
similar magnetic poles on each edge of flux gap 22. In Figs. 3(c) and 3(d), a
"shallow" flux
gradient region is formed in flux gap 22 by virtue of the dissimilar magnetic
poles on each edge
of flux gap 22. In Fig. 3(a), coil 20 is disposed in flux gap 22 such that any
vertical motion Z(t)
of mass 26 with respect to mass 24 and coil 20 produces a rapid change in
magnetic flux at coil
20. Similarly, in Fig. 3(b) coil 20 is disposed in flux gap 22 such that any
synchronous vertical
motion Z(t) of both masses 24-26 together with respect to coil 20 produces a
rapid change in
magnetic flux at coil 20. In contrast, in Fig. 3(c) coil 20 is disposed in
flux gap 22 such that any
vertical motion Z(t) of mass 26 with respect to mass 24 and coil 20 produces a
limited change in
magnetic flux at coil 20. Similarly, in Fig. 3(d) coil 20 is disposed in flux
gap 22 such that any
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synchronous horizontal motion Y(t) of both masses 24-26 together with respect
to coil 20
produces a limited change in magnetic flux at coil 20. Clearly, the coil/flux
configurations
illustrated in Figs. 3(a) and 3(b) are preferred and, in particular, the
configuration in Fig. 3(b) is
preferred for implementation of the micro-generator of this invention.
Moreover, additional
magnetic masses may also be added and the present masses reorganized to form
other useful
geometric configurations are well-suited for implementation as alternative
embodiments of the
micro-generator of this invention.
Fig. 4 is a diagram illustrating an edge perspective of an exemplary
embodiment 28 of
the micro-generator of this invention. Micro-generator 28 includes a coil 30
consisting of a
plurality of turns of electrically-conductive material coupled to the coil
terminals 32 and 34. Coil
30 is disposed in the flux gap 36 bounded by the inner surfaces 38 and 40 of
the magnetic masses
42 and 44, respectively. Inner surfaces 38 and 40 are shown as the N-poles of
magnetic masses
42 and 44 but may be either polarity provided that both inner surfaces 38 and
40 have the same
magnetic polarity. Magnetic mass 42 is supported by a plurality of compliant
elements (springs)
exemplified by the compliant element 46. Similarly, magnetic mass 44 is
supported by a
plurality of compliant elements exemplified by the compliant element 48. The
free ends of
compliant elements 46 and 48 are fixed in any useful manner (not shown) with
respect to coil 30,
thereby allowing magnetic masses 42 and 44 to move in the Z(t) direction with
respect to coil 30
in response to external mechanical vibration.
Fig. 5 is a diagram illustrating an edge perspective of an exemplary
embodiment 50 of
the micro-electro-mechanical system (MEMS) power generator system of this
invention. MEMS
power generator 50 includes a plurality of the micro-generators of this
invention, exemplified by
micro-generator 28, with the individual coil terminals interconnected such
that the electrical
power generated by each micro-generator is aggregated at the MEMS power
generator terminals
52 and 54. Preferably, the plurality of micro-generators composing MEMS
generator 50 are
coupled together for fixed exposure to the same ambient vibration.
Fig. 6, comprising Figs. 6(a)-(d), is a diagram illustrating an edge view of
an exemplary
magnet layer fabrication process of this invention. This process begins as
shown in Fig. 6(a) with
a semiconductor wafer 56. The material may be crystalline silicon or any other
useful
semiconductor material. Although the following discussion is limited to the
preparation of a
single magnet layer, practitioners in the art can readily appreciate that many
such magnet layer
elements may be simultaneously fabricated on a single semiconductor wafer in a
single process
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and separated from the wafer in a wafer dicing process well known in the art.
Fig. 6(a) illustrates
the results of the first step in this process, which is the preparation of the
upper surface 58 and
the lower surface 60 for processing in the usual fashion by cleaning and
polishing as necessary.
Fig. 6(b) illustrates the results of the next step of this process, which is
the masking and deep
reactive ion etching (DRIB) of lower surface 60 to define the magnet well 62.
Fig. 6(c) illustrates
the results of the next step of this process, which is the masking and DRIE of
upper surface 58 to
define the coil layer recesses 64. Fig. 6(d) illustrates the results of the
next two steps of this
process, which is the masking and DRIE of upper surface 58 to define the
integral compliant
regions 66 and the bonding posts 68, thereby completing the magnet layer sub-
element 69
substantially as shown. Bonding posts 68 are also shown in Fig. 8 in a wafer
facial view (magnet
well 62 should be demarcated with hidden lines to illustrate the exemplary
process of Fig. 6 and
in solid lines for the exemplary process of Fig. 7). The final thickness of
integral compliant
regions 66 is established to provide the spring constant necessary for the
desired resonant
frequency of the final micro-generator (Fig. 11 below). The open region 71 in
Fig. 8 is etched
away completely to leave magnet well 62 coupled only by compliant regions 66.
The final step
of this magnet layer fabrication process is the disposition of a ferromagnetic
mass 70 into magnet
well 62 of magnet layer sub-element 69 (shown in Fig. 11(c)), which may be
accomplished
immediately following the completion of magnet layer sub-element 69 shown in
Fig. 6(d) or, as
illustrated herein, may be deferred until after the assembly of the micro-
generator magnet layer
and coil layer elements (Fig. 11).
Fig. 7, comprising Figs. 7(a)-(e), is a diagram illustrating an edge view of
an alternative
magnet layer fabrication process of this invention. This process also begins
as shown in Fig. 7(a)
with semiconductor wafer 56. Fig. 7(a) illustrates the results of the first
step in this process,
which is the preparation of upper surface 58 and lower surface 60 for
processing in the usual
fashion by cleaning and polishing as necessary. Fig. 7(b) illustrates the
results of the next step of
this process, which is the masking and DRIE of upper surface 58 to define the
coil layer recesses
64. Fig. 7(c) illustrates the results of the next step of this process, which
is the masking and
DRIE of upper surface 58 to define the magnet well 62. Fig. 7(d) illustrates
the results of the
next two steps of this process, which is the masking and DRIE of upper surface
58 to define the
integral compliant regions 66 and the bonding posts 68, which are also shown
in Fig. 8 in a
wafer facial view (magnet well 62 should be demarcated with hidden lines to
illustrate the
exemplary process of Fig. 6 and in solid lines for the exemplary process of
Fig. 7). The final
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thickness of integral compliant regions 66 is established to provide the
spring constant necessary
for the desired resonant frequency of the final micro-generator (Fig. 12
below).
Fig. 8 shows the open region 71, which may be etched away completely to leave
magnet
well 62 coupled only by compliant regions 66. Fig. 7(e) illustrates the
results of the final step of
__ this process, which is the disposition of ferromagnetic mass 70 into magnet
well 62.
Ferromagnetic mass 70 should include a suitably "hard" ferromagnetic material,
for example,
sputtered CoPtCr having a 40K0e field, and must be disposed with one magnetic
pole bonded to
the bottom of magnet well 62 and the other pole exposed at the top of mass 70,
thereby
completing the magnet layer element 72 substantially as shown.
Fig. 9, comprising Figs. 9(a)-(d), is a diagram illustrating an edge view of
an exemplary
coil layer fabrication process of this invention. This process begins as shown
in Fig. 9(a) with a
semiconductor wafer 74. The material may be crystalline silicon or any other
useful
semiconductor material. Although the following discussion is limited to the
preparation of a
single coil layer, practitioners in the art can readily appreciate that many
such coil elements may
__ be simultaneously fabricated on a single semiconductor wafer in a single
process and separated
from the wafer in a wafer dicing process well known in the art. Fig. 9(a)
illustrates the results of
the first step in this process, which is the preparation of the upper surface
76 and the lower
surface 78 for processing in the usual fashion by cleaning and polishing as
necessary. Fig. 9(b)
illustrates the results of the next step of this process, which is the masking
and DRIE of upper
__ surface 76 to define the coil well 80. Fig. 9(c) illustrates the results of
the next step of this
process, which is the disposition of a conductive coil 82 within coil well 80.
The disposition of
coil 82 may be accomplished using any of several useful techniques well known
in the art, such
as, for example, ion deposition of copper or aluminum conductors in a masked
pattern, or by
bonding a conductive layer (not shown) to the bottom of coil well 80 and
masking and etching
__ the conductive layer to create the desired coil geometry, for example. The
coil may, for example
include 2,500 turns in a radius of 1 mm. Fig. 9(d) illustrates the results of
the final step of this
process, which is the masking and DRIE of either upper surface 76 or lower
surface 78 to define
the bonding post through holes 84 thereby completing the coil layer element 86
substantially as
shown.
Fig. 10 shows the bonding post through holes 84 in a wafer facial view. Fig.
10 also
illustrates the two conductive terminals 88 and 90 disposed to permit
electrical connection to coil
82.
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Fig. 11, comprising Figs. 11(a)-(c), is a diagram illustrating an edge view of
the
fabrication of a first exemplary embodiment 92 of the micro-generator of this
invention, which is
shown in Fig. 11(c). Fig. 11(a) illustrates the results of the first step in
this process, which is the
bonding of a coil layer element 86 to a first magnet layer sub-element 69A at
the bonding
surfaces 94A. Fig. 11(b) illustrates the results of the second step in this
process, which is the
bonding of a second magnet layer sub-element 69B to coil layer element 86 at
the bonding
surfaces 94B and to first magnet layer sub-element 69A at the bonding post
surfaces 96. Note
that sufficient clearance is provided to permit coil 82 to remain mechanically
isolated from
bonding post surfaces 96 except for the mechanical coupling provided by
compliant regions 66.
The final step of this micro-generator fabrication process is the disposition
of ferromagnetic
masses 70A and 70B into magnet well 62 of magnet layer sub-elements 69A and
69B,
respectively, which may instead be accomplished immediately following the
completion of
magnet layer sub-element 69 before beginning the assembly of micro-generator
92.
Fig. 12, comprising Figs. 12(a)-(b), is a diagram illustrating an edge view of
the
fabrication of a second exemplary embodiment 98 of the micro-generator of this
invention,
which is shown in Fig. 12(b). Fig. 12(a) illustrates the results of the first
step in this process,
which is the bonding of a coil layer element 86 to a first magnet layer
element 72A at the
bonding surface 100A. Fig. 12(b) illustrates the results of the second step in
this process, which
is the bonding of a second magnet layer element 72B to coil layer element 86
at the bonding
surfaces 100B and to first magnet layer element 72A at the bonding post
surfaces 102. Note that
sufficient clearance is provided to permit coil 82 to remain mechanically
isolated from bonding
post surfaces 102 except for the mechanical coupling provided by compliant
regions 66.
Based on measurements and calculations, the inventors suggest that the MEMS
power
generator of this invention can provide an output power from 10 to 500 mW/cc
at an output
voltage from 100 mV to 5,000 mV.
Clearly, other embodiments and modifications of this invention may occur
readily to
those of ordinary skill in the art in view of these teachings. Therefore, this
invention is to be
limited only by the following claims, which include all such embodiments and
modifications
when viewed in conjunction with the above specification and accompanying
drawing.
It will be understood that many additional changes in the details, materials,
steps and
arrangement of parts, which have been herein described and illustrated to
explain the nature of
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the invention, may be made by those skilled in the art within the principal 5
and scope of the
invention as expressed in the appended claims.
From the above description of the System and Method for Detecting an Object in
a
Search Space, it is manifest that various techniques may be used for
implementing the concepts
of system 10 without departing from its scope. The described embodiments are
to be considered
in all respects as illustrative and not restrictive. It should also be
understood that system 10 is
not limited to the particular embodiments described herein, but is capable of
many embodiments
without departing from the scope of the claims.
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