BACKGROUND OF THE INVENTION
The field of the invention relates generally to energy
harvesting and, more particularly, to a tunable vibration energy harvester.
Energy harvesting is a process for use in recovering power that
would otherwise be dissipated or lost in a system. For example, known energy
harvesting may be used to obtain energy from light, heat, wind, vibrations, wave
action, water currents, and the like. In many known systems, energy harvested may be
used in conjunction with battery power to provide power to electronic devices.
Sensor assemblies are often used in industrial settings to
monitor the condition of associated machinery and operations thereof. Known sensor
assemblies are often battery-powered. However, labor costs associated with changing
batteries on a regular basis may limit commercial viability of such sensor assemblies,
especially if the sensors are in remote or inaccessible locations. Because of the limited
lifetime of batteries, the limited ability to recycle the batteries, and the cost of frequent
battery change-outs, it is desirable to improve sensor powering.
BRIEF DESCRIPTION OF THE INVENTION
In one embodiment, an energy harvester is provided. The
energy harvester includes, an energy conversion device configured to convert
vibrational energy to electrical energy, a mass coupled to the energy conversion
device, and at least one biasing mechanism coupled to the mass. The biasing
mechanism is selectively adjustable and selectively adjusting the biasing mechanism
adjusts a resonance frequency of the energy conversion device and the mass.
In another embodiment, a system is provided. The system
includes a sensor and an energy harvester. The energy harvester includes an energy
conversion device, a mass coupled to the energy conversion device and at least one
biasing mechanism, and an actuator. The actuator is configured to selectively adjust
the at least one biasing mechanism to selectively adjust a resonance frequency of the
energy conversion device and the mass. The sensor is powered by electrical energy
generated by the energy harvester.
A method of harvesting energy from a device producing
vibrations at a driving frequency is described. The method includes providing energy
harvester including an energy conversion device configured to convert vibrational
energy into electrical energy, a mass coupled to the energy conversion device, and at
least one biasing mechanism coupled to the mass, the biasing mechanism being
selectively adjustable to adjust a resonance frequency of the energy conversion device
and the mass. The method further includes coupling the energy harvester to the device
producing vibrations and adjusting the biasing mechanism such that the resonance
frequency substantially matches the driving frequency of the device producing
vibrations.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram of an exemplary power system;
FIG. 2 is a schematic view of an exemplary energy harvester
that may be used with the power system shown in FIG. 1 ;
FIG. 3 is a cross-sectional view taken along line 3-3 of the
energy harvester shown in FIG. 2;
FIG. 4 is a cross-sectional view of an alternate energy
harvester that may be used with the power system shown in FIG. 1 ; and
FIG. 5 is a perspective view of an alternate energy harvester
that may be used with the power system shown in FIG. 1.
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a block diagram of an exemplary power system 10
that generally includes an energy harvesting device 12 that may be used to provide
power to a load 14. Energy harvester 12 is a generation device that converts various
types of mechanical vibrations into electrical power. For example, energy harvesting
device 12 may use vibrations generated from motors, pumps, turbines, engines and the
like, depending on specific applications.
In the exemplary embodiment, a rectifier 16 converts varying
or alternating current (AC) generated by energy harvesting device 12 into a direct
current (DC) signal. By way of non-limiting example, half-wave, full-wave, or
voltage-doubling rectifiers may be used as well as voltage-multiplying circuits in
general. The rectified power output discharged from rectifier 16 is used to power load
14. Alternatively, an optional energy storage device 18 may provide supplemental
power to load 14 if the power generated by energy harvesting device 12 is insufficient
to power load 14. In one embodiment, energy storage device 18 is, for example, a
Lithium-ion battery and/or a super capacitor.
FIG. 2 is a schematic view of the exemplary power system 10
implemented with an exemplary motor 20, which includes a shaft 21 rotatably
supported by a bearing housing 22. Shaft 21 is coupled to a motor driven system 23
and rotates to power motor driven system 23. Bearing housing 22 of motor 20
typically vibrates to some degree during operation. Power system 10 is housed in a
substantially cylindrical housing 26 attached to bearing housing 22 via any known
means such as mechanical fastener, and/or adhesive, etc. Alternatively, housing 26
may have any shape or be fabricated from any suitable material that enables system 10
to function as described herein.
FIG. 3 is a cross-sectional view of energy harvesting device 12
taken along line 3-3. More specifically, in the exemplary embodiment, energy
harvesting device 12 includes housing 26, an energy conversion device 24, a proof
mass 30, and at least one biasing mechanism 32. In the exemplary embodiment,
energy conversion device 24 is a piezoelectric device 28. In an alternative
embodiment, energy conversion device 24 is an electromagnetic, electrostatic,
magnetostrictive or any other device that enables energy harvesting device 12 to
function as described herein,
In the exemplary embodiment, piezoelectric device 28 is a
cantilever beam 29 that includes a first end 34, a second end 36, a first piezoelectric
layer 38, a second piezoelectric layer 40, and a substrate 42. Piezoelectric device 28
converts vibrational energy to electrical energy when piezoelectric material 38 and 40
is subjected to tension and compression, as is known. Piezoelectric device 28 may be
fabricated from any suitable material such as, for example, lead zirconate titanate
(PZT). In addition, piezoelectric device may include any number of piezoelectric
layers 38 and 40 that enables piezoelectric device 28 to function as described herein.
Further, in an alternative embodiment, piezoelectric device 28 may include a single
piezoelectric layer that may or may not include a substrate.
In the exemplary embodiment, piezoelectric device 28 extends
from a base 44 coupled to housing 26. First end 34 of beam 29 is coupled to base 44
and second end 36 is coupled to mass 30. Alternatively, first end 34 of beam 29 may
be coupled to housing 26 or directly to a device that produces vibrations, such as motor
20. Substrate 42 reinforces first and second piezoelectric layers 38 and 40 and
increases the tension and compression thereon to increase electrical energy generation.
In an alternative embodiment, first and second ends 34 and 36 are each coupled to base
44 and/or housing 26 with mass 30 positioned between ends 34 and 36.
Piezoelectric device 28 and mass 30 have a resonance
frequency corresponding to their oscillatory deflection from a rested state. In the
exemplary embodiment, the resonance frequency of piezoelectric device 28 and mass
30 is mechanically tuned (i.e. adjusted) to substantially match the driving vibration
frequency of motor 20, which is the frequency of the vibrations produced by motor 20
during operation. Matching the resonance frequency to the driving frequency
facilitates maximum oscillatory deflection of device 28 and mass 30, thereby
improving power output.
The design of piezoelectric device 28 may be adjusted or
modified to fit specific applications or devices from which energy will be harvested.
For example, the design of device 28 may be varied to optimize device characteristics
such as resonance frequency tuning range, power output, size, weight and minimum
base acceleration. For example, the length, width, thickness, stiffness and/or mass
distribution of piezoelectric device 28 are variably selected to mechanically tune
device 28 to facilitate optimizing power output. Similarly, the shape, weight, density
and size of mass 30, as well as the location of mass 30, may also be variably selected
to optimize power output. In the exemplary embodiment, piezoelectric device 28 has a
length L between approximately 1 and 3 inches. More particularly, device 28 has a
length L of approximately 2 inches.
In the exemplary embodiment, mass 30 includes a body 50
having a first side 52 and a second side 54. In one exemplary embodiment, mass 30
has a weight that is between approximately 1 and 1200g. However, the design weight
of mass 30 depends on the amount of power required to be produced by piezoelectric
device 28. Thus, the weight of mass 30 may be variably selected. Power generated by
piezoelectric device 28 generally increases as the weight of mass 30 increases and vice
versa. In the exemplary embodiment, mass 30 is fabricated from a dense material that
enables mass 30 to have a relatively small physical size. In the exemplary
embodiment, mass 30 is generally cubic and each side has a length between
approximately 40 and 100 mm. Alternatively, mass 30 may have any other shape that
enables harvesting device 12 to function as described herein. Moreover, harvesting
device 12 may be provided with a more compact design by utilizing one or more
components of harvesting device 12 in mass 30 to provide the weight of mass 30. For
example, an actuator 46, a gearbox and/or a motor (not shown) of actuator 46,
electronics 90 andlor energy storage device 18 may be incorporated into mass 30.
The resonance frequency of piezoelectric device 28 and mass
30 is varied through adjustments of biasing mechanisms 32 and/or actuator 46. In the
exemplary embodiment, biasing mechanisms 32 are non-linear springs such as
preloaded conical springs 60. Alternatively, biasing mechanisms 32 may be any other
device that exhibits a spring constant that changes when the device is compressed, for
example, any mechanical, magnetic, and/or electronic device having such
characteristics. In an alternative embodiment, biasing mechanisms 32 are tapered wire
springs having an increased spring constant when compressed.
In the exemplary embodiment, springs 60 each include a first
end 62 having a first diameter 64 and a second end 66 having a second diameter 68
that is larger than first diameter 64. Spring first ends 62 are each respectively coupled
to first side 52 and to second side 54 of mass 30 such that mass 30 is positioned
between springs 60.
In the exemplary embodiment, actuator 46 includes first
surfaces 70, second surfaces 72, and a drive (not shown). The drive may include a
motor and gearbox (not shown) and be coupled to base 44, incorporated into mass 30,
or positioned anywhere else that enables the drive to actuate actuator 46 as described
herein. First surfaces 70 are coupled to spring second ends 66, and second surfaces 72
are coupled to housing 26. Alternatively, springs 60 may be inverted such that first
ends 62 are coupled to first actuator surfaces 70, and second ends 66 are coupled to
mass 30. The drive actuates actuator 46 to move surfaces 70 and/or 72 away from
housing. Thus, actuator 46 enables selective adjustments of a distance D between first
and second surfaces 70 and 72 resulting in selective adjustment of a compression
distance 74 of springs 60. In an alternative embodiment, actuator 46 may have any
configuration that enables actuator 46 to selectively adjust compression distance 74 as
described herein.
In the exemplary embodiment, energy harvester 12 also
includes a controller 88 comprising electronics 90 such as sensors 92, a processor (not
shown) and a memory 94. Electronics 90 receive and analyze system data and control
operations of harvester 12 such as movement of actuator 46 and resonance frequency
tuning of piezoelectric device 28 and mass 30. In the exemplary embodiment,
electronics 90 are incorporated into mass 30 (FIG. 3) and enable actuation of actuator
46. Alternatively, electronics 90 are coupled to base 44, housing 26 and/or any other
suitable location in energy harvester 12.
In the exemplary embodiment, sensors 92 gather data to enable
electronics 90 to tune the resonance frequency of device 28 and mass 30 to the driving
frequency of motor 20. Sensor 92 positioned on base 44 or housing 26 measures the
driving frequency of motor 20, and sensor 92 positioned in or near mass 30 determines
distance D between actuators 46, compression distances 74, andfor drive motor
revolutions of actuators 46. In an alternative embodiment, sensors 92 are located
anywhere that enables sensors 92 to function as described herein. Additionally, sensor
92 may measure the output voltage, current and/or power of the piezoelectric device
28.
In the exemplary embodiment, sensor 92 transmits a signal
representing sensor measurements to electronics 90. Alternatively, or additionally,
load 14 may include a sensor (not shown) that provides electronics 90 with a signal
representing the driving frequency of motor 20 or other data about motor 20 or load 14.
Data measured by sensors 92 may be used to selectively adjust actuator 46 andlor may
be stored in memory 94. For example, if the measured data indicates harvester 12 is
out of tune with the driving frequency of motor 20, adjustments are made to
substantially match the resonance frequency to the driving frequency. Memory 94
stores a pre-calibrated look-up table of driving frequencies, resonance frequencies, and
any other data that may enable tuning of energy harvester 12. Thus, if harvester 12 is
out of tune, measured data and the look-up table are used to tune energy harvester 12.
Memory 94 may alternatively, or additionally, store a linear or polynomial relationship
correlating between a particular measurement and a resonance frequency of device 28.
FIG. 4 illustrates an exemplary alternative energy harvesting
device 100 that is similar to energy harvesting device 12 (shown in FIG. 3), and
identical reference numbers are used to identify the same components in FIG. 4 as
were used in FIG. 3. Energy harvesting device 100 is similar to energy harvesting
device 12, except device 100 includes an alternative arrangement of actuator 46. In the
exemplary embodiment, actuator 46 is positioned between mass 30 and each biasing
mechanism 32. More particularly, first actuator surfaces 70 are coupled to first side 52
and second side 54 of mass 30, respectively, while second actuator surfaces 72 are
coupled to spring first ends 62, respectively. Spring second ends 66 are coupled to
housing 26. Alternatively, springs 60 may be inverted such that first ends 62 are
coupled to housing 26, and second ends 66 are coupled to second actuator surfaces 72.
Actuator 46 is actuated to selectively adjust distance D between surfaces 70 and/or 72
resulting in selective adjustment of compression distances 74.
FIG. 5 illustrates an exemplary alternative energy harvesting
device 200 that is similar to energy harvesting devices 12 and 100 (shown in FIGS. 3
and 4, respectively), and identical reference numbers are used to identify the same
components in FIG. 5 as were used in FIGS. 3 and 4. Energy harvesting device 200 is
similar to energy harvesting device 12 (shown in FIG. 3), except device 200 includes
an alternative arrangement of mass 30 and actuator 46. More particularly, mass 30
includes opposed first and second portions 232 and 234 positioned between opposed
third and fourth sections 236 and 238. First and second portions 232 and 234 are
coupled to beam second end 36. Third and fourth sections 236 and 238 are coupled to
first and second portions 232 and 234, respectively, and each have respective arms 240
and 242 extending therefrom.
In the alternative exemplary embodiment, actuator 46 is
coupled to a portion of base 44 adjacent to first and second portions 232 and 234. A
pair of platforms 244 and 246 is coupled a top and bottom actuator surface 250 and
252, respectively. Platforms 244 and 246 are moved towards and away from surfaces
250 and 252, respectively, by a motor 254 and gearbox (not shown) of actuator 46. A
pair of guides 258 (one is removed in FIG. 5 for clarity) is positioned on either side of
actuator 46 to support and guide platforms 244 and 246. A spring 60 is coupled
between arm 240 and platform 244 and another spring 60 is coupled between arm 242
and platform 246. Actuator 46 selectively adjusts the distance D between platforms
244 and 246 resulting in selective adjustment of spring compression distances 74.
Thus, the resonance frequency of piezoelectric device 28 and mass 30 is selectively
adjusted. Resulting electrical energy produced by device 28 is provided via connector
256 to rectifier 16.
During operation, system 10 is coupled to a vibration
producing device, such as motor 20. Vibrations generated by motor 20 are converted
into electrical power by energy harvesting device 12, 100 or 200. In the exemplary
embodiment, load 14 is a wireless sensor that is powered by energy harvesting device
12. Wireless sensor 14 may be, for example, a machine condition monitoring system
that measures key indicators such as vibrations, temperatures and pressures of critical
machines, and tracks the information over time to look for abnormalities. In the
exemplary embodiment, wireless sensor 14 is an accelerometer that assesses health,
alignment andlor balance of motor 20 based on captured vibration data. For example,
vibrations generated by motor 20 change with aging of motor 20. The changes may be
detected and transmitted to a remote location by wireless sensor 14 for storage or
further processing, for example, to assess the condition of motor 20 and its need for
maintenance.
As described above, energy harvesting devices 12, 100 and
200 convert vibrations into electrical energy. During operation, base 44 is subjected to
vibration energy causing movement of mass 30 and deflection of piezoelectric beam
28. Deflection of first and second piezoelectric layers 38 and 40 generates AC voltage.
The AC voltage is delivered to rectifier 16 wherein it is converted into DC voltage that
is provided to wireless sensor 14 to power sensor operations.
During operation, energy harvester 12 power output is
optimized by substantially matching (or tuning) the harvester resonance frequency to
the driving frequency of the source vibration. Because many known modem industrial
processes are often variable speed, the resonance frequency of energy harvester 12 is
variably selected to substantially match the frequency of the changing source vibration.
Power is generated more effectively when the resonance frequency of harvester 12
substantially matches the source frequency of motor 20.
In the exemplary embodiment, the resonant frequency of
energy harvester 12 depends on the total spring constant of the system, which is equal
to the sum of the spring constant of piezoelectric beam 28 and of springs 60. While the
spring constant of beam 28 is relatively constant due to design, the spring constant of
springs 60 increases as compression distance 74 is increased. Thus, the resonant
frequency of energy harvester 12 is tuned by adjusting compression distance 74 of
each spring 60. Tuning of energy harvester 12 is facilitated by selectively increasing
or decreasing distance D between actuator surfaces 70 and 72 or platforms 244 and
246, such that compression distances 74 of biasing mechanisms 32 are selectively
varied.
During operation, if harvester 12 is out of tune, electronics 90
automatically adjusts compression distances 74 by actuating actuator 46 based on the
frequency look-up table stored in memory 94. Compression distance 74 is adjusted
based on the frequency look-up table stored in memory 94. More specifically, the
look-up table includes data usable to determine a desired position of actuator surfaces
70 andlor 72 or platforms 244 and 246, and/or a desired compression distance 74.
Based on the measured driving frequency, electronics 90 determines the required
compression distance 74 in the look-up table required to match the driving frequency
and adjusts actuator 46 accordingly. In addition, the look-up table may store any other
data usable to tune harvesting device 12 such as, but not limited to, temperature and
humidity adjustments, aging of the piezoelectric material and/or drive motor
revolutions of actuator 46. Moreover, the look-up table may be automatically updated
to improve system efficiency.
Sensor 92 measures the driving frequency of the vibration
source 20, and electronics 90 determines compression distance 74 that corresponds to
the measured driving frequency based on the look-up table stored in memory 94. The
range of compression distances 74 corresponds to a range of resonance frequencies for
energy harvester 12. Thus, based on the measured driving frequency, actuator 46
adjusts compression distances 74 to substantially match the resonance frequency of
energy harvester 12 with the driving frequency of vibration source 20. As such, energy
output of harvester 12 is facilitated to be maximized. Thus, in the exemplary
embodiment, electronics 90 are configured to automatically tune the resonance
frequency of energy harvester 12 as the vibration source 20 changes.
The exemplary energy harvester described above efficiently
generates power over a wide range of vibration frequencies by automatically tuning the
resonance frequency of the harvester. Such adjustments enable the energy harvester to
be useful in physically small and/or remote locations. In addition, because of the
relatively few moving parts of the system, wear is reduced and the harvester may be
manufactured at a lower cost without the need for high precision and/or consistency, as
compared to known harvesters. For the same reason, mechanical damping is
minimized, which facilitates a higher energy output. Further, by harvesting power
from the environment, sensors can be made self sufficient over their lifetime with
virtually no maintenance. Thus, the exemplary energy harvester described herein can
be built into wireless sensors or systems for maintenance free machine-condition
monitoring. Furthermore, batteries used to power wireless sensors may be reduced in
size or even eliminated, thus reducing maintenance and environmental impact.
This written description uses examples to disclose the
invention, including the best mode, and also to enable any person skilled in the art to
practice the invention, including making and using any devices or systems and
performing any incorporated methods. The patentable scope of the invention is
defined by the claims, and may include other examples that occur to those skilled in
the art. Such other examples are intended to be within the scope of the claims if they
have structural elements that do not differ from the literal language of the claims, or if
they include equivalent structural elements with insubstantial differences from the
literal languages of the claims.
PARTS LIST
power system ............................................................................................ 10
energy harvesting device ........................ .... .......................................... 12
loadlwireless sensor .................................................................................. 14
rectifier .................................................................................................... 16
energy storage device ................................................................................ 18
motor ......................................................................................................... 20
shaft ........................................................................................................... 21
bearing housing ......................................................................................... 22
motor driven system .................................................................................. 23
energy conversion device .......................................................................... 24
housing ...................................................................................................... 26
piezoelectric device ...................................................................................2 8
beam .......................................................................................................... 29
mass ........................................................................................................ ...30
biasing mechanism .................................................................................... 32
beam first end ............................................................................................ 34
beam second end ....................................................................................... 36
first piezoelectric layer .............................................................................. 38
second piezoelectric layer ......................................................................... 40
substrate .................................................................................................... 42
base ........................................................................................................... 44
actuator ..................................................................................................... -46
mass body .................................................................................................. 50
mass first side ............................................................................................ 52
mass second side .......................................................................................5 4
spring ......................................................................................................... 60
spring first end .......................................................................................... 62
spring first diameter .................................................................................. 64
spring second end ...................................................................................... 66
spring second diameter ........................................................................... 68
first actuator surfaces ................................................................................ 70
second actuator surfaces ..........................................................................7. 2
compression distance ............................................................................7..4.
controller ......................... .. ................................................................8. 8
electronics ................................................................................................. 90
sensor ........................................................................................................ 92
memory ..................................................................................................... 94
energy harvesting device ............................. .......... .................................. 100
energy harvesting device ......................................................................... 200
mass first portion ..................................................................................... 232
mass second portion ................................................................................. 234
mass third section ...................................................................................2. 36
mass fourth section ............................................................................2.3..8..
arm .......................................................................................................... 240
arm ......................................................................................................... -242
platform ..................................................................................................2. 44
platform .................................................................................................... 246
top actuator surface ................................................................................. 250
bottom actuator surface ........................................................................... 252
motor ....................................................................................................... 254
connector ................................................................................................. 256
guide ........................................................................................................ 258

We Claims:
1. An energy harvester comprising:
an energy conversion device configured to convert vibrational energy into electrical
energy;
a mass coupled to said energy conversion device; and
at least one biasing mechanism coupled to said mass, said biasing mechanism being
selectively adjustable, wherein selectively adjusting said biasing mechanism adjusts a
resonance frequency of said energy conversion device and said mass.
2. The energy harvester of Claim 1, wherein said biasing mechanism has a
selectively adjustable compression distance, wherein selectively adjusting said compression
distance adjusts said resonance frequency.
3. The energy harvester of Claim 1, wherein said energy conversion device
comprises one of a piezoelectric device, an electromagnetic device, an electrostatic device,
and a magnetostrictive device.
4. The energy harvester of Claim 3, wherein said piezoelectric device further
comprises a first piezoelectric layer, a second piezoelectric layer, and a substrate extending
therebetween.
5. The energy harvester of Claim 1, wherein said at least one biasing mechanism
comprises a non-linear spring.
6. The energy harvester of Claim 1, wherein said at least one biasing mechanism
comprises a conical spring.
7. The energy harvester of Claim 6, wherein said conical spring comprises a first
end having a first diameter and a second end having a second diameter that is larger than said
first diameter, said first end coupled to said mass.
8. The energy harvester of Claim 1, further comprising an actuator configured to
selectively adjust said biasing mechanism.
9. The energy harvester of Claim 8, further comprising a housing, wherein said
actuator is coupled to said housing and to a portion of said at least one biasing mechanism
opposite said mass.
10. The energy harvester of Claim 8, wherein said actuator is coupled to and
positioned between said mass and said at least one biasing mechanism.
1 1. The energy harvester of Claim 8, further comprising a first and second
platform, said first and second platforms movably coupled to opposite sides of said actuator,
a first biasing mechanism coupled between said first platform and said mass and a second
biasing mechanism coupled between said second platform and said mass, wherein said
actuator is configured to selectively adjust a distance between said first and second platforms.
12. The energy harvester of Claim 8, further comprising a sensor configured to
sense at least one of a position of said actuator, a compression distance of said biasing
mechanism, motor revolutions of said actuator, and a driving frequency of an object said
harvesting device is configured to couple to.
13. The energy harvester of Claim 1 1, further comprising a controller comprising
a memory, said controller programmed to control said actuator based on a look-up table of
resonance frequencies stored in said memory.
14. A system comprising:
a sensor; and
an energy harvester comprising an energy conversion device, a mass coupled to said
energy conversion device and at least one biasing mechanism, and an actuator configured to
selectively adjust said at least one biasing mechanism to selectively adjust a resonance
frequency of said energy conversion device and said mass,
wherein said sensor is powered by electrical energy generated by said energy
harvester.
15. The system of Claim 14, wherein said actuator is configured to selectively
adjust a compression distance of said at least one biasing mechanism to selectively adjust said
resonance frequency.
16. The system of Claim 14, wherein said energy conversion device comprises
one of a piezoelectric device, an electromagnetic device, an electrostatic device, and a
magnetostrictive device.
17. The system of Claim 14, wherein said actuator is configured to adjust said at
least one biasing mechanism to mechanically tune said resonance frequency to substantially
match a vibration frequency to maximize said power generated by said energy harvester.
18. The system of Claim 14, wherein said sensor is coupled to a device producing
vibrations and is configured to provide data about said device producing vibrations to a
remote monitoring system.
19. The system of Claim 14, wherein said sensor is configured to monitor the
health of at least one of an engine, a motor, a turbine, and an industrial process.
20. A method of harvesting energy from a device producing vibrations at a driving
frequency, said method comprising:
providing energy harvester including an energy conversion device configured to
convert vibrational energy into electrical energy, a mass coupled to the energy conversion
device, and at least one biasing mechanism coupled to the mass, the biasing mechanism being
selectively adjustable to adjust a resonance frequency of the energy conversion device and
the mass;
coupling the energy harvester to the device producing vibrations; and
adjusting the biasing mechanism such that the resonance frequency substantially
matches the driving frequency of the device producing vibrations.
21. The method of Claim 20, wherein said adjusting the biasing mechanism
comprises adjusting a compression distance of the biasing mechanism.
22. The method of Claim 21, wherein the energy harvester further includes a
controller including a memory, wherein said adjusting the compression distance of the
biasing mechanism comprises adjusting the compression distance of the biasing mechanism
based on a look-up table stored in the memory.