energy harvesting for mems - twin cities - university of minnesota
TRANSCRIPT
ENERGY HARVESTING FOR
MICRO-ELECTROMECHANICAL-SYSTEMS
(MEMS)
GURKAN ERDOGAN
TABLE OF CONTENTS
ABSTRACT (223 words) .......................................................................................................... 2
INTRODUCTION (758 words) .................................................................................................. 3
A CRITICAL LITERATURE REVIEW (1867 words) .................................................................... 6
SUMMARY AND CONCLUSION (682 words) .......................................................................... 13
BIBLIOGRAHY .................................................................................................................... 15
APPENDIX A – DETAILED EXAMINATION OF A PAPER (513 words) ...................................... 16
APPENDIX B – SEARCH AND SELECTION PROCEDURE OF THE PAPERS (245 words) ............ 18
APPENDIX C – CURRICULUM VITAE ................................................................................... 19
APPENDIX D – UNIVERSITY TRANSCRIPT .......................................................................... 20
APPENDIX E – ORIGINAL DESCRIPTION OF THE TOPIC ...................................................... 21
2
ABSTRACT
Sensors that can be used in remote or not easily accessible places are becoming an
attractive solution in a wide variety of applications such as habitat or structural
monitoring. Advances in low power VLSI (Very Large Scale Integration) design and
CMOS (Complementary Metal Oxide Semiconductor) fabrication have considerably
reduced power requirements of these sensors. However, one aspect of the approach –
how to wirelessly generate power – tends to cancel out the “low power” advantage. In
addition, the limitations in providing power with batteries and distance constraints in
passive wireless strategies have led to a growing interest in “energy harvesting”.
“Energy harvesting” is a technology that converts the excess energy available in an
environment into usable energy for low power electronics. Many ambient energy sources
have been considered for this purpose such as incident light, vibration, electromagnetism,
radio frequency (RF), human body functions, temperature gradient etc. However, each of
these energy sources has its own drawbacks. For example, although the solar cells offer
excellent power supply in direct sun light, they are inadequate in dim office lighting. On
the other hand, the circuit design for transmitting the power harvested from low level
vibrations is another challenging problem.
In the critical literature review, different energy sources and harvesting techniques for
powering MEMS sensors will be discussed briefly. Vibration-based energy harvesting
techniques will be examined in detail.
3
INTRODUCTION
Energy harvesting, also known as “Energy Scavenging”, “Parasitic Energy”, or “Micro-
Generators” in the literature, is a process performed by a conversion mechanism for
generating electric power from available ambient energy sources. Incident light, thermal
gradients, machine vibrations and human body functions are the well known examples of
ambient energy sources receiving the attention of many researchers. Since energy
harvesting systems offer maintenance-free, long-lasting, green power supply for many
portable, low-powered electronic devices, they are likely to become an essential part of
power management systems.
Figure (1) Wireless Self-powered Sensor Nodes
The growing interest in the field of energy harvesting systems is also due to great
developments in related technologies such as micro-electromechanical-system (MEMS)
technology, wireless sensor network (WSN) technology, very large scale integration
(VLSI) design technology, and complementary metal oxide semiconductor (CMOS)
fabrication technology. Sensors emerge as a promising application of energy harvesting
techniques where these state of the art technologies work together as shown in figure (1).
While advances in micro fabrication techniques have allowed the development of various
MEMS sensors that integrate intelligent electronic control systems with a mechanical
system on the micro scale, VLSI design and CMOS fabrication techniques have reduced
power requirements of the sensors to the range of tens to hundreds microwatts. Such low
power dissipation opens up the possibility of powering the sensors by scavenging
ambient energy from the environment, eliminating the need for batteries and extending
the lifetimes indefinitely [1]. In addition, WSN consisting of large numbers of sensor
nodes capable of wireless communication makes it possible to locate sensor nodes in
remote and sometimes unrecoverable locations. With the development of WSN, long-
4
lasting wireless power supplies have become a must in applications since it is impractical
to use and replace batteries, even long-lived types. The labor needed and other costs
associated with changing hundreds of batteries not only make systems more expensive,
but also inefficient. Furthermore, since the size of the sensor nodes is also critical, nodes
not bigger than a dime are required in many applications where batteries might be too
bulky.
In table (1), some battery types and most applicable energy conversion mechanisms are
compared with respect to their long term and short term power densities. Power density,
meaning the amount of average energy generated per unit time and volume, is the most
convenient and widely used criterion in the literature.
Table (1) Comparison of Energy Sources [1]
According to this table, batteries are reasonable for one year applications, whereas energy
harvesters are required for long lifetime applications. In addition, if we ignore the direct
sun light case which is highly ambient dependent, especially “piezoelectric” and “shoe
insert” mechanisms stand out as the main vibration energy conversion mechanisms.
In figure (2), components of a vibration energy harvesting system are depicted. This flow
chart can be generalized for all energy harvesting systems in which an energy source, a
conversion device, a conditioning circuit and an electric load are the main components of
the general energy harvesting system.
5
Figure (2) Vibration Energy Harvesting System Components
The general system basically aims to accomplish five consecutive tasks:
• Collecting the maximum energy from the energy source
• Converting the ambient energy into electric energy efficiently
• Rectifying and storing the maximum amount of electric energy
• Regulating the output voltage level depending on the application
• Transmitting the electric energy to the load when it is required
Constructing mathematical models and manufacturing prototypes in order to estimate or
ameliorate the efficiency and the performance of an energy conversion mechanism
constitute the major areas of research. Many energy harvesting mechanisms are at their
very early stage of being prototyped and more efficient systems can be obtained in the
future by optimizing the tasks listed above.
Availability of the ambient sources, the power densities of the converters, the duty cycles
and the power needs of the electric loads, however, are the primary limitations of the
energy harvesting systems. For example, solar cells can generate excellent power
densities in direct sun light; but they need to be optimized for conditions of dim light or
no light at all. Thermoelectric energy converters need large energy gradients to generate
substantial power. Power delivery and user comfort are critical while generating power
by means of body functions such as breathing, blood pressure, walking etc. Since there
are abundant and continuous vibration sources such as machinery, wave, and wind
vibrations, vibration energy converters seem to be the most promising mechanism thus
far, and will be examined in detail in the next section.
6
A CRITICAL LITERATURE REVIEW
Energy harvesting from a vibration source for low power electronic devices and sensors
is an appealing idea, since there are various kinds of vibration sources around ranging
from the wind and sea waves to human body motion and vibrating machinery in the
industry. Vibration sources are usually preferable to incident light or thermal gradient
energy sources requiring an appropriate operating time and running condition. Therefore,
many research programs focusing specifically on “vibration to electric energy converters”
have been conducted for various medical, industrial and military applications for more
than a decade.
Despite the large variety of prototypes designed for this purpose so far, the technology
behind these conversion mechanisms is mainly based on three well-known effects in
physics, namely the electrostatic, electromagnetic and piezoelectric effects. In brief,
electrostatic, electromagnetic and piezoelectric designs require a variable capacitor, a
magnet and a piezoelectric material respectively inducing a voltage on plates, in a coil
and between the electrodes as they oscillate. However, the design of an energy converter,
especially in microscale, becomes a little more sophisticated and therefore attractive for
the researchers, when the system emerges as a vibration energy dissipation problem
needing to be examined for various aspects to achieve a maximum power density and
efficiency. While some of the reported generators have already been fabricated using
MEMS techniques, others have been made on a mesoscale with the intention of later
miniaturizing the devices using MEMS [2].
Williams et al. (1995) [1] introduced a generic model for estimating the power that can
be generated in a microscale device. In this model, any electric component in which the
energy conversion takes place is considered as an energy dissipation element (other than
the inherent mechanical dissipation element) of the mechanical system as depicted in
figure (3). The vibration source here is assumed to be infinitely large with respect to the
system so that it is not affected by the motion of the conversion system.
(1)
7
An electromagnetic micro-generator with dimensions of around 5x5x1mm and a
deflection of 50µm is analyzed and assuming a viscous damping model as given in
equation (1), power generations of 1µW and 100µW are estimated from vibration sources
at a frequency of 70Hz and 330Hz, respectively.
Figure (3) Generic Model for a Vibration Energy Converter
In order to generate power, the relative motion of the mass, the voltage, the current and
the damping force induce one another in the given sequence. One important result of this
process is that the damping force changing with the current depends on the load
resistance (RL) accordingly.
(2)
(3)
The generated power (P) is calculated as the rate of work done by the electrically induced
damping force as described in equation (2) and consequently its magnitude is obtained as
given in equation (3). The magnitude of the power as a function of the excitation
frequency is also depicted in figure (3) for various damping factors. It is obvious that the
maximum power generation is possible when the total damping factor (ζ) is minimal and
the excitation frequency (ω) matches the undamped frequencies (ωn) of the system.
However, in case of a distributed frequency spectrum of the source, large damping
factors are desired since it helps the converter harvest more energy from a broad band.
8
Mitcheson et al. (2004) [2], classified the vibration-driven micro-generators reported in
the literature so far based on three fundamental architectures, namely the velocity-
damped resonant generators (VDRG), coulomb-damped resonant generators (CDRG),
and coulomb-force parametric generator, for establishing a unified analytical framework
for such devices and providing a methodology for designing optimized generators for
particular applications.
First of all, they adapted the deflection limit of the proof mass, a key constrained in a
MEMS application, to the general formulation.
Roundy et al. [2] analyze the design parameters of electrostatic and piezoelectric
converters, and then fabricate and test their prototypes shown in figure (4).
Figure (4) Piezoelectric (on the left) and Capacitive (on the right) Converter Prototypes
The mathematical model introduced by Williams et al. is modified for each mechanism
by substituting the system specific design parameters. The estimated powers of the
optimized converters are given in table (3) where a vibration source with a fundamental
frequency of 100Hz and an acceleration magnitude of 2.25m/s2 is employed. On the
experimental side, the piezoelectric prototype without an optimum design is reported to
generate an average power of 60 µW, however no comparable output power is stated for
the electrostatic converter prototype.
9
Table (2) Estimated Powers with an Optimum Design
Three types of electrostatic conversion mechanism topologies, namely (a) in-plane
overlap, (b) in-plane gap closing, and (c) out-of-plane gap closing as depicted in figure
(5), are also compared. The dark areas are fixed to the substrates, while the light areas are
free to move in the arrow directions. Designs allowing the light areas move parallel and
vertical to the substrate’s surface in order to create a change in capacitance are called “in-
plane” and “out-of-plane”, respectively. In addition, the terms “overlap” and “gap
closing” are used to indicate area and distance changes in the capacitor, respectively.
Since the design (a) had stability problems and the design (c) suffered surface adhesion
problems design (b) is chosen as the most convenient topology, despite its extra
mechanical stops.
Figure (5) (a) in-plane overlap, (b) in-plane gap closing and (c) out-of-plane gap closing
Umeda et al. [3] first studied a piezoelectric converter which transforms mechanical
impact energy to electric energy. The efficiency of the system with respect to the input
energy and the load resistance RL were discussed. A thorough examination of this work
can be found in Appendix A.
Umeda et al. [4], next study energy storage characteristics of the same system examined
in [3]. The load resistance in the first work is substituted by a bridge-rectifier and a
10
capacitor for storing electric energy. The efficiency and the amount of energy stored in
the capacitor are examined with respect to the capacity and the initial voltage of the
capacitor while the initial potential energy of the ball is fixed.
In the case where the ball bounced only once, the energy conversion efficiency is defined
as the ratio between the stored energy in the capacitor and the initial potential energy of
the ball. They observed that a capacitor having an optimum capacitance stored a great
portion of the input energy since it continues to be charged until the end of the plate
oscillations and, as a result, achieved a maximum efficiency of 7%. However, efficiencies
are low and the stored energy amounts are small for the higher capacitances due to
having the same electric charge, but the lower voltage levels. That is the case for lower
capacitances as well, due to both low electric charges and voltages. It is also observed
that the efficiency of the converter increases and the stored charge amount decreases with
the increasing initial capacitor voltage and after a certain voltage level, the efficiencies
depend little on the capacitance.
In the case in which the ball is allowed to bounce repeatedly until it stops, the energy
stored by a single impact is replaced with the total energy by multiple impacts in the
efficiency expression. The other considerations are exactly the same as the ones stated in
the single impact case only if the multiple impacts case is considered as an accumulation
of the energy generated by a sequence of single impact cases. A maximum efficiency of
35%, being over three times that of a solar cell, is achieved under the multiple impacts
and high initial voltage conditions. However, it is mentioned that in most practical uses
the electrical charge is more useful than the high efficiencies reached by means of high
initial voltages.
Starner [5] notes the possible energy harvesting locations around the human body and
hence a great interest in wearable power supplies rapidly began to grow following his
survey. The amount of power generated from a number of human activities ranging from
body heat and exhalation to walking and typewriting are estimated for an average person
by using some fundamental laws of physics and were given in table (3). Although the
estimations highly depend on the constitution of a person and the activity being
11
performed, they are promising since a small percentage of them can power a
microprocessor.
Table (3) Power from Body Driven Sources
Approximately 67W of power is calculated from the walking of an average man which is
relatively a large value among the other body functions. The question, however, is how
this power can be recovered without adding a disagreeable load on the user. Piezoelectric
materials and rotary generators are proposed as conversion mechanisms. It is estimated
that about 5W of power from a piezoelectric shoe insert application and 8.4W of power
from a rotary generator application can be achieved. Since the efficiencies are obtained
by means of some crude assumptions and comparisons, the estimations seem somewhat
optimistic when they are compared with the other results in the literature.
Kymissis et al. [6] study three different prototypes as in figure (6) that can be built into a
shoe to harvest excess energy and generate electrical power parasitically while walking.
Stave multilayer PVDF foil is one way of parasitically tapping energy to harness the
bending of the sole, which is attempted in the first device. Uniform strip PZT is another
promising mode of harnessing parasitic power in shoes to exploit the high pressure
exerted in a heel strike. Rotary magnetic generator is the last system for extracting power
from foot pressure by adapting a standard electromagnetic generator.
Figure (6) Prototypes for Harvest Energy While Walking
12
The piezoelectric generators are terminated with a 250KΩ load resistance which is
approximately equal to the equivalent source resistance at the excitation frequencies,
hence yielded maximum efficiency. A peak power of 20mW for the PVDF stave and
80mW for the PZT unimorph were achieved. Because of the slow excitation rate, i.e.
normal gait rate of an average person, the average powers were considerably lower; the
PVDF stave produced about 1mW in average, while the unimorph did about twice that
value. In contrast, the shoe mounted magnetic generator terminated with a 10Ω generated
230mW of power in average, but it was far less applicable because of its bulky design.
The reported results for piezoelectric materials here are about three orders less than the
powers estimated by Starner. This discrepancy is mainly due to the difference between
the deflections assumed in theory and those that can be achieved by the systems in
practice, aiming not to interfere greatly with one’s gait.
Figure (7) Power Circuit Design
Piezoelectric systems are used together to power an RFID tag which has immediate
applications in active environments, enabling the user to transmit their identity. A circuit
as in figure (7), which has later found use in the work of several other researchers, was
designed for rectifying, accumulating (6.5>V>12.6), and regulating (5V) the generated
voltage.
13
SUMMARY AND CONCLUSION
Energy harvesting from ambient energy sources for MEMS sensors and low-power
electronic devices is an active research topic with growing application areas such as
wireless sensor networks and wearable devices. As the power consumptions of the
electronic devices are decreased by the advancements in micro fabrication techniques,
various energy sources including incident light, thermal gradient, human body functions
and vibrating industrial machinery which are available in the environment have aroused
the interest of many researchers as ambient energy sources convertible into electric
energy. However, ambient vibrations stand out as a promising and convenient energy
source for many applications among others, since they are usually available continuously
and abundantly in the surroundings of the energy harvesting systems.
Vibration conversion mechanisms are mainly based on three physical effects, namely
electrostatic, electromagnetic, and piezoelectric effects. Inducing voltage from a relative
motion, which is a common feature of these effects, appears to be a vital phenomenon in
the conversion process and is made use of in the development of a variety of prototypes
examined in literature.
The conversion mechanism is described by a linear model consisting of a damped spring
– mass system coupled with an oscillating platform. The proof mass creates a relative
motion with respect to the vibrating platform, while the spring stores and discharges
potential energy in the vibrating system. Since energy conversion can be considered as a
way of dissipating energy, the electrical component where energy conversion
phenomenon takes place can be modeled as a damper other than the inherent damping
element of the vibrating system. The viscous damping model gives satisfactory results in
many applications in which damping force is directly proportional to the relative velocity
of the proof mass. Consequently, the amount of generated power can be calculated from
the rate of work done by the electrically induced damping force on the proof mass.
The power expression obtained from the previous analysis contains the fundamental
design parameters including proof mass, electrically induced and total viscous damping
factors, amplitude of the source acceleration and the excitation frequency. With the
appropriate selection of these parameters maximum energy transformation efficiency
14
should be achieved. However, when microscale energy converters are aimed, the size of
the system becomes a primary constraint for reaching large amounts of power. This is
mainly because a large amount of power means large deflection which is available in
resonance condition and limited by the size. If most of the energy is available in the low
frequency bands of the source, the system requires a bigger proof mass in order to be in
resonance, which is also limited by the size. On the other hand, the efficiency of the
system depends highly on the electrically induced damping factor of the system
controlled by the load resistance. A very low damping factor increases the output power
of the system, but decreases the selectivity of the converter meaning that the converter
can only harvest energy from a very narrow band in the vicinity of the resonance
frequency.
Many prototypes are being fabricated and tested, some of which have already been in
microscale, while others have been in mesoscale and are intended to be miniaturized
later. Of the three types of vibration to electrical energy conversion mechanisms,
electrostatic and piezoelectric converters appear to be more suitable for microscale
implementations, because an electromagnetic generator requires a neat design for that
purpose despite its relatively high power density.
The generated powers are generally satisfactory and sufficient to power a MEMS sensor
or a microprocessor. However, power management occurs to be an issue for researchers
because of the duty cycles and regulated voltage needs of these low-power devices.
Storing the harvested energy in a capacitor or a battery might be an effective solution for
some applications in order to accord the availability times of the sources and running
periods of the devices. There is a vast amount of work done in literature on this issue,
which is mostly studied by the researchers specialized in electronics. However, only an
overview of the circuit design could be given in this literature review, since the topic is
out of the author’s scope.
15
BIBLIOGRAPHY
1. C.B. Williams, R.B. Yates, “Analysis of a Micro-Electric Generator for Micro-
Systems”, Proceedings of the Transducers 95/Eurosensors IX (1995) 341-344
2. S. Roundy, P.K. Wright, J. Rabaey, “A study of low level vibrations as a power
source for wireless sensor nodes”, Computer Communications, v 26, n 11, Jul 1,
2003, p 1131-1144
3. M. Umeda, K. Nakamura, S. Ueha, “Analysis of the Transformation of
Mechanical Impact Energy to electric Energy Using Piezoelectric Vibrator”,
Japanese Journal of Applied Physics, Part 1: Regular Papers & Short Notes &
Review Papers, v 35, n 5B, May, 1996, p 3267-3273
4. M. Umeda, K. Nakamura, S. Ueha, “Energy storage characteristics of a piezo-
generator using impact induced vibration”, Japanese Journal of Applied Physics,
Part 1: Regular Papers & Short Notes & Review Papers, v 36, n 5B, May, 1997, p
3146-3151
5. T. Starner, “Human Powered Wearable Computing” IBM Systems Journal 35 (3)
(1996) 618-629
6. J. Kymissis, C. Kendall, J. Paradiso, N. Gershenfeld, “Parasitic Power Harvesting
in Shoes”, 2nd IEEE International Conference on Wearable Computing pp 132-7
16
APPENDIX A – A DETAILED EXAMINATION OF [4]
[3] Umeda et al. propose a conversion mechanism which transforms mechanical impact
energy into electrical energy. In their experimental setup, an impact force acting on the
center of a circular plate with a piezoelectric material underneath is created by the free
falling of a steel ball from a certain height as depicted in figure (8).
Figure (8) Experimental Setup
The phenomenon is investigated by separating the action into two sequential time
periods; the first one starting when the ball hits the center of the plate and continuing
until the moment the ball bounces up and leaves the plate and the second one starting
when the ball leaves the plate and continuing until the vibration of the plate is decayed to
zero. In addition, it is assumed that there were two distinct mechanical systems: one in
the first period in which the ball and the plate are adhered to each other, and so they are
oscillating together, and the other one in the second period in which the plate is
oscillating by itself.
The equivalent circuit model of the systems given in figure (9) is constructed by means of
variable circuit elements maintaining the continuity between two time periods. Two
critical assumptions are made at this point; one is that the system is operated in the linear
region meaning the impact force is not too big to create large deflections causing
nonlinearity and the other one is that only the first bending mode is dominating the
motion in both cases, so the effects of other modes can be ignored. These assumptions
can be violated if we let the ball fall from a relatively high point or strike a point on the
plate other than its center.
17
Figure (9) Equivalent Circuit Model
After the circuit parameters are estimated from the measured admittance characteristics
of the systems, the output voltage is solved from the constructed equivalent model for an
initial potential energy of the ball. The output voltage is also measured, and then
compared with the simulated output voltage in order to verify the equivalent circuit
accuracy. This validated model is employed to examine the transformation efficiency.
Transformation efficiency is defined as the ratio between the dissipated energy in the
load resistance and the input energy, i.e. the initial potential energy of the steel ball.
Depending on the efficiencies calculated for various initial potential energies, it is
observed that an increase in the potential energy of the ball would decrease the
transformation efficiency. The reason for this phenomenon is not analyzed deeply and is
guessed as a result of nonlinear effects. From the energy budget of the system it is seen
that a significant amount of energy was spent for bouncing of the ball and is also
concluded that the generated energy would be larger if the steel ball did not bounce off
after an impact but rather vibrated with the plate. A maximum efficiency of 52% was
simulated for this case. Finally, effects of the piezoelectric vibrator are examined briefly
and it is stated that the efficiency increased as the quality factor, Q, and coupling
coefficient, k2, increased, and the dielectric loss, tan(δ), decreased.
18
APPENDIX B – SEARCH AND SELECTION PROCEDURE
OF THE PAPERS
Compendex®/Engineering Index program available in the university library website was
used to carry out a literature survey. General keywords associated with the topic were
searched as a first attempt, including “energy”, “source”, “harvesting”, “scavenging”,
“micro-generator”, “parasitic”, “electric” and “conversion”. However, a vast amount of
published works on various energy sources, conversion mechanisms and power circuits
were obtained. Therefore, specific terms such as “vibration”, “piezoelectric”,
“electrostatic”, “electromagnetic”, “MEMS”, and “sensor” were employed for reaching
distinctive journal papers and conference proceedings that focus on energy conversion
mechanisms utilizing ambient vibrations as an energy source. A reasonable number of
papers were obtained through this iterative search process and the abstracts of papers
were reviewed carefully. The full texts of the most fundamental and interesting works
were supplied from library resources or internet.
The papers examined in this literature review were selected according to three criteria.
First, the sophisticated studies with specific application areas were eliminated and more
fundamental works were preferred for maintaining a basic understanding of the topic.
Consequently, those papers appeared to be the most frequently cited works in literature at
the same time. Secondly, after drawing the outline of this review work, the ones that were
highly related to the context were preferred. In case of a serial work of authors such as [3]
and [4] of Umeda et al., both were tried to be covered and included in this review work.
Lastly, a balanced presentation of experimental and analytical works in literature was
sought.
19
APPENDIX C – CURRICULUM VITAE
EDUCATION
2000 – 2003 Ph.D. ITU*, Construction and Manufacturing Program (not finished)
1998 – 2000 M.Sc. ITU, Theory of Machines and Control Program
1994 – 1998 B.S. ITU, System Dynamics and Control Program
(*) ITU stands for Istanbul Technical University, Turkey
PUBLICATION
M. Gurgoze, G. Erdogan, S. Inceoglu, “Bending Vibrations of Beams Coupled by a Double
Spring – Mass System”, Journal of Sound and Vibration (2001) 243(2), 361-369
EMPLOYMENT
2000 – 2003 Full-time Research and Development Engineer in Arcelik**
1999 – 2000 Part-time Graduate Student Team Member in Arcelik
(**) Arcelik AS (Leading Home Appliance Company in Turkey, 7th in Europe), R&D Department, Vibration and Acoustics Lab.
COMPLETED PROJECTS
[1] Vibro-Acoustic Design of Exhaust Pipes in Hermetic Refrigerator Compressors
[2] Vibration Path Analysis of Dishwasher Motors
[3] Measurement of the Mechanical Properties of the Visco-Elastic Damping Materials
[4] Subjective Evaluation of Dishwasher Noise with Sound Quality Metrics and Jury Test
20
APPENDIX D – UNIVERSITY TRANSCRIPT
University of Minnesota Unofficial Transcript
Name : Erdogan, Gurkan
Student ID : 3441668
Birth date : 08-16
Print Date : 03-18-2005
University of Minnesota, Twin Cities
__________________________________________________________________________
MOST RECENT PROGRAMS
Institution : University of Minnesota, Twin Cities
Program : Graduate School
Plan : Mechanical Engr Ph D Major
Degree Sought: Doctor of Philosophy
__________________________________________________________________________
- - - - - Beginning of Graduate Record - - - - -
Spring Semester 2005
University of Minnesota, Twin Cities
Graduate School
Mechanical Engr Ph D Major
Attempted Earned Points
AEM 8442 Nav. and Guidance Sys. 3.00
EE 5141 Microsystem Technology 4.00
GRAD 5102 Prep Univ Tchg NN Eng Spkrs 2.00
TERM GPA : 0.000 TERM TOTALS : 9.00 0.00 0.000
University of Minnesota Summary Information
Graduate Career Totals
Attempted Earned Points
UMN GPA : 0.000 UMN TOTALS : 9.00 0.00 0.000
Transferred Courses
Engineering Mathematics 3.00 BA
Advanced System Dynamics and Control 3.00 AA
Mechanics of Multi Body Systems 2.00 AA
Industrial Applications of Fuzzy Logic 3.00 AA
Intelligent Systems and Software Computing 3.00 BA
Applied Numerical Methods 3.00 AA
Nonlinear Vibrations 2.00 BA
Finite Element Method 3.00 BA
Nonlinear Analysis an Control 2.00 BA
21
APPENDIX E – ORIGINAL DESCRIPTION OF THE TOPIC
[1] The development of micro-electromechanical-systems has highlighted a wide range of
applications for miniature sensors and actuators. This has made it possible to implant
micro sensors and actuators into a host of different structures for applications such as
medical implants and embedded sensors in buildings and bridges.
In many applications, the microsystem must be completely embedded in the structure,
with no physical connection to the outside world. The problem with this is that a remote
device has to have its own power supply. The conventional solution is to use batteries,
but batteries can be undesirable for many reasons: they tend to be quite bulky, contain a
finite amount of energy, have a limited shelf life, and contain chemicals that could cause
a hazard. A promising alternative to batteries is miniature self-contained renewable
power supplies.
Renewable power supplies convert energy from an existing source within their
environment into electrical energy. The source of energy available will depend on the
application. Some possible energy sources are:
• Light energy – from ambient light source such as sunlight
• Thermal energy – miniature thermoelectric generators that generate electricity
when placed across a temperature gradient.
• Volume flow – flow of liquids or gases.
• Mechanical energy – energy from movement and vibration
Of these sensors, light and thermal energy have already been exploited for use in micro
power supplies. However there are many applications where there is insufficient light or
thermal energy, and so other sources of energy should be considered. Therefore, we
propose a new power supply that generates electricity from mechanical energy. This is
intended for use in vibrating structure.