Note: Descriptions are shown in the official language in which they were submitted.
CA 02715129 2011-12-16
1
CA 2,715,129 125-28 CA
ENERGY HARVESTING FROM ROADS AND AIRPORT RUNWAYS
FIELD OF THE INVENTION
The present invention relates to an apparatus, system and method for power
harvesting
from roads, highways, railways and airport runways using piezoelectric
generators.
BACKGROUND OF THE INVENTION
Piezoelectricity is the ability of certain crystalline materials to develop an
electrical
charge proportional to an applied mechanical stress. The converse effect can
also be seen in
these materials where strain is developed proportional to an applied
electrical field. It was
originally discovered by the Curie's in the 1880's. Today, piezoelectric
materials for industrial
applications are lead based ceramics available in a wide range of properties.
Piezoelectric
materials are the most well known active material typically used for
transducers as well as in
adaptive structures.
Virgin ceramic materials must be first poled to utilize their complete
piezoelectric effect.
Poling consists of applying a high electrical field to the material. During
the poling process the
crystal dipoles in the material are aligned with the applied electrical field
and the material
expands in the direction of the electrical field. By applying a field in the
opposite direction, strain
of opposite sign is observed. If the magnitude of this opposite field is
increased, the material first
depoles and finally repoles.
CA 02715129 2010-08-04
WO 2009/098676 PCT/IL2009/000075
2
Poled piezoelectric material is considered transversely isotropic, i.e.: one
plane is isotropic while the out-of-plane direction has different properties.
The
standard coordinate convention adopted by the IEEE [IEEE Standard on
Piezoelectricity, 176 - 1978] assigns the 1-2 plane as the plane of symmetry
and
the 3-direction as the-out of-plane poling direction. For a small applied
electrical
field, the response of the piezoelectric ceramic can be modeled by the
following
linear piezoelectric constitutive [Jaffe, B., Cook Jr., W.R., and H. Jaffe,
1971,
"Piezoelectric Ceramics", Academic Press] expressed in engineering matrix
notation as:
S sE (d)T T
1D = d T E (1)
where D - electrical displacement, S - strain, E - electric field, T - stress,
6T -
constant stress (unclamped) dielectric, d - induced strain constant, 5E -
constant
field compliance.
Mechanical compression or tension on a poled piezoelectric ceramic
element changes the dipole moment, creating a voltage. Compression along the
direction of polarization, or tension perpendicular to the direction of
polarization,
generates voltage of the same polarity as the poling voltage. Tension along
the
direction of polarization, or compression perpendicular to the direction of
polarization, generates a voltage with polarity opposite that of the poling
voltage.
These actions are generator actions - the ceramic element converts the
mechanical
energy of compression or tension into electrical energy. This behavior is used
in
fuel-igniting devices, solid state batteries, force-sensing devices, and other
products. Values for compressive stress and the voltage (or field strength)
generated by applying stress to a piezoelectric ceramic element are linearly
CA 02715129 2010-08-04
WO 2009/098676 PCT/IL2009/000075
3
proportional up to a material-specific stress. The same is true for applied
voltage
and generated strain.
If a voltage of the same polarity as the poling voltage is applied to a
ceramic element, in the direction of the poling voltage, the element will
lengthen
and its diameter will become smaller. If a voltage of polarity opposite that
of the
poling voltage is applied, the element will become shorter and broader. If an
alternating voltage is applied, the element will lengthen and shorten
cyclically, at
the frequency of the applied voltage. This is motor action - electrical energy
is
converted into mechanical energy. The principle is adapted to piezoelectric
motors, sound or ultrasound generating devices, and many other products.
Figure 1a. Schematically depicts the generator action of a piezoelectric
element as known in the art.
The piezoelectric material has a considerable impact on the achievable
performance of the transducer. Commonly used piezoelectric materials are based
on lead zirconate titanate (PZT) ceramics.
Assuming that a PZT element is directly used as a transducer, the
significant material parameters can be outlined to provide the material figure
of
merit. There are many factors that influence the selection of the PZT
composition.
The constitutive equations for a linear piezoelectric material under low
stress (T)
levels can be written as
x = SDT + gD (2)
and
E=-gT+/3YD (3)
where x is the strain, D is the electric displacement, E is the electric
field, s is the
elastic compliance, and g is the piezoelectric voltage coefficient given as
CA 02715129 2010-08-04
WO 2009/098676 PCT/IL2009/000075
4
d
g 6 X (4)
Here, d is the piezoelectric constant and E is the dielectric constant. The
constant (3 in eq. (3) is the dielectric susceptibility, and is equal to the
inverse
dielectric permittivity tensor component. Under an applied force F = T = A,
(where
A is the area), the open circuit output voltage (U) of the ceramic can be
computed
from eq. (3), and is given as
U=Et=-gTt=- Ft
(5)
where t is the thickness of the ceramic. The charge (Q) generated on the
piezoelectric ceramic can be determined from eq. (2) and is given as
E US sX
D~=X= t
(6)
or
Q/U = s.Ys A =
t C
(7)
where C is the capacitance of the material. The above relationship shows that
at
low frequencies a piezoelectric plate can be assumed to behave like a parallel
plate
capacitor. Hence, the electric power available under the cyclic excitation is
given
by eq. (8) as follows:
P=1 dz F21JP=1CV2f=1(dg)T2Vf (8)
2 s sX A 2 2
where V = A x t is volume of the piezoelectric generator
Under certain experimental conditions, for a given material of fixed area
and thickness, the electrical power is dependent on the d2/Ex ratio of the
material.
A material with a high d2/Ex ratio will generate high power when the
piezoelectric ceramic is directly employed for harvesting energy.
CA 02715129 2010-08-04
WO 2009/098676 PCT/IL2009/000075
Figure lb(i) depicts the construction of a single element transducer and
figure lb(ii) depicts a multi-layered transducer.
In a multilayered construction of figure lb(ii), the same force F is applied
to all the layers. However, due to the smaller thickness of each layer, the
voltage
5 developed in each of the layer, (which is the voltage developed on the
entire
structure, as the layers are electrically connected in parallel) is lower.
Electrically
connecting all the layer in parallel increases the capacitance of the
structure.
Figure lb(iii) depicts a preferred embodiment of a multilayer PZT
generator wherein the polling directions of consecutive layers are reversed.
In this
embodiment, a common electrode is used between two, oppositely oriented
layers.
The review article "Advances In Energy Harvesting Using Low Profile
Piezoelectric Transducers"; by Shashank Priya; published in J Electroceram
(2007) 19:165-182; provides a comprehensive coverage of the recent
developments in the area of piezoelectric energy harvesting using low profile
transducers and provides the results for various energy harvesting prototype
devices. A brief discussion is also presented on the selection of the
piezoelectric
materials for on and off resonance applications.
The paper "On Low-Frequency Electric Power Generation With PZT
Ceramics"; by Stephen R. Platt, Shane Farritor, and Hani Haider; published in
IEEE/ASME Transactions On Mechatronics, VOL. 10, NO. 2, April 2005;
discusses the potential application of PZT based generators for some remote
applications such as in vivo sensors, embedded MEMS devices, and distributed
networking. The paper points out that developing piezoelectric generators is
challenging because of their poor source characteristics (high voltage, low
current,
high impedance) and relatively low power output.
CA 02715129 2011-12-16
CA 2,715,129 125-28 CA
6
The article " Energy Scavenging for Mobile and Wireless Electronics"; by
Joseph A.
Paradiso and Thad Starner; Published by the IEEE CS and IEEE ComSoc, 1536-
1268/05/;
reviews the field of energy harvesting for powering ubiquitously deployed
sensor networks and
mobile electronics and describers systems that can scavenge power from human
activity or
derive limited energy from ambient heat, light, radio, or vibrations.
In the review paper "A Review of Power Harvesting from Vibration using
Piezoelectric
Materials"; by Henry A. Sodano, Daniel J. Inman and Gyuhae Park; published in
The Shock and
Vibration Digest, Vol. 36, No. 3, May 2004 197-205, Sage Publications;
discusses the process
of acquiring the energy surrounding a system and converting it into usable
electrical energy -
termed power harvesting. The paper discuss the research that has been
performed in the area
of power harvesting and the future goals that must be achieved for power
harvesting systems to
find their way into everyday use
Patent application W007038157A2; titled "Energy Harvesting Using Frequency
Rectification"; to
Carman Gregory P. and Lee Dong G.; filed: 2006-09-21 discloses an energy
harvesting
apparatus for use in electrical system, having inverse frequency rectifier
structured to receive
mechanical energy at frequency, where force causes transducer to be subjected
to another
frequency.
Several patents discuss power harvesting from piezoelectric elements embedded
into
road systems. US patent application 2005/0127677; titled "Roadway generating
electric power
by incorporating piezoelectric materials"; filed by Jeffrey K. Luttrull on
2004-01025 describes a
process for generating electricity from vehicular traffic using a plurality of
piezoelectric elements.
UK patent GB2389249; titled "Electricity generating abstract"; to Mark Colin
Porter; filed 2002-
05-29 describes a power harvesting device using piezoelectric cylinders to be
embedded into
CA 02715129 2011-12-16
CA 2,715,129 125-28 CA
6a
road surfaces. China patent CN 1633009; titled "Method and system for
piezoelectric
power generation by using vibration energy of road system"; to University XI
AN JIAOTONG;
filed 2005-06-29 also discusses power harvesting of vibration energy on road
systems by using
piezoelectric devices.
However, the arrangement of the piezoelectric elements mentioned in the cited
patent
documents is not quite optimized for efficiency. It will be appreciated
therefore, that strain
energy produced by passing vehicles will be lost, calling for efficiency
improvements in the
power harvesting system.
CA 02715129 2010-08-04
WO 2009/098676 PCT/IL2009/000075
7
SUMMARY OF THE INVENTION
The present invention relates to an apparatus system and method for power
harvesting on roads and highways using piezoelectric generator.
One aspect of the invention is to provide a system for power
harvesting comprising: a plurality of piezoelectric devices configured to
produce electrical power when a vehicle traverses their locations; a power
conditioning unit; and electrical conductors connecting said piezoelectric to
said power conditioning unit.
In some embodiments, the piezoelectric devices are embedded in a road.
In some embodiments, the power conditioning unit is further connected to
the main power grid.
In some embodiments, the power conditioning unit is further connected to a
power storage unit.
In some embodiments, the power conditioning unit supplies electrical
power to battery charging station for charging batteries of electrical
vehicles.
In some embodiments, the power conditioning unit supplies electrical
power to roadside lights.
In some embodiments, the power conditioning unit supplies electrical
power to a signaling unit.
Another aspect of the invention is to provide a system for power
harvesting wherein said piezoelectric devices comprise plurality of PZT
roads embedded in a binder.
In some embodiments, said binder is epoxy resin.
CA 02715129 2010-08-04
WO 2009/098676 PCT/IL2009/000075
8
In some embodiments, said binder can be selected from a group of binders
such as thermoplastic polymer, rubber, or other natural or synthetic resilient
material.
Another aspect of the invention is to provide a method of harvesting energy
comprising: embedding a plurality of piezoelectric devices capable of
producing
electrical power in a road; connecting power conditioning unit to said
plurality of
piezoelectric devices by electrical conductors; wherein electrical power is
generated when a vehicle traverses said piezoelectric devices locations.
In some embodiments, said embedding a piezoelectric device-based energy
harvesting system comprising: positioning said plurality of piezoelectric
devices
and said electrical conductors over a concrete base of a road; and pouring
asphalt
over said piezoelectric devices and said electrical conductors.
In some embodiments, said embedding a piezoelectric device-based energy
harvesting system comprising: pouring first asphalt layer over road
foundation;
positioning said plurality of piezoelectric devices and said electrical
conductors
over first asphalt layer; and pouring a second asphalt layer over said
piezoelectric
devices and said electrical conductors.
In some embodiments, said embedding a piezoelectric device-based energy
harvesting system comprising: partially removing an asphalt layer off an
already
paved road leaving a first asphalt layer; positioning said plurality of
piezoelectric
devices and said electrical conductors over said first asphalt layer; and
pouring a
second asphalt layer over said piezoelectric devices and said electrical
conductors.
In some embodiments, said embedding a piezoelectric device-based energy
harvesting system comprising: removing an asphalt layer off an already paved
road along a narrow trench parallel to the long dimension of said road;
positioning
said plurality of piezoelectric devices and said electrical conductors in said
trench;
CA 02715129 2010-08-04
WO 2009/098676 PCT/IL2009/000075
9
and pouring asphalt over said piezoelectric devices and said electrical
conductors
thus filling said trench.
In some embodiments, said removing an asphalt layer off an already paved
road along a narrow trench parallel to the long dimension of said road
comprises
creating a trench reaching a concrete foundation of said road.
In some embodiments, said removing an asphalt layer off an already paved
road along a narrow trench parallel to the long dimension of said road
comprises
creating two narrow trenches parallel to the long dimension of said road per
each
lane of said road.
Unless otherwise defined, all technical and scientific terms used herein
have the same meaning as commonly understood by one of ordinary skill in the
art
to which this invention belongs. Although methods and materials similar or
equivalent to those described herein can be used in the practice or testing of
the
present invention, suitable methods and materials are described below. In case
of
conflict, the patent specification, including definitions, will control. In
addition,
the materials, methods, and examples are illustrative only and not intended to
be
limiting.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention is herein described, by way of example only, with reference
to the accompanying drawings. With specific reference now to the drawings in
detail, it is stressed that the particulars shown are by way of example and
for
purposes of illustrative discussion of the preferred embodiments of the
present
invention only, and are presented in the cause of providing what is believed
to be
the most useful and readily understood description of the principles and
conceptual
CA 02715129 2011-12-16
CA 2,715,129 125-28 CA
aspects of the invention. In this regard, no attempt is made to show
structural details of the
invention in more detail than is necessary for a fundamental understanding of
the invention, the
description taken with the drawings making apparent to those skilled in the
art how the several
forms of the invention may be embodied in practice.
IN THE DRAWINGS:
Figures 1 a and 1 b schematically depict the generator actions of a
piezoelectric element
as known in the art.
Figures 2(i) and 2(ii) schematically depict an apparatuses for electrical
signal generation,
rectification and storage.
Figure 3(i), 3(ii) and 3(iii) schematically depict views a piezoelectric
transducer according
to an exemplary embodiment of the invention.
Figure 4 schematically depicts a box shaped piezoelectric transducer according
to a
preferred embodiment of the invention.
Figure 5 schematically depicts a view of a system for power harvesting
implemented on
a railway according to an exemplary embodiment of the current invention.
Figure 6 schematically depicts an implementation of a system for energy
harvesting and
energy use according to an exemplary embodiment of the invention.
Figure 7 schematically depicts the implementation of energy harvesting system
in a new
road having a concrete foundation during road paving according to a preferred
embodiment of
the current invention.
CA 02715129 2010-08-04
WO 2009/098676 PCT/IL2009/000075
11
Figure 8 schematically depicts the implementation of energy harvesting
system in a new road not having a concrete foundation during road paving
according to a preferred embodiment of the current invention.
Figure 9 schematically depicts the method of implementation of energy
harvesting system in a new road not having a concrete foundation during road
paving according to a preferred embodiment of the current invention
Figures 10(a)-(d) schematically depict the method of implementation of
energy harvesting system in an existing road having a concrete foundation
according to an embodiment of the current invention. The figures depict stages
of
the retrofitting process.
Figures 11(a)- (d) schematically depict the method of implementation of
energy harvesting system in an existing road having a concrete foundation
according to an embodiment of the current invention. The figures depict the
stages
of the retrofitting process.
Figure 12a schematically depicts a side cross sectional view of a composite
piezoelectric generator according to another aspect of the current invention.
Figure 12b schematically depicts a side view of a composite piezoelectric
generator according to another aspect of the current invention.
Figure 12c schematically depicts a top view of a composite piezoelectric
generator according to another aspect of the present invention.
Figure 12d schematically depicts a system for energy harvesting using
composite piezoelectric generators according to an exemplary embodiment of the
current invention.
CA 02715129 2010-08-04
WO 2009/098676 PCT/IL2009/000075
12
Figure 12e schematically depicts a system for energy harvesting using
composite piezoelectric generators according to an exemplary embodiment of the
current invention.
Figure 13 schematically depicts tilted placement of piezoelectric generator
according to another aspect of the current invention.
Figure 14 schematically depicts a front view of a commercial airliner,
showing typical dimensions.
Figure 15 schematically depicts the footprint of a commercial airliner,
showing the wheels' configuration and typical dimensions.
Figure 16a schematically depicts the installation of Piezoelectric Energy
Generators (PEG) on a runway according to an exemplary embodiment of the
invention.
Figure 16b schematically depicts the implementation of PEG in a runway
according to exemplary embodiments of the current invention.
Figure 17 schematically depicts a box shaped piezoelectric transducer 1700
according to another preferred embodiment of the invention.
CA 02715129 2010-08-04
WO 2009/098676 PCT/IL2009/000075
13
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention relates to an apparatus system and method for power
harvesting on roads and highways using piezoelectric generator.
Before explaining at least one embodiment of the invention in detail, it is to
be understood that the invention is not limited in its application to the
details of
construction and the arrangement of the components set forth in the following.
description or illustrated in the drawings. The invention is capable of other
embodiments or of being practiced or carried out in various ways. Also, it is
to be
understood that the phraseology and terminology employed herein is for the
purpose of description and should not be regarded as limiting.
The drawings are generally not to scale. Some optional parts were drawn
using dashed lines.
For clarity, non-essential elements were omitted from some of the
drawings.
As used herein, an element or step recited in the singular and proceeded
with the word "a" or "an" should be understood as not excluding plural
elements
or steps, unless such exclusion is explicitly recited.
Figures 1 a and b schematically depict the generator actions of a
piezoelectric element as known in the art and as discussed in the background
section.
Figure 1 a(i) depicts a PZT disk 110, showing its polling direction in the
absence of external force. In this case, voltmeter 120 shows no generated
charge.
CA 02715129 2010-08-04
WO 2009/098676 PCT/IL2009/000075
14
Figures 1 a(ii) and 1 a(iii) show the same PZT disk 110 with compression
and extension forces applied to it respectively. In this case, voltmeter 120
shows
positive and negative generated charge respectively.
Figure lb(i) depicts a single element PZT similar to the one depicted in
figure I a. The length "L" of the element and its surface area "A" are marked
in
this figure.
Figure lb(ii) depicts a multi element PZT stack comprising n PZT disks
111(1) to 11(n), each having substantially the same thickness t and surface
area
"A". In this case all the PZT disks 111(1) to 111(n) are polled in the same
direction, and all are electrically connected in parallel. Electrical
insulator need to
be inserted between contact electrodes of adjacent elements.
Charge output appears at the connectors 113(+) and 113(-). For
convenience, we may refer to these connectors as "top electrode" and "bottom
electrode" respectively.
Figure lb(iii) depicts a multi element PZT stack comprising n PZT disks
112(1) to 112(n), each having substantially the same thickness and surface
area. In
this case all the PZT disks 111(1) to 11(n) are polled in alternate direction
as
depicted by the arrows. Common electrodes are preferably used between faces of
adjacent elements.
Charge output appears at the connectors 114(+) and 114(-). For
convenience, we may refer to these connectors as "top electrode" and "bottom
electrode" respectively.
CA 02715129 2010-08-04
WO 2009/098676 PCT/IL2009/000075
PIEZOELECTRIC GENERATORS
An important application area for PZT is in the conversion of mechanical
energy into electrical energy, and this chapter describes the conditions under
which PZT should be used to convert the maximum amount of energy.
5 A PZT cylinder can generate voltages that are high enough to draw a spark
across an electrode gap, and such sparks can be used to ignite combustible
gases in
for instance cigarette lighters or gas stoves.
Moreover, a part of the energy generated by a PZT transducer can be stored
in a capacitor and can be used to power a circuit as can be seen in Figure 2.
10 In the generation and storage apparatuses depicted in Figure 2, charge
generated by the piezoelectric transducer is stored in the energy storage
device
such a capacitor. The rectifier, schematically depicted by diode D1, holds the
collected charge at the capacitor until it is utilized by the energy utilizing
load.
Figure 2(i) depicts a single diode rectifier, while Figure 2(ii) shows a full
15 rectifier comprising a four diodes bridge.
Figure 2(i) depicts an energy harvesting system 200(i) using a single diode
rectifier D1. Although the PZT transducer in both Figures 2a and 2b appear as
a
single element having top electrode 211 and bottom electrode 212, the PZT
transducer may be a multi-element structure such as depicted in Figurelb(ii)
or
preferably as depicted in Figurelb(iii).
Rectifying diode D1 prevent electrical charge accumulated on capacitor Cp
from returning to the transducer once the load is removed from said
transducer.
Thus, the charge on capacitor Cp remains until it is utilized by a load
connected to
load output 220(i).
CA 02715129 2010-08-04
16
Figure 2(ii) depicts an energy harvesting system 200(ii) using a full
rectifier
comprising a four diodes bridge FR.
Rectifying bridge FR comprising four diodes directs charge generated by
both compression and extension forces applied to the PZT transducer to
capacitor
Cp. Rectifying bridge FR prevent electrical charge accumulated on capacitor Cp
from returning to the transducer once the load is removed from said
transducer.
Thus, the charge on capacitor Cp remains until it is utilized by a load
connected to
load output 220(ii), however, it is clear to see that system 200(11) better
utilizes the
generated charge and thus has higher energy efficiency.
Figures 3(i), (ii), and (iii) schematically depict views of a piezoelectric
transducer according to an exemplary embodiment of the invention.
Figure 3(i) depicts an isometric view of piezoelectric transducer 300
showing top electrode 310 and bottom electrode 311.
The composite disk made of piezoelectric rods 320 joined by epoxy or
other binding resin 321 as schematically depicted in the cross section seen in
Figure 3(ii) and the vertical cross section seen in Figure 3(iii). For
example, binder
may be a thermoplastic polymer, rubber or other natural or synthetic resilient
material.
Each rod may be made of a single structure plurality of layers as seen in
Figures lb(i), lb(ii) or lb(iii).
Preferably the electrodes of all the rods are connected n parallel to the top
and bottom electrode as depicted in Figure 3(iii).
It should be clear to the man of the art the circular shape of the transducer
and rods, the rods' position and the aspect ratio of the transducer are for
AMFNnIII r%PI:PT
CA 02715129 2010-08-04
17
demonstration only and actual parameters are to be chosen according to the
application taking into accounts requirements such as available space, load,
etc.
Pigure 4 schematically depicts a box shaped piezoelectric transducer 400
according to a preferred embodiment.of the invention.
The composite box made of piezoelectric rods 420 joined by epoxy or other
binding resin 421 as schematically depicted in the figure.
Although the rods are depicted as having square cross section, cylindrical or
other
shapes may be used.
Typical dimensions of 4x4 cm and 2 cm height are given as example. Other shape
and dimensions may be used.
Preferably, the ratio of active piezoelectric material to binder filing is
approximately 50%. However, larger or smaller ratio may be used.
Typically, the binder is softer than the piezoelectric material.
Each rod may be made of a single structure or plurality of layers.
Preferably the electrodes of all the rods are connected n parallel to the top
and
bottom electrode (not seen in this figure).
In test apparatus, the ratio of active piezoelectric material to binder filing
is
approximately 64%. However, larger or smaller ratio may be used. Preferably,
the
binder ratio is 30% to 40%.
In the test apparatus, an array of 8x8 (total 64) piezoelectric stacks was
embedded
in the binder, wherein each stack is 4x4 mm and 20 mm high.
Typically, the binder is softer than the piezoelectric material.
AMENDED SHEET
CA 02715129 2010-08-04
18
Each rod may be made of plurality of layers as known in the art. Preferably,
each
rod has a multilayer construction as depicted in figure lb(iii). Preferably
the
electrodes of all the rods are connected n parallel to the top and bottom
electrode
(not seen in this figure).
In the tested apparatus, each PZT rod is 20 mm high. Typically, polling
voltage is
in the order of 50,000 Volts per 1 cm. Using this polling technique would
require
100,000 Volts which may leads to sparking and necessitate very high voltage
source. According to the preferred embodiment of the invention, plurality of
rods
were connected in parallel and placed in an oven and heated to temperature
close
or preferably above the Curie temperature (approximately 300 degrees C for the
ceramic used). Polling voltage of only 5,000 V/cm (total of - 10,000 V) was
used.
Preferably the rods were cooled to room temperature under the polling voltage.
The rods were than integrated into the transducer structure by pouring the
binder.
Figure 5 schematically depicts a top view of a system. for power harvesting
500
implemented on a two lane roadway 505 according to an exemplary embodiment
of the current invention. A section of road 505 is shown in an enlarged view.
In the depicted embodiments, a plurality of energy generating devices 520 is
embedded in the road. Preferably, the devices 520 are piezoelectric transducer
as
depicted in Figure 3 or Figure 4.
In the preferred embodiment, the energy generating devices 520 are positioned
below the road surface at regular intervals. Axial distance of 30 cm may be
chosen
as depicted in the enlarged section of Figure 5. It should be noted the
distance
between energy generating devices 520 is preferably depends on the spread of
strain within the road structure and thus depends on road construction and
materials. Generally, distance between devices is determined by optimizing
payoff
AMENDED SHEET
CA 02715129 2010-08-04
WO 2009/098676 PCT/IL2009/000075
19
from harvested energy and cost of the system which influenced by installation
cost
and price per piezoelectric device.
Preferably, two rows of transducers are position in each lane of roadway,
wherein
each row is positioned where wheels of passing cars are likely to traverse.
Electrical cables 510 connected to the energy generating devices, are used to
transfer the generated energy to the energy management unit 530. Conditioned
energy is than transferred to energy utilizing system 540.
In one embodiment, each cable 510 is made of two conductors and all the energy
generating devices are connected in parallel. Alternatively, the energy
generating
devices are connected in series. Combination of parallel and series connection
is
also possible.
In some embodiments, electric rectification is done at each of the energy
generating device, or at a group of energy generating devices and the
rectified
electric signal is transferred by a cable.
The energy management unit 530 may includes voltage conversion and regulation
needed to convert the generated electric signal to useful form.
For example, the energy management unit 530 may comprise of DC to AC
converter, converting the rectified generated signal to AC power ready to
power
devices designed to be powered by the usual household main power grid.
In the preferred embodiment, energy management unit 530 is positioned in the
center of, and services a section of road, for example 1 km of road. It should
be
appreciate that optimization of the distance between energy generating devices
and
energy management units depends on the cost of cabling, cost of devices,
energy
loss in the cables, etc.
CA 02715129 2010-08-04
WO 2009/098676 PCT/IL2009/000075
Preferably, the depicted power harvesting system is duplicated along the road
for
additional power harvesting.
In some embodiment the rows of energy generating devices are positioned closer
to the curb of the road rather than symmetrically about the lane center where
care
5 are more likely to travel over it.
In some embodiment the rows of energy generating devices are positioned at
average axle width apart from each other.
It should be noted that the example of implementation in a two lane road in
this
figure is for demonstration and simplicity only. The system may be used in
single
10 or multilane roads.
Figure 6 schematically depicts an implementation of a system 600 for energy
harvesting and energy use according to an exemplary embodiment of the
invention.
In the depicted embodiment, energy 610 generated by the energy generating
15 devices embedded in the roadway 605 is converted to an electrical power in
useful
form by the energy management unit 630.
The exemplary embodiment of Figure 6 depicts a four lane highway having two
lanes in each direction, however other types of roads may be used within the
scope
of the current invention. Generally, cars are more likely to travel in the
right lane
20 (Left lane in UK and similar countries) than in the left lane. Thus, it may
be cost
effective to implant the energy generator in the busiest lanes only.
Preferably, one
energy management unit 630 serve a section of a road including lanes in both
traveling direction as to minimize the energy loss due to cabling electrical
resistance.
CA 02715129 2010-08-04
WO 2009/098676 PCT/IL2009/000075
21
Optionally, energy storage 620, such as large capacitor, or preferably a
rechargeable battery is used for storing the energy to be used when needed.
Since
the generated energy is present only when cars passes over the energy
generating
devices, energy storage may be useful so that the power supply is not
interrupted
when cars are absent or traffic is slow or the number of cars is small.
Energy is utilized by the energy utilization system 630. Optionally energy
utilization system 630 is located in proximity to the energy management unit
630
and the optional energy storage 620.
For example:
Energy may be used for lighting the road at night. In this case, energy
generated
and stored during the day may be used at the following night when car traffic
may
be too small to provide the full power requirement.
Signaling lights and roadside signs may be powered, specifically, at remote
and
unpopulated locations and intersection where the cost of providing power using
power lines from main power grid may be high. Other uses may be to power
emergency communication units; mobile communication base stations and
roadside advertisements.
As electric cars become popular, there is a growing need for roadside battery
recharging stations. Power harvested from passing cars may be used.
In some embodiments, all the generated power, or extra power left over after
local
power demand was met, is exported to the main electrical power grid for a fee
paid
by electric company. In these embodiments, energy management unit may convert
the generated electrical power to high voltage used in the high tension power
lines.
In these embodiments, the optional main grid connection 690 may be used as
backup power source to be used locally when traffic is thin.
CA 02715129 2010-08-04
WO 2009/098676 PCT/IL2009/000075
22
Figure 7 schematically depicts the implementation of energy harvesting system
in
a new road having a concrete foundation during road paving according to a
preferred embodiment of the current invention.
In this embodiment, after the gravel layer 720 was deposited over soil 710,
and
concrete foundation 730 has been prepared, the rows of energy generation
devices
750 and their connecting cable 760 are laid on the concrete and the layer of
asphalt
740 is paved over it.
This implementation is the simplest and requires only minimal departure from
normal road paving practices. In these embodiments there is almost absolute
freedom as to the configuration of the connecting cables and their direction.
Figure 8 schematically depicts the implementation of energy harvesting system
in
a new road not having a concrete foundation during road paving according to a
preferred embodiment of the current invention.
In this embodiment, the energy generating devises and the connecting cables
are
embedded in the asphalt.
Figure 9 schematically depicts the method of implementation of energy
harvesting
system in a new road not having a concrete foundation during road paving
according to a preferred embodiment of the current invention.
In this embodiment, after the gravel foundation 720 has been prepared, a firs
layer
940 of asphalt is paved. The rows of energy generation devices 750 and their
connecting cables 760 are laid on the first layer of asphalt 940 and a second
layer
941 of asphalt is paved over it.
CA 02715129 2010-08-04
WO 2009/098676 PCT/IL2009/000075
23
This implementation is the simple and requires only paving the asphalt in two
layers instead of one. In this embodiment, there is almost absolute freedom as
to
the configuration of the connecting cables and their direction.
Figure 10 schematically depict the method of implementation of energy
harvesting
system in an existing road not having a concrete foundation according to an
embodiment of the current invention.
In this embodiment, trenches 1010 are cut along the road, for example using a
circular disk. Each trench is deep enough to partially penetrate the layer of
asphalt
740. The trench is wide enough to accommodate the energy generating device 750
and its connecting cable 760. The row of energy generation devices and their
connecting wires are laid on the bottom of the trench and the trench is than
refilled
with asphalt refill 1020.
Figure 10(a) to Figure 10(d) depicts the stages of the retrofitting process.
Figure 11 schematically depict the method of implementation of energy
harvesting
system in an existing road having a concrete foundation 730 according to an
embodiment of the current invention.
In this embodiment, trenches 1110 are cut along the road, for example using a
circular disk. Each trench is deep enough to fully penetrate the layer of
asphalt 740
and reach the concrete layer 730. The trench is wide enough to accommodate the
energy generating device 750 and its connecting cable 760. The row of energy
generation devices and their connecting wires are laid on the bottom of the
trench
against the concrete and the trench is than refilled with asphalt refill 1120.
Figure 11(a) to Figure 11(d) depicts the stages of the retrofitting process.
Figure 11 a shows the road before retrofitting.
CA 02715129 2010-08-04
WO 2009/098676 PCT/IL2009/000075
24
Figure 1 lb depicts the stage of digging a trench in the upper pavement layer.
Figure 11c shows the stage of placing the energy harvesting devices.
Figure 11d shows the road after the trench was re-paved.
Figure 12a schematically depicts a side cross sectional view of a composite
piezoelectric generator according to another aspect of the current invention.
According to an exemplary embodiment of the invention, a composite
piezoelectric generator 1200 comprises a plurality piezoelectric generators
1244
(four are shown in this figure, but more or less may be used).
For example each of piezoelectric generators 1244 may be a box shaped
piezoelectric transducer 400 of Figure 4, or other shaped piezoelectric
generator.
Preferably, piezoelectric generators 1244 are placed on a base plate 1232 and
covered with top plate 1231.
Elastic members such as springs 1211, preferably at ends of plate 1231 and
1232
holds the structure together and preferably applies a compression force
between
base plate 1232 and top plate 1231. This compression force is applied to
piezoelectric generators 1244. When a car or a truck passes over or near a
composite piezoelectric generator 1200, the pressure and vibration caused by
the
vehicle propagate in the road and affect base plate 1232 and top plate 1231
creating time varying forces on piezoelectric generators 1244 which generate
electrical power. It should be realized that the fact that the structure is
"pre-
stressed" by Elastic members 1211 ensures that electricity will be generated
also
in the pulling parts of the vibration cycle. Thus, preferably, the force
exerted by
Elastic members 1211 is comparable or exceeds the maximum pooling force
anticipated during vibration cycle.
CA 02715129 2010-08-04
WO 2009/098676 PCT/IL2009/000075
Preferably, piezoelectric generators 1244 are electrically connected to each
other
and to local energy conditioning unit 1293 via electrical conductors 1291 and
1292. However, optionally each of piezoelectric generators 1244 may be
connected separately to local energy conditioning unit 1293. Local energy
5 conditioning unit 1293 may be for example in the form disclosed in Figure 2.
Conditioned energy from local energy conditioning unit 1293 is transferred to
outside energy utilization via cable 1294. Optionally, local energy
conditioning
unit 1293 is missing in all or in few of the composite piezoelectric
generators 1200
and energy conditioning is performed outside the 'composite piezoelectric
10 generator.
Preferably, composite piezoelectric generator 1200 is approximately 60 cm
long, 4
cm wide and 3 cm high, wherein height includes 2 cm of active piezoelectric
material and the thickness of the base plate 1232 and top plate 1231. However,
other dimensions may be used
15 Optionally, the entire composite piezoelectric generator 1200 is housed in
a
protective flexible cover for example for protection from dirt and moisture
and for
example for preventing asphalt from entering the generator during embedding in
a
road. Additionally or alternatively, composite piezoelectric generator 1200
may be
potted with elastic material.
20 Figure 12b schematically depicts a side view of a composite piezoelectric
generator according to another aspect of the current invention.
According to an exemplary embodiment of the invention, a composite
piezoelectric generator 1200 comprises a plurality piezoelectric generators
1244..
Preferably, piezoelectric generators 1244 are placed on a base plate 1232 and
25 covered with top plate 1231.
CA 02715129 2010-08-04
WO 2009/098676 PCT/IL2009/000075
26
Elastic members such as springs 1211 holds the structure together and
preferably
applies a compression force between base plate 1232 and top plate 1231 (two
are
seen in this side view, but one or more than two may be used).
Figure 12c schematically depicts a top view of a composite piezoelectric
generator
according to another aspect of the current invention.
According to an exemplary embodiment of the invention, a composite
piezoelectric generator 1200 comprises plurality piezoelectric generators
1244.
Preferably, piezoelectric generators 1244 are placed on a base plate 1232 and
covered with top plate 1231 (only top plate is seen here).
Elastic members such as springs 1211 holds the structure together and
preferably
applies a compression force between base plate 1232 and top plate 1231 (two
elastic members at each side are seen in this top vie, but one or more than
two may
be used).
Figure 12d schematically depicts a system for energy harvesting using
composite
piezoelectric generators according to an exemplary embodiment of the current
invention.
Energy harvesting system 1266 is preferably embedded in a road. In this
schematic
depiction, one road lane defined by its outer boundary 1262 (which may be the
road curb, or the boundary of another lane) and its inner boundary 1263.
Energy
harvesting system 1266 comprises a plurality of composite piezoelectric
generators 1200, preferably arranged in two rows.
According to an exemplary embodiment of the invention, composite piezoelectric
generators 1200 are placed so as to maximize the harvested energy. Maximizing
CA 02715129 2010-08-04
WO 2009/098676 PCT/IL2009/000075
27
the harvested energy may be done by placing the generators 1200 in locations
that
maximize the probability that wheels of passing vehicle pass over their
centers.
In an exemplary embodiment of the invention generators 1200 are placed
substantially parallel to each other at approximately 30 cm intervals along
the two
rows corresponding to the same traffic lane. In an exemplary embodiment of the
invention centers of generators 1200 are placed approximately 60 cm from
lane's
outer boundary 1262. In an exemplary embodiment of the invention centers of
generators 1200 of second rows are placed approximately 180 cm from centers of
generators 1200 of the first row. It should be noted that other distances
among
generators 1200 may be used.
Cables 1294 electrically connect generators 1200 to energy utilization system
via
main cable 1295.
Figure l2e schematically depicts a system for energy harvesting using
composite
piezoelectric generators according to an exemplary embodiment of the current
invention.
Energy harvesting system 1267 differs from system 1266 by its cabling
topology.
In this exemplary embodiment, row collecting cables 1267 connects generators
1200 in each row to outside energy utilization system.
It should be realized that other cabling topologies may be used and that the
invention is not limited to a one-lane road.
Figure 13 schematically depicts tilted placement of piezoelectric generator
according to another aspect of the current invention.
CA 02715129 2010-08-04
WO 2009/098676 PCT/IL2009/000075
28
According to a general aspect of the current invention, piezoelectric
generators
1300 may be embedded in the pavement 740 at an angle a to the surface 1320 of
the road.
Preferably, tilt angle is in the direction 1310 of the prevailing moving
vehicle over
the generators 1300.
Generators 1300 may be selected. from any type of piezoelectric generator.
Preferably, piezoelectric generators 1300 are composite piezoelectric
generators as
seen in figures 12.
In another preferred embodiment, the energy generating devices are positioned
under an airfield runway tarmac. Although airport traffic is less frequent,
the stress
cased by a airliner landing is much larger than that of a car. Preferably, the
energy
harvesting system is positioned at the landing section of the field where the
stress
is at its peak.
Figure 14 schematically depicts a front view of a commercial airliner, showing
typical dimensions.
Commercial jet airliner 1400 for example Boeing 747-400 depicted in this
figure
usually has a landing gear comprising front wheels assembly 1410 connected to
the front of the fuselage and two main wheels assemblies 1420 connected to the
base of the wings.
Typically most of the airplane weight rest on the two main wheels assemblies
1420. For the depicted Boeing 747, maximum (takeoff) load on front wheels
assembly 1410 is approximately 17 tons and approximately 60 tones for each of
the two main wheels assemblies 1420.
CA 02715129 2010-08-04
WO 2009/098676 PCT/IL2009/000075
29
Depending on the type and size of the airplane, the distance between the
centers of
the two main wheels assemblies 1420 vary. Typical distance is approximately 11
M.
Figure 15 schematically depicts the footprint of a commercial airliner,
showing the
wheels' configuration and typical dimensions.
Commercial jet airliner for example Boeing 767 the footprint of which is
depicted
in this figure usually has a landing gear comprising front wheels assembly
1410
connected to the front of the fuselage and two main wheels assemblies 1420
connected to the base of the wings.
The distance between the centers of the two main wheels assemblies 1420 is
approximately 9.3 in.
PAVEMENT
The choice of material used to construct the runway depends on the use and the
local ground conditions. Generally speaking, for a major airport, where the
ground
conditions permit, the most satisfactory type of pavement for long-term
minimum
maintenance is concrete. Although certain airports have used reinforcement in
concrete pavements, this is generally found to be unnecessary, with the
exception
of expansion joints across the runway where a dowel assembly, which permits
relative movement of the concrete slabs, is placed in the concrete. Where it
can be
anticipated that major settlements of the runway will occur over the years
because
of unstable ground conditions, it is preferable to install asphaltic concrete
surface,
as it is easier to patch on a periodic basis. For fields with very low traffic
of light
planes, it is possible to use a sod surface.
The development of the pavement design proceeds along a number of paths.
Exploratory borings are taken to determine the subgrade condition, and based
on
CA 02715129 2010-08-04
WO 2009/098676 PCT/IL2009/000075
relative bearing capacity of the subgrade, different pavement specifications
are
established. Typically, for heavy-duty commercial aircraft, the pavement
thickness, no matter what the top surface, varies from as little as 10 inches
(25 centimeters) to as much as 4 ft (1 m), including subgrade.
5 Historically, airport pavements have been designed by two methods. The
first,
Westergaard, is based on the assumption that the pavement is an elastic plate
supported on a heavy fluid base with' a uniform reaction coefficient known as
the
K value. Experience has shown that the K values on which the formula was
developed are not applicable for newer aircraft with very large footprint
pressures.
10 Because airport pavement construction is so expensive, every effort is made
to
minimize the stresses imparted to the pavement by aircraft. Manufacturers of
the
larger planes design landing gear so that the weight of the plane is supported
on
larger and more numerous tires. Attention is also paid to the characteristics
of the
landing gear itself, so that adverse effects on the pavement are minimized.
15 However, in the final analysis, if plane weights continue to increase as
they have
in the past, it will be necessary to provide substantially stronger pavements
than
those that are generally in use in Europe and the United States. Sometimes it
is
possible to reinforce a pavement for higher loading by applying an overlay of
asphaltic concrete or Portland cement concrete that is suitably bonded to the
20 original slab.
Post tensioning concrete has been developed for the runway surface. This
permits
the use of thinner pavements and should result in longer concrete pavement
life.
Because of the susceptibility of thinner pavements to frost heave, this
process is
generally applicable only where there is no appreciable frost action.
25 RUNWAY LENGTH
CA 02715129 2010-08-04
WO 2009/098676 PCT/IL2009/000075
31
Although runway length may be of some academic interest, in terms of usability
for air carrier operations, a runway of at least 6,000 ft (1,829 m) in length
is
usually adequate for aircraft weights below approximately 90,718 kg. Larger
aircraft will usually require at least 2,438 in at sea level and somewhat more
at
higher altitude airports. International wide body flights may also have
landing
requirements of 3,048 in or more and takeoff requirements of 3,962 m or more.
At sea level , 3,048 in can be considered an adequate length to accommodate
virtually any aircraft. Any given aircraft will need a longer runway at a
higher
altitude due to decreased density of air at higher altitudes, which reduces
lift and
engine power. Most commercial aircraft carry manufacturer's tables showing the
adjustments required for a given temperature.
Figure 16a schematically depicts the installation of Piezoelectric Energy
Generators (PEG) on a runway according to an exemplary embodiment of the
invention.
Runway energy harvesting system 1150 is installed in an airport having a
runway
1510. For clarity, cabling and energy conditioning and storing elements were
omitted from this drawing. However, these element follows the general
construction and operation modes discloses in the preceding figures.
At least at proximity of one end of the runway, a landing mark 1520 is pained
on
the pavement. Pilots aim the plane to touchdown at this mark. Usually, takeoff
starts at the same mark or near it. Direction of takeoff and landing is
generally
against the wind direction, thus at location where wind direction vary, a
landing
mark will be painted on both ends of the runway. However, prevailing wind
direction determine the probability of landing in one direction or the other.
In
some airports, different runways are used for landing and for takeoff.
CA 02715129 2010-08-04
WO 2009/098676 PCT/IL2009/000075
32
In landing, stress on the landing gear is high throughout the landing run. In
contrast, during takeoff, aerodynamic lift reduces the stress when airplane
speed
increases.
Preferably, PEGs are installed under the runway pavement where stress caused
by
the landing gear of the airplanes using the runway is large and frequent.
In the depicted exemplary embodiment of figure 16a, the PEG's 1540 are
installed, starting at the landing mark 1520 in groups 1530. Each group of
PEGs
1530 comprises a plurality of PEG 1540 (four are seen in this figure, but
number
of PEGs in a group may vary). Each group is preferably 1 to 6 in long. Groups
1530 are situated in parallel configuration at specified distance to form two
rows
of groups 1535. In the exemplary embodiment depicted in figure 16a the
distance
between the groups is approximately 30 cm and the distance between centers of
two rows 1535 is approximately 11 m. Generally, the distance between centers
of
two rows 1535 is determined by the average distance between the main landing
gears of the planes using the runway. Generally, the distance between groups
1540
and distance between PEGs in the group is a tradeoff between the increase cost
of
PEG's and the increase energy harvesting efficiency with higher number of
PEGs.
In the depicted embodiment, the PEGs are installed at the beginning of the
runway
and up to the point where probability of stress caused by passing plane
reduces to
the point that the decreased expected energy harvested makes PEG installation
not
cost effective. For example, most takeoff runways are longer than average
takeoff
run and thus PEG installation will be restricted to the beginning of the
runway.
Similar consideration may be made for landing runways, landing and takeoff
runways, and runways at locations where wind direction varies. At runways at
locations where wind direction vary, PEGs may be installed starting at both
ends
or through the entire length of the runway.
CA 02715129 2010-08-04
WO 2009/098676 PCT/IL2009/000075
33
Figure 16b schematically depicts the implementation of PEG in a runway
according to exemplary embodiments of the current invention.
Figure 16b(i) depicts a runway comprising a concrete layer 1620 laid over
foundation 1610 and an asphalt layer 1630 deposited over it. In this
embodiment,
PEGs 1540 are preferably are attached to the concrete layer 1620 and are
covered
with asphalt.
Alternatively, PEGs may be installed under the concrete layer 1620.
Figure 16b(ii) depicts a runway comprising a concrete layer 1620 laid over
foundation 1610 without an asphalt layer. In this embodiment, PEGs 1540 may be
installed within the concrete layer 1620. In this embodiment the PEG may be
attached to the reinforcement structure of the reinforced concrete if used.
Alternatively, PEGs may be supported by a support structure 1545 while the
concrete is being poured.
Alternatively, PEGs may be installed under the concrete layer 1620.
Figure 17 schematically depicts a box shaped piezoelectric transducer 1700
according to another preferred embodiment of the invention.
The composite box made of piezoelectric rods 1720 joined by binding resin 1721
as schematically depicted in the figure. Preferably, binding resin is made of
a
bitumen-polymeric mix. Preferably, resin properties are chosen such that the
average mechanical properties of generator 1700 (a matrix with piezoceramic
rods
installed in it) correspond to requirements to mechanical properties of a
runway
pavement.
CA 02715129 2010-08-04
1
34
Although the rods are depicted as having square cross section, cylindrical or
other
shapes may be used. In the depicted embodiment, "checker board" configuration
of rod was chosen. However different packing configuration may be used.
Typical dimensions of 12.5x5 cm and 2.5 cm height are given as example. Other
shape and dimensions may be used. In the depicted embodiment, 40 % of the
volume is occupied by piezoelectric rods, however other rods to resin ratios
may
be used. In the depicted embodiment. 125 piezoelectric rods are used, arranged
in
rows of alternating 13 and 12 rods per row, however other rods configurations
may be used.
10 Each rod may be made of a single structure or plurality of layers.
In the depicted embodiment all top electrodes of all the rods are connected in
parallel to the top electrode 1730. Top electrode 1730 is connected to top
electrode
wire 1732 at top contact 1733.
Similarly, all bottom electrodes of all the rods are connected in parallel to
the
bottom electrode (not seen in this figure). Bottom electrode is connected to
bottom
electrode wire 1742 at top contact 1743. Wires 1742 and 1732 joined to cable
1750 that leads to the energy conditioning and utilization units (not seen in
this
figure).
In another preferred embodiment, the energy generating devices are positioned
under train railway tracks. . Although train traffic is less frequent, the
stress cased
by a train is much larger than that of a car. Additionally, the stress cased
by a
passing train is concentrated under the rails and may be easier to harvest.
It is appreciated that certain features of the invention, which are, for
clarity,
described in the context of separate embodiments, may also be provided in
combination in a single embodiment. Conversely, various features of the
AAArI1rlrr% ci irr-r
CA 02715129 2011-12-16
CA 2,715,129 125-28CA
invention, which are, for brevity, described in the context of a single
embodiment, may also be
provided separately or in any suitable sub combination.
Although the invention has been described in conjunction with specific
embodiments
thereof, it is evident that many alternatives, modifications and variations
will be apparent to
those skilled in the art. In addition, citation or identification of any
reference in this application
shall not be construed as an admission that such reference is available as
prior art to the
present invention.
