WO2010116348A1

WO2010116348A1 - Modular piezoelectric generators

Info

Publication number: WO2010116348A1
Application number: PCT/IL2009/000365
Authority: WO
Inventors: Haim Abramovich; Eugeny Harash; Charles Milgrom; Lucy Edery Azulay; Eugeny Tsikhotsky; Uri Amit
Original assignee: Innowattech Ltd.
Priority date: 2009-04-05
Filing date: 2009-04-05
Publication date: 2010-10-14

Abstract

A modular piezoelectric generator for converting mechanical energy from passing vehicles to electrical energy may be imbedded below a road's upper asphalt layer. Placing several generators enables large areas cover. Load spreading layers (122a, 122b), optionally used as electrodes for the piezoelectric elements, evenly spreads stress among the piezoelectric elements (110). Optional upper and lower layers made of material such as bitumen, enabling good integration with road structures. Optional heating elements in upper layer are powered by piezoelectric elements located in the central matrix layer. Energy harvested may be used for: lighting, advertising, battery charging, deicing or connecting to electric grid. Modular apparatus may be used where mechanical energy is available; for example: imbedded below road's upper asphalt layer to harvest energy from passing vehicles; used in airport's runway; in railroad or pavements. The apparatus may be used outdoors or indoor at any location where large number of pedestrians passing.

Description

MODULAR PIEZOELECTRIC GENERATORS

FIELD OF THE INVENTION

The present invention relates to a modular energy harvesting apparatus, system for using said apparatus and method for implementation said apparatus.

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. The Curie's originally discovered it 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. 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 proportional up to a material-specific stress. The same is true for applied voltage and generated strain. 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.

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. lnman and Gyuhae Park; published in The Shock and Vibration Digest, Vol. 36, No. 3, May 2004 197-205, Sage Publications; discuses 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 WO07038157A2; 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.

US patent 5,265,481 ; to Sonderegger, Hans C, et. al.; titled "Force sensor systems especially for determining dynamically the axle load, speed, wheelbase and gross weight of vehicles"; discloses sensor system incorporated in road surface - has modular configuration for matching different road widths.

SUMMARY OF THE INVENTION

According to an aspect of the current invention, a modular power harvesting apparatus is provided, the apparatus comprising: an upper load spreading layer; a lower load spreading layer; a matrix layer between said upper and lower load spreading layers; and a plurality of piezoelectric elements embedded in said matrix layer, wherein said piezoelectric elements are adopted to generate electric energy in response to pressure applied to said upper layer. In some embodiments the apparatus is adopted to be embedded in road such that said upper load spreading layer is facing the upper road layer.

In some embodiments the apparatus is adopted to be attached to a road such that said upper load spreading layer is facing the traveling vehicles. In some embodiments the matrix layer has thickness smaller than the length of said piezoelectric elements allowing stress applied to said upper load spreading layer to be spread among said plurality of said piezoelectric elements.

In some embodiments the matrix layer is rigid.

In some embodiments the matrix layer is made of compressible material having thickness compatible with the length of said piezoelectric elements, allowing stress applied to said upper load spreading layer to be spread among said plurality of said piezoelectric elements. In some embodiments the cross section of the apparatus, the total area of said piezoelectric element is less than 30 percent of the total area of said apparatus.

In some embodiments the cross section of the apparatus, the total area of said piezoelectric element is less than 10 percent of the total area of said apparatus.

In some embodiments the load spreading layers are rigid.

In some embodiments the load spreading layers are semi-rigid.

In some embodiments the apparatus further comprising electric cables for transferring said generated energy to energy utilization unit external to said modular apparatus.

In some embodiments the apparatus further comprising electronic module located blow said lower load spreading layer, wherein said electronics module receives electrical power generated by said piezoelectric elements in response to mechanical force applied to said upper load spreading layer.

In some embodiments the electronic module comprises electrical energy storage.

In some embodiments the electronic module further comprises a temperature sensor. In some embodiments the apparatus further comprising heating elements embedded in a heating layer located above said upper load spreading layer, wherein said heating elements receives electrical power from said electronic module in response to signal receives from said temperature sensor. In some embodiments the apparatus further comprising heating elements embedded in said upper load spreading layer, wherein said heating elements receives electrical power from said electronic module in response to signal receives from said temperature sensor.

In some embodiments the apparatus further comprising: an upper electrode layer located above, and making electrical contact with said plurality of piezoelectric elements embedded in said matrix layer; and a lower electrode layer located below, and making electrical contact with said plurality of piezoelectric elements embedded in said matrix layer.

In some embodiments the upper electrode layer and said lower electrode layer are load spreading layers configured to evenly spread external mechanical load among said piezoelectric elements.

In some embodiments the upper surface of said apparatus comprises bitumen.

In some embodiments the apparatus lower surface of said apparatus comprises bitumen. In some embodiments the apparatus upper layer and said lower surfaces of said apparatus are adapted to integrate to road structure.

In some embodiments the apparatus layer and said lower surfaces are adapted to provide moisture protection.

In some embodiments the apparatus further comprising a wrapper adapted to provide moisture protection.

According to another aspect of the invention, a modular energy harvesting system is provided, the system comprising: a road; and a plurality of modular apparatuses, wherein at least one of said modular apparatuses comprises: an upper load spreading layer; a lower load spreading layer; a matrix layer between said upper and lower load spreading layers; and a plurality of piezoelectric elements embedded in said matrix layer, wherein said piezoelectric elements are adopted to generate electric energy in response to pressure applied to said upper layer, wherein said apparatus is adopted to be attached to a road such that said upper load spreading layer is facing the traveling vehicles.

In some embodiments the at least one modular apparatus further comprises heating elements.

In some embodiments the generated energy is used to power said heating elements. In some embodiments the system further comprising energy storage for storing said generated energy. In some embodiments the plurality modular apparatus are attached side by side to said road such that gaps between adjacent apparatuses are substantially smaller than the size of an apparatus.

In some embodiments the system further comprising a covering asphalt layer, covering said modular apparatus.

According to yet another aspect of the current invention, a method of energy harvesting is provides, the method comprising the steps of: attaching at least one modular energy harvesting apparatus to a road, said apparatus comprising: an upper load spreading layer; a lower load spreading layer; a matrix layer between said upper and lower load spreading layers; and a plurality of piezoelectric elements embedded in said matrix layer, wherein said piezoelectric elements are adopted to generate electric energy in response to pressure applied to said upper layer; and harvesting energy generated by said piezoelectric element in response to pressure applied to said upper layer by a vehicle passing over said modular apparatus.

In some embodiments attaching said modular apparatus to the road comprises applying an asphalt covering layer over said modular apparatus.

In some embodiments attaching said modular apparatus to the road comprises adding a covering bitumen layer over said modular apparatus. 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 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.

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.

In discussion of the various figures described herein below, like numbers refer to like parts. The drawings are generally not to scale. For clarity, non-essential elements were omitted from some of the drawings.

In the drawings:

Figure 1a(i) schematically depicts a cross section of a modular energy harvesting apparatus 100a according to an exemplary embodiment of the current invention.

Figure 1a(ii) schematically depicts a cross section of a modular energy harvesting apparatus 100a¹ according to another exemplary embodiment of the current invention. Figure 1a(iii) schematically depicts a cross section of a modular energy harvesting apparatus 100a" according to yet another exemplary embodiment of the current invention.

Figure 1b schematically depicts a cross section of a modular energy harvesting apparatus 100b according to another exemplary embodiment of the current invention.

Figure 1c schematically depicts a cross section of a modular energy harvesting apparatus 100c according to another exemplary embodiment of the current invention.

Figure 1d schematically depicts a cross section of a stand alone modular energy harvesting device 150 according to another exemplary embodiment of the current invention.

Figure 2a schematically depicts a partial horizontal cross section of a modular energy harvesting apparatus 100 according to an exemplary embodiment of the current invention.

Figure 2b schematically depicts a partial horizontal cross section of a modular energy harvesting apparatus 100 according to another exemplary embodiment of the current invention.

Figure 3a schematically depicts partial view of load spreading layer with printed contacts 322 according to exemplary embodiments of the current invention.

Figure 3b schematically depicts heating layer 160 with embedded heaters 162 according to an exemplary embodiment of the current invention. Figure 4 schematically depicts optional location of energy harvesting apparatuses 100 embedded in a road 410 according to an exemplary embodiment of the current invention.

Figure 5a schematically depicts stages of embedding apparatus 100 in an existing road 510 according to an exemplary embodiment of the current invention.

Figure 5b schematically depicts stages of embedding apparatus 100 in an existing road 510' according to another exemplary embodiment of the current invention.

Figure 5c schematically depicts stages of embedding apparatus 100 in a newly constructed or resurfaced road 530 according to another exemplary embodiment of the current invention.

Figure 5d schematically depicts a side cross section of a heated road system 540 according to an exemplary embodiment of the current invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

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. Figure 1a(i) schematically depicts a cross section of a modular energy harvesting apparatus 100a according to an exemplary embodiment of the current invention.

Modular energy harvesting apparatus 100a comprised a plurality of piezoelectric elements 110 configured to produce electrical charge when compressed vertically by external force applied to them. Preferably, generated charge is due to the effective piezoelectric coefficient d₃,₃ . Each piezoelectric element 110 makes electrical contact with upper conductive layer 112a and with lower conductive layer 112b at its upper and lower end respectively. Piezoelectric elements 110 are preferably arranged as a 2D array: Conductive layer 112a and 112b are connected to energy harvesting electronic unit 114 via leads 115. Harvested energy is transferred to energy using system (not shown in this figure) through electrical cable 116.

Piezoelectric elements 110 are held in place by a matrix layer 118 having holes 120. Holes 120 are sized to accept piezoelectric elements 110, but prevent them from tumbling over. Preferably, holes 120 are slightly larger than piezoelectric elements 110; however, holes 120 may be of different shape than piezoelectric elements 110. For example, piezoelectric elements 110 may be rectangular, yet fit in round holes, etc. Alternatively, even matrix layer 118 may be created by injection of plastic or epoxy material around piezoelectric elements 110 held in position by a holder, thus holes 120 are formed by the piezoelectric elements 110 themselves during the injection.

Preferably, matrix 118 is thinner than the length of piezoelectric elements 110. Upper load spreading layer 122a and lower load spreading layer 122b ensures that force applied to modular energy harvesting apparatus 100a is spread among the plurality of piezoelectric elements 110. Load spreading layers 122 are made of rigid or semi-rigid material having thickness adopted to spread the load applied. For high loads, harder and or thicker load spreading layers 122 are selected. For example, hard plastic material may be used. Matrix 118 may be constructed from flexible or elastic material, such as plastic foam, rubber or bitumen, since load is mainly supported by the load spreading layers 122 and piezoelectric elements 110. However hard plastic material may be used. Optional fasteners 124, preferably located near the edges of load spreading layers 122 hold the structure together. Optionally, optional fasteners 124 are made of flexible material such as nylon or other flexible material. Optionally, fastener 124 is a thin plastic strip inserted trough and tied to holes (not shown in this figure) in load spreading layers 122 and matrix layer 118.

Typical, non limiting dimensions of modular energy harvesting apparatus 100a may be 30x30 cm with a thickness of 1.82 cm. In this non- limiting example, length of each piezoelectric element 110 is approximately 1.2 cm; thickness of each load spreading layers 122 is approximately 0.3 cm and thickness of each conductive layer 112 is approximately 0.01 cm.

Figure 1a(ii) schematically depicts a cross section of a modular energy harvesting apparatus 100a¹ according to another exemplary embodiment of the current invention.

For simplicity, only the differences between modular energy harvesting apparatus 100a' and previously depicted embodiment are detailed in the figure and explained herein.

In a modified embodiment of the invention, matrix layer 118 is replaced with even bottom matrix layer 118'. In the embodiment depicted in figure 1a(i), both upper and lower edges of piezoelectric elements 110 protrude above and below matrix layer 118. In contrast, in the modified embodiments depicted in figure 1 a(ii), only upper edge of piezoelectric elements 110 protrude above even bottom matrix layer 118'. Force applied to upper load spreading layer 122a is spread among the plurality of piezoelectric elements 110. In this embodiment even bottom matrix layer 118' may be glued to lower conductive layer 112b, For example, lower load spreading layer 122b; lower conductive layer 112b and even bottom matrix layer 118' may be prepared together, and piezoelectric elements 110 inserted in holes 120. Alternatively, even bottom matrix layer 118' may be created by injection of plastic or epoxy material around piezoelectric elements 110 held in position by a holder thus holes 120 are formed by the piezoelectric elements 110 themselves during the injection. Figure 1a(iii) schematically depicts a cross section of a modular energy harvesting apparatus 100a" according to yet another exemplary embodiment of the current invention.

For simplicity, only the differences between modular energy harvesting apparatus 100a" and previously depicted embodiment are detailed in the figure and explained herein.

In a second modified embodiment of the invention, matrix layer 118 is replaced with flexible matrix layer 118". In the embodiment depicted in figure 1a(iii), both upper and lower edges of piezoelectric elements 110 are at the same level as edges of flexible matrix layer 118". In this embodiment, flexible matrix layer 118" is made of a flexible material such as rubber, silicon rubber, foam, etc. Flexible matrix layer 118" holds piezoelectric elements 110 and provides some resistance to horizontal shear forces that may be applied to the structure. Force applied between upper load spreading layer 122a and lower load spreading layer 122b is spread among the plurality of piezoelectric elements 110, squeezing flexible matrix layer 118".

This embodiment may be preferred where shear forces are limited such as pedestrian use, or implementation of the device 100a" inside a sole of a shoe.

In this embodiment flexible bottom matrix layer 118" may be glued to lower conductive layer 112b and to upper conductive layers 112a, holding the entire device 100a" together, In this case, optional fasteners 124 may be missing.

Optionally, matrix layer 118" may be created by injection of flexible material around piezoelectric elements 110 held in position by a holder thus holes 120 are formed by the piezoelectric elements 110 themselves during the injection. Figure 1b schematically depicts a cross section of a modular energy harvesting apparatus 100b according to another exemplary embodiment of the current invention.

For simplicity, only the differences between modular energy harvesting apparatus 100b and previously depicted embodiment are detailed in the figure and explained herein.

According to this exemplary embodiment of the current invention, upper and lower conductive load spreading layers 130a and 130b respectively are used for both spreading the load and electrically connect piezoelectric elements 110. Preferably, conductive load spreading layers 130 are metallic, mage of bronze, aluminum or other metal. Optionally steel is used.

Galvanized steel or similar corrosion protected metal may be used to ensure

• good electrical contact.

Preferably, electrical insulation layers 132a and 132b are applied or attached to load spreading layers 130a and 130b respectively.

Optionally, a cover layer 134 is affixed to upper part of apparatus 100b. Optional cover layer may be ceramic or wood decorative layer, thus enabling using module 100b as floor tiles.

For simplicity, only the differences between modular energy harvesting apparatus 100c and previously depicted embodiments are detailed in the figure and explained herein. According to this exemplary embodiment of the current invention, modular energy harvesting apparatus 100c is encased in insulation layer 140. For example, after assembling the modular energy harvesting apparatus 100c and connecting the leads, the entire structure may be dipped in insulating material such as molten bitumen. Alternatively, other insulation material may be used. However using bitumen is advantageous as it provides good moisture and electrical insulation. Additionally, bitumen advantageously and naturally adheres to asphalt used in roads and pavements. Optionally, modular energy harvesting apparatus 100a and or 100b may also be coated or dipped in bitumen.

Stand alone modular energy harvesting device 150 comprises a modular energy harvesting apparatus such as modular energy harvesting apparatus 100 (which may be any of 100a, 100b, or 100c or similar modular energy harvesting apparatus). Additionally, modular energy harvesting device 150 comprises an electronic module 152. Electronic module 152 is located under the modular energy harvesting apparatus 100 and preferably is attached to or glued to the modular energy harvesting apparatus 100.

Electronic module 152 comprises an energy harvesting electronic unit 114 receiving electrical energy from piezoelectric elements in energy harvesting apparatus 100 via leads 115.

Optionally, harvested energy is transferred to energy using system (not shown in this figure) through optional electrical cable 116.

Optionally, Energy harvesting electronic unit 114 is replaced with energy control unit 154. Energy control unit 154 receiving electrical energy from piezoelectric elements in energy harvesting apparatus 100 via leads 115 charges the energy storage 158. Energy storage 158 may be a rechargeable battery or a capacitor.

Stored energy is used for heat production in heaters 162 embedded in heating layer 160 affixed to upper layer of apparatus 100. Heating layer 160 may be made of bitumen or coated with bitumen to enable integration of alone modular energy harvesting device 150 in roads or pavements. Heaters

162 preferably comprise resistive heaters receiving electrical energy from energy control unit 154 via cable 164 when freezing temperature is detected by temperature sensor 167.

Optionally, electrical cable 166 is a two ways electric conduit, used to transfer energy to external energy utilization system when freezing conditions are not detected, such as during summer, and optionally receives external electrical energy to assist heating heaters 162 while temperature is low and traffic is sparse causing depletion of charge in energy storage 158, for example during cold winter nights. Preferably, electronic module 152 is encapsulated to protect it from moisture.

Additionally and optionally, a lower bitumen layer 168 enable integration of alone modular energy harvesting device 150 in roads or pavements. Figure 2a schematically depicts a partial horizontal cross section of a modular energy harvesting apparatus 100 according to an exemplary embodiment of the current invention.

Figure 2a depicts a horizontal cross section along the line A— A depicted in fig 1a. The figure shows matrix 118 having holes 120 for piezoelectric elements 110. The figure also shows optional hole 224 for optional fastener 124.

Lowe row in the drawing schematically depicts different exemplary shapes of holes and piezoelectric elements such as rectangular or square holes 120' and piezoelectric elements 110'. Alternatively, other shapes and combinations of shapes may be used.

Figure 2b depicts a horizontal cross section along the line A— A depicted in fig 1a. The figure shows light matrix 218 having holes 120 for piezoelectric elements 110. The figure also shows optional hole 224 for optional fastener 124.

In addition to holes 120, light matrix 218 have holes 220 reducing the amount of material used for making light matrix 218. Preferably, light matrix 218 is casted or made from extruded or injected plastic, thus reducing the amount of material used for manufacturing light matrix 218 reduces its cost. Alternatively, other shapes and combinations of shapes may be used for holes 120 and 220.

Load spreading layer with printed contacts 322 may replace both load spreading layer and the conductive layer. Any or both upper or lower layers may be replaced.

Load spreading layer with printed contacts 322 is preferably made of electrically insulating, rigid or semi-rigid material. An electrical conductive pattern of contacts 312 connected with traces 314 is printed onto the load spreading layer with printed contacts 322. Contacts 314 are located to make contacts with piezoelectric elements when the apparatus is assembled.

Preferably, production methods used in manufacturing electronic printed circuits are employed to manufacture the load spreading layers with printed contacts 322.

Electrical lead 115 is connected to the conductive pattern.

Optional hole 324 for optional fastener is also seen in this figure.

Preferably identical lower and upper load spreading layers with printed contacts 322 are used with the conductive patterns facing towards the piezoelectric elements.

Figure 3b schematically depicts heating layer 160 with embedded heaters 162 according to an exemplary embodiment of the current invention.

The electrical heater 162 is preferably made of electrical resistive wire patterned through heating layer 160 and having electrical contacts 364 to connect with cable 164 (not seen in this figure).

Figure 4 schematically depicts optional location of energy harvesting apparatuses 100 embedded in a road 410 according to an exemplary embodiment of the current invention. In the depicted example road 410 is a two lanes road or highway, however other number of lanes may be in the road. Preferably in at least on of the lanes, and optionally in few or all the lanes, energy apparatuses 100 are installed under the road's surface in two rows located where tires of passing vehicles are most probably make contact with the road. For example, a first row of apparatuses 100 may be located approximately 56 cm from the right curb or shoulder (left curb in country where traffic is on left of the road), and a second row at approximately 130 cm from the first row.

Preferably, apparatuses 100 are abutted to each other. Preferably, apparatuses 100 have mechanical properties, such as Young's module similar or identical to the asphalt used for the construction of the road. The close proximity of the apparatuses and the similarity in mechanical properties reduce the chance of creating vertical variation in road surface along the vehicles propagation direction due to pressure from passing vehicles. Such variations in the road surface may cause vibration to the passing vehicles and possibly loss of energy to said vehicles.

A typical asphalt road can be described as a visco-elasto-plastic material, with the elasticity being its dominant material characteristic. When vehicles travel on the road, the road's elasticity yields a vertical motion of the asphalt due to loading and unloading. Generators are typically embedded 3-4 cm beneath the top surface of the road during construction or re-pavement of roads. Embedding the piezoelectric generators under the upper asphalt layer enables harvesting the energy, which would otherwise be wasted. This "wasted" energy is stored in the piezoelectric generators and used to produce electricity, which is then accumulated in the storage system. The system works optimally when the traffic of cars and trucks is approximately 600 vehicles per hour.

For simplicity, electric cables connecting apparatuses 100 to energy utilization and/or storage unit, for example energy conditioning unit optionally supplying energy to electrical main grid, was omitted from this drawing. Figure 5a schematically depicts stages of embedding apparatus 100 in an existing road 510 according to an exemplary embodiment of the current invention.

At first stage (i), a trench 512 is cut into the road 510. Apparatuses 100 are than placed (ii) in the trench. The trench is then filled with a cover of asphalt 514 to the level of the original road surface.

Figure 5b schematically depicts stages of embedding apparatus 100 in an existing road 510' according to another exemplary embodiment of the current invention. At first stage (i), a shallow trench 512' is cut into the road 510'. Shallow trench 512' has a depth configured to fit the height of apparatus 100. Apparatuses 100 are than placed (ii) in the trench. The road is than covered (iii) with a bitumen sheet 520. This implementation method is preferred for roads where vehicle traffic is light or for pedestrian use. Figure 5c schematically depicts stages of embedding apparatus 100 in a newly constructed or resurfaced road 530 according to another exemplary embodiment of the current invention.

At first stage (i) road foundation is prepared during road construction or upper layer of a road is removed in preparation for road resurfacing. Apparatuses 100 are than placed on the road at stage (ii).

An asphalt cover layer 532 is than applied covering apparatuses 100 at stage (iii).

It should be noted that in figures 5a, 5b and 5c, apparatuses 100 may be any of the types disclosed herein and may comprise heating elements and/or energy conditioning and/or energy storage capabilities.

According to the depicted embodiment, energy harvesting apparatuses 100a, 100b or 100c are embedded in road 542. The plurality of energy harvesting apparatuses is connected to electronic module 552. Electronic module 552 is located in proximity to road 542 and receives electrical energy from piezoelectric elements in energy harvesting apparatus 100 via leads 515.

Electronics module 552 receiving electrical energy from piezoelectric elements in energy harvesting apparatus 100 via leads 515 and charges energy storage within said electronics module. Energy storage may be a rechargeable battery or a capacitor.

Stored energy is used for heat production in heaters 562 embedded in heating layer 560. Heating layer 560 may be made of bitumen or coated with bitumen to enable integration in roads or pavements. Heaters 562 preferably comprise resistive heaters receiving electrical energy from electronics module

552 via cable 564 when freezing temperature is detected by temperature sensor 567.

Optionally, electrical cable 166 is a two ways electric conduit, used to transfer energy to external energy utilization system when freezing conditions are not detected, such as during summer, and optionally receives external electrical energy to assist heating heaters 562 while temperature is low and traffic is sparse causing depletion of charge in energy storage 158, for example during cold winter nights.

It should be noted that the modular energy harvesting apparatus disclosed in the embodiments of the invention may be used in locations where mechanical energy is available in a form of recitative applied force.

The modular energy harvesting apparatus disclosed in the embodiments of the invention may be used outdoors. The outdoors use is not limited to roads. The apparatus may be used in streets and pavements and parking lots. Additionally, the apparatus may be adopted to be used in airport runways by being placed under, or integrated into the tarmac. Additionally, the apparatus may be adopted to be used in train railways by being placed under the sleepers or between a sleeper and a rail.

Alternatively, the modular energy harvesting apparatus disclosed in the embodiments of the invention may be used indoors. For example at any location where large number of pedestrians passing, as in entrances to theater halls, shopping malls, train stations, etc. 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 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. Accordingly, it is intended to embrace all such alternatives, modifications and variations that fall within the spirit and broad scope of the appended claims. All publications, patents and patent applications mentioned in this specification are herein incorporated in their entirety by reference into the specification, to the same extent as if each individual publication, patent or patent application was specifically and individually indicated to be incorporated herein by reference. 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.

Claims

1. A modular power harvesting apparatus comprising: an upper load spreading layer; a lower load spreading layer; a matrix layer between said upper and lower load spreading layers; and a plurality of piezoelectric elements embedded in said matrix layer, wherein said piezoelectric elements are adopted to generate electric energy in response to pressure applied to said upper layer.

2. The apparatus of claim 1 wherein said apparatus is adopted to be embedded in road such that said upper load spreading layer is facing the upper road layer.

3. The apparatus of claim 1 wherein said apparatus is adopted to be attached to a road such that said upper load spreading layer is facing the traveling vehicles.

4. The apparatus of claim 1 wherein said matrix layer has thickness smaller than the length of said piezoelectric elements allowing stress applied to said upper load spreading layer to be spread among said plurality of said piezoelectric elements.

5. The apparatus of claim 4 wherein said matrix layer is rigid.

6. The apparatus of claim 1 wherein said matrix layer is made of compressible material having thickness compatible with the length of said piezoelectric elements, allowing stress applied to said upper load spreading layer to be spread among said plurality of said piezoelectric elements.

7. The apparatus of claim 1 wherein in the cross section of the apparatus, the total area of said piezoelectric element is less than 30 percent of the total area of said apparatus.

8. The apparatus of claim 1 wherein in the cross section of the apparatus, the total area of said piezoelectric element is less than 10 percent of the total area of said apparatus.

9. The apparatus of claim 1 wherein said load spreading layers are rigid.

10. The apparatus of claim 1 wherein said load spreading layers are semirigid.

11. The apparatus of claim 1 and further comprising electric cables for transferring said generated energy to energy utilization unit external to said modular apparatus.

12. The apparatus of claim 1 and further comprising electronic module located blow said lower load spreading layer, wherein said electronics module receives electrical power generated by said piezoelectric elements in response to mechanical force applied to said upper load spreading layer.

13. The apparatus of claim 12 wherein said electronic module comprises electrical energy storage.

14. The apparatus of claim 12 wherein said electronic module further comprises a temperature sensor.

15. The apparatus of claim 14 and further comprising heating elements embedded in a heating layer located above said upper load spreading layer, wherein said heating elements receives electrical power from said electronic module in response to signal receives from said temperature sensor.

16. The apparatus of claim 14 and further comprising heating elements embedded in said upper load spreading layer, wherein said heating elements receives electrical power from said electronic module in response to signal receives from said temperature sensor.

17. The apparatus of claim 1 and further comprising: an upper electrode layer located above, and making electrical contact with said plurality of piezoelectric elements embedded in said matrix layer; and a lower electrode layer located below, and making electrical contact with said plurality of piezoelectric elements embedded in said matrix layer.

18. The apparatus of claim 17, wherein said upper electrode layer and said lower electrode layer are load spreading layers configured to evenly spread external mechanical load among said piezoelectric elements.

19. The apparatus of claim 1 wherein upper surface of said apparatus comprises bitumen.

20. The apparatus of claim 19 wherein lower surface of said apparatus comprises bitumen.

21. The apparatus of claim 20 wherein said upper layer and said lower surfaces of said apparatus are adapted to integrate to road structure.

22. The apparatus of claim 20 wherein said upper layer and said lower surfaces are adapted to provide moisture protection.

23. The apparatus of claim 1 and further comprising a wrapper adapted to provide moisture protection.

24. A modular energy harvesting system comprising: a road; and a plurality of modular apparatuses, wherein at least one of said modular apparatuses comprises: an upper load spreading layer; a lower load spreading layer; a matrix layer between said upper and lower load spreading layers; and a plurality of piezoelectric elements embedded in said matrix layer, wherein said piezoelectric elements are adopted to generate electric energy in response to pressure applied to said upper layer; wherein said apparatus is adopted to be attached to a road such that said upper load spreading layer is facing the traveling vehicles.

25. The system of claim 24 wherein said at least one modular apparatus further comprises heating elements.

26. The system of claim 25 wherein said generated energy is used to power said heating elements.

27. The system of claim 24 and further comprising energy storage for storing said generated energy.

28. The system of claim 24 wherein a plurality modular apparatus are attached side by side to said road such that gaps between adjacent apparatuses is substantially smaller than the size of an apparatus.

29. The system of claim 28 and further comprising a covering asphalt layer, covering said modular apparatus.

30. A method of energy harvesting comprising: attaching at least one modular energy harvesting apparatus to a road, said apparatus comprising: an upper load spreading layer; a lower load spreading layer; a matrix layer between said upper and lower load spreading layers; and a plurality of piezoelectric elements embedded in said matrix layer, wherein said piezoelectric elements are adopted to generate electric energy in response to pressure applied to said upper layer; and harvesting energy generated by said piezoelectric element in response to pressure applied to said upper layer by a vehicle passing over said modular apparatus.

31. The method of claim 30 wherein attaching said modular apparatus to the road comprises applying an asphalt covering layer over said modular apparatus.

32. The method of claim 30 wherein attaching said modular apparatus to the road comprises adding a covering bitumen layer over said modular apparatus.