Broadband energy harvester apparatus and method

An energy harvesting apparatus and method for harvesting vibration energy over a wide frequency band and at low amplitudes. The apparatus includes a reaction component that is supported by a plurality of independent piezoelectric flexures from a base. The flexures are secured to the base and to portions of the reaction component so that they create equal but opposite constant moments applied to the reaction component that cancel one another out. As the base experiences lateral vibration energy, this causes a swinging or rolling motion of the reaction component, that causes changes in stress and/or strain experienced by the flexures. This causes the flexures to generate electrical signals that can be used powering external devices.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is related in general subject matter to U.S. patent application Ser. No. 11/613,893, filed Dec. 20, 2006, which is also hereby incorporated by reference into the present application.

FIELD

The present disclosure relates to energy harvesting devices and methods, and more particularly to a broadband energy harvesting apparatus and method that is able to generate electric signals in response to vibration experienced by a component from which the apparatus is supported.

BACKGROUND

Vibration energy is experience by many types of apparatuses and systems, and particularly with mobile platforms such as aircraft, land based vehicles, marine vehicles, rotorcraft, etc. Various attempts have been made to harvest such vibration energy to generate electric signals that can be used for various purposes, for example for powering actuators, sensors, or various other electronic devices.

Present day energy harvesting devices and methods, however, are not particularly sensitive to vibration energy over a broad frequency range. Often, present day energy harvesting devices must be designed with a specific operating frequency, or a specific, relatively narrow frequency operating range in mind, to provide acceptable energy harvesting results. Additionally, many present day energy harvesting devices are not especially sensitive to low amplitude vibration signals.

Accordingly, there still exists a need for an energy harvesting device and method which is responsive to vibration energy over a wide frequency band and at low amplitudes. There further exists a need for an energy harvesting apparatus and method that can be implemented with a relatively small number of independent component parts.

SUMMARY

The present disclosure relates to an energy harvesting apparatus and method that is well suited for use over a broad frequency band of vibration energy, and is further highly responsive to low amplitude vibration energy. In one implementation a base component is secured to a structure experiencing vibration. A reaction component is supported adjacent to the base by at least one flexure. The flexure is secured at a first portion to a portion of the base, and at a second portion to the reaction component. The flexure is capable of generating electrical signals in response to flexing movement thereof caused by motion of the reaction component.

In operation, as the structure experiencing vibration vibrates, the vibration is transmitted to the base. As the base vibrates, this causes a lateral motion of the reaction component, which in turn causes flexing of the flexure. The flexing causes the flexure to experience stress and/or strain. The stress and/or strain experienced by the flexure causes the flexure to generate electrical signals. The electrical signals can be used for a wide variety of purposes, for example, for powering sensors, actuators or other electronic devices or instruments.

In one implementation the flexure includes a piezoelectric material that is supported on a flexible support substrate. The piezoelectric material responds to stress and/or strain by generating electrical signals.

In one specific implementation a portion of the base has a curved surface, and a portion of the reaction component also has a curved shape. As the reaction component experiences vibration it moves in a rolling motion about an arc defined by the curvature of the curved surface of the base component.

In still another implementation, a plurality of flexures support the reaction component from the base. In one implementation the reaction component is supported so as to be spaced apart from the base portion. In still another implementation the reaction component is supported so that it is suspended from the base. The reaction component resists movement as the base experiences vibration energy, which causes stress and/or strain to be experienced by the flexures, which in turn causes the flexures to generate electrical signals.

In still another implementation, at least one flexure is used that is comprised of a support substrate having a plurality of electrically independent electrodes formed on a continuous length of a piezoelectric material layer. The use of a plurality of electrically independent electrodes on the piezoelectric material layer eliminates the parasitic capacitance that can be induced in those areas of the flexure that are not undergoing stress and/or strain as the reaction mass is moving in response to vibration. This significantly improves the efficiency of the electrical output of the flexure.

DETAILED DESCRIPTION

Referring toFIGS. 1 and 2, there is shown an energy harvesting apparatus10in accordance with an embodiment of the present disclosure. In this embodiment, the apparatus10generally includes a base12, a reaction component14and three flexure components16,18and20. The flexure components16,18and20are used to support the reaction component closely adjacent to the base component while allowing a rolling motion of the reaction component14about the base12. The flexures16,18and20are able to generate electrical signals in response to stress and/or strain that they experience during flexing motion as the reaction component14rolls about the base12. The electrical signals are fed to a signal conditioning circuit22and thereafter may be used to power various forms of electronic devices such as actuators, sensors, etc.

Referring further toFIGS. 1 and 2, the base12includes a pair of flanges24which may be used to receive conventional threaded fastening elements26through threaded openings (not shown) to allow the base12to be secured to a vibrating structure28. The vibrating structure28may form a portion of the mobile platform, for example, an aircraft, rotorcraft, an automotive vehicle, a train, marine vessel or any other form of vehicle or structure that experiences vibration energy that would be desirable to harvest. The base12includes a curved upper surface30forming an arc. The reaction component14is supported by the flexures16,18and20so that lateral vibration energy experienced by the base12causes a rolling or rocking motion of the reaction component14about an arc defined by the curved upper surface30. The base12may be made from aluminum, steel, plastic, composites, or any other suitably strong material.

The reaction component14includes a semi-circular portion32having a curved surface34, and a block36acting as a mass that is secured to the semi-circular portion32. The block36may be made from aluminum or steel or any other component that adds tangible mass to the reaction component14. Alternatively, the reaction component14may be formed as a single piece component from a single piece of material. If manufactured as a single piece component, then the reaction component14may be manufactured from aluminum or steel, or any other suitable material that enables a tangible amount of mass to be added by the block36portion of the overall reaction component14.

The mass of the block36functions to move the center of gravity away from the fulcrum area38of the semi-circular portion32, thus significantly increasing the moment produced by the reaction component14as a lateral vibration force is experienced. This significantly increases the tendency of the reaction component14to roll back and forth on the base12in response to an oscillating, lateral vibration force experienced by the base12. In one implementation, the radius of curvature of the curved surface34is approximately 0.375 inch (9.525 mm), and the width of the semi-circular portion32is approximately 1.25 inch (31.75 mm). In this implementation, the radius of curvature of the curved surface30of the base12is also about 0.375 inch (9.525 mm). It will be appreciated that these dimensions may vary significantly depending on the vibrating structure to which the apparatus10is secured, the magnitude of lateral vibration energy that is being harvested, and even the materials used for the base12and the reaction component14.

Referring toFIGS. 3 and 4, the attachment of the flexure18(FIG. 3) and the flexure20(FIG. 4) to the base12is illustrated. Referring initially toFIG. 3, a bead of adhesive40is used to secure an inside surface42of flexure18to the curved surface34of the reaction component14. As noted from the drawing figure, the adhesive40may be placed adjacent one outermost end18aof the flexure18, rather than continuously along its inside surface42. The adhesive may comprise epoxy or any other suitable adhesive that provides a secure bond. The opposite end of flexure18is similarly secured by a bead of epoxy or suitable adhesive, as indicated by dashed line44inFIG. 2. Thus, the flexure18may be secured only at its outermost end portions to the reaction component14and to the base12allowing maximum roller travel. The flexure16is secured to the reaction component14and to the base12in the same fashion as described above for flexure18.

Referring toFIG. 4, the flexure20is similarly secured by a bead of adhesive46, possibly comprising epoxy or any other suitable strong adhesive, at one outermost end20athereof. The bead of adhesive46is placed along an inner surface48of the flexure20along its outermost end20a. The opposite end of the flexure20is secured by a similar bead of adhesive as indicated by dashed line50inFIG. 1. Thus, the flexure20may also be secured only at its outermost end portions to the reaction component14and to the base12.

Referring toFIGS. 5 and 6, the construction of flexures18and20, respectively, can be seen in greater detail. In this example the construction of flexure18is identical to that of flexure16, although the two flexures need not necessarily be constructed in identical fashion. The flexures16,18and20are all constructed so that they are flat prior to being installed. Once installed, each is held in a flexed orientation under tension. The biasing forces provided by flexures16and18counter balance the biasing force of flexure20so that the reaction component14is held in the neutral position shown inFIGS. 1 and 2. In this example the flexures16,18and20each form unimorph piezoelectric flexures.

InFIG. 5, flexure18, in one embodiment, includes a support substrate54on which is disposed an electrically responsive layer of piezoelectric material52, which in this example may be a piezoceramic material layer. The piezoelectric material layer52includes a plurality of independent, electrically conductive electrode segments52aformed one of its surfaces. The independent electrode segments52aeach have a conductive lead52a1extending therefrom. Electrode segments52amay be formed during manufacture of the flexure18by first depositing a conductive material, for example copper, onto the piezoceramic material layer52and then etching a plurality of spaced apart parallel slots completely through the thickness of just the conductive layer. This results in the plurality of independent, electrically conductive electrode segments52athat do not impact the overall thickness or flexibility of the flexure18. Each electrode segment52ais used to capture and transmit the electrical energy generated by the stress and/or strain experienced in the area of the piezoceramic material layer52immediately beneath it.

In this example the support substrate54has a width “W” and a thickness denoted by arrows55. The width of the piezoelectric material layer52is approximately equal to the width (W) of the substrate54, but does not necessarily need to be equal. The support substrate54may be formed from any material that is able to be flexed repeatedly without breaking or fracturing. For example, composite materials or spring steel may be used to form the support substrate54. A uniaxial composite beam is especially well suited for use as the support substrate54.

The piezoelectric material electrode segments52aare also shown inFIG. 5as all being of the same length, width and thickness, although this is merely meant to illustrate one example of a suitable configuration of electrode segments for use with the flexure18. In practice, the independent electrode segments52amay vary from one another in one or more dimensions of length and width to suit the needs of a specific application. In the exemplary configuration shown inFIG. 5, the length and width of each electrode segment52aform a generally square shape. The overall thickness of the piezoelectric material layer52and the electrode segments52amay vary significantly to suit the needs of a specific application, but in one example is between about 0.005-0.020 inch (0.127-0.508 mm).

The use of independent piezoelectric material electrode segments52aprovides the additional advantage of reducing parasitic capacitance for those segments that are not experiencing stress and/or strain during rolling motion of the reaction component14. This increases the efficiency of each flexure16and18in generating electrical signals in response to small amplitude vibration energy. However, if high sensitivity to low amplitude vibration is not an important design criterion, of if the cost of manufacture is an especially important concern, then a single length of electrode material may be used in place of the plurality of independent electrode segments52aon the piezoelectric material layer52.

When the flexure18is flexed into the position shown inFIGS. 1 and 2, the piezoelectric material electrode segments52that are in contact with the curved surface34are mostly in compression. Thus, for example, if flexures16and20were not present in the apparatus10shown inFIG. 1, the reaction component10would roll to the left in the drawing ofFIG. 1(i.e., to straighten out as much as possible).

The flexure20ofFIG. 6is essentially identical in construction to the flexure18with the exception that its width “W” may be about twice the width (i.e., “2W”) of the flexure18inFIG. 5. This is so that the flexure20can provide a biasing force that is approximately equal and opposite to the biasing force provided by the flexures16and18, to thus maintain the reaction component14centered on the base12when no vibration energy is being experienced. The flexure20similarly includes an independent, electrically responsive material layer, which in this example comprises a piezoelectric material layer56that is secured to a flexible support substrate58.

The support substrate58may also comprise a composite material, such as a uniaxial composite beam, or possibly a length of spring steel, or any other suitable material that is flexible and resistant to breaking or fracturing during repeated flexing. The dimensions of the piezoelectric material layer56may be similar to those given for layer52, or they may differ from that of material layer52. Independent electrode segments56aare formed on the piezoelectric material layer56that each have a conductor56a1extending therefrom. Each of the piezoelectric electrode segments56aenable the electrical signals generated by its associated area of the piezoelectric material layer56to be routed to the signal conditioning circuit22. Adhesives such as HYSOL® 9330 or LOCTITE® 3411 epoxy may be used to secure the piezoelectric material layer56to the support substrate58, as well as to secure the piezoelectric material layer52to the support substrate54(FIG. 5).

While the flexures16,18and20have been described above as comprising piezoelectric material on one surface thereof (to thus form unimorph piezoelectric structures), it will be appreciated that other electrically responsive materials could just as readily be incorporated. For example, in lieu of piezoelectric material, magnetostrictive material could used. Virtually any other type of material that is able to generate electrical signals in response to changes in stress and/or strain that it experiences could potentially be implemented.

As noted inFIGS. 1 and 2, the flexure20is secured to the curved surface34of the reaction component14along the opposite side as those of flexures16and18. For example, if flexures16and18were not present, the biasing force provided by flexure20would cause the reaction component14to roll to the right inFIG. 1. However, when all three flexures16,18and20are secured to the reaction component14, the biasing forces provided by flexures16and18work against the biasing provided by flexure20, thus creating a “constant moment” for the reaction component14. This arrangement also overcomes the inherent stiffness of the flexures16,18and20, which enables the reaction component14to be highly sensitive to even small degrees of lateral vibration energy experienced by the base20.

Referring toFIGS. 7 and 8, the operation of the apparatus10will be described in greater detail. InFIG. 7, when the base12experiences a lateral vibration force in accordance with directional arrow60, a moment is created that causes the reaction component14to roll along the path defined by the curved upper surface30of the base12, in accordance with arrow62. This causes unflexing of the flexures16and18(i.e., de-compression), thus causing the piezoelectric material layer52disposed adjacent the curved surface30to experience a change in the stress and/or strain from that experienced when the reaction component14is at its neutral, resting position. This change in the stress and/or strain being experienced by the piezoelectric material layer52causes the piezoelectric electrode segments52ato generate electrical signals. Similarly, the area of the flexure20adjacent the point of contact between the reaction component14and the base12experiences different levels of stress and/or strain as it becomes compressed, as the reaction component rolls to the left inFIG. 7. This causes the piezoelectric material layer56of the flexure20to experience changing levels of stress and/or strain. This results in the electrode segments56agenerating electrical signals simultaneously with those being generated by the flexures16and18. All of these electrical signals are transmitted to the signal conditioning circuit22and subsequently output from the circuit22for use in powering and/or controlling other electrical components.

Referring toFIG. 8, as the lateral vibration force changes direction in accordance with arrow64, the reaction component14is caused to roll to the right in accordance with arrow66. This causes the piezoelectric material layers52of flexures16and18to flex into compression, thus experiencing changing levels of stress and/or strain and causing electrical signals to be generated by specific ones of the electrode segments52a. Simultaneously, flexure20is urged into a more planar configuration, which causes its piezoelectric material layer56to de-compress, and thus to also experience a change in the level of stress and/or strain that it is experiencing. The changing levels of stress and/or strain result in electrical signals being generated by specific ones of the electrode segments56a. Thus, during this rolling motion, all of the flexures16,18and20generate electrical signals. Once the vibration energy stops, the biasing force provided by the flexures16,18and20returns the reaction component14to the orientation (i.e., neutral position) shown inFIGS. 1 and 2. Thus, regardless of the lateral direction of the vibration force being experienced by the base20, the flexing imparted to the flexures16,18and20by the rolling motion of the reaction component14causes electrical signals to be generated by each flexure16,18, and20. This is so regardless of the direction of rolling movement of the reaction component14

Referring now toFIG. 9, an apparatus100in accordance with another embodiment of the present disclosure is illustrated. Components in common with apparatus10are designated with reference numerals increased by 100 over those used in connection with the description of apparatus10. The apparatus100includes a base112and a reaction component114. A plurality of flexures116and120are used to support the reaction component114from the base. Flexures116and118are arranged with flexure118being positioned between a pair of flexures116(only one of flexures116being visible in the side view ofFIG. 9) in a manner identical to that described for flexures16,18and20of apparatus10(FIGS. 1 and 2). However, rather than the reaction component114rolling about the curved surface30of the base12illustrated inFIG. 1, the flexures116and118are used to support the reaction component114a distance above the base112. Lateral vibrational movement in accordance with directional arrow170causes a swinging motion of the reaction component114in accordance with arc172inFIG. 9. The flexures116and118operate in the manner described for flexures16,18and20to generate electrical signals, regardless of the direction in which the swinging component114is moving, as they each experience changing levels of stress and/or strain while flexing.

FIG. 10illustrates an apparatus200in accordance with yet another embodiment of the present disclosure. The apparatus200is identical in construction to apparatus100ofFIG. 9, and components in common with those described in connection withFIG. 9are increased by100over the numbers used inFIG. 9. However, with the apparatus200, a reaction component214is suspended from a base212. Lateral vibration energy in accordance with directional arrow170causes a swinging motion of the reaction component214in accordance with arc172. Flexures216and218each generate electrical signals with each swinging motion of the reaction component214, regardless of the direction in which the component214is moving, as the flexures216and218experience changing levels of stress and/or strain during flexing movement. The biasing force provided by flexures216and218operates to return the reaction component214to its initial (i.e., neutral) position, shown in solid lines inFIG. 10, once the vibration energy ceases.

Referring toFIG. 11, still another embodiment300of the present disclosure is illustrated. Components in common with those of the apparatus10are designated with reference numerals increased by200over those used to describe apparatus10. The apparatus300includes a reaction component314that is supported on a base312. Flexures316,318and320are used to secure the reaction component314to the base312in a manner identical to that described in connection with apparatus10. The principal difference is that the base312includes a flat upper surface330, rather than the curved upper surface30of base12. As such, the reaction component314rolls along a flat, planar surface as it experiences a lateral vibration force in accordance with directional arrow172. The operation of the flexures316,318and320are otherwise identical to that described for flexures16,18and20.

The various embodiments described herein all provide for an energy harvesting apparatus and method that enables a wide frequency band of vibration energy to be harvested to power various forms of external device or to perform other useful functions. A particular advantage of the embodiments described herein is that each of the embodiments are sensitive to low amplitude vibration energy as a result of the constant moment supporting arrangement provided by the flexures described herein. The use of flexures having segmented piezoelectric material electrodes improves even further the efficiency of the apparatus10in generating electrical signals from small amplitude vibration energy. The various embodiments described herein may be responsive to vibration energy having a frequency as low as 2.5 Hz-20 Hz, or possibly even lower. Usable electrical power may be produced from vibration energy having as little as 0.01 G rms acceleration, or possibly even lower amounts of vibration energy. The various embodiments of the present disclosure are especially well suited to aircraft, aerospace and automotive applications where remote sensors and actuators need to be used, but where routing power supply lines to the sensor or actuator would be difficult or impossible, as well as costly.