WO2020190215A1

WO2020190215A1 - Dielectric-elastomer-amplified piezoelectrics to harvest low frequency motions

Info

Publication number: WO2020190215A1
Application number: PCT/SG2020/050147
Authority: WO
Inventors: Soo Jin Adrian KOH; Anup Teejo MATHEW; Chong LIU; Tian Yao Nicholas NG
Original assignee: National University Of Singapore
Priority date: 2019-03-21
Filing date: 2020-03-19
Publication date: 2020-09-24

Abstract

An apparatus includes a dielectric elastomer generator (DEG) and a priming circuit. The DEG generates electrical energy from elastic energy. The priming circuit provides voltage to prime the DEG and includes a piezoelectric generator coupled to the DEG via a full-wave rectifier.

Description

Dielectric-Elastomer-Amplified Piezoelectrics to Harvest Low Frequency

Motions

TECHNICAL FIELD

[0001] The present invention generally relates to methods and apparatuses that harvest low frequency motions known as dielectric-elastomer-amplified piezoelectrics.

BACKGROUND OF THE DISCLOSURE

[0002] Electroactive polymers (EAPs) are flexible, compliant, and light-weight electromechanical transducers. In addition, noiseless operation and high-energy density accords EAPs the promise of being a versatile actuator comparable in performance with biological muscles and an energy harvester. Dielectric elastomers are electronic-based EAPs that are activated by means of electric field and charge polarization. Being electronic-based, the time scale for electromechanical activation is in the order of milliseconds or lesser.

[0003] A mechanically stretched dielectric elastomer may be pie-charged via a high voltage source while it is stretched. Upon relaxation, elastic energy works against the electrostatic force and thereby increases the electrical potential of the charges placed on the dielectric elastomer. Elastic energy is thus converted to electrical energy. The dielectric elastomer thus generates electrical energy from a mechanical input.

[0004] Having to pre-charge a dielectric elastomer presents a significant disadvantage compared with existing electromechanical energy conversion systems like the piezoelectric, triboelectric, and electromagnetic systems. However, having the ability to undergo large mechanical deformation and thereby packing in large amounts of mechanical energy suggests that the dielectric elastomer could be used as a viable source of energy if various technical challenges with dielectric elastomers can be overcome.

SUMMARY

[0005] Example embodiments include methods and apparatus that utilize dielectric- elastomer-amplified piezoelectrics to harvest low frequency motions.

[0006] One example embodiment is an apparatus that includes a dielectric elastomer generator (DEG) and a priming circuit. The DEG generates electrical energy from elastic energy. The priming circuit provides voltage to prime the DEG and includes a piezoelectric generator coupled to the DEG via a full- wave rectifier.

[0007] Another example embodiment is an apparatus that harvests energy. The apparatus includes a dielectric elastomer (DE) that generates electrical energy from compressive loading that stretches the DE. A piezoelectric generator electrically couples to the DE. A ripple structure includes a top structure and a bottom structure.

The DE is positioned between the top and bottom structures that deform ripples into the DE to generate the electrical energy from the compressive loading.

[0008] Another example embodiment is an energy harvester that includes a dielectric elastomer generator (DEG) and a circuit. The DEG generates electrical energy from compressive loading that deforms ripples into a dielectric elastomer. The circuit provides voltage to prime the DEG and includes a piezoelectric generator.

[0009] Other example embodiments are discussed herein. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The accompanying figures, where like reference numerals refer to identical or functionally similar elements throughout the separate views and which together with the detailed description below are incorporated in and form part of the specification, serve to illustrate various embodiments and to explain various principles and advantages in accordance with example embodiments.

[0011] Figure la shows a dielectric elastomer generator (DEG) being charged prior to mechanical relaxation in accordance with an example embodiment.

[0012] Figure lb shows the DEG being relaxed with a voltage boost in accordance with an example embodiment.

[0013] Figure 2 shows an electrical circuit for a dielectric-elastomer-amplified piezoelectric (DEAmP) in which a piezoelectric is used as a priming source in accordance with an example embodiment.

[0014] Figure 3 is a diagram showing the triangular DEAmP cycle which represents the energy harvesting process on a voltage-charge plane in accordance with an example embodiment.

[0015] Figure 4 shows a DE membrane to illustrate the ripple mode of deformation in accordance with an example embodiment.

[0016] Figure 5 shows a mechanism to deform the DE in ripple mode and to create an interlocking system in accordance with an example embodiment.

[0017] Figure 6a is a dielectric elastomer (DE) frame in accordance with an example embodiment.

[0018] Figure 6b is the DE frame attached to a pre-stretched DE membrane in accordance with an example embodiment.

[0019] Figure 7a is a base structure in accordance with an example embodiment. [0020] Figure 7b is a buzzer type piezoelectric assembled on the base structure in accordance with an example embodiment.

[0021] Figure 8 is a piezo-presser to deform a piezoelectric in accordance with an example embodiment.

[0022] Figure 9a is a top view of a ripple bottom structure in accordance with an example embodiment.

[0023] Figure 9b is a bottom view of the ripple bottom structure in accordance with an example embodiment.

[0024] Figure 10a is a top view of ripple top structure in accordance with an example embodiment.

[0025] Figure 10b is a bottom view of ripple top structure in accordance with an example embodiment.

[0026] Figure 11a is an exploded view of a piezoelectric structure in accordance with an example embodiment.

[0027] Figure lib is a cross-sectional view of the piezoelectric structure in accordance with an example embodiment.

[0028] Figure 12 is an electrical circuit for a DEAmP in accordance with an example embodiment.

[0029] Figure 13a is a DEAmP in an undeformed state in accordance with an example embodiment.

[0030] Figure 13b is the DEAmP in a fully deformed state in accordance with an example embodiment.

[0031] Figure 14 is a DEAmP adapted as a heel strike generator in accordance with an example embodiment. [0032] Figure 15 is a DEAmP prototype integrated into a traffic speed bump 1500 in accordance with an example embodiment.

[0033] Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been depicted to scale.

DETAILED DESCRIPTION

[0034] The following detailed description is merely exemplary in nature and is not intended to limit example embodiments or their uses. Furthermore, there is no intention to be bound by any theory presented in the preceding background or the following detailed description. It is the intent of the present embodiments to present unique methods and apparatus that utilize dielectric-elastomer-amplified piezoelectrics to harvest low frequency motions.

[0035] Dielectric elastomer generators (DEGs) are rubbery membranes made active by coating compliant electrodes on both its planar surfaces. Cyclically stretching and relaxing a piece of DEG stores and releases both mechanical energy and electrical charges that allows DEGs to perform as a charge pump.

[0036] Advantages of DEGs compared with other energy harvesting technologies include low cost, noise-free operation, excellent resistance to corrosion, good impedance matching to many energy sources, and high energy density. Further, the energy density of a DEG is at least one order of magnitude higher than existing technologies, such as piezoelectrics, triboelec tries, and electromagnetic generators.

[0037] In spite of these advantages, conventional DEGs have shortcomings. For example, a conventional DEG can only pump charges from a low electrical potential to a high electrical potential when a charge source supplies charges to it. This usually requires a high voltage transfer on the order of 200V and above. Also, to achieve a high energy density, a conventional DEG must be deformed to strains in excess of

100%. These and other shortcomings present technical challenges for DEGs to be used in small and medium-scale energy harvesting.

[0038] For example, several prior attempts were done to provide high voltage priming to a dielectric elastomer. For instance, one conventional approach proposed a self-priming circuit (SPC) that makes the dielectric elastomer generator (DEG) to be able to progressively step up voltage from a low voltage source of 10V. However, the self-priming DEG still requires an external low voltage priming source. Microbial fuel cells and solar cell arrays are used as alteratives. However, microbial fuel cells and solar cells harvests energy from sources other than mechanical motion, presenting a physical mismatch to DEG. A self-primed DEG requires a number of cycles to increase its low voltage into a desirable range (~ 1000 V). If the mechanical source is not periodic or of very low frequency, excessive charge leakage will lead to a voltage step-down rather than a voltage boost, making its operation ineffective.

[0039] Another conventional approach used an electret as priming source. However, electrets are not readily available and are expensive to purchase or produce. Electrets also require priming from plasma discharge and its charges will eventually be depleted, requiring further charging.

[0040] Piezoelectrics were previously studied as priming sources, such as a mechanism to integrate the elastomer and a piezoelectric generator. With these techniques, however, the prototype relies on stretching motion to operate, which presents great challenges for small-scale integration. By contrast, as discussed further below, an example embodiment of the invention instead relies on a compressive type loading to stretch the elastomer, which enables easy integration to small-scale energy harvesting.

[0041] Prior works also exist that induce large deformation in a constrained space for the dielectric elastomer. Deformation modes such as, fluid inflated diaphragm configuration, stack configuration, compression mat configuration, and loudspeaker or diaphragm configuration are investigated for this purpose. From the geometry of the initial and deformed shape, the maximum change in capacitance for a fluid inflated diaphragm type DE (inflated into a hemisphere) is about 4 times. For an ideal stack mode to have a capacitance change of 4 times it must compress to half of its initial height. For the compression mat design, the elastomer is stretched very lightly due to its small amplitude ripples aligned in a single direction, giving very small capacitance changes of less than 2 times. Also, the elastomer has open edges which affect its durability. In a diaphragm or loudspeaker mode the elastomer is stretched into its out of plane direction using an inner disk.

[0042] Example embodiments solve these problems and other prior technical challenges associated with dielectric elastomers and enable them to be an efficient and effective source of energy.

[0043] One or more example embodiments couple a dielectric elastomer (DE) or dielectric elastomer generator (DEG) with a piezoelectric generator that enables pie- charging of the dielectric elastomer with a high voltage source. By introducing the ripple mode of deformation, the example embodiment enables large capacitance changes of 10 to 50 times within a constrained space. As such, this example embodiment can be adapted into various apparatus and methods that harvest low frequency and sporadic motions. [0044] The ripple mode of deformation has a capacitance change similar to that of a diaphragm mode, but within a smaller space. The ripple mode of deformation induces one or more ripples in an axis-symmetric formation, thereby utilizing the entire planar surface of the membrane. In an example embodiment of the invention, the mode of deformation is amenable to user-designed number of ripples over a given circular planar area, allowing a capacitance ratio of between 10 and 50 times to be achieved in a constrained space. In one embodiment, the DE film for ripple mode has all its edges reinforced and secured by a rigid frame and is easy to produce and to stack.

[0045] An example embodiment is a hybrid energy harvester in which the DEG is coupled with a piezoelectric generator. In this way, the piezoelectric generator acts as a high voltage priming source for the DEG, and the DEG amplifies the voltage of the piezoelectric charges. This embodiment is termed a dielectric-elastomer-amplified piezoelectric (DEAmP).

[0046] Example embodiments can be utilized in a variety of methods and apparatus. By way of example, such apparatus and method include human motion, such as integrating an example embodiment into footwear or a device worn on or attached to a person. Other examples include harvesting energy from motion from a machine, such as a bicycle or automobile. Still other examples include stationary objects, such as harvesting energy from speed strips of speed bumps in the road.

[0047] For small-scale applications, like harvesting energy from human motion, an example embodiment utilizes the ripple mode to maximize capacitance change via mechanical deformation within a constrained space. Such embodiments include mechanical and/or electrical apparatus that synchronize charging and discharging of the dielectric elastomer for optimal charge transfer. [0048] Consider an example embodiment that extracts energy from a heel strike.

The available mechanical power from an average human heel strike is estimated to be around 7 Watts. Traditional energy harvesters like electromagnetic generators or piezoelectric generators typically require high frequency motion. Hence, they cannot effectively harvest such low frequency (~ 1 Hz) and medium heel compression stroke of 5 cm without complex mechanical components coupled to them. An example embodiment of the invention solves this problem.

[0049] The example embodiment includes a heel-like energy harvester that deforms the dielectric elastomer in ripple mode with an integrated energy harvesting circuit. This embodiment is adapted as a heel strike energy harvester to harvest energy from human motion, such as walking, jogging, running, etc. Consider an example in which the DEAmP is integrated into a sole or heel of a shoe that harvests energy from heel strikes. The harvested energy is used to power a body sensor, charge a battery, power an electronic device, illuminate a light, etc.

[0050] Example embodiments can also be expanded to harvest motions from any low frequency or sporadic mechanical or electrical sources. For example, speed strips or speed bumps are deployed in roads to regulate the vehicle speed. DEAmP can be used with such speed bumps to harvest energy from vehicular motion. As the vehicle moves over the speed strip or speed bump, the tires exert a downward force that presses the DEAmP prototype to generate energy. The generated energy may be used to supply power for traffic lights and traffic monitoring and sensing systems.

[0051] Figure la shows a dielectric elastomer generator (DEG) 100 being charged prior to mechanical relaxation in accordance with an example embodiment. An equal biaxial force of P acts on the elastomer. F is the voltage applied. [0052] Figure lb shows the DEG 100 being relaxed with a voltage boost in accordance with an example embodiment. F’ is the voltage boost upon full mechanical relaxation.

[0053] The DEG 100 includes an elastomer membrane 101 sandwiched by compliant electrodes 102. In-principle, the DEG 100 is a stretchable capacitor. When the DEG is mechanically stretched, it stores elastic energy. When it is charged via a priming source (Figure la), a small amount of electrical energy gets stored in a capacitive form. When the elastomer is mechanically relaxed, elastic energy works against the electrostatic pressure, thereby increasing the electrical potential (Figure lb).

[0054] Conventionally, a DEG is primed using a high voltage source. An example embodiment, however, uses a piezoelectric as its priming source to spare the need for the DEG to be tethered to an external electrical source. This will allow the DEG to be fully autonomous and free-standing.

[0055] Figure 2 shows an electrical circuit 200 for a DEAmP in which a piezoelectric is used as a priming source in accordance with an example embodiment.

[0056] The piezoelectric 201 provides voltages in excess of 150 V to prime the

DEG. The DEG is represented as a variable capacitor 202. The circuit 200 is divided into two parts: the priming circuit 210 and the harvesting circuit 220.

[0057] The priming circuit 210 consists of components to prime the DEG. A piezoelectric generator 201 is connected to the DEG via a full- wave rectifier 203. The purpose is to reverse the polarity of the negative phase for a piezoelectric voltage profile during its deformation, so that all charges generated from the piezoelectric will go to the DEG. [0058] The deformed piezoelectric generator charges the DEG when the DEG is fully stretched. Upon mechanical relaxation, the voltage from the piezoelectric charges will be amplified in an open circuit condition (assuming negligible charge leakage through DE). The reverse-biased diodes on the full- wave rectifier and the open switch 204 in the harvesting circuit 220 ensures that the voltage boost takes place in an open circuit condition. Finally, when the voltage peaks at full mechanical relaxation, the switch 204 is closed to transfer the energy to an electrical load 205.

[0059] Figure 3 is a diagram 300 showing the triangular DEAmP cycle which represents the energy harvesting process on a voltage-charge plane in accordance with an example embodiment. The X-axis shows charge, and the Y-axis shows voltage.

Four states (1 ) - (4) are shown in the diagram 300 and discussed below.

[0060] At state 1, the DEG is undeformed. The DEG at state 1 has a minimum capacitance. States 1 2 denotes stretching of the DEG, giving a capacitance increase.

At state 2, the DEG attains its maximum capacitance (CD_MAX)· At this point, the piezoelectric generator deforms and charges the DEG. The charging follows the capacitance law for a parallel plate capacitor. Hence, the inverse of slope of the line 2-

3 is CD_MAX- The bottom triangle in Figure 3 represents the electrical energy transferred to the DEG from the piezoelectric generator. When the DEG is relaxed in an open circuit condition (states 3 4), its capacitance decreases, which results in a voltage boost. At state 4, the DEG reverts to its minimum capacitance state ( C_{D_MIN} ) and a peak voltage. The switch 204 in the harvesting circuit (Figure 2) is then activated to ensure that maximum energy is transferred to the electrical load. Once all the energy is transferred the elastomer returns to state 1. [0061] In order to achieve the proposed triangular cycle, the process of priming and output charge transfer is properly synchronized. The DEG priming by the piezoelectric takes place when the DEG is fully stretch, thereby attaining CD_MAX- The mechanism deforms and relaxes the piezoelectric generator while the DEG is in its fully stretched state. Furthermore, to ensure that the switch is closed when the elastomer voltage peaks, an example embodiment includes an inbuilt mechanism. The switch is open throughout the process of 2®3 4 to ensure that no energy leaks out before amplification is achieved. The detailed working mechanism is discussed more fully below.

[0062] Figure 4 shows a DE membrane to illustrate the ripple mode of deformation in accordance with an example embodiment. In this figure, the cross-sectional portions (left and top right) show the ripple mode of deformation, and the arrows indicate the direction of force applied to deform the DE membrane.

[0063] For Figure 4, an example embodiment stretches a flat, circular DE membrane 401 in an out of plane direction at its center, forming the deformed shape of a cone with a height of h_c. This embodiment uses concentric circles to create folded ripples, (dashed lines 402 and 403), so that less space is required to produce the same deformation as compared with that applied only at its center. The deformed shape of the elastomer will resemble ripples in water, hence, termed ripple mode of deformation. An example embodiment defines the order of ripple by the number of folds made in an axisymmetric fashion.

[0064] Various combinations of the order and aspect ratio (height: radius) are possible. First 402 and second 403 order ripple are shown in Figure 4. The order and aspect ratio of the embodiment is chosen to have a compact design, adequate elastomer deformation, and safe operation.

[0065] Figure 5 shows a mechanism to deform the DE in ripple mode and to create an interlocking system in accordance with an example embodiment.

[0066] Figure 5 shows the structures to realize the second order ripple mode. The elastomer 501 is sandwiched or positioned between the top structure 503 and the bottom structure 502. The elastomer is fixed to the bottom rigid structure 502 on the outer edge 502b and pressed by the top structure 503. The rigid structures are basically concentric cylinders (502a, 503b and central cylinder 503a) that stretch the elastomer in a circular pattern in out of plane direction. The direction of force is indicated by arrows 504.

[0067] Figure 6a is a dielectric elastomer (DE) frame 601 in accordance with an example embodiment, and Figure 6b is the DE frame 601 attached to a pre-stretched

DE membrane 602 in accordance with an example embodiment.

[0068] The frame 601 has a circular shape and is used to secure the pre-stretched

DE membrane 602. An example embodiment uses an acrylic-based elastomer, VHB series elastomer by 3M. It is an adhesive and hence, the pre-stretched membrane 602 directly sticks to the frame 601 without the need for additional adhesives. For non- sticky DE membranes, additional adhesives can be used secure it.

[0069] Anchoring a DE on a circular frame removes exposed edges of a DE membrane, thereby maintaining a uniform pre-stretch for good working performance.

Free from exposed edges also enhances durability for the active DE layers. The anchored DE with conductive and compliant electrodes 602 will look like that as shown in Figure 6b. [0070] Figure 7a is a base structure in accordance with an example embodiment, and Figure 7b is a buzzer type piezoelectric assembled on the base structure in accordance with an example embodiment.

[0071] The base structure 700 has a cylindrical configuration in a cross-sectional view and includes a circular hole 701 in its center. A thin circular ring 702 extends in the base structure adjacent to this hole 701 and includes a PZT ceramic 703 on it. The depth of the hole 701 limits the deformation of the piezoelectric, which may be user- designed or determined.

[0072] The base structure 700 also includes a rectangular groove 704 that creates a path for the electrode wires (PI and P2) of the piezoelectric. There are three circular pillars (705a, 705b and 705c) on the base structure to align and attach the rest of the components. The dimensions of the pillars are ensured to be a sliding fit for the three holes for the piezo presser (e.g., as in Figure 8).

[0073] The piezoelectric generator 703 used in this example embodiment is a commercial product made of PZT ceramic for buzzer applications. The central area is the PZT material 703a and the surrounding area 703b is the copper electrode. The piezoelectric is placed inside the circular hole, and the electrode wires are arranged in the slot described previously. The electrodes of the piezoelectric are termed as PI and

P2.

[0074] This example embodiment uses a full-wave rectifier (e.g., 203 in Figure 2) and hence does need to specify the positive or negative terminals. This design will ensure that piezoelectric is secured in the base structure and will allow for the smooth motion of the prototype.

[0075] Figure 8 is a piezo-presser 800 to deform a piezoelectric in accordance with an example embodiment. [0076] The piezoelectric generator is deformed by the piezo-presser 800 in Figure 8.

The circular extrusion 801 at the center is to press the piezoelectric to deform it through the circular hole 701 of the base structure 700 shown in Figures 7a and 7b.

The dimension of the extrusion 801 is designed to just touch the center of the piezoelectric while the elastomer is being stretched and to give the optimum deformation for the piezoelectric during the DE charging process. The three holes 802 align with the arrangement of three pillars 705 ensuring a smooth sliding fit.

[0077] Figure 9a is a top view of the ripple bottom structure 900 in accordance with an example embodiment, and Figure 9b is a bottom view of the ripple bottom structure 900 in accordance with an example embodiment.

[0078] Figure 10a is a top view of ripple top structure 1000 in accordance with an example embodiment, and Figure 10b is a bottom view of ripple top structure in accordance with an example embodiment.

[0079] The DE film in Figure 6b is deformed in ripple mode by two components, ripple bottom structure 900 (Figure 9) and ripple top structure 1000 (Figure 10).

Depending on the design requirement and material limits, an example embodiment deforms the DE film into different orders of ripple as discussed herein.

[0080] Figures 9 and 10 are the bottom and top structures for the fifth order ripple mode. However, the central cylinder (503a in Figure 5) is removed to avoid stress concentration on the elastomer. Hence the ripple bottom structure has three concentric cylinders 901a, 901b and 901c and the ripple top structure has three concentric cylinders 1001a, 1001b and 1001c arranged in equal distance in radial direction to deform the DE film.

[0081] The outer edge 901c of the ripple bottom structure secures the DE film (Figure 6b). Hence its width is the same as that of the DE frame 601. The ripple bottom structure has three blind holes 902a, 902b and 902c at the bottom to be tight fitted with three pillars 705a, 705b and 705c respectively in the base structure (Figure

7). There are two extruded handles 903a and 903b near the top surface on both sides of the ripple bottom structure. One of the handles 903a is wrapped with a wire S1 where the wrapping area is conducting 904 (copper wire) and the rest is covered with an insulating cover. This arrangement acts as a switch (204 in Figure 2) for die discharge of the DEG at peak voltage. The second handle on the other side improves the balance for the structure during the operational process. The handles also serve a function to control the stroke length of the prototype.

[0082] Another wire D1 is wrapped tightly over one of the inner walls 901b so that when the DE film is placed on the top of ripple bottom structure, it will be in contact with the DE film. The wrapping part 905 is conductive. The extended part of the D1 wire has an insulative cover and is placed in a slot provided at the bottom of the structure 906. Two small holes 907 are provided near 901b at the bottom to insert and to take out the wire. There are circular holes 908 through all the cylindrical walls for the air to escape while DE film is stretched, avoiding the pressure raise which restricts the deformation of the DE film.

[0083] The final component of the prototype is the ripple top structure shown in

Figure 10. The position of each of the cylinders 1001 a, 1001b and 1001c was designed considering the positions of the cylinders in the ripple bottom structure

(Figure 9) so that each cylinder is arranged in the middle of adjacent cylinders in its counterpart. To compliment with the handles 903a and 903b in the ripple bottom structure as a switch and to fix the stroke, L shaped cuts 1003a and 1003b are made on the outer cylindrical edge 1002 of the structure. A wire S2 is wrapped on a handle near 1003a and extended. The wrapped area is conductive 1004 and the rest has insulative cover. Together with its counterpart SI in the ripple bottom structure, they will act as a switch S, further explained herein.

[0084] The cut 1003a and 1003b is for allowing the downward motion of the ripple top structure avoiding a contact with the extruded handles 903a and 903b on the ripple bottom structure and for the assembly of the ripple top and bottom structures at the right position. It will also restrict the return motion of the DE film when the force is removed. Similar to D1 in the ripple bottom structure, a wire D2 is wrapped tightly around cylindrical wall 1001c of the ripple top structure.

[0085] During the assembly, the conducting part 1005 of D2 will be in contact with the DE film. Two small holes 1006 are provided near 1001c at the bottom to insert and to take out the wire D2. A slot 1007 is provided at the top of the structure to place the D2 wire. Several holes 1008 are made on the top part of the component for the ease of escape of air. A small cut 1009 is made at the bottom of the structure so that the ripple top structure my not compress the D1 wire from the ripple bottom structure during the operation.

[0086] The components with their specified designs help for the easy assembly and smooth operation. It also helps the operation of an example embodiment to follow the working principal described. All the wires P1, P2, SI, S2, D1 and D2 of this example embodiment are arranged in order to make the product look aesthetic and compactable.

[0087] Figure 11a is an exploded view of a piezoelectric structure 1100 in accordance with example embodiment, and Figure 11b shows a cross-sectional view of the piezoelectric structure 1100 in accordance with an example embodiment.

[0088] All the components described in Figures 6 to 10 are assembled as shown in

Figures 11a and 11b and include a top structure 1101, a DE membrane 1102, a bottom structure 1103, a presser 1104, and a base structure 1105. [0089] The piezoelectric is placed into the base structure (Figure 7) with wires PI and P2 extending outside. Next, the piezo-presser (Figure 8) is inserted on the top of the base structure so that its three holes 802 align with three pillars 705 of the base structure. After the piezo-presser is placed, the ripple bottom structure (Figure 9) is assembled by tight fitting the pillars 705 of the base structure on to the three blind holes of the ripple bottom structure 902. An equal-biaxially pie-stretched DE is secured on the dielectric elastomer frame and is covered with compliant electrode layers on both sides (e.g., use carbon grease or carbon powder for ease coating and high conductivity).

[0090] The DE film (Figure 6) is placed on the top of the ripple bottom structure. If a sticky elastomer like VHB is used, it can directly adhere to the surface of the ripple bottom structure, otherwise an adhesive layer is needed.

[0091] The ripple top structure (Figure 10) is assembled and aligned with the rest through the L slot feature mentioned in Figure 10. The process involves inserting and a clockwise turning of the ripple top structure, resulting S2 to come in contact beneath

S1. D1 and D2 become the two electrodes of DEG and SI and S2 becomes two ends of the discharge switch. The electrical connection for the example embodiment is shown in Figure 12.

[0092] Figure 12 is an electrical circuit 1200 for a DEAmP in accordance with an example embodiment. Circuit 1200 is similar to the circuit discussed in Figure 2 and includes a piezoelectric 1201, DEG 1202, full-wave rectifier 1203, and load 1205. In addition, Figure 12 shows placement of PI, P2, Dl, D2, and S discussed herein.

[0093] An example embodiment allows a single compressive force applied on the ripple top structure to deform both the DE membrane and the piezoelectric, as well as to control the switch automatically following the designed operational process. [0094] Figure 13a is a DEAmP 1300 in an undeformed state in accordance with an example embodiment, and Figure 13b is the DEAmP in a fully deformed slate in accordance with an example embodiment.

[0095] Figure 13a shows the prototype for the elastomer in the undeformed state. A slight contact was made between the interlocking concentric circles with the elastomer membrane ensures that switch S is closed (Figure 13a). The prototype now establishes state 1 on the operation cycle described in Figure 3. When a compressive force is applied on the top structure, the elastomer is stretched and the switch S opens. As the elastomer gets fully stretched as shown in Figure 13b, the top structure comes into contact with the piezo-presser (Figure 13b and state 1 2 in

Figure 3).

[0096] Further pressure on the top structure will now deform the piezo-presser to apply pressure on the piezoelectric (Figure 13b). Following the electrical circuit described in Figure 12, the DEG will now be charged by the piezoelectric. The charging continues until the top structure retracts due to force relaxation. At this point, the piezoelectric will instantaneously return to its original undeformed stated assuming that it is elastically deformed (state 2 3 in Figure 3).

[0097] The elastomer then relaxes to its undeformed state by its own mechanical stored energy, and this pushes the ripple top structure back upwards. This results in an open circuit voltage boost by the DEG as the switch S is open (state 3 4 in

Figure 3). When S1 and S2 comes into contact, switch S closes and the DEG transfers the energy at high voltage to an electrical load in its minimum stretched or minimum capacitance state (state 4 1 in Figure 3). This completes a cycle operation. [0098] Example embodiments include a wide array of applications. For example. any mechanical source that generates a low frequency compressive force is suited for its energy to be harvested by a DEAmP of an example embodiment. We present two such examples illustrating a small-scale (Figure 14) and a medium-scale application (Figure 15).

[0099] Figure 14 is a DEAmP adapted as a heel strike generator 1400 in accordance with an example embodiment. The compressive load from the human heel strike is harvested by the DEAmP 1402 to generate electrical energy. The harvested energy can be used, for example, to power body sensors or to charge a battery.

[00100] Figure 15 is a DEAmP integrated into a traffic speed bump 1500 in accordance with an example embodiment. The speed bump is designed to move downwards when the wheels 1501 of a vehicle roll over it. The downward motion exerts a compressive load on the DEAmP 1502 that harvests energy from vehicular motions to generate electricity. The generated energy can be used, for example, to power static traffic installations or to power traffic monitoring sensors.

[00101] In some example embodiments, the methods illustrated herein can be executed with one or more electronic devices, circuits, computers, and other electrical and/or mechanical structures.

[00102] While exemplary embodiments have been presented in the foregoing detailed description of the present embodiments, it should be appreciated that a vast number of variations exist. It should further be appreciated that the exemplary embodiments are only examples, and are not intended to limit the scope, applicability, operation, or configuration of the invention in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing exemplary embodiments of the invention, it being understood that various changes may be made in the function and arrangement of steps and method of operation described in the exemplary embodiments without departing from the scope of the invention as set forth in the appended claims.

Claims

CLAIMS What is claimed is:

1. An apparatus, comprising:

a dielectric elastomer generator (DEG) that generates electrical energy from elastic energy; and

a priming circuit that provides voltage to prime the DEG and includes a piezoelectric generator coupled to the DEG via a full-wave rectifier.

2. The apparatus of claim 1, wherein the full- wave rectifier reverses a polarity of a negative phase for a piezoelectric voltage during deformation of the DE.

3. The apparatus of claim 1 further comprising:

a switch between the priming circuit and an electrical load, wherein when voltage peaks at full mechanical relaxation of the DEG, the switch is closed to transfer energy to the electrical load.

4. The apparatus of claim 1, wherein the piezoelectric generator deforms and charges the DEG when the DEG stretches and attains maximum capacitance.

5. The apparatus of claim 1, wherein when the DEG is relaxed in an open circuit condition, capacitance of the DEG decreases and results in a voltage boost.

6. The apparatus of claim 1, wherein the priming circuit utilizes a ripple mode to maximize capacitance of the DEG during mechanical deformation.

7. The apparatus of claim 1, wherein the DEG includes a circular DE membrane stretched out of plane from a center to form a shape of a cone that includes folded ripples.

8. The apparatus of claim 1, wherein a plurality of concentric cylinders stretch the DEG in a circular pattern in an out of plane direction.

9. An apparatus that harvests energy, comprising:

a dielectric elastomer (DE) that generates electrical energy from compressive loading that stretches the DE;

a piezoelectric generator electrically coupled to the DE; and a ripple structure with a top structure and a bottom structure, wherein the DE is positioned between the top and bottom structures that deform ripples into the DE to generate the electrical energy from the compressive loading.

10. The apparatus of claim 9, wherein the ripples have concentric circular shapes.

11. The apparatus of claim 9, wherein the top and bottom structures include a plurality of concentric cylinders that generate the ripples in the DE.

12. The apparatus of claim 9, wherein the piezoelectric generator fits in a circular hole in a base structure and a circular extrusion presses and deforms the piezoelectric generator through the circular hole.

13. The apparatus of claim 9, further comprising:

a circuit that provides voltage to prime the DE.

14. The apparatus of claim 13, wherein the circuit further includes a switch that closes when a voltage of the DE peaks and opens when the DE attains maximum capacitance.

15. The apparatus of claim 13, wherein the circuit further includes a full- wave rectifier that reverses a polarity for a piezoelectric voltage profile during deformation of the piezoelectric generator.

16. The apparatus of claim 9, wherein the piezoelectric generator primes the DE when the DE is fully stretched, and the piezoelectric generator deforms and relaxes while the DE is in a fully stretched state.

17. An energy harvester, comprising:

a dielectric elastomer generator (DEG) that generates electrical energy from compressive loading that deforms ripples into a dielectric elastomer; and a circuit that provides voltage to prime the DEG and includes a piezoelectric generator.

18. The energy harvester of claim 17, wherein the ripples have a concentric

circular shape.

19. The energy harvester of claim 17, wherein deformation of the piezoelectric generator charges the DEG when the DEG is fully stretched.

20. The energy harvester of claim 17, wherein the circuit includes reverse-biased diodes and a switch that ensure a voltage boost to the DEG occurs in an open circuit condition.