WO2023192102A1

WO2023192102A1 - Piezoelectric harvester

Info

Publication number: WO2023192102A1
Application number: PCT/US2023/016085
Authority: WO
Inventors: Yutaka Ohmori; Yiling Zhang
Original assignee: Nitto Denko Corporation
Priority date: 2022-03-30
Filing date: 2023-03-23
Publication date: 2023-10-05
Also published as: TW202346786A

Abstract

Described herein is piezoelectric harvester (10) providing both desired levels of power generation and conformity to arcuate surfaces, comprising a threshold hardness silicone polymer (22) used to produce a cross-linked silicone polymer and piezoelectric particles (24A) disposed therein. In some embodiments, the silicone polymer may be platinum doped. Also described is a method for making a piezoelectric harvester having such power generation and conformity characteristics.

Description

PIEZOELECTRIC HARVESTER

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application No. 63/325,527, filed March 30, 2022, which is incorporated by reference in its entirety.

FIELD

The present disclosure relates to a piezoelectric harvester. In particular, the present disclosure relates to a flexible piezoelectric composite including a three- dimensional interconnected piezoelectric ceramic framework based on an organic template with sufficient stiffness and infiltrated with a flexible polymer matrix.

BACKGROUND

Unless otherwise indicated in the present disclosure, the materials described in the present disclosure are not prior art to the claims in the present application and are not admitted to be prior art by inclusion in this section.

The piezoelectric effect is the induction of an electric charge in response to an applied mechanical strain, which can be used to convert mechanical energy into electrical energy. As a result, piezoelectric materials have been widely used to scavenge energies from the environment and body movement to power personal electronics, nanodevices and wireless sensors, etc. To extend the application fields of piezoelectric materials, good mechanical flexibility is often considered to be desirable. However, bulk piezoelectric ceramics such as lead zirconate titanate (PZT) have high piezoelectric coefficients but low flexibility, while piezoelectric polymers such as polyvinylidene difluoride (PVDF) have good flexibility but relatively low piezoelectric coefficients. PVDF has limitations in that it can have difficulties in conforming to three- dimensional curved surfaces due to lack of stretchability and PVDF based piezoelectric harvesters can easily detach or lift off from the attached surface by repeated deformation. This can be an especially difficult issue when the target surface is constantly flexing, for example upon the inside surface of a vehicle’s inflatable tire. Polydimethylsiloxane (PDMS, or silicone) based harvesters have been described, but while conventional piezocomposites employing PDMS are tolerant to deformation, power generated is significantly low.

Thus there is a need for piezoelectric harvesters that have both flexibility and high piezoelectric coefficients to provide efficient harvesters for non-planar substrates.

SUMMARY

The embodiments of the disclosure generally relate to a piezoelectric harvester architecture that generates power in the context of a non-planar environment.

In some embodiments, the piezoelectric harvester includes a piezoelectric layer including a cross-linked silicone elastomeric matrix and piezoelectric particles, with the piezoelectric particles dispersed within the elastomeric matrix. In some embodiments, the piezoelectric harvester further includes a pair of elastic electrodes placed on upper and lower side of the piezoelectric layer. In some embodiments, the piezoelectric harvester has the tensile strength of 0.5-5 megapascals (MPa) at 1% elongation. In some embodiments, the cross-linked elastomeric matrix may be formed from a reactive silicone oligomer that has a hardness of 45-90, as measured by the Shore hardness scale, Type A. In some embodiments, the reactive silicone oligomer has a fraction of reactive functional units in the reactive elastomeric matrix that may be 5 mol% or above. In some embodiments, the elastomeric matrix may include a reactive oligomer having reactive functional groups selected from hydroxyl, vinyl, alkoxy and hydride. In some embodiments, the elastomeric matrix may include a doped polyalkylsiloxane matrix and piezoelectric particles dispersed within the polyalkylsiloxane matrix. In some embodiments, the dopant may be platinum (Pt). In some embodiments, the polyalkylsiloxane may include polydimethylsiloxane. In some embodiments, the volume fraction of the piezoelectric particles in the piezoelectric layer may be 35-65%. In some embodiments, the cross-linked elastomeric matrix may include a volume fraction of 65% to 35% silicone. In some embodiments, the elastic electrodes may include carbon as a conductive element. In other embodiments, a tire includes the piezoelectric harvester described above. Some embodiments include a method for preparing a piezoelectric harvesting composite. In some embodiments, the method may include preparing a mixture including a silicone oligomer, that after curing has a hardness of 45-90 as measured by Shore A, and piezoelectric particles dispersed within; casting the mixture on a thin layer of elastic electrode to form a composite sheet; curing the composite sheet; coating the composite sheet with a layer of thin elastic electrode to form a 3-layer composite structure; and polarizing the piezoelectric particles within the 3-layer composite structure.

Additional features and advantages will be set forth in the description. The features and advantages may be realized and obtained by means of the instruments and combinations particularly pointed out in the following description and appended embodiments, examples, and figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an example piezoelectric harvester described herein.

FIG. 2 illustrates the piezoelectric harvester of FIG. 1 separated into layers.

FIG. 3 illustrates an example sensor element described herein.

FIG. 4 is a diagram of an energy generating circuit and/or element described herein.

DETAILED DESCRIPTION

For purposes of promoting an understanding of the present disclosure, reference will now be made to the following embodiments and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the disclosure is thereby intended, such alterations and further modifications in the described subject matter, and such further applications of the disclosed principles as described herein being contemplated as would normally occur to one skilled in the art to which the disclosure relates.

The present disclosure generally relates to piezoelectric power generating elements (also referred to as piezoelectric harvesters). In some embodiments, the piezoelectric harvesters described herein include materials having one or more material properties that may provide a balance between hardness and flexibility, e.g., a balance between volume fractions of piezoelectric particles and a polymer (e.g., PDMS), to concurrently provide flexibility to enable power generation. In some embodiments, the piezoelectric harvester may show improved conformity to a three- dimensional morphology with sufficient toughness to increase durability under conditions consistent with its use (e.g., on the inside of a vehicular tire).

In the present disclosure, a piezoelectric harvester is described. As shown in FIGs. 1 and 2, the piezoelectric harvester, such as piezoelectric harvester 10, may include a piezoelectric layer, such as layer 12, having a first piezoelectric layer side (such as side 14) and a second piezoelectric layer side (such as side 16) and a first elastic electrode (such as electrode 18) and a second elastic electrode (such as electrode 20). In some embodiments, the first elastic electrode may be disposed on the first piezoelectric layer side and the second elastic electrode may be disposed on the second piezoelectric layer side. In some embodiments, the piezoelectric layer may include a cross-linked elastomeric matrix, such as matrix 22. In some embodiments, the elastomeric matrix may include a reactive oligomer (not shown) and plural piezoelectric particles (such as particles 24A), where the piezoelectric particles may be dispersed within the elastomeric matrix. In some embodiments, the piezoelectric particles may be polarized (alignment of the piezoelectric particles’ dipole moment) as indicated by arrows 26A. In some embodiments, the aforedescribed piezoelectric harvester may have a device tensile strength at 1% elongation of about 0.5 to about 5 MPa, about 0.7-3 MPa, about 1 -3 MPa, about 0.5-2 MPa, or about 0.55 MPa, about 0.75 MPa, about 0.76 MPa, about 1 MPa, about 1.4 MPa, about 1.6 MPa, or any tensile strength in a range bounded by any of these values.

In some embodiments, silicone (e.g., PDMS) may be utilized to form the crosslinked elastomeric matrix. In some embodiments, the cross-linked elastomeric matrix may have a hardness between the range of about 45 to about 90, as measured using the Shore hardness scale, type A (hereinafter referred to as Shore A). In some embodiments, the cross-linked elastomeric matrix, may have a Shore A hardness of about 50-90, about 65-90, about 50-55, about 55-60, about 60-65, about 65-70, about 70-75, about 75-80, about 80-85, about 85-90, or about 50, about 80, or any Shore A hardness in a range bounded by any of these values. In some embodiments, the silicone used to form the cross-linked elastomeric matrix may include about 75% silicone, about 85% silicone, about 90% silicone, about 95% silicone, about 99% silicone, about 99.5% silicone, or about 99.9% silicone. In some embodiments, the silicone may be essentially pure silicone. The specific silicone polymer, dopant and/or crosslinker may contribute to a balancing of the hardness and flexibility and amount of power generation by the piezoelectric functionality of the piezoelectric harvester. Any suitable means to determine hardness may be employed, for example using ASTM D2240 standard, type A (hardened steel rod 1 .1 millimeters (mm) - 1 .4 mm diameter with a truncated 35° cone, 0.79 mm diameter, with an applied mass (kilograms (kg)) of about 0.822 kg and with a resulting force of about 8.064 Newtons (N)). Suitable means to determine material tensile strength may use a tensile tester utilizing 5 mm/minute stroke speed, as described in the experimental information in the examples herein.

In some embodiments, the piezoelectric layer includes a cross-linked elastomeric matrix. In some embodiments, the elastomeric matrix may include a silicone elastomer. In some embodiments, the silicone elastomeric matrix may include a polyalkylsiloxane. In some embodiments, the polyalkylsiloxane may include polydimethylsiloxane (PDMS). The type of cross-linking reaction of silicone is not limited to noble metal catalyzed, and may include any suitable method of cross-linking reactions of silicone. In some embodiments, the polyalkylsiloxane may be doped with a noble metal. In some embodiments, the noble metal dopant may include Ag, Au, Pd, Ni, Pt, or a combination thereof. It is believed that the noble metal dopant may catalyze the cross-linking reaction. In some embodiments, the noble metal is platinum (Pt). In some embodiments, the PDMS elastomeric matrix may be doped with between 0.001 wt% to about 5 wt% noble metal, e.g., Pt. The doping of the silicone elastomeric matrix may contribute to the hardening of the elastomeric matrix to achieve a hardness level of about 45-90 Shore A. In some embodiments, the presence of the dopant may catalyze crosslinking of the piezoelectric layer.

In some embodiments, the cross-linked elastomeric matrix may include a reactive silicone oligomer. In some embodiments, the reactive oligomer may include a reactive functionalized silicone monomer. In some embodiments, the reactive functionalized silicone monomer may include a reactive hydrogen group (e.g., a silicone hydride), a reactive vinyl group, a reactive hydroxyl group, a reactive alkoxy group, or a combination thereof. In some embodiments, the reactive elastomeric matrix may include silicone hydride (the silicone reactive functional group) and/or a poly-silicone vinyl (another silicone reactive functional group). In some embodiments, the fraction of reactive functional units in the reactive elastomeric matrix may be about 5-10 mol%, about 8-10 mol%, about 5-6 mol%, about 6-7 mol%, about 7-8 mol%, about 8-9 mol%, about 9-10 mol%, or about 8.5 mol%, about 9.4 mol%, or any mol% in a range bounded by any of these values.

In some embodiments, the piezoelectric particles are lead zirconate titanate (also called lead zirconium titanate, abbreviated as PZT). In some embodiments, the piezoelectric harvester may include PZT piezoelectric particles dispersed or disposed within a polymer matrix. In some embodiments, the volume fraction of the piezoelectric particles in the piezoelectric layer may be about 35-65%, about 35-40%, about 40- 45%, about 45-50%. about 50-55%, about 55-60%, about 60-65%, or about 44%, about 50%, or any volume percentage in a range bounded by any of these values for adjusting power generation. In some embodiments, the volume fraction of the piezoelectric particles in the piezoelectric layer may be more preferably about 40-60%, about 40-45%, about 45-50%. about 50-55%, about 55-60%, or about 44%, about 50%, about 56%, or any volume percentage in a range bounded by any of these values for adjusting the toughness.

In some embodiments, the elastic electrodes may include carbon as a conductive filler element. The conductive fillers may be dispersed within the polymer matrix. The conductive filler may be introduced into a medium by any suitable method. The conductive filler is a compound which, in the presence of an electric current, brings about the appearance of an electric current in the medium. The conductive filler may be a graphitized or partially graphitized carbon black, also known as conductive blacks. In some embodiments, the conductive blacks may be, for example, those sold by Timcal under the trade name “Ensaco 350G”, with a specific surface (BET, measured according to Standard ASTM D3037) of 770 square meters per gram (m²/g), or “Ensaco 260G”, with a specific surface of 70 m²/g. In some embodiments, the conductive filler may be an electro-conductive or graphitized carbon black with a specific surface (BET, measured by Standard ASTM D3037) of greater than 65 m²/g, greater than 100 m²/g, or greater than 500 m²/g. In some embodiments, the amount of conductive filler in the polymer matrix composition may be within a range extending from about 35% to about 65% by volume, about 35-40%, about 40-45%, about 45- 50%, about 50-55%, about 55-60%, about 60-65%, or about any amount in a range bounded by any of these values. The size of the conductive fillers may vary from 50 nm to 500 pm.

In some embodiments, the piezoelectric materials may have their dipole moments aligned by an external electric field. In some embodiments, the volume fraction of the piezoelectric particles may be from about 40% to about 65%, about 40- 45%, about 45-50%, about 50-55%, about 55-60%, about 60-65%, or any amount in a range bounded by any of these values.

In some embodiments, a tire of a vehicle (automobile, truck, tractor, motorcycle, bicycle, aircraft, amphibious boat, etc.) may be equipped with and/or include a piezoelectric harvester such as described herein. The piezoelectric harvester described herein may be useful in coordination with capacitive tire sensors, such as those described in International Patent Cooperation Treaty (PCT) application PCT/US2021/018825 filed February 19, 2021 (published August 26, 2021 , as WO 2021/168286), which is incorporated herein by reference in its entirety.

FIG. 3 illustrates an example sensor module, such as module 200, that may generally include a detector patch, such as patch 202, and an electronics unit, such as unit 204, and optionally an electric power source, such as source 206. In some embodiments, the electronics unit 204 is connected to the detector patch 202 and the electric power source 206 where the electric power source may include a piezoelectric harvester system such as described herein.

The detector patch 202 may include a mounting surface 208 and one or more sensor regions 210. The mounting surface 208 may be configured to be attached to a surface of a tire or other object and/or may include a lower or bottom surface of the detector patch 202. Alternatively or additionally, the mounting surface 208 may include an adhesive, such as adhesive 212, disposed thereon to adhere the detector patch 202 to a desired position, e.g., within a tire cavity of a tire or exterior of an inner tube. The adhesive 212 may include thermoplastic adhesive or any other suitable adhesive. The sensor region 210 may generally include a capacitor. In some embodiments, the capacitor and/or the sensor region 210 may be flexible, extensible, distensible, deformable, layered, and/or lamellar. Alternatively, or additionally, the sensor region 210 may be at least partially covered, bound, and/or surrounded by one or more protective layers, such as protective layer 214, as part of the detector patch 202. The protective layers 214 may include an elastomeric material such as silicone or the like. While the electric power source 206 has been described as including a piezoelectric harvester such as described herein, more generally the electric power source 206 may include a battery, an energy generating circuit, an energy harvesting system (EHS) module, a dielectric elastomeric matrix generating material, a piezoelectric harvester as described herein, and/or a receiver coil and circuitry of an inductive charging unit. The electronics unit 204 may be in electrical communication with the detector patch 202 and the power source 206 via one or more corresponding electrical connectors 216. Alternatively, or additionally, the electronics unit 204 and the electric power source 206 may be mechanically coupled together by epoxy resin and/or may be disposed within a housing or encapsulant, such as housing or encapsulant 218, that is mechanically coupled to the detector patch 202.

In some embodiments, a capacitive tire sensor may include an energy generating circuit and/or element and the energy generating circuit and/or element may include some or all of a piezoelectric harvester such as described herein. As shown in FIG. 4, the energy generating circuit, such as energy generating circuit 300, may include an electricity generating element, such as electricity generating element 302, an energy harvesting module (or energy harvesting system, or EHS), such as EHS module 304, an energy storing circuit, such as energy storing circuit 306, and/or a battery, such as battery 308. In some embodiments, the EHS module 304 may be electrically coupled to the electricity generating element 302, the energy storing circuit 306, and/or the battery 308. In some embodiments, the electricity generating element 302 may include a dielectric generating material, a piezoelectric generating material, or other material, system, or device that generates electricity when subject to motion, mechanical stress, or other input, or a combination thereof. In some embodiments, the electricity generating element may be the piezoelectric harvester described herein. In some embodiments, flexing of the electricity generating element 302, e.g., implemented as a piezoelectric harvester described herein, and/or portions of a detector patch that has such materials, may generate a charge on the surface of the electricity generating element 302. In some embodiments, the electricity generating element may be disposed in close proximity to a tread portion, a shoulder portion, and/or a sidewall portion of a tire.

The following embodiments are described.

EMBODIMENTS

Embodiment 1. A piezoelectric harvester comprising: a piezoelectric layer comprising a cross-linked silicone elastomeric matrix and piezoelectric particles, the piezoelectric particles dispersed within the elastomeric matrix; and a pair of elastic electrodes placed on upper and lower side of the piezoelectric layer; and wherein the tensile strength at 1 % elongation is 0.5-5MPa.

Embodiment 2. The piezoelectric harvester of embodiment 1 , wherein the cross-linked elastomeric matrix is formed from a reactive silicone oligomer that after curing has a hardness of 45-90 in Shore A.

Embodiment 3. The piezoelectric harvester of embodiment 1 , wherein the fraction of the reactive functional units in the reactive elastomeric matrix is 5mol% or above.

Embodiment 4. The piezoelectric harvester of embodiment 1 , wherein the elastomeric matrix comprises a doped polyalkylsiloxane matrix, and piezoelectric particles, the piezoelectric particles dispersed within the polyalkylsiloxane matrix.

Embodiment 5. The piezoelectric harvester of embodiment wherein the elastomeric matrix comprises a reactive oligomer having reactive functional groups selected from hydroxyl, vinyl, alkoxy and hydride.

Embodiment 6. The piezoelectric harvester of embodiment 4, wherein the doped polyalkylsiloxane comprises Pt. Embodiment 7. The piezoelectric harvester of embodiment 4 wherein the polyalkylsiloxane comprises polydimethylsiloxane.

Embodiment 8. The piezoelectric harvester of embodiment 2, wherein the volume fraction of the piezoelectric particles in the piezoelectric layer is between 35- 65%.

Embodiment 9. The piezoelectric harvester of embodiment 2, wherein the cross-linked elastomeric matrix primarily consists of silicone.

Embodiment 10. The piezoelectric harvester of embodiment 2, wherein the elastic electrodes comprise carbon as a conductive element.

Embodiment 11. A tire equipped with the piezoelectric harvester of any one of embodiments 1 -10.

Embodiment 12. A method for preparing a piezoelectric harvesting composite, comprising: providing a silicone oligomer that after curing has a hardness of 45-90 shore A; providing a mixture comprising the silicone oligomer and piezoelectric particles, the piezoelectric particles dispersed within the silicone oligomer; casting the mixture to form composite sheets; curing the composite sheets; polarizing the piezoelectric particles within the composite.

Preparing composites

Example 1

An electrode ink, which was a uniform mixture of 60.5 g of polydimethylsiloxane (PDMS), made as described in Sci Rep 9, 1 (2019), 6.3 g of carbon black and 131.7 g of toluene, was coated on a fluorinated polymer substrate (PTFE coated glass cloth fabrics, by Tapes and Technical Solutions, LLC, Nashville, TN) followed by heattreatment in an oven at 80 °C for 15 minutes and then at 200 °C for 15 minutes to make a thin layer of elastic electrode.

14 g of piezoelectric (PZT) particles was mixed with 2 g of polydimethylsiloxane (PDMS) (Shore A Hardness 80, reactive unit at 9.4 mol%), and 2.8 g of toluene in a planetary centrifugal mixer for 4 minutes. A uniform slurry was obtained. The slurry was cast at a wet thickness of 24 mil on top of the layer of elastic electrode using a film applicator. The cast film then was heated in an oven at 80 °C for 15 minutes to remove the solvent and then at 200°C for 30 minutes to complete the cross-linking reaction. A composite film was obtained.

The same electrode ink was coated on top of the composite film, followed by heat-treatment in an oven at 80 °C for 15 minutes and then at 200 °C for 15 minutes to make a second thin layer of elastic electrode. A 3-layer composite structure was obtained.

The composite structure was then sandwiched between two copper plates on a hotplate set at 130°C. A voltage of 6.0 kV was applied on one of the copper plates, creating an electric field across the composite structure to polarize the PZT particles dispersed within for 60 min. A poled composite sample was obtained.

Examples 2-6

Example 2-Example 6 were made in a similar manner to Example 1 , except that the hardness and/or the molar fraction of reactive unit of the silicone used to form the elastomeric polymer matrix and/or the amounts of the PZT materials were varied as set forth in Table 1 .

Comparative Examples 1-11

Comparative Examples 1 -11 were made in a similar manner to Example 1 , except that the hardness and/or the molar fraction of reactive unit of the silicone used to form the elastomeric polymer matrix and/or the amounts of the PZT materials were varied as set forth in Table 1 .

Measurement of stress at 1% elongation

A 1 x3 cm² specimen was cut from a composite sample. The average thickness of 1 x1 cm² at the center of the specimen was measured. The specimen was clamped on an AGS-X tensile tester (Shimadzu, Japan) to have that 1x1 cm² at center stretched at a stroke rate of 5 mm/min. The stress value at 1 % elongation (0.1 mm) was recorded.

Measurement of power generation A composite sample was fixed on an ACT165DL linear actuator (Aerotech, Pittsburgh, PA). Its elastic electrodes were connected to an oscilloscope with a load resistor R of 1 kQ. The sample was subject to 3% tensile deformation at a frequency of 20 Hz. The generated power was calculated by ^rms/_R. Conformity of sample

A 10x10 cm² sample was laminated on a patch on the inner liner of a tire which was abraded beforehand to make the surface smooth. The conformity of the sample was considered good if there were no wrinkles, no lift-off, or no cracks. On the other hand, the conformity was considered poor if there were wrinkles, partial lift-off, or cracks.

Results

Table 1

power@3% tensile deformation excellent:^5uW/cm2 good: ^0.5uW/cm2 poor: <0.5uW/cm2

The results in Table 1 above illustrate benefits that may be provided by one or more embodiments herein. For example, embodiments of the currently disclosed improved piezoelectric harvester may provide both desired levels of conformity and power generation at 3% tensile deformation, when a piezoelectric generator was constructed as described herein.

For the processes and/or methods disclosed, the functions performed in the processes and methods may be implemented in differing order, as may be indicated by context. Furthermore, the outlined steps and operations are only provided as examples, and some of the steps and operations may be optional, combined into fewer steps and operations, or expanded into additional steps and operations.

This disclosure may sometimes illustrate different components contained within, or connected with, different other components. Such depicted architectures are merely examples, and many other architectures may be implemented which achieve the same or similar functionality. The terms used in this disclosure, and in the appended embodiments, are generally intended as “open” terms (e.g., the term “including” should be interpreted as “including, but not limited to,” the term “having” should be interpreted as “having at least,” the term “includes” should be interpreted as “includes, but is not limited to,” etc.)- In addition, if a specific number of elements is introduced, this may be interpreted to include at least the recited number, as may be indicated by context (e.g., the bare recitation of "two recitations," without other modifiers, includes at least two recitations, or two or more recitations). As used in this disclosure, any disjunctive word and/or phrase presenting two or more alternative terms should be understood to contemplate the possibilities of including one of the terms, either of the terms, or both terms. For example, the phrase “A or B” will be understood to include the possibilities of “A” or “B” or “A and B.”

The terms and words used are not limited to the bibliographical meanings but are merely used to enable a clear and consistent understanding of the disclosure. It is to be understood that the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to "a component surface" includes reference to one or more of such surfaces.

By the term "substantially" it is meant that the recited characteristic, parameter, or value need not be achieved exactly, but that deviations or variations, including for example, tolerances, measurement error, measurement accuracy limitations and other factors known to those skilled in the art, may occur in amounts that do not preclude the effect the characteristic was intended to provide.

Aspects of the present disclosure may be embodied in other forms without departing from its spirit or essential characteristics. The described aspects are to be considered in all respects illustrative and not restrictive. The embodied subject matter is indicated by the appended embodiments rather than by the foregoing description. All changes, which come within the meaning and range of equivalency of the embodiments, are to be embraced within their scope.

Claims

1 . A piezoelectric harvester comprising: a piezoelectric layer comprising a cross-linked elastomeric matrix and piezoelectric particles, wherein the piezoelectric particles are dispersed within the elastomeric matrix; and a first elastic electrode placed on a first side of the piezoelectric layer and a second elastic electrode placed on an opposing second side of the piezoelectric layer; and wherein tensile strength of the piezoelectric harvester at 1 % elongation is about 0.5 MPa to about 5 MPa.

2. The piezoelectric harvester of claim 1 , wherein the cross-linked elastomeric matrix is formed from a reactive silicone oligomer that after curing has a hardness of 45-90 as measured using the Shore hardness scale, type A.

3. The piezoelectric harvester of claim 2, wherein the reactive silicone oligomer comprises polyalkylsiloxane.

4. The piezoelectric harvester of claim 2 or 3, wherein the reactive silicone oligomer has a fraction of reactive functional groups of about 5 mol% to about 10 mol%.

5. The piezoelectric harvester of claim 4, wherein the reactive functional groups comprise hydroxyl, vinyl, alkoxy, hydride, or a combination thereof.

6. The piezoelectric harvester of claim 1 , wherein the elastomeric matrix comprises a doped polyalkylsiloxane matrix and wherein the piezoelectric particles are dispersed within the polyalkylsiloxane matrix.

7. The piezoelectric harvester of claim 6, wherein the polyalkylsiloxane matrix is doped with a noble metal.

8. The piezoelectric harvester of claim 7, wherein the noble metal comprises platinum (Pt).

9. The piezoelectric harvester of claim 3, wherein the polyalkylsiloxane is polydimethylsiloxane (PDMS).

10. The piezoelectric harvester of claim 1 , 2, 3, 4, 5, 6, 7, 8, or 9, wherein a volume fraction of the piezoelectric particles in the piezoelectric layer is about 35% to about 65%.

11 . The piezoelectric harvester of claim 1 , 2, 3, 4, 5, 6, 7, 8, 9, or 10, wherein the piezoelectric particles comprise lead zirconate titanate (PZT).

12. The piezoelectric harvester of claim 1 , 2, 3, 4, 5, 6, 7, 8, 9, 10, or 1 1 , wherein the first elastic electrode and the second elastic electrode comprise carbon.

13. The piezoelectric harvester of claim 1 , 2, 3, 4, 5, 6, 7, 8, 9, 10, 1 1 , or 12, wherein the piezoelectric particles comprise piezoelectric particles polarized by an applied electric field.

14. A tire equipped with the piezoelectric harvester of any one of claims 1 -13.

15. A method for preparing a piezoelectric harvesting composite, comprising: preparing a mixture comprising a silicone oligomer having a hardness of 45-90, as measured using the Shore hardness scale type A after curing, and piezoelectric particles, wherein the piezoelectric particles are dispersed within the silicone oligomer; casting the mixture onto a first layer of elastic electrode to form a first composite film; curing the first composite film; coating the cured first composite film with a second layer of elastic electrode to form a second composite film; curing the second composite film; and applying an electric field to the cured second composite film to polarize the piezoelectric particles within the cured second composite film.