Novel design and manufacturing techniques for synthetic jet actuators.

Abstract

The clampless synthetic jet actuator includes a cavity layer having an internal cavity for receiving a fluid volume and an orifice providing fluid communication between the cavity and ambient air, and a vibratory membrane having a piezoelectric material adapted to deflect the vibratory membrane in response to an electronic signal. The cavity has an opening in at least one planar surface of the cavity layer, and the cavity layer and the vibratory membrane are bonded by an adhesive material having a high strength and low shear modulus. The vibratory membrane is positioned proximate to the planar surface having the cavity opening and adapted as an encapsulating surface for the cavity opening. The vibratory membrane is adapted to compress and expand a volume within the cavity based on the deflection generated by the piezoelectric material to generate fluid flow between the cavity and ambient air through the orifice.

Description

[Technical field]

[0001] SYNTHETIC JET ACTUATORS AND METHODS OF MAKING AND USING SAME FIELD OF THEINVENTION The present invention is directed to improvements in synthetic jet actuators suitable for use in zero net mass flow applications. [Background technology]

[0002] Piezoelectrically actuated membranes have been used to generate synthetic jets in a variety of active flow control applications, such as wind turbine blade fatigue reduction, electronic cooling, and drag reduction for air and ground vehicles. Studies have shown that using these actuators, active flow control (AFC) systems can dramatically change the airflow regime around a bluff body, resulting in improved aerodynamic performance.

[0003] As an example, when applied to a ground vehicle such as a tractor trailer truck, synthetic jet-based AFC can create virtual surface modifications, effectively changing the airflow around the vehicle, i.e., the aerodynamic drag on the vehicle, without changing the vehicle's geometry. Although AFC systems are known in academic research, previous attempts to apply the technology to ground vehicles have been limited by high noise levels, low jet velocity, and low jet thrust, as well as high power consumption by the actuators.

[0004] Conventional AFC systems have involved the use of clamped actuators in zero net mass flow (ZNMF) designs, which generate a jet of flow through manipulation of the surrounding fluid without requiring an additional fluid supply, whereby the jet of flow is generated without any change in the net mass of the surrounding fluid. However, to date, conventional clamped actuators have been deemed to have several undesirable limitations, including limited performance, limited scaling factor, and limited integration factor.

[0005] Nuventix has developed acoustically optimized clamped edge actuators for use in cooling LED lights, however these actuators reach very low ejection velocities that are insufficient for applications such as vehicle drag reduction that instead require high ejection velocities. Although laboratory experiments at Rensselaer Polytechnic Institute suggest that clamped edge actuators may be capable of achieving ejection velocities in excess of 200 m / s, such actuators are not considered commercially viable because they require them to be constructed with excessive size and mass through complex assembly methods with low repeatability and poor sealing capabilities, the assembled actuators do not allow for fine tuning of resonant frequencies (e.g., to avoid high decibels), and require high power consumption.

[0006] Other attempts in actuator design to reduce noise levels include modifications to the actuators that prevent their use in many commercial applications, which require high jet velocities, integration into constrained spaces such as the surface of a vehicle, or the use of multiple actuators operated simultaneously (actuator arrays) to achieve the desired result. One example of an actuator design directed at reducing noise is provided in U.S. Pat. No. 8,564,217, in which noise reduction is achieved for a single actuator for very low jet velocities (<30 m / s) through the use of fixed phase angles applicable in the case of an individual actuator, but which are not valid for use in an array of actuators. Another example is provided in U.S. Pat. No. 8,308,078, in which a synthetic jet actuator comprises two orifices made to face different directions in order to reduce the overall noise level generated by the jets generated therefrom, but at the expense of limited directional jet velocities, making these actuators unsuitable for use in any application where directional control of the jets is required, including ejection of the jets in a common direction. A further example is provided in EP 2 873 609, in which the actuator is provided with a surrounding muffler, which substantially increases the volume of the actuator and effectively prevents the actuator from being used in applications requiring integration of the actuator into a small space (e.g. surface integration applications). Despite the advances in technology to date, there remains a need for improvements in synthetic jet actuators to still further advance the prior art, and to improve ZNMF designs in general. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] U.S. Pat. No. 8,564,217 [Patent Document 2] U.S. Pat. No. 8,308,078 Summary of the Invention [Means for solving the problem]

[0008] The synthetic jet actuator comprises a first cavity layer having an internal cavity for receipt of a fluid quantity and an orifice providing fluid communication between the cavity and an outside atmosphere, and a first vibratory membrane having a piezoelectric material adapted to deflect the first vibratory membrane in response to an electronic signal. The cavity has an opening in at least one planar surface of the first cavity layer, the first cavity layer and the first vibratory membrane are joined by an adhesive material having a high strength low shear modulus, and the first vibratory membrane is positioned proximate to the planar surface having the cavity opening and adapted as an encapsulating surface for the cavity opening. The first vibratory membrane is adapted to compress and expand a volume within the cavity to generate a fluid flow between the cavity and the outside atmosphere through the orifice based on the deflection generated by the piezoelectric material.

[0009] The first vibratory membrane comprises a substrate having a high storage modulus and low loss factor, and a tan delta of less than 0.5. The piezoelectric material is bonded to the substrate by an adhesive material having a covalent and tacky adhesive with a high strength low shear modulus. The substrate and adhesive material are electrically conductive, and the substrate and adhesive material are adapted to act as electrical connections for delivering electrical power to the piezoelectric material, and the electrical connections are configured to provide a non-uniform spatial extent on the piezoelectric material to generate anisotropic deflection of the vibratory membrane.

[0010] The adhesive material bonding the vibratory membrane and the cavity layer comprises at least one of an adhesive film positioned between the first cavity layer and the first vibratory membrane and an adhesive liquid applied to a surface of at least one of the first cavity layer and the first vibratory membrane. The first vibratory membrane is positioned such that a central axis of the vibratory membrane is aligned with a central axis of the cavity in the first cavity layer and such that a central axis of the piezoelectric material is also aligned with a central axis of the cavity in the first cavity layer.

[0011] The first vibratory membrane is adapted to have a preload condition such that in an unpowered state, the first vibratory membrane rests at a neutral axis that provides a slightly expanded state relative to the cavities of the first cavity layer, and is forced to buckle when the first vibratory membrane is deflected to a compressed state under the power of the piezoelectric material. Preferably, the first vibratory membrane is adapted to have a preload condition of at least 0.01 inches.

[0012] In some examples, the first cavity layer includes an expansion chamber embedded within the orifice, the expansion chamber including a series of baffles to cushion the fluid flow passing through the orifice. In some examples, the bounding surfaces of the cavities in the first cavity layer include one or more sloped surfaces having a predefined curvature to correspond to the curvature of the first vibratory membrane in the deflected compressed state to minimize a volume within the cavity predefined to accommodate stagnant fluid flow. The actuator is configured to generate a jet velocity greater than 50 m / s at a resonant frequency less than 500 Hz, i.e., a jet velocity in the range of greater than 50 m / s to 100 M / s, preferably at a resonant frequency in the range of about 150 Hz to 475 Hz.

[0013] In one example, the actuator further comprises a second vibratory membrane comprising a piezoelectric material adapted to deflect the second vibratory membrane in response to an electronic signal, the cavity of the first cavity layer being formed as a through hole passing through the entire cavity layer and having two openings in opposing planar surfaces of the first cavity layer. The first vibratory membrane is positioned proximate to a first planar surface of the first cavity layer having the first opening of the cavity and adapted as an encapsulating surface for the first cavity opening, and the second vibratory membrane is positioned proximate to a second planar surface of the first cavity layer having the second opening of the cavity and adapted as an encapsulating surface for the second cavity opening. Both the first and second vibratory membranes are adapted to compress and expand a volume within the cavity based on the deflection generated by the respective piezoelectric material within the separate vibratory membranes, generating a fluid flow between the cavity and the outside air through the orifice. Both the first and second vibrating membranes are positioned such that the central axis of both respective vibrating membranes is aligned with the central axis of the cavity in the first cavity layer, and the central axis of the piezoelectric material of both respective vibrating membranes is also aligned with the central axis of the cavity in the first cavity layer.

[0014] In another example, the actuator further comprises a second cavity layer having an internal cavity for receiving a volume of fluid and an orifice providing fluid communication between the cavity and the outside air, a second vibratory membrane having a piezoelectric material adapted to deflect the second vibratory membrane in response to an electronic signal, and a third vibratory membrane having a piezoelectric material adapted to deflect the second vibratory membrane in response to an electronic signal. The cavities in both the first and second cavity layers are formed as through holes passing entirely through the respective cavity layers, and both cavities have two openings in opposing planar surfaces of the respective cavity layers. The first vibratory membrane is positioned proximate to a first planar surface of the first cavity layer having a first opening of the cavity in the first cavity layer, and is adapted as an encapsulating surface for the first cavity opening of the cavity in the first cavity layer. The second vibratory membrane is positioned proximate to both the second planar surface of the first cavity layer having the second opening of the cavity in the first cavity layer and the first planar surface of the second cavity layer having the first opening of the cavity in the second cavity layer, and is adapted as an encapsulating surface for both the second cavity opening of the cavity in the first cavity layer and the first cavity opening of the cavity in the second cavity layer. The third vibratory membrane is positioned proximate to the second planar surface of the second cavity layer having the second opening of the cavity in the second cavity layer, and is adapted as an encapsulating surface for the second cavity opening of the cavity in the second cavity layer.

[0015] In this example, the first and second vibratory membranes are adapted to compress and expand a volume within a cavity of the first cavity layer based on a deflection generated by the respective piezoelectric material in the separate vibratory membranes to generate a fluid flow between the cavity and the outside air through the orifice. The second and third vibratory membranes are adapted to compress and expand a volume within a cavity of the second cavity layer based on a deflection generated by the respective piezoelectric material in the separate vibratory membranes to generate a fluid flow between the cavity and the outside air through the orifice. The second vibratory membrane is adapted to compress the volume within the cavity of the first cavity layer while simultaneously expanding the volume within the cavity of the second cavity layer and to compress the volume within the cavity of the second cavity layer while simultaneously expanding the volume within the cavity of the first cavity layer.

[0016] In another example, the actuator further comprises a second cavity layer comprising an internal cavity for receipt of a quantity of fluid and an orifice providing fluid communication between the cavity and the outside atmosphere, the cavity in both the first and second cavity layers being formed as a blind hole having only a single opening in one planar surface of the respective cavity layer. The first vibratory membrane is positioned between the first and second cavity layers proximate to a planar surface of the first cavity layer having a cavity opening of the cavity in the first cavity layer and proximate to a planar surface of the second cavity layer having a cavity opening of the cavity in the second cavity layer, adapted to compress and expand a volume within the cavity of the first cavity layer and to compress and expand a volume within the cavity of the second cavity layer. The first vibrating membrane is adapted to compress a volume within the cavity of the first cavity layer while simultaneously expanding a volume within the cavity of the second cavity layer, and to expand a volume within the cavity of the first cavity layer while simultaneously compressing a volume within the cavity of the second cavity layer.

[0017] The actuator according to the invention may also comprise a first cavity layer for containing noise generated by the first vibratory membrane and an acoustic enclosure provided outside the first vibratory membrane, the acoustic enclosure comprising an outer shell with an absorbent material and a sound barrier positioned within the outer shell, the absorbent material being positioned outside the vibratory membrane and the sound barrier being positioned outside the absorbent material.

[0018] The actuator according to the invention may also comprise an acoustic nozzle positioned outside the orifice of the first cavity layer and adapted to extend a flow path for fluid flow passing into and out of the orifice. The acoustic nozzle comprises an outer annulus made of a sound-insulating barrier material, an acoustic substrate and an acoustic absorbing layer provided within the outer annulus, the acoustic substrate positioned outside the extended flow path provided in the orifice of the cavity layer, and the acoustic absorbing layer positioned outside the acoustic substrate. The acoustic nozzle may be a monolithically integrated component of the cavity layer, and the flow path provided in the acoustic nozzle comprises a flow expansion chamber.

[0019] The invention also includes a method of making an actuator, the method including forming a vibrating membrane by bonding a piezoelectric material to a substrate; preloading the vibrating membrane during assembly through thermoforming via voltage compression and / or electrical actuation of the piezoelectric material; positioning the first vibrating membrane proximate a planar surface of a first cavity layer having a cavity opening and bonding the first vibrating membrane and the cavity layer with an adhesive material; positioning a free-standing mass structure within the vibrating membrane proximate the piezoelectric material and fixing the free-standing mass structure in place with a high strength, low shear modulus adhesive; generating a vacuum pressure to apply a uniform air pressure and press the cavity layer and the vibrating membrane together; and heat curing the cavity layer and the vibrating membrane while applying the uniform air pressure.

[0020] The foregoing general description and the following detailed description are exemplary and explanatory only and are intended to provide further explanation of the invention as claimed. The accompanying drawings are included to provide a further understanding of the invention, are incorporated in and constitute a part of this specification, illustrate embodiments of the invention, and together with the description, serve to explain the principles of the invention. [Brief description of the drawings]

[0021] Further features and advantages of the present invention can be ascertained from the following detailed description, taken in conjunction with the drawings in which: [Figure 1] 1a-1b show schematic diagrams of a conventional synthetic jet actuator, including (a) an assembled view of a clamp-type actuator and (b) an exploded view of a clamp-type actuator.

[0022] [Diagram 2] 2a-2c show schematic diagrams of one example of an actuator according to the present invention, including (a) an assembled view of the actuator, (b) an exploded view of the actuator with the vibratory membrane layer separated from the cavity layer, and (c) a further exploded view of the actuator with the individual layers of the composite vibratory membrane separated.

[0023] [Diagram 3] FIG. 3 shows an exploded view of the vibratory membrane of FIG. 2c connected to a power source.

[0024] [Figure 4] 4a-4b show schematic diagrams of the unimorph assembly of the vibratory membrane within the actuator of FIGS. 2a-2c, including (a) an assembled view of the unimorph membrane and (b) an exploded view of the unimorph membrane.

[0025] [Diagram 5] 5a-5b show schematic diagrams of the assembly of the unimorph membrane of FIGS. 4a-4b with a cavity layer, including (a) an assembled view of the cavity and unimorph membrane layer, and (b) an exploded view of the cavity and unimorph membrane layer.

[0026] [Figure 6] 6a-6b show schematic diagrams of the cavity and unimorph membrane layer assembly of FIGS. 5a-5b with an added mass provided to the unimorph membrane, including (a) an assembled view of the cavity and unimorph membrane layer with the added mass, and (b) an exploded assembled view of the cavity and unimorph membrane layer with the added mass.

[0027] [Figure 7] FIG. 7 shows a schematic diagram of an actuator with a preloaded composite vibratory membrane.

[0028] [Figure 8] FIG. 8 shows a schematic diagram of the assembly of a covalently and adhesively fully bonded actuator as seen in FIGS. 2a-2c.

[0029] [Figure 9] 9a-9c show schematic diagrams of one example of an actuator according to the present invention having two cavities for noise reduction, including (a) an exploded view of the actuator layers, (b) a cross-sectional view of the assembled actuator, and (c) an operational schematic showing the function of the vibrating membrane within the actuator.

[0030] [Figure 10] 10a-10c show schematic diagrams of another example of an actuator according to the present invention having two cavities for noise reduction, including (a) an exploded view of the actuator layers, (b) a cross-sectional view of the assembled actuator, and (c) an operational schematic showing the action of a vibrating membrane within the actuator.

[0031] [Figure 11] 11a-11c show schematic diagrams of one example of an actuator according to the present invention having a centrally aligned cavity and vibrating membrane, including (a) an exploded view of the actuator layers, (b) a cross-sectional view of the assembled actuator, and (c) a relative schematic diagram of the arrangement of the off-center and centered actuators.

[0032] [Figure 12] 12a-12b show schematic diagrams of one example of an actuator according to the present invention having a composite acoustic enclosure for side-based noise reduction, including (a) an exploded view of the actuator layers and (b) a cross-sectional view of the assembled actuator.

[0033] [Figure 13] 13a-13b show schematic diagrams of one example of an actuator according to the present invention having a noise reducing acoustic nozzle, including (a) an exploded view of the actuator layers and (b) a cross-sectional view of the assembled actuator.

[0034] [Figure 14] 14a-14b show schematic diagrams of one example of an actuator according to the present invention with an integrated acoustic nozzle, including (a) an exploded view of the actuator layers and (b) a cross-sectional view of the assembled actuator with a cross-sectional view of the embedded acoustic nozzle airflow path.

[0035] [Figure 15]15a-15b show schematic diagrams of one example of an actuator according to the present invention having an embedded acoustic nozzle, including (a) an exploded view of the actuator layers and (b) a cross-sectional view of the embedded acoustic nozzle airflow path.

[0036] [Figure 16] 16a-16b show schematic diagrams of one example of an actuator according to the present invention having a tilted cavity, including (a) an exploded view of the actuator layers and (b) a cross-sectional view of the assembled actuator.

[0037] [Figure 17] FIG. 17 shows a schematic diagram of a synthetic jet actuator arrangement adapted for noise reduction through phase synchronization. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0038] The following disclosure will discuss the invention with reference to examples illustrated in the accompanying drawings, without, however, limiting the invention to these examples.

[0039] The use of any and all examples or exemplary language (e.g., "etc.") provided herein is intended merely to better clarify the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential or otherwise required to the practice of the invention unless the context is clear.

[0040] As used herein, the singular forms "a," "an," and "the" include plural referents unless the context clearly indicates otherwise. The term "or" is to be understood as an inclusive "or" unless the context dictates otherwise. The terms "first," "second," "third," etc., when used to describe multiple devices or elements, are so used only to convey the relative action, positioning, and / or functionality of the separate devices and do not require a particular order to such devices or elements or any particular quantity or ranking of such devices or elements.

[0041] The word "substantially," as used herein with respect to any property or circumstance, refers to a degree of deviation that is small enough so as not to materially impair the identified property or circumstance. The exact degree of deviation that is permissible in a given situation will depend on the particular context, as will be understood by one of ordinary skill in the art.

[0042] Use of the term "about" or "approximately" is intended to describe values ​​above and / or below a stated value or range, as would be understood by one of skill in the art in each context. In some cases, it includes values ​​in a range of about + / - 10%, in other cases, values ​​in a range of about + / - 5%, in still other cases, values ​​in a range of about + / - 2%, and in still further cases, it includes values ​​in a range of about + / - 1%.

[0043] The terms "comprises" and / or "comprising", as used herein, unless otherwise indicated herein or clearly contradicted by context, should be understood to specify the presence of stated features, integers, steps, operations, elements, and / or components, but not to preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof.

[0044] The recitation of ranges of values ​​herein, unless otherwise indicated, serves as a shorthand notation for referring individually to each separate value falling within the stated range, including the endpoints of that range, each separate value within that range, and all intermediate ranges encompassed by the entire range, each value being incorporated herein as if it were individually listed herein.

[0045] Unless otherwise indicated or clearly contradicted by context, methods described within this specification can be performed with individual steps carried out in any suitable order, including the exact order as disclosed, without any intermediate steps intervening between the disclosed steps, or with one or more intervening steps, the disclosed steps being performed in an order other than the exact order as disclosed, one or more steps being performed simultaneously, and one or more disclosed steps being excluded.

[0046] 1a-1b show an example of a conventional synthetic jet actuator 100, shown both assembled (FIG. 1a) and disassembled (FIG. 1b) in the form of a clamped actuator. In this conventional example, the actuator 100 is shown to include several layers, including a central cavity layer 110, two vibrating membrane layers 120a / 120b, and two outer layers 130a / 130b. The several layers in the conventional actuator 100 are held together by several clamping elements 140, illustrated in this example by several bolts and mating nuts (not shown). Each bolt has a head, which has a threaded shaft extending therefrom. The threaded shaft of each bolt extends through a corresponding set of through holes in the several layers and is mated to a respective nut, and the several layers of the actuator 100 are compressed between the nuts and the bolt heads.

[0047] Conventional actuators such as actuator 100 have been found to have several undesirable limitations, including limited performance, limited scaling factor, and limited integration factor. The performance issues arise as a result of impaired robustness of the several layers in the assembled state, impaired repeatability due to uneven pressure distribution within the cavity layer 110, and inefficiency due to air leakage of the assembled actuator 100. The limited scaling factor is realized due to each actuator requiring manual assembly, and many components are required to mechanically fasten the several layers of each actuator. These conventional actuators are also limited by integration factors, such as the assembled actuator having excessive mass that is prohibitive for small applications requiring positioning the actuator in tight spaces (e.g., aircraft wings, wind turbine blades, or automotive body parts) due to the additional weight required by clamping elements and associated hardware.

[0048] The present invention is directed to synthetic jet actuators that employ one or more piezoelectrically driven vibrating membranes to generate a compressed jet stream, including actuators that are particularly suitable for integration into aerodynamic surfaces, as required in many commercial applications, and methods for producing such actuators. The stacked layers in the actuators according to the invention are secured together through bonding, and the resulting actuators are lightweight, have small overall dimensions, and are easy to produce in a cost- and energy-efficient process.

[0049] Generally, in a piezoelectrically driven actuator, a voltage is supplied to deflect a piezoelectric material along with a corresponding vibrating membrane to increase pressure within a corresponding cavity and force fluid out of the cavity through a shaped orifice. The present invention provides novel material combinations, design features, and fabrication techniques to achieve unprecedented performance beyond that enabled by conventional actuators, which allows for optimized performance parameters previously thought to be mutually exclusive, such as aerodynamic performance, acoustic performance, integration into tight spaces, and the use of multiple simultaneous acoustically synchronized actuators.

[0050] Synthetic jet actuators according to the present invention are capable of generating synthetic jets at reduced noise levels without compromising the aerodynamic performance of the generated jet. The reduction in noise levels can be achieved in a number of ways, including but not limited to modifications to the geometry of the actuators and the equipment used to operate them, overcoming previous approaches with unprecedented performance in reducing noise levels while allowing for further optimization of performance parameters.

[0051] Systems and methods according to the present invention are proposed for producing a synthetic jet actuator based on a piezoelectric actuated membrane that overcomes limitations of prior art systems and methods by allowing for maximizing jet velocity and jet thrust while reducing the resonant frequency (e.g., below 500 Hz), minimizing the amount of piezoelectric material, minimizing power and energy consumption, and minimizing the overall actuator weight and size.

[0052] Systems and methods according to the present invention are also proposed to achieve high ejection velocities and thrust, achieving compliance with regulatory standards such as those set forth by the US Federal Motor Carrier Safety Administration (FMCSA) and the European Union, while remaining suitable for integration into tight spaces (e.g., surface integration in commercial applications).

[0053] 2a-2c show an example of a clampless actuator 200 according to the present invention, the actuator 200 being shown both assembled (FIG. 2a) and disassembled (FIG. 2b), with FIG. 2c showing a further exploded view.

[0054] As shown in Fig. 2a-2c, the actuator 200 comprises a cavity layer 210 sandwiched between two composite vibratory membrane layers 220a / 220b. The cavity layer 210 comprises a body having first and second planar surfaces, an outer periphery, and an inner periphery, the inner periphery defining a cavity 211 within the cavity layer 210. The cavity 211 is open to at least one of its two planar surfaces, and may be open to both planar surfaces. When placed in proximity to the cavity 211, the vibratory membrane layer 220 serves as an encapsulating surface covering the opening to the cavity 211, thereby defining an enclosed space within the cavity 211 for holding a fluid volume. The cavity layer 211 further comprises an orifice 212, which provides an airflow path between the cavity 211 and the atmosphere outside the actuator 200 for the intake and output of airflow into and from the cavity 211.

[0055] As shown in FIG. 2c, both vibratory membranes 220a / 220b include a substrate 221 that is integrally bonded to a piezoelectric disk 223 through a covalent and adhesive adhesive 222 having high strength and low shear modulus. The adhesive adhesive 222 may be formed by one-part or two-part thermosetting resins such as, but not limited to, two-part epoxy resin, one-part methacrylate resin, or low melting metal such as silver solder. In some examples, the adhesive adhesive 222 may be formed through a thermosetting film adhesive, or "prepreg." In some examples, the adhesive adhesive 222 may be conductive, as will be discussed in more detail hereinafter. Both vibratory membranes 220a / 220b further include an outer layer 224 that encapsulates and secures in place several layers of the respective membrane 220.

[0056] In use, the piezoelectric disk 223 is operable through the application of power from a power source 226, via electrical connection 225 (see FIG. 3). The application of power to the piezoelectric disk 223 causes the disk to deform, and due to the integral bonding of the disk 223 to the substrate 221, the deformation of the disk 223 causes a corresponding deflection of the substrate 221 in the same direction. Preferably, the substrate 221 is formed using a substantially thin material and has a high storage modulus and low loss factor resulting in a minimized tangent of delta (tan delta). Ranges for these parameters, along with their preferred values, are provided in Table I.

[0057] In some examples, the substrate 221 can be a metal such as, but not limited to, steel, aluminum, titanium, brass, copper, etc., including alloys thereof. In some examples, the metal can be selected from corrosion resistant grades such as, but not limited to, stainless steel. The metal can be modified to provide additional corrosion resistance or improved adhesion strength through the use of surface treatments such as, but not limited to, solvent cleaning, polishing, acid etching, caustic treatment, electroplating, as well as combinations thereof. The surface can also be treated with high energy processes such as flame, corona, plasma, or electric arc. In one preferred embodiment, the substrate is 0.005 inch 6061 aluminum that is cleaned with acetone, polished with 120 grit alumina, and chromate etched prior to bonding to the piezoelectric.

[0058] In some examples, the substrate 221 may comprise a high modulus polymer, a filled polymer, or a fiber reinforced polymer. These polymers may include thermoplastics or thermosets, and may comprise solid materials such as, but not limited to, particles, hollow microspheres, nanocomposites, clays, fibers, or flakes of polymers, metals, or minerals, including, but not limited to, glass, talc, carbon, and graphite. The fibers may be chopped, discontinuous, short or long, or continuous, woven, nonwoven, or randomly oriented mats. Examples of suitable fibers include, but are not limited to, glass fiber, e-glass, s-glass, cr-glass, carbon fiber, low modulus carbon, medium modulus carbon, high modulus carbon, polyethylene, polypropylene, nylon, polyester, aramid, Kevlar, PPS, and combinations thereof. Fiber reinforced matrices may also be produced from "prepregs."

[0059] The substrate 221 may comprise multiple layers, each of which is independently selected from the materials disclosed herein, with different layers having independent fiber orientations. The fiber laminate may be balanced or unbalanced, symmetric or asymmetric. The polymer matrix may include thermosets or thermoplastics, including, but not limited to, epoxy, urethane, polyester, vinyl ester, PPS, polypropylene, PTFE, Teflon®, polyethylene, or phenolic. The matrix may include toughening agents, softeners, wetting agents, defoamers, Tg enhancers, 2.6 g / cm 3 It may be further modified with materials having greater density, or other materials known to those skilled in the art of composite materials. In one preferred embodiment, the substrate is a preformed 0.005 inch 0 / 90 woven laminate of glass in an amine cured epoxy matrix that is solvent cleaned with isopropanol, sanded with 220 grit sandpaper, and wiped dry prior to adhering the piezoelectric disk.

[0060] In some examples, the piezoelectric disk 223 may be covalently bonded to the substrate 221 during fabrication of the substrate 221, which may be accomplished through processes including, but not limited to, injection molding, overmolding, thermoforming, heat sealing, RTM, VARTM, SCRIMP, vacuum bagging, autoclaving, or wet layup. In a preferred embodiment, the piezoelectric disk 223 is mounted onto a square woven 7 oz. e-glass mat wetout with an amine curing epoxy. Vacuum bagging techniques may be used to apply a uniform pressure application during high temperature curing, during which the disk 223 is integrally bonded to the substrate 221 as it is formed.

[0061] As shown in Figures 2a-2c, the layered composite vibratory membrane 220 includes one or more outer layers 224 positioned on the outside of the piezoelectric disk 223. Previously, conventional actuators used low modulus outer layers or no layers at all because it was common knowledge that high modulus layers bonded to the piezoelectric disk and away from the neutral bending axis could not be used because they would prevent or inhibit the membrane from deflecting. However, surprisingly, with the present invention, it has been found that the use of a high modulus outer layer 224, which may be formed from a material substantially similar to the substrate 221, such as a thermoplastic, a thermoset, or a metal, can lead to an unexpected increase in the jetting velocity. Without being bound by theory, bonding the piezoelectric disk 223 to the substrate 221 at the edge of the disk 223 increases the bonding with the substrate 221, which also increases the deflection of the substrate 221. In one preferred embodiment, the one or more outer layers 224 are provided in the form of 7 ounce square woven fiberglass in a cycloaliphatic amine cured epoxy laminate.

[0062] 3 shows an exploded view of a single composite vibratory membrane 220. As illustrated in this example, the piezoelectric disk 223 is deformed through the supply of power via electrical connection 225, which is illustrated in this example in the form of an electrode that provides electrical communication between a power source 226 and the surface of the piezoelectric disk 223. Suitable examples of electrical connections include, but are not limited to, wires, ribbons, conductive metal tapes, fibers, as well as stencils, silk screens, or printed circuits. In some examples, the substrate 221 may comprise a conductive material, such as metal or carbon fiber, which serves a dual role as an electrode and a mechanical component of the layered composite membrane.

[0063] The electrical connection 225 may be connected anywhere and over any percentage of the surface of the piezoelectric disk 223. In some examples, the electrical connection 225 may be connected only to the edge or center of the piezoelectric disk 223, while in other examples, the electrical connection 225 may be shaped as a ring or shaped like a spiral to reduce bending strain thereon. The electrical connection 225 may further comprise a conductive pressure sensitive adhesive, a methacrylate, a filled thermoset, a solder, or a conductive veil such as a metal coated non-woven fiber or wire mesh, or an anisotropic conductive adhesive film (ACF). In a preferred embodiment, the electrical connection 225 comprises a 1 / 8 inch wide copper tape with a conductive pressure sensitive adhesive (PSA). In another preferred embodiment, the electrical connection 225 comprises a 20 g / m 2 The piezoelectric disk 223 may comprise a Ni or Cu coated carbon veil having an air weight of 1000 .mu.m. The surface of the piezoelectric disk 223 may also comprise a conductive layer which may be thin with low bending stiffness such as, but not limited to, a nickel plated or copper clad, although in some examples the piezoelectric disk 223 may have a nickel surface deposited as thin as 20 microns.

[0064] In a preferred embodiment, the electrical connection 225 may be designed to purposefully provide a non-uniform spatial coverage on the piezoelectric disk 223. In combination with the electrical resistance from the surface of the piezoelectric disk 223, the non-uniform coverage produces anisotropic deflection of the vibrating membrane 220 that is non-uniform in both time and position. By careful selection of the orientation of the electrical connection 225 and the surface resistance of the piezoelectric disk 223, unexpected improvements in jetting rate may be observed. In a preferred embodiment, 1 / 8 inch copper tape runs perpendicular to the orientation of the orifice 212 and is connected to the Ni sputtered surface of the piezoelectric disk 223 using a conductive PSA, the PSA having a resistance of less than 2 ohms across the entire connection, while the surface of the electrode has a resistance of 10-40 ohms per inch away from the copper ribbon. Supplying power to the copper tape causes a deflection along the central axis of the piezoelectric disk 223 with the highest amplitude, but due to resistive losses across the surface of the disk 223, the amplitude decreases as it approaches its edge. This induces partial corrugations to form in the piezoelectric disk 223 and the vibrating membrane 220 as a whole, thereby directing the fluid in the cavity 211 towards the orifice 212, producing an increase in ejection velocity of up to 5%. In addition, it has been found that reducing actuation of the piezoelectric disk 223 near its periphery reduces distortion in material transmission, resulting in a significant improvement to the life of the disk 223.

[0065] Piezoelectric materials are well known to those skilled in the art and may be selected from a group including, but not limited to, PZT, quartz, zinc oxide, PVDF, barium titanate, and the like. Because these materials are relatively expensive, attention has been given to limiting the amount of material used in the vibratory membrane 220. In some examples, reduction in piezoelectric material may be achieved through the use of relatively thin piezoelectric disks 223, such as 0.01 to 0.1 inches thick, including only one piezoelectric disk 223 per vibratory membrane 220. A vibratory membrane that uses only a single piezoelectric disk 223 may be referred to as a unimorph. FIGS. 4a-4b show an example of a unimorph membrane 220', and for ease of illustration, the illustrated example forgoes depiction of the adhesive adhesive 222 and outer layer 224.

[0066] By using only a single piezoelectric disk 223, the unimorph membrane 220' has the advantage of a low resonant frequency as well as reduced power and energy consumption. In the unimorph membrane 220', the piezoelectric disk 223 can be placed on the neutral bending axis of the vibrating membrane inside or outside the cavity 211 of the cavity layer 210, as shown in Figures 4a-4b. In a preferred embodiment, the unimorph membrane 220' is designed such that the single piezoelectric disk 223 is on the side of the substrate 221 facing the cavity 211. Figures 5a-5b show an example of a unimorph membrane 220', which is assembled into an actuator 200 employing only a single vibrating membrane 220, and the piezoelectric disk 223 of the single unimorph membrane 220' is positioned on the outer surface facing the cavity 211 of the substrate 221. Again, for ease of illustration, the illustrated example forgoes depiction of adhesive glue 222 and outer layer 224 .

[0067] In some examples, the deflection and resonant frequency of the vibrating membrane 220 can be further tuned through the use of high density materials. Through empirical studies, it has been discovered that increasing the mass of the vibrating membrane 220 can dramatically change the response of the membrane 220 without significantly changing other mechanical properties. Such an increase in mass can be achieved by inlaying a high density material, such as tungsten, into the substrate 221 or by forming the substrate 221 substantially of tungsten. In other examples, added mass can be achieved by filling the thermoplastic and thermoset resins of the composite vibrating membrane 220 with a high density material, such as barium sulfate. In some examples, additional independent mass structures can be incorporated into the composite vibrating membrane 220. FIGS. 6a-6b illustrate one example of an actuator 200 in which a 5 ounce lead disk 227 is attached to the center of the outer surface of a piezoelectric disk 223 using a high strength, low shear modulus adhesive (not shown). Due to the attachment location and the low shear modulus of the adhesive, the piezoelectric disc 223 is still allowed to flex freely while the added mass 227 reduces the resonant frequency by 40% without significantly affecting the jet velocity.

[0068] Without being bound by theory, it is believed that the added mass increases the momentum of the vibratory membrane 220, causing a larger displacement as it is cyclically powered. In addition, the increased weight both reduces and broadens the resonant frequency. This is particularly beneficial in the use of net zero mass flow clampless actuators in aerodynamic applications, including tractor trailer trucks, because the market demands a resonant frequency of less than 500 Hz. By increasing the mass of the vibratory membrane 220, it is possible to reduce and broaden the resonant frequency from 800 Hz down to frequencies within the range of about 150 to about 475 Hz.

[0069] Buckling actuators are well known to those skilled in the art. In the design according to the invention, the unpowered vibrating membrane 220 is at its neutral bending axis, resulting in a slightly extended state as illustrated in FIG. 7. When powered, the vibrating membrane 220 is forced to buckle and snap away from the neutral bending axis, which is expected to reduce the resonant frequency while increasing the force the membrane exerts against the air inside the cavity, resulting in higher ejection velocity values ​​(compared to a smaller sized non-buckling actuator) at lower noise levels (reduced actuation frequency equals lower noise levels).

[0070] As an alternative to traditional mechanical displacement as a means for preloading, the present invention includes that voltage compression may be used to displace the vibrating membrane 220 through thermoforming by raising the temperature of the membrane 220 above its softening and melting points and then cooling it in the deformed state. Thermoforming may be performed before or after assembly of the actuator. In some examples, to fine-tune performance metrics, actuators may be made with variable capacitance by assembling the actuator using mechanically fastened plates, the fasteners allowing the membrane to be repeatedly displaced, repositioned, and then clamped.

[0071] The buckling geometry of the actuator 200 can be optimized by electrically actuating the piezoelectric disk 223 during assembly of the actuator. The actuated piezoelectric disk 232 deforms to a desired geometry, and thus, by actuating the piezoelectric disk 223 during assembly of the actuator, the assembled actuator 200 will be pre-optimized for a particular piezoelectric disk 223 and substrate 221 combination. Control of the electrostatic voltage can further fine-tune the buckling geometry and performance parameters.

[0072] The present invention includes an actuator 200 as well as a method for making a vibrating membrane 220 that incorporates such a membrane to produce a synthetic jet actuator having a fully adhesively and covalently bonded structure with uniform bond strength and minimized internal stress.

[0073] Previous approaches to assembling zero net mass flow clamped edge piezoelectric driven synthetic jet actuators have relied on mechanical clamping. These conventional approaches have the downside of increased mass and volume as well as an increased number of parts and assembly steps that present the possibility of leakage through interfaces, and further the possibility of mechanical failure due to fasteners loosening over time during operation of the actuator. Non-mechanical approaches that have been explored include injection molding, overmolding, or hot compression. While these techniques boast high throughput, the use of high thermal stresses and non-uniform pressures have been found to result in in-situ distortion and poor repeatability in the actuator. Other approaches include the use of liquid adhesives, but these have been found to not allow for tight control of the bond line and present the risk of clogging small design features such as the orifice 212 in the cavity layer 210.

[0074] The present invention instead avoids the negative aspects of previous approaches by employing a novel use of B-staged thermoset adhesive films and vacuum bagging (improving jetting performance, reducing complexity, decreasing overall weight, and improving part-to-part consistency) to produce actuators with tight control of the bond lines and spatially uniform interlayer bond strength.

[0075] Assembly of one or more vibratory membranes 220 to the cavity layer 210 may include surface preparation of the layer faces, as previously described. In one embodiment, a B-staged thermosetting adhesive film is cut and punched from sheet material and placed between the membrane 220 and the cavity layer 210. The film adhesive may be applied as a liquid to either or both layers and is B-staged prior to assembly. The film adhesive may also be provided in the same form as the tacky / adhesive adhesive 222. As shown in FIG. 8, several layers are then sealed in a bag 30 connected to a vacuum source 40, which removes air from the bag 30, thereby applying air uniformly to the surfaces of the layered components. In contrast to previous approaches using hot compression that create point loads and misalignments to small features, the use of vacuum-based air pressure ensures perfectly uniform lamination of each layer and greatly reduces capital costs by not requiring expensive molds. A number of vacuum bags 30 can be assembled and loaded into a processing oven where the temperature is raised, causing the film adhesive to briefly reflow and form adhesive covalent bonds between each layered component prior to curing.

[0076] The layered components may be cured at temperatures ranging from about 140°F to about 350°F for about 1 hour to about 4 hours for the thermoset to reach full properties. In multi-step assembly, the maximum cure temperature may be reserved for the final step to "co-cure" all layers of the composite actuator. Testing of such post-cure bond lines has been found to result in control of adhesive flow to within 0.030 inches. It has also been found that actuators fabricated under such conditions are capable of increasing jetting velocities by up to 25% over those produced by mechanically fastened actuators.

[0077] Without being bound by theory, it is believed that the method according to the invention with high modulus adhesion of greater than about 8,000 PSI provides a better and more spatially uniform vibratory membrane interface to the cavity than that achieved with mechanical fasteners, while also eliminating leak paths. The method of the invention also provides significant weight, cost, and parts savings by not requiring external clamps, allowing these net zero mass flow clampless actuators to be used in practical applications including improving the aerodynamics of tractor trailer trucks.

[0078] Some materials, especially those that are corrosion resistant and essentially non-reactive, may be difficult to covalently bond with thermosetting resins. These may include materials such as stainless steel, aluminum, or polypropylene. If desired, a "tie layer" may be used in place of the thermosetting resin to achieve similar results. A "tie layer" is usually one or a combination of two or more mutually compatible materials that form an adhesive layer between two mutually incompatible materials. For example, the tie layer may include a thermoplastic material that provides adhesion to two adjacent materials, most often through melt processing or chemical reaction, and may include modified acrylic, or anhydride grafted polymers, or similar to, but not limited to, DuPont's Bynel, Nucrel, and Fusabond grades, or those described and referenced as further examples in U.S. Patent Nos. 8,076,000, 7,807,013, and 7,285,333. The melting point and melt index of the tie layer may be selected such that the tie layer may be post-processed without substantially melting or flowing other non-metals in the remainder of the actuator.

[0079] The method according to the invention, including the use of one or more of non-uniform electrodes, high modulus outer layers, covalent adhesive bonding, vacuum bagging, and careful control of substrate thickness, storage, and loss modulus as well as mass distribution, as detailed in Table I below, is effective in producing synthetic jet actuators that are capable of overcoming the limitations of conventional designs, including producing jet velocities greater than 100 m / s, at frequencies less than 500 Hz, and having a size and weight that is viable for practical applications. [Table 1]

[0080] The present invention includes additional designs for synthetic jet actuators, including designs that incorporate multiple cavity layers with one or more vibrating membrane arrangements (which may include unimorph membranes), including arrangements where a common vibrating membrane is shared between two cavity layers, as well as arrangements that include additional noise reduction elements.

[0081] 9a-9c show an example of a synthetic actuator 300 consisting of a laminated stack of layers, comprising three vibrating membranes 320a / 320b / 320c and two cavity layers 310a / 310b, each cavity layer 310 having a separate cavity 311 and an orifice 312. As shown in FIG. 9c, several layers are stacked, The two cavity layers 310a / 310b cyclically share a common vibrating membrane 320b, which switches between a first mode in which it compresses the volume of the top cavity 311a and expands the volume of the bottom cavity 311b, and a second mode in which it expands the volume of the top cavity 311a and compresses the volume of the bottom cavity 311b. Thus, the actuator 300 is adapted such that the air flows at the two orifices 312a / 312 are always in opposite directions to each other.

[0082] As one skilled in the art would understand, the noise level generated by a synthetic actuator is a function of the sound waves generated by the airflows traveling out and into the orifices of the actuator. With the arrangement shown in FIG. 9c, since the airflows travel in opposite directions, the sound waves generated by the individual airflows will be opposed to each other and there will be interference generated between them, resulting in partial cancellation of the sound waves, i.e., a reduction in the overall noise level. Acoustic testing of an actuator having a three vibrating membrane design as shown in FIGS. 9a-9c was found to result in a 14.7 dB reduction in acoustic output level compared to that generated by an individual synthetic jet actuator. Advantageously, since both orifices 312a / 312b face a common direction, the reduction in noise level is achieved with negligible loss to aerodynamic performance. Additional parameters of a preferred embodiment of the actuator 300 are provided below in Table II.

[0083] 10a-10c show another example of a synthetic actuator 400 consisting of a laminated stack of layers, which comprises two capped cavity layers 410a / 410b and a middle piezoelectric vibrating membrane 420, each of which has a cavity 411a / 411b and an orifice 412a / 412b. As shown in FIG. 10c, the actuator 400 is adapted such that the two cavity layers 411a / 411b share a common vibrating membrane 420 in a cyclical manner, so that the airflows at the two orifices 412a / 412b are always in opposite directions to each other, and there is interference between the sound waves generated by the two airflows, resulting in a reduction in noise. In this example, the use of a single vibrating membrane 420 reduces the cost and power consumption. Additional parameters of a preferred embodiment of the actuator 400 are provided below in Table II.

[0084] 11a-11c show a further example of a synthetic actuator 500 consisting of a laminated stack of layers, comprising two vibrating membranes 520a / 520b and a single cavity layer 510 having a cavity 511 and an orifice 512. In contrast to mechanically fastened actuators in which fastening elements (e.g. screws, bolts, etc.) are arranged around the cavity 511 and limit the cavity volume, the use of a laminated layer in actuator 500 not only allows the cavity volume to be significantly larger, but also allows alignment of the central axis of the vibrating membrane with the central axis of the cavity layer 511.

[0085] As can be seen in the comparison shown in FIG. 11c, the conventional clamped actuator 100 has a cavity 111 with a central axis offset from the central axis of the vibrating membrane 120a / 120b, while the actuator 500 according to the present invention has additional space for the central positioning of the cavity 511, whereby the central axis of the cavity is aligned with the central axis of the vibrating membrane 520a / 520b. Since the piezoelectric disk is positioned at the center of the vibrating membrane 520a / 520b, the alignment of the cavity central axis with the membrane central axis simultaneously results in the alignment with the piezoelectric disk. This alignment of the cavity 511 with a larger volume with the central axis of the vibrating membrane 520a / 520b and the centered piezoelectric disk allows for a larger displacement of the membrane 520a / 520b, resulting in not only a larger ejection volume but also a reduction in the resonant frequency. Additional parameters of a preferred embodiment of the actuator 500 are provided below in Table II.

[0086] 12a-12b show a further example of an actuator 600 consisting of a laminate stack, comprising two vibrating membranes 610a / 610b and one cavity layer 610 with a cavity 611 and an orifice 612. On each side of the actuator 600, an acoustic enclosure 630 is provided to contain the noise generated by each vibrating membrane 620. The enclosure 630 has a minimal volume to avoid inhibiting the performance of the actuator 600. Generally, as the frequency decreases by a third octave, the volume of the enclosure doubles. The volume of the enclosure 630 on each side of the sealed section of the actuator 600 is about 40 times the volume of air displaced by each piezoelectric disk during actuation. This volume is filled with an acoustic absorbing material 631, such as melamine foam, fiberglass insulation, or mineral wool material, to increase the apparent volume and lower the resonant frequency. A sound barrier 632, such as mass loaded vinyl, surrounds the absorbing material 631. Both materials are encapsulated within an outer shell 633. These materials have transmission loss (TL) values ​​of about 24 at 360 Hz and about 29 at 675 Hz. Additional parameters of a preferred embodiment of actuator 600 are provided below in Table II.

[0087] 13a-13b show a further example of an actuator 700 made of a laminate stack, comprising two vibrating membranes 720a / 720b and a cavity layer 710 having a cavity 711 and an orifice 712. An acoustic nozzle 740 attached to the outer plane of the orifice 712 provides an extended airflow path into and out of the cavity 711. The acoustic nozzle 740 is adapted to reduce the sound level by providing an airflow path 741 that serves as an extension of the cavity 712, the inside of which is formed with an acoustic absorbing layer 742 and an acoustic substrate 743 made of a material having high absorption properties at one or more acoustic frequencies of interest. Suitable examples of highly absorbent acoustic materials include, but are not limited to, melamine and acoustic foam. The acoustic nozzle 740 further includes an outer annulus 744 made of a sound-insulating barrier material for further attenuation of the sound level. Additional parameters of a preferred embodiment of actuator 700 are provided below in Table II.

[0088] 14a-14b show a further example of an actuator 800 consisting of a laminate stack, the laminate stack comprising two vibratory membranes 820a / 820b and a cavity layer 810 having a cavity 811 and an orifice 812. An acoustic nozzle 840 extends from the outer plane of the orifice 812 to provide an extended airflow path 841 into and out of the cavity 811. In this example, the airflow path 841 of the acoustic nozzle 840 is formed with an extension chamber 842 to attenuate the sound level. Additional parameters of a preferred embodiment of the actuator 800 are provided below in Table II.

[0089] 15a-15b show a further example of an actuator 900 consisting of a laminate stack, the laminate stack comprising two vibrating membranes 920a / 920b and one cavity layer 910 with a cavity 911 and an orifice 912. FIG. 15a shows the actuator 900 in an exploded view, the cavity layer 910 separated into two halves 910-1 / 910-2 and the orifice 912 also separated into two halves 912-1 / 912-2. In this example, the cavity layer 910 comprises an integrated expansion chamber 940 including a baffle arrangement 941, which is embedded in the orifice 912 through the formation of an etched pattern in both orifice halves 912-1 / 912-2 of FIG. 15a. 15b shows a partial close-up of orifice half 912-2, showing the baffle arrangement 941 etched therein. Baffle arrangement 941 provides a cushioning effect to the airflow passing through orifice 912, effectively reducing the sound level generated by the airflow. Additional parameters of a preferred embodiment of actuator 900 are provided below in Table II.

[0090] 16a-16b show a further example of an actuator 1000 consisting of a laminate stack, comprising two vibratory membranes 1020a / 1020b and one cavity layer 1010, the cavity layer having a cavity 1011 and an orifice 1012. FIG. 16a omits the illustration of the upper vibratory membrane 1020a to provide a more complete view of the cavity 1011. In this example, the boundary surface forming the open volume of the cavity 1011 opposite the orifice 1012 is formed with a sloping surface 1013, which eliminates dead spaces and improves the internal pressure distribution within the cavity 1011. The sloping surface 1013 optimizes the shape of the cavity 1011 to further correspond to the properties and operating frequency of the vibratory membranes 1020a / 1020b. In particular, the inclined surface 1013 is formed with an opposing surface having a curvature corresponding to the maximum curvature that occurs in the membranes 1020a / 1020b when they are at their maximum inward displacement towards the cavity 1011, but a slight offset is provided in the inclined surface so that the membrane does not contact the surface, thereby avoiding friction that could cause mechanical and thermal wear to the membrane. This construction of the angled surface 1013 reduces the volume of the internal cavity 1011 by eliminating a portion that would normally hold pockets of stagnant air that would not be compressed into a jet, thereby improving the efficiency of the actuator and reducing noise levels and power consumption. Additional parameters of a preferred embodiment of the actuator 1000 are provided below in Table II.

[0091] FIG. 17 shows an example of a system 1 consisting of an array formed of multiple actuators 200, each mounted on a common transport platform (e.g., surface mount for commercial applications), each operated by a common arrangement of a multi-channel driver 10, a controller 20, and one or more sensors 30. An AC voltage is supplied to each actuator 200 with individual phase adjustment to control the noise level generated at distances greater than that of two wavelengths, the waves being effectively plane waves. Phase control can be used to target the sound waves generated by each linear row of actuators 200, and the degree of acoustic advantage is adjustable depending on the phase coherence of the system 1. If each driver has a different phase response, the acoustic advantage will not be as great as a system 1 with similar phase drivers. By basic calculations, with perfect phase at a distance equal to two wavelengths, the system 1 can be controlled to generate zero acoustic levels. Achieving such an ideal result is difficult in practice due to challenges in aligning the drivers, and further due to inconsistencies in driver manufacturing that result in phase differences. In an example in accordance with the invention, the phase difference between neighboring actuators 200 is adjusted based on the noise level measured while the driver scans different phase angles for each actuator 200 on two separate channels. Although system 1 is discussed in this example as comprising multiple actuators 200, it should be understood that system 1 may include multiple actuators of any type discussed herein, including combinations of multiple different actuator types. Additional parameters of a preferred embodiment of system 1 are provided below in Table II.

[0092] As shown in further detail in Table II below, systems and methods according to the present invention are effective for producing synthetic jet actuators, including systems conforming to one or more of the above examples, as well as systems combining elements of two or more of the above examples, that can overcome limitations of conventional designs and are also capable of producing jet velocities at reduced noise levels below what was previously thought possible. [Table 2]

[0093] Although the present invention has been described with reference to detailed embodiments, it will be understood by those skilled in the art that the foregoing disclosure deals only with exemplary embodiments, and that the scope of the present invention is not limited to the disclosed embodiments, but may include additional embodiments encompassing various changes and modifications relative to the examples disclosed herein without departing from the scope of the present invention as defined in the accompanying claims, etc.

[0094] Although some of the foregoing examples forgo illustration and / or discussion of some elements discussed in other examples, it should be understood that each example may include or be included with each element from one or more examples. For example, although some examples forgo illustration and / or explicit discussion of a tacky adhesive layer and / or an outer layer (such as tacky adhesive 222 and outer layer 224 in FIG. 2c and FIG. 3), it should be understood that each example discussed herein may include these elements. Similarly, although some examples discuss configurations with only a single cavity layer and with a single cavity and orifice, it should be understood that each example discussed herein is envisioned as including multiple cavity layers, each with its own cavity and orifice. (For example, the examples of Figures 10-16 are shown with a single cavity layer, but may each include multiple cavity layers, as illustrated in the example of Figure 9.) Additionally, while the above examples are discussed in relation to airflow, it should be understood that jet actuators in accordance with the present invention are not limited to generating air and airflow, but may be used with any suitable fluid for generating a corresponding fluid flow.

[0095] To the extent necessary to understand and complete the disclosure of the present invention, all publications, patents, and patent applications mentioned herein are expressly incorporated herein by reference to the same extent as if each was individually incorporated as such. No license, express or implied, is granted to any patent incorporated herein.

[0096] The present invention is not limited to the exemplary embodiments illustrated herein, but is instead characterized by the accompanying claims, which do not in any way limit the scope of the present disclosure.

Claims

1. A synthetic jet actuator, comprising: a first cavity layer having an interior cavity for receiving a quantity of fluid and an orifice providing fluid communication between the cavity and the outside atmosphere; a first vibrating membrane comprising a piezoelectric material; Equipped with the piezoelectric material is adapted to deflect the first vibrating membrane in response to an electronic signal; the cavity has an opening in at least one planar surface of the first cavity layer, the first vibratory membrane being positioned proximate to the planar surface having the cavity opening and adapted as an encapsulating surface for the cavity opening; the first vibrating membrane is adapted to compress and expand a volume within the cavity based on a deflection generated by the piezoelectric material to generate a fluid flow between the cavity and the outside air through the orifice; A synthetic jet actuator, wherein the first cavity layer and the first vibratory membrane are bonded by an adhesive material having high strength and low shear modulus.

2. 2. The synthetic jet actuator of claim 1, wherein the adhesive material comprises at least one of an adhesive film positioned between the first cavity layer and the first vibrating membrane and an adhesive liquid applied to a surface of at least one of the first cavity layer and the first vibrating membrane.

3. The synthetic jet actuator of claim 1 , wherein the first vibrating membrane comprises a substrate, the piezoelectric material being bonded to the substrate by an adhesive material.

4. The synthetic jet actuator of claim 3 , wherein the adhesive material is a covalent and tacky adhesive with high strength and low shear modulus.

5. 4. The synthetic jet actuator of claim 3, wherein the substrate and the adhesive material are electrically conductive, and the substrate and the adhesive material are adapted to serve as electrical connections for delivery of power to the piezoelectric material.

6. The synthetic jet actuator of claim 5 , wherein the electrical connections are configured to provide a non-uniform spatial extent on the piezoelectric material to generate anisotropic deflection of the vibrating membrane.

7. The synthetic jet actuator of claim 3 , wherein the substrate has a high storage modulus and a low loss factor, and a tan delta of less than 0.

5.

8. The synthetic jet actuator of claim 1 , wherein the first vibrating membrane is positioned such that a central axis of the first vibrating membrane is aligned with a central axis of the cavity in the first cavity layer.

9. The synthetic jet actuator of claim 8 , wherein a central axis of the piezoelectric material is aligned with the central axis of the cavity in the first cavity layer.

10. 2. The synthetic jet actuator of claim 1, wherein the first cavity layer comprises an expansion chamber embedded within an orifice, the expansion chamber comprising a series of baffles for cushioning the fluid flow passing through the orifice.

11. 2. The synthetic jet actuator of claim 1, wherein a boundary surface of the cavity in the first cavity layer comprises one or more sloped surfaces having a predefined curvature, the predefined curvature corresponding to a curvature of the first vibrating membrane in a deflected compressed state to minimize a volume within the predefined cavity to accommodate stagnant fluid flow.

12. 2. The synthetic jet actuator of claim 1, wherein the first vibrating membrane is adapted to have a preloaded state whereby in an unpowered state, the vibrating membrane rests at a neutral axis that provides a slightly expanded state for the cavities of the first cavity layer, and the first vibrating membrane is forced to buckle upon deflection of the piezoelectric material to a compressed state under power.

13. The synthetic jet actuator of claim 12 , wherein the first vibratory membrane is adapted to have a preload condition of at least 0.01 inches.

14. The synthetic jet actuator of claim 1 , wherein the actuator is configured to generate jet velocities greater than 50 m / s at a resonant frequency less than 500 Hz.

15. 15. The synthetic jet actuator of claim 14, wherein the actuator is configured to generate jet velocities in the range of greater than 50 m / s to 100 M / s at a resonant frequency in the range of approximately 150 Hz to 475 Hz.

16. a second vibratory membrane comprising a piezoelectric material adapted to deflect the second vibratory membrane in response to an electronic signal; the cavities of the first cavity layer are formed as through holes passing entirely through the cavity layer, the cavities having two openings in opposing planar surfaces of the first cavity layer; the first vibratory membrane is positioned adjacent to a first planar surface of the first cavity layer having a first opening of the cavity and adapted as an encapsulating surface for the first cavity opening, and the second vibratory membrane is positioned adjacent to a second planar surface of the first cavity layer having a second opening of the cavity and adapted as an encapsulating surface for the second cavity opening; 2. The synthetic jet actuator of claim 1, wherein both the first and second vibrating membranes are adapted to compress and expand a volume within the cavity based on deflections generated by the respective piezoelectric materials within the separate vibrating membranes to generate fluid flow between the cavity and the outside air through the orifice.

17. 17. The synthetic jet actuator of claim 16, wherein both the first and second vibrating membranes are positioned such that a central axis of both respective vibrating membranes is aligned with a central axis of the cavity in the first cavity layer.

18. The synthetic jet actuator of claim 17 , wherein a central axis of the piezoelectric material of both respective vibrating membranes is aligned with the central axis of the cavity in the first cavity layer.

19. a second cavity layer having an interior cavity for receiving a quantity of fluid and an orifice providing fluid communication between the cavity and the outside atmosphere; a second vibratory membrane comprising a piezoelectric material, the piezoelectric material adapted to deflect the second vibratory membrane in response to an electronic signal; and a third vibratory membrane comprising a piezoelectric material, the piezoelectric material adapted to deflect the second vibratory membrane in response to an electronic signal; and Further equipped with the cavities in both the first and second cavity layers are formed as through holes passing entirely through the respective cavity layers, each cavity having two openings in opposing planar surfaces of the respective cavity layers; the first vibratory membrane is positioned proximate to a first planar surface of the first cavity layer having a first opening of the cavity in the first cavity layer and adapted as an encapsulating surface for the first cavity opening of the cavity in the first cavity layer; the second vibratory membrane is positioned proximate to both a second planar surface of the first cavity layer having a second opening of the cavity in the first cavity layer and a first planar surface of the second cavity layer having a first opening of the cavity in the second cavity layer, and adapted as an encapsulating surface for both the second cavity opening of the cavity in the first cavity layer and the first cavity opening of the cavity in the second cavity layer; the third vibratory membrane is positioned proximate to a second planar surface of the second cavity layer having a second opening of the cavity in the second cavity layer and adapted as an encapsulating surface for the second cavity opening of the cavity in the second cavity layer; both the first and second vibratory membranes are adapted to compress and expand a volume within the cavity of the first cavity layer based on deflections generated by the respective piezoelectric materials within the separate vibratory membranes to generate a fluid flow between the cavity and the outside air through the orifice; 2. The synthetic jet actuator of claim 1, wherein both the second and third vibrating membranes are adapted to compress and expand a volume within the cavity of the second cavity layer based on deflections generated by the respective piezoelectric materials in the separate vibrating membranes to generate a fluid flow between the cavity and the outside air through the orifice.

20. 20. The synthetic jet actuator of claim 19, wherein the second vibrating membrane is adapted to compress a volume within the cavity of the first cavity layer while simultaneously expanding a volume within the cavity of the second cavity layer, and to expand a volume within the cavity of the first cavity layer while simultaneously compressing a volume within the cavity of the second cavity layer.

21. a second cavity layer having an interior cavity for receiving a quantity of fluid and an orifice providing fluid communication between the cavity and the outside atmosphere; the cavities in both the first and second cavity layers are formed as blind holes having only a single opening in one planar surface of the respective cavity layer; the first vibratory membrane is positioned between the first and second cavity layers adjacent a planar surface of the first cavity layer having the cavity openings of the cavities in the first cavity layer and adjacent a planar surface of the second cavity layer having the cavity openings of the cavities in the second cavity layer; 2. The synthetic jet actuator of claim 1, wherein the first vibrating membrane is adapted to compress and expand a volume within the cavity of the first cavity layer and to compress and expand a volume within the cavity of the second cavity layer.

22. 22. The synthetic jet actuator of claim 21 , wherein the first vibrating membrane is adapted to compress a volume within the cavity of the first cavity layer while simultaneously expanding a volume within the cavity of the second cavity layer, and to expand a volume within the cavity of the first cavity layer while simultaneously compressing a volume within the cavity of the second cavity layer.

23. 10. The synthetic jet actuator of claim 1, further comprising an acoustic enclosure provided outside the first cavity layer and the first vibrating membrane for containing noise generated by the first vibrating membrane.

24. 24. The synthetic jet actuator of claim 23, wherein the acoustic enclosure comprises an outer shell with an absorbing material and a sound barrier positioned within the outer shell, the absorbing material being positioned outside the vibratory membrane and the sound barrier being positioned outside the absorbing material.

25. 10. The synthetic jet actuator of claim 1, further comprising an acoustic nozzle positioned outside the orifice in the first cavity layer, the acoustic nozzle adapted to extend a flow path for fluid flow passing into and out of the orifice.

26. 26. The synthetic jet actuator of claim 25, wherein the acoustic nozzle comprises an outer annulus made from an acoustic barrier material, an acoustic substrate and an acoustic absorbing layer provided within the outer annulus, the acoustic substrate positioned outside the elongated flow path provided at the orifice in the cavity layer, and the acoustic absorbing layer positioned outside the acoustic substrate.

27. 26. The synthetic jet actuator of claim 25, wherein the acoustic nozzle is a monolithically integrated component of the cavity layer, and the flow path provided within the acoustic nozzle comprises a flow expansion chamber.

28. 13. A method of making the actuator of claim 1, the method comprising: positioning the first vibratory membrane proximate to a planar surface of the first cavity layer having the cavity opening; bonding the first vibratory membrane and the cavity layer with an adhesive material; A method comprising:

29. 30. The method of claim 28, further comprising forming the vibrating membrane by bonding the piezoelectric material to a substrate.

30. 30. The method of claim 28, further comprising preloading the vibratory membrane during assembly through thermoforming.

31. 31. The method of claim 30, wherein the thermoforming of the vibrating membrane is performed via voltage compression.

32. 30. The method of claim 28, further comprising preloading the vibrating membrane during assembly by electrically actuating the piezoelectric material.

33. 30. The method of claim 28, further comprising positioning an independent mass structure within the vibrating membrane in proximity to the piezoelectric material.

34. 34. The method of claim 33, wherein the free-standing mass structure is bonded to the piezoelectric material with an adhesive having a high strength and low shear modulus.

35. 30. The method of claim 28, further comprising generating a vacuum pressure and applying a uniform air pressure to press the cavity layer and vibratory membrane together.

36. 36. The method of claim 35, further comprising heat curing the cavity layer and vibratory membrane while applying the uniform air pressure.

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