Source: http://www.google.com/patents/US7608989?dq=5311516
Timestamp: 2014-09-02 14:10:10
Document Index: 590780160

Matched Legal Cases: ['Application No. 60', 'Application No. 60', 'Application No. 60', 'Application No. 60', 'Application No. 60', 'Application No. 60', 'Application No. 60', 'Application No. 60', 'Application No. 10']

Patent US7608989 - Compliant electroactive polymer transducers for sonic applications - Google PatentsSearch Images Maps Play YouTube News Gmail Drive More »Sign in<nobr>Advanced Patent Search</nobr>PatentsDescribed herein are compliant electroactive polymer transducers for use in acoustic applications. A compliant electroactive polymer transducer includes a compliant electroactive polymer at least two electrodes. For sound production, circuitry in electrical communication with the transducer electrodes...http://www.google.com/patents/US7608989?utm_source=gb-gplus-sharePatent US7608989 - Compliant electroactive polymer transducers for sonic applicationsAdvanced Patent SearchPublication numberUS7608989 B2Publication typeGrantApplication numberUS 11/676,977Publication dateOct 27, 2009Filing dateFeb 20, 2007Priority dateJul 20, 1999Fee statusPaidAlso published asUS7898159, US20070200467, US20100013356, WO2007100606A2, WO2007100606A3Publication number11676977, 676977, US 7608989 B2, US 7608989B2, US-B2-7608989, US7608989 B2, US7608989B2InventorsRichard P. Heydt, Ronald E. Pelrine, Roy D. Kornbluh, Neville A. Bonwit, Joseph S. EckerleOriginal AssigneeSri InternationalExport CitationBiBTeX, EndNote, RefManPatent Citations (35), Non-Patent Citations (11), Referenced by (12), Classifications (8), Legal Events (2) External Links: USPTO, USPTO Assignment, EspacenetCompliant electroactive polymer transducers for sonic applicationsUS 7608989 B2Abstract Described herein are compliant electroactive polymer transducers for use in acoustic applications. A compliant electroactive polymer transducer includes a compliant electroactive polymer at least two electrodes. For sound production, circuitry in electrical communication with the transducer electrodes is configured to apply a driving signal that causes the electroactive polymer to deflect in the acoustic range.
1. A sonic actuator comprising:
an electroactive polymer transducer including a portion of an electroactive polymer and a first electrode in contact with the portion and a second electrode in contact with the portion, wherein the electroactive polymer transducer is arranged in a manner which causes the portion to deflect in response to a change in electric field that is applied via at least one of the first electrode and the second electrode;
a biasing mechanism that is configured to position the portion in a bias position that differs from a resting position of the portion when no external forces are applied to the electroactive polymer transducer; and
a circuit in electrical communication with the first electrode and the second electrode and configured to provide an actuation signal to the at least one of the first electrode and second electrode, wherein the actuation signal causes the portion to deflect from the bias position at a frequency less than about 50 kHz.
2. The sonic device of claim 1 wherein the portion includes a) a planar shape when the biasing mechanism does not position the portion in the bias position and b) a non-planar shape when the portion is in the bias position.
3. The sonic device of claim 1 wherein the biasing mechanism is configured to receive a control signal that determines the bias position.
4. The sonic device of claim 3 wherein the biasing mechanism includes a second electroactive polymer transducer, the second electroactive polymer transducer including a second electroactive polymer and at least two electrodes in contact with a portion of the second electroactive polymer.
5. The sonic device of claim 1 wherein the electroactive polymer transducer includes a greater stiffness when the portion is in the bias position than the electroactive polymer transducer includes without the bias position of the portion.
6. The sonic device of claim 1 further comprising a third electrode in contact with a second portion of the electroactive polymer.
7. The sonic device of claim 6 further comprising a second biasing mechanism that is configured to position the second portion in a second bias position that differs from a resting position of the second portion.
8. The sonic device of claim 7 wherein the sonic device, when actuated, does not have a null frequency between about 0 Hz and about 50 kHz.
9. The sonic device of claim 7 wherein the sonic device is configured to radiate into a space surrounding the sonic device without any null spots less than 90 degrees from a centerline of the sonic device.
a biasing mechanism that is configured to position the portion in a first bias position and a second bias position that each differ from a resting position of the portion when no external forces are applied to the electroactive polymer transducer; and
a circuit in electrical communication with the first electrode and the second electrode and configured to provide an actuation signal to the at least one of the first electrode and second electrode, wherein the actuation signal causes the portion to deflect from the first bias position or the second bias position at a frequency less than about 50 kHz,
wherein, upon deflection, the first bias position and the second bias position include a different directivity of acoustic output.
11. The sonic device of claim 10 wherein the electroactive polymer includes a planar shape when the portion is in the resting position and the electroactive polymer includes a non-planar shape when the portion is in the bias position.
12. The sonic device of claim 10 wherein the biasing mechanism includes a pump or compressor that applies a positive air pressure onto a surface of the electroactive polymer.
13. The sonic device of claim 10 wherein the biasing mechanism includes a spring coupled to the portion.
14. The sonic device of claim 10 wherein the biasing mechanism includes a foam coupled to the portion.
15. The sonic device of claim 10 wherein the biasing mechanism is configured to receive a control signal used to determine the second bias position.
16. The sonic device of claim 15 wherein the biasing mechanism includes a second electroactive polymer transducer, including a second electroactive polymer and at least two electrodes in contact with a portion of the second electroactive polymer.
17. The sonic device of claim 16 wherein the biasing mechanism is configured to move the position the portion in the second bias position in real time.
18. A sonic actuator comprising:
an electroactive polymer transducer including
a first portion of an electroactive polymer and at least two electrodes in contact with the first portion, wherein the electroactive polymer transducer is arranged in a manner which causes the first portion to deflect in response to a change in electric field that is applied via the at least two electrodes in contact with the first portion, and
a second portion of the electroactive polymer and at least two electrodes in contact with the second portion, wherein the electroactive polymer transducer is arranged in a manner which causes the second portion to deflect in response to a change in electric field that is applied via the at least two electrodes in contact with the second portion;
a first biasing mechanism that is configured to position the first portion in a first bias position that differs from a resting position of the first portion when no external forces are applied to the electroactive polymer transducer;
a second biasing mechanism that is configured to position the second portion in a second bias position that differs from a resting position of the second portion when no external forces are applied to the electroactive polymer transducer; and
a circuit in electrical communication with the at least two electrodes in contact with the first portion and in electrical communication with the at least two electrodes in contact with the second portion and configured to provide an actuation signal to the at least two electrodes in contact with the first portion and an actuation signal to the at least two electrodes in contact with the second portion, wherein the actuation signal causes the first portion or the second portion to deflect at a frequency less than about 50 kHz.
19. The sonic device of claim 18 wherein the sonic device, when actuated, is configured to operate above its fundamental mode.
20. The sonic device of claim 18 wherein the sonic device, when actuated, does not have a null frequency between about 0 Hz and about 50 kHz.
21. The sonic device of claim 20 wherein the sonic device is configured to radiate into a space surrounding the sonic device without any null spots less than 90 degrees from a centerline of the sonic device.
CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority under 35 U.S.C. �119(e) from U.S. Provisional Patent Application No. 60/776,265 filed Feb. 24, 2006, naming Roy Kornbluh et al. as inventors, and titled �Compliant Polymer Usage in Sonic Applications�; this application also claims priority under U.S.C. �120 and is continuation-in-part of co-pending U.S. patent application Ser. No. 11/335,805, filed Jan. 18, 2006 and entitled, �ELECTROACTIVE POLYMERS�, which is incorporated herein for all purposes; this '805 patent application claimed priority under U.S.C. �120 from U.S. Pat. No. 7,049,732, filed Jul. 16, 2004 and entitled, �ELECTROACTIVE POLYMERS� (and co-pending at filing of '983); this '732 patent claimed priority from U.S. Pat. No. 6,812,624 (which was co-pending at filing of '732); '624 claimed priority under 35 U.S.C. �119(e) from a) U.S. Provisional Patent Application No. 60/144,556 filed Jul. 20, 1999, naming R. E. Pelrine et al. as inventors, and titled �High-speed Electrically Actuated Polymers and Method of Use�, b) U.S. Provisional Patent Application No. 60/153,329 filed Sep. 10, 1999, naming R. E. Pelrine et al. as inventors, and titled �Electrostrictive Polymers As Microactuators�, c) U.S. Provisional Patent Application No. 60/161,325 filed Oct. 25, 1999, naming R. E. Pelrine et al. as inventors, and titled �Artificial Muscle Microactuators�, d) U.S. Provisional Patent Application No. 60/181,404 filed Feb. 9, 2000, naming R. D. Kombluh et al. as inventors, and titled �Field Actuated Elastomeric Polymers�, e) U.S. Provisional Patent Application No. 60/187,809 filed Mar. 8, 2000, naming R. E. Pelrine et al. as inventors, and titled �Polymer Actuators and Materials�, f) U.S. Provisional Patent Application No. 60/192,237 filed Mar. 27, 2000, naming R. D. Kornbluh et al. as inventors, and titled �Polymer Actuators and Materials II�, g) U.S. Provisional Patent Application No. 60/184,217 filed Feb. 23, 2000, naming R. E. Pelrine et al. as inventors, and titled �Electroelastomers and their use for Power Generation�; all of these provisional patent applications, patent applications, and patents are incorporated by reference in their entirety for all purposes.
GOVERNMENT RIGHTS This application was made in part with government support under contract number N66001-97-C-8611 awarded by the Office of Naval Research. The government has certain rights in the invention.
FIELD OF THE INVENTION The present invention relates to compliant electroactive polymers. In particular, the invention relates to compliant electroactive polymers used in sonic applications such as sound production and noise cancellation.
BACKGROUND OF THE INVENTION Acoustic actuators most commonly act as point sources for producing sound, i.e., are used as speakers, but are also used for active noise and vibration control. The most common of these acoustic actuators or speakers are electromagnetic-based and electrostatic-based systems.
Electrostatic speakers are constructed with two electrode plates having different electrical potentials and positioned with a narrow air gap in between, with air being used as the dielectric medium. To produce sound, one of the plates is held stationary and the other is moved relative to the stationary plate. The movable plate is electrostatically attracted to the stationary plate While electrostatic speakers are lightweight and can be made to have a relatively low profile, they have several disadvantages for many applications. These speakers tend to be costly since it is necessary to carefully construct the speaker so that the moving plate does not contact the stationary plate, but with a small enough air gap so that the driving voltage is not required to be excessive. Additionally, because the radiating plate must maintain a nearly constant spacing from a rigid stationary plate, these speakers are limited to flat-mounted applications. Further, as electrostatic speakers typically operate with a bias voltage of several thousand volts, limitations on the driving voltage will also limit the acoustic power output.
U.S. Pat. No. 6,343,129 discloses speakers using electroactive polymers having low moduli of elasticity in which the in-plane strains of the compliant electroactive polymer dielectric are used to induce out-of-plane deflection of the film to produce sound. The stiffness and mass of polymer films operating in this out-of-plane configuration are orders of magnitude less than that for compression of the more rigid polymers used in the electrostrictive and piezoelectric devices mentioned above. This allows for higher acoustic output per surface area and per weight at lower driving voltages than is possible with other electrostatic devices. Other advantages of speakers made with elastomeric polymer films is that they can be made in a wide variety of form factors, i.e., they can be conformed to any shape or surface, they are very lightweight and have very low-profiles that can be unobtrusively located on walls, ceilings or other surfaces, and they are relatively easy to manufacture and use low cost materials.
SUMMARY OF THE INVENTION The present invention relates to the use of compliant electroactive polymer transducers in acoustic applications. A compliant electroactive polymer transducer includes a compliant electroactive polymer with at least two electrodes. For sound production, circuitry in electrical communication with the transducer electrodes is configured to apply a driving signal that causes the electroactive polymer to deflect in the acoustic range.
FIG. 5A is a perspective view of a frustum shaped diaphragm transducer; and
FIG. 5B is a sectional perspective view of a transducer comprised of a plurality of frustum transducers of FIG. 5A stacked in a parallel-stacked arrangement.
DETAILED DESCRIPTION OF THE INVENTION Before describing particular embodiments of the sonic devices, systems and applications, a discussion of compliant electroactive polymer transducers and their material properties and performance characteristics is provided, followed by a description of several suitable electroactive polymer actuators.
Electroactive Polymer Transducers FIGS. 1A and 1B illustrate an electroactive polymer transducer 10, the basic functional element of the present invention. A portion of thin elastomeric polymer 12, also commonly referred to as a film or membrane, is sandwiched between compliant electrodes 14 and 16. In this elastomeric polymer transducer, the elastic modulus of the electrodes is generally less than that of the polymer, and the length �L� and width �W� of the film are much greater than the thickness �t�.
s = ɛ r ⁢ ɛ 0 ⁢ E 2 = ɛ r ⁢ ɛ 0 ⁢ v 2 t 2 ( Equation ⁢ ⁢ 1 ) where s is the effective actuation stress or pressure on a dielectric elastomer diaphragm, ∈r is the relative dielectric constant of the polymer film, ∈o is the dielectric constant of free space, E is the electric field (equal to the applied voltage divided by the film thickness) and Y is Young's modulus of elasticity. This effective pressure includes the effect of both the electrostatic attractive and repulsive forces.
Polymer materials may be selected based on one or more material properties or performance characteristics, including but not limited to a low modulus of elasticity, a high dielectric constant, strain, energy density, actuation pressure, specific elastic energy density, electromechanical efficiency, response time, operational frequency, resistance to electrical breakdown and adverse environmental effects, etc. Polymers having dielectric constants between about 2 and about 20, and particularly between about 2.5 and about 12, are also suitable. Specific elastic energy density�defined as the energy of deformation of a unit mass of the material in the transition between actuated and unactuated states�may also be used to describe an electroactive polymer where weight is important. Polymer 12 may have a specific elastic energy density of over 3 J/g. The performance of polymer 12 may also be described by efficiency�defined as the ratio of mechanical output energy to electrical input energy. Electromechanical efficiency greater than about 80 percent is achievable with some polymers.
There many commercially available polymer materials that may be used for polymer 12 including but not limited to: acrylic elastomer, silicone elastomer, polyurethane, PVDF copolymer and adhesive elastomer. In one embodiment, the polymer is an acrylic elastomer comprising mixtures of aliphatic acrylate that are photocured during fabrication. The elasticity of the acrylic elastomer results from a combination of the branched aliphatic groups and cross-linking between the acrylic polymer chains. One suitable material is NuSil CF19-2186 as provided by NuSil Technology of Carpenteria, Calif. Other exemplary materials suitable for use as polymer 12 include any dielectric elastomeric polymer, silicone rubbers, fluoroelastomers, silicones such as Dow Corning HS3 as provided by Dow Corning of Wilmington, Del., fluorosilicones such as Dow Corning 730 as provided by Dow Corning of Wilmington, Del., etc, and acrylic polymers such as any acrylic in the 4900 VHB acrylic series as provided by 3M Corp. of St. Paul, Minn. Other suitable polymers may include one or more of: silicone, acrylic, polyurethane, fluorosilicone, fluoroelastomer, natural rubber, polybutadiene, nitrile rubber, isoprene, SBS, and ethylene propylene diene.
The addition of a plasticizer may, for example, improve the functioning of a transducer by reducing the elastic modulus of the polymer and/or increasing the dielectric breakdown strength of the polymer. Examples of suitable plasticizers include high molecular-weight hydrocarbon oils, high molecular-weight hydrocarbon greases, Pentalyne H, Piccovar� AP Hydrocarbon Resins, Admex 760, Plastolein 9720, silicone oils, silicone greases, Floral 105, silicone elastomers, nonionic surfactants, and the like. Of course, combinations of these materials may be used. Alternatively, a synthetic resin may be added to a styrene-butadiene-styrene block copolymer to improve the dielectric breakdown strength of the copolymer. For example, pentalyn-H as produced by Hercules, Inc. of Wilmington, Del. was added to Kraton D2104 as produced by Shell Chemical of Houston, Tex. to improve the dialectic breakdown strength of the Kraton D2104. Certain types of additives may be used to increase the dielectric constant of a polymer. For example, high dielectric constant particulates such as fine ceramic powders may be added to increase the dielectric constant of a commercially available polymer. Alternatively, polymers such as polyurethane may be partially fluorinated to increase the dielectric constant.
The desired performance of an electroactive polymer transducer may be controlled by the extent of prestrain applied to the polymer film and the type of polymer material used. For some polymers of the present invention, pre-strain in one or more directions may range from about −100 percent to about 600 percent. The pre-strain may be applied uniformly across the entire area of the polymer film or may be unequally applied in different directions. In one embodiment, pre-strain is applied uniformly over a portion of the polymer 12 to produce an isotropic pre-strained polymer. By way of example, an acrylic elastomeric polymer may be stretched by about 200 to about 400 percent in both planar directions. In another embodiment, pre-strain is applied unequally in different directions for a portion of the polymer 12 to produce an anisotropic pre-strained polymer. In this case, the polymer 12 may deflect more in one direction than another when actuated. By way of example, for a VHB acrylic elastomer having isotropic pre-strain, pre-strains of at least about 100 percent, and preferably between about 200 to about 400 percent, may be used in each direction. In one embodiment, the polymer is pre-strained by a factor in the range of about 1.5 times to about 50 times the original area. In some cases, pre-strain may be added in one direction such that a negative pre-strain occurs in another direction, e.g., 600 percent in one direction coupled with�100 percent in an orthogonal direction. In these cases, the net change in area due to the pre-strain is typically positive.
FIGS. 1A and 1B may be used to show one manner in which the transducer portion 10 converts mechanical energy to electrical energy. For example, if the transducer portion 10 is mechanically stretched by external forces to a thinner, larger area shape such as that shown in FIG. 1B, and a relatively small voltage difference (less than that necessary to actuate the film to the configuration in FIG. 1B) is applied between electrodes 14 and 16, the transducer portion 10 will contract in area between the electrodes to a shape such as in FIG. 1A when the external forces are removed. Stretching the transducer refers to deflecting the transducer from its original resting position�typically to result in a larger net area between the electrodes, e.g. in the plane between the electrodes. The resting position refers to the position of the transducer portion 10 having no external electrical or mechanical input and may comprise any pre-strain in the polymer. Once the transducer portion 10 is stretched, the relatively small voltage difference is provided such that the resulting electrostatic forces are insufficient to balance the elastic restoring forces of the stretch. The transducer portion 10 therefore contracts, and it becomes thicker and has a smaller planar area (orthogonal to the thickness between electrodes). When polymer 12 becomes thicker, it separates electrodes 14 and 16 and their corresponding unlike charges, thus raising the electrical energy and voltage of the charge. Further, when electrodes 14 and 16 contract to a smaller area, like charges within each electrode compress, also raising the electrical energy and voltage of the charge. Thus, with different charges on electrodes 14 and 16, contraction from a shape such as that shown in FIG. 1B to one such as that shown in FIG. 1A raises the electrical energy of the charge. That is, mechanical deflection is being turned into electrical energy and the transducer portion 10 is acting as a generator.
Devices Deflection of an electroactive polymer according to the present invention may include bending, axial deflection, linear expansion or compression in one or more directions, deflection out of a hole provided in a substrate, etc. The transducer deflection may be translated to a desired output function or motion based at least in part on the manner and object to which the transducer is mounted. This section describes several suitable devices that incorporate an electroactive polymer transducer. Other suitable electroactive polymer devices are described in U.S. Pat. No. 6,812,624, which was incorporated by reference above.
Given the desire in many applications for low-profile actuators, particularly in sonic applications, the electroactive polymer may have a number of smaller curved film areas (�bubbles�, where each bubble has a correspondingly smaller out-of-plane displacements rather than a single large area that moves a greater distance out of plane. The use of smaller film areas also prevents the generation of higher-order displacement modes at the higher frequencies. In fact, the upper limit for bubble area in some applications would be determined by the minimum frequency at which these higher-order modes (which reduce the radiation efficiency of the actuator) appear. Since electroactive polymers can be easily manufactured in a variety of patterns, bubbles of different areas, each driven over a different range of frequencies, may be combined in a single actuator in order to maximize the power output for a given actuator area, while maintaining high fidelity.
A bias pressure applied to membrane 68 causes an out-of-plane and concave protrusion of the membrane. That is, a protrusion, bulge, or �bubble� 70 is formed by a biasing force on the membrane 68 which is substantially perpendicular to the plane P of the membrane 68. The signal from the driver (not shown) can cause further movement or modulation of the bubble 70 to, for example, a position 70′. The sound-emitting surface may either be the top side (concave emission) or bottom side (convex emission) of polymer 68.
As disclosed in U.S. patent application Ser. Nos. 11/085,804, incorporated by reference in its entirety, stacking diaphragms in parallel is one way in which to maximize power output for out-of-plane or Z-axis input/output. Doing so amplifies the force potential of the system. The number of layers stacked may range from 2 to 100 or more.
In order to effect this force distribution, a weight or cap 84 is affixed to the diaphragm layers. The cap may be a solid disc, an annular member or otherwise constructed cap which may be affixed to the diaphragm 82 by means of adhesive bonding, thermal bonding, friction welding, ultrasonic welding, or the constituent pieces may be mechanically locked or clamped together. Furthermore, the capping structure may comprise a portion of the film which is made substantially more rigid through thermal, mechanical or chemical techniques�such as curing and vulcanizing.
The shape and size of the cap is selected to produce a perimeter of sufficient dimension/length to adequately distribute stress applied to the material. The ratio of the size of the cap 84 to the diameter of the frame 86 holding the Electroactive Polymer Artificial Muscle (EPAM�) layers may vary as desired; however, the larger the cap, the greater the stress/force the cap applies to the diaphragm. When diaphragm 82 is stretched in a direction perpendicular to the plane of the cap 84, as illustrated, it produces the frustum form. The degree of truncation of the structure may be selected to reduce the aggregate volume or space that the transducer occupies. Further, as taught in U.S. patent application Ser. No. 11/361,703, the mass of the cap may be set or tuned in order to provide a system that operates at resonance or within a band of frequencies near resonance, thereby delivering the desired performance at desirably high frequencies. In variable frequency applications, a system may be designed so that the peak performance range covers a broader section of frequencies, e.g. from about 0.001 to about 10,000 Hz or more. In any case, the mass of the system may be tuned so as to offer maximum displacement at a desired frequency of operation.
The frustum-shaped diaphragms can be stacked as described above to provide single-sided frustum transducers or double-sided structures. In double-sided frustum transducers, one side typically provides preload to the other. FIG. 5B illustrates a double-frustum architecture 90. Here, opposing layers 94 and 96 of EPAM� material or one side of EPAM� film and one side of basic elastic polymer are held together, either directly or by way of a cap, under tension along an interface section 92. To actuate the transducer for simple Z-axis motion, one of the concave/frustum sides is expanded by applying voltage while the other side is allowed to relax. Such action increases the depth of one cavity while decreasing that of the other, and visa-versa, resulting in an actuator which moves in/out or up/down relative to a neutral position. By actuating both sides in parallel, the stiffness of the system can be adjusted by means of adjusting the applied voltage.
Sonic Usage Somewhat conflicting objectives of conventional sonic actuators are the displacement of a large volume of air and the provision of a low-profile, lightweight construction. The electroactive polymer actuators described above achieve both of these goals by using the area change developed in the diaphragm to produce out-of-plane displacement with a minimum of additional structure.
Using dielectric elastomers as loudspeakers requires the ability to charge and discharge the electroactive polymer diaphragm at acoustic frequencies. This requirement can put more stringent demands on electrode conductivity (specifically on the RC time constant) than it does in other, lower frequency, dielectric-elastomer actuator applications. For instance, the film capacitance of the exemplary loudspeaker is about 5.6 nF. Thus, for acoustic response up to 10 kHz, the film surface resistivity should be about 5 kΩ/square, or less.
s AC = ɛ r ⁢ ɛ 0 t 2 ⁢ ( 2 ⁢ BA + A 2 ) ( Equation ⁢ ⁢ 2 ) For an electroactive polymer loudspeaker diaphragm, if B is the DC voltage on the film and A is the drive or signal voltage, the time-varying actuation response, sAC, corresponding to Equation 1 (above) is:
Assuming that radiated sound pressure is proportional to the film oscillation amplitude, the speaker response varies in proportion to the voltage term in parentheses in Equation 2, where A is the drive voltage and B is the bias voltage. When bias voltage is significantly greater than the drive voltage, i.e., B>>A, the actuation pressure and sound pressure level vary linearly with changes in the bias and drive voltages. The condition B >>A is sufficient to achieve low levels of harmonic distortion, except at low frequencies (<500 Hz). At higher drive voltages, when A is not small compared to B, it is possible to compensate for harmonic distortion.
To illustrate the effect of voltage on sound pressure level (SPL), two different drive voltages (differing by factor of 3) were applied to the exemplary loudspeaker. Specifically, drive voltages of 135 V AC and 405 V AC were each applied with a 1.5 kV bias voltage to the speaker with their respective SPL response curves illustrated in FIG. 7. The measured increase in SPL (measured at a distance of 1 meter from the speaker diaphragm surface) was in the range from about 8 dB to about 10 dB over most of the audible frequency range. These results corresponded to the predicted change in SPL based on Equation 2.
Electroactive polymer acoustic actuators have distinct advantages over other types of speakers (discussed above) in that they are lightweight and can be fabricated in a wide variety of form factors, i.e., they are able to conform to any shape or surface. Electroactive polymer acoustic actuators can be flat, for example, as freestanding or wall-mounted speakers, but can also conform easily to arbitrarily curved surfaces, such as those in vehicle interiors. This distinguishes them from electrostatic loudspeakers, which are usually flat because the radiating film must maintain a nearly constant spacing from a rigid stationary electrode. These characteristics make the electroactive polymer acoustic actuators ideal for sound production applications as well as active noise control (ANC) applications, e.g. for use within the interiors of automobiles, aircraft and other vehicles to control cabin noise, or attached to vibrating machinery or structures to control radiated noise.
When the two electroactive polymers are implemented in an opposing or �push-pull� arrangement, such as that shown in FIG. 5B, the nonlinear part of the voltage response of each polymer may cancel each other out provided they are supplied with similar or the same bias voltages but equal and opposite driving signals. This effectively eliminates the A2 (or voltage square) term in Equation 2, which creates simpler control since the polymer acoustic response will now be linear based on A (and B, which is usually constant).
The biasing mechanism may also change shape of the polymer transducer as a function of frequency output of the speaker. For direct radiator loudspeakers, including electromagnetic (voice-coil) and electrostatic speakers, the ideal size of an acoustically radiating element of the speaker surface decreases as frequency increases. This is because sound radiation becomes more directional at higher frequency; specifically, it becomes more directional as the product ka increases, where k is wavenumber and a is the radius or characteristic dimension of the radiating surface. One way to reduce extreme directionality is to use a curved radiating surface. This is a motivation for using dome-shaped loudspeakers at mid- and high-range audio frequencies. However, with conventional (voice-coil) speakers, domes are a fixed size and are comparatively rigid�the dome material and shape are selected in part to put spatial resonances in desired frequency ranges. On the other hand, with electrostatic loudspeakers it is difficult to build the speaker surface in a domed or curved shape. Thus electrostatic loudspeakers are usually flat and sound directionality is an issue if the speaker surface area is very large. Electroactive polymer sonic devices, on the other hand, can be readily adapted to a specific shape and hence can have controlled directivity.
Bias position control also improves off-axis sound radiation. Specifically, the bias position may also be set such that the speaker radiates without a null spot into a room or space. In audio applications like home stereo systems, it is generally desirable to have isotropic sound radiation, so that there are no �dead spots� for listeners away from the speaker centerline. The same is often true for secondary sources in ANC applications, depending on the noise characteristics of the primary source. In cases in which the spatial extent of the �quiet zone� is limited�by design or by physics�it may be acceptable, or even preferable, to have non-isotropic secondary sources. In all cases it is important to know the directional characteristics of the secondary sources.
As mentioned, loudspeaker shape (as determined by the bias position) influences directivity of the speaker output. To evidence this, consider the above-referenced 10 cm speaker when in each of the positive biased (concave shape) and the negative biased (convex shape) configurations. The directivity of each configuration was measured with the audio input voltage applied at various frequencies, with the resulting measurements plotted in the graphs of FIGS. 9A and 9B with the directivity being normalized to 0 dB SPL at 0� at all frequencies. In the selected frequency range, FIG. 9A indicates that there are null spots within its radiation beam of the concave speaker configuration, while no such null spots are produced in the radiation beam pattern of the convex speaker configuration, as shown in FIG. 9B. These results are consistent with theoretical productions, and indicate that speaker output directivity can be controlled and optimized by selectively defining the speaker's shape (mechanical approach) with phased-array beam-forming (electrical and system design approach).
Sonic actuators described herein may also operate in multi-modal regimes. In most operation instances, the polymer only deflects in its first mode of actuation, where the entire surface of the film moves in the same direction. The size of the electroactive polymer area that is actuated (e.g., in diaphragm mode) typically determines the maximum frequency for unimodal actuation. Above this frequency, the polymer will have a portion of its surface moving in a different direction. This multimodal actuation may decrease or increase the total sound output possible with the film area at a given frequency. Additionally, the amplitude of motion of the film may increase at its fundamental (unimodal) and higher-order resonances. The presence of modally influenced motion is evidenced in a frequency spectrum of the speaker by resonant peaks and resonant nulls. It is generally desired to �smooth� away these peaks and nulls to make the level of sound output more constant as a function of frequency.
Thickness or stiffness variations that allow multi-modal performance in a polymer may also be introduced by a variety of means, such as spraying on polymers or other materials or molding. While not a requirement, the added material is typically attached external to the electrode-dielectric polymer-electrode structure of the transducer (i.e. not between the electrodes). In some cases, stiffened regions, of a uniform or patterned nature, of the dielectric polymer may be created through the use of chemical treatments.
For audio applications, such as home theater systems, the sonic energy devices may be tuned for their desired frequency range and enclosures. For example, a sonic energy device designed as a high frequency �tweeter� speaker would likely have a different design from a mid-range speaker or a low-range �woofer� speaker.
When tuning a sonic energy device, parameters that affect tuning include the geometry and mass of the sonic energy device, as well as how it is physically attached to the supporting structure. These parameters affect the natural resonance modes of the sonic energy device. For example, geometry changes which are likely to affect the resonance characteristics include the diameters and shape of the inner and outer edges of the diaphragm configuration and how much the cap is biased out of plane. Similarly, the mass may be tuned by the number of layers of EPAM� material, the material type, design, and thickness of each EPAM� layer, and the material and geometry of the cap. The manner of the physical attachment of the sonic energy device to the supporting structure may also affect the net sonic output, as a device rigidly connected to the supporting structure would resonate differently than one compliantly connected, using a rubber spacer pad, for instance.
Another factor affecting the manufacture and operation of the sonic energy device includes the material, design, and manufacturing method of the bias element. For instance, in some applications, it may be advantageous to have a concave diaphragm speaker. While this has been achieved via pulling a vacuum on a plenum behind an EPAM� diaphragm element, such an approach may not be practical for some applications for a variety of reasons. Another method to achieve a similarly concave shape would be to coat a concave foam surface with an adhesive, and pull a vacuum in a manufacturing fixture, drawing the EPAM� diaphragm element onto the adhesive-coated foam surface. Depending on the shape of the foam surface, e.g., flat, concave, rippled, etc, different shapes of the EPAM� diaphragm layer could be achieved.
Another method to achieve a concave surface without the use of vacuum would be to sandwich a compression spring between a diaphragm cap (see FIG. 5B) and a supporting structure, possibly in the shape of an �X� or a perforated disc, across the front of the diaphragm. Such geometry would allow for the passage of sound waves, yet also is simple, robust and economical. The resonant frequency of the bias element will affect the overall resonance frequency of the speaker. For this and other reasons, the same bias element type and design may not be beneficial in all applications. For example, the compression spring bias element just described may work better for a low-frequency �woofer� than for high-frequency noise cancellation over large surfaces, where lighter-weight and more economical foam biasing may be the bias element of choice.
Methods associated with the subject devices are contemplated in which those methods are carried out with the subject sonic devices. The methods may comprise the act of providing a suitable speaker, device, transducer, actuator, etc. Such provision may be performed by the end user. In other words, the �providing� merely requires the end user obtain, access, approach, position, set-up, activate, power-up or otherwise act to provide the requisite device in the subject method. The methods also include biasing the polymer or a portion thereof to a bias position, and then actuating the portion.
Yet another aspect of the invention includes kits having any combination of devices described herein�whether provided in packaged combination or assembled by a technician for operating use, instructions for use, etc. A kit may include any number of transducers/actuators/devices/speakers according to the present invention. A kit may include various other components for use with the transducers including mechanical or electrical connectors, power supplies, etc. The subject kits may also include written instructions for use of the devices or their assembly.
Also, it is contemplated that any optional feature of the inventive variations described may be set forth and claimed independently, or in combination with any one or more of the features described herein. Reference to a singular item, includes the possibility that there are plural of the same items present. More specifically, as used herein and in the appended claims, the singular forms �a,� �an,� �said,� and �the� include plural referents unless specifically stated otherwise. In other words, use of the articles allow for �at least one� of the subject item in the description above as well as the claims below. It is further noted that the claims may be drafted to exclude any optional element. As such, this statement is intended to serve as antecedent basis for use of such exclusive terminology as �solely,� �only� and the like in connection with the recitation of claim elements, or use of a �negative� limitation. Without the use of such exclusive terminology, the term �comprising� in the claims shall allow for the inclusion of any additional element�irrespective of whether a given number of elements are enumerated in the claim, or the addition of a feature could be regarded as transforming the nature of an element set forth in the claims. Stated otherwise, unless specifically defined herein, all technical and scientific terms used herein are to be given as broad a commonly understood meaning as possible while maintaining claim validity.
Patent CitationsCited PatentFiling datePublication dateApplicantTitleUS3403234Sep 11, 1964Sep 24, 1968Northrop CorpAcoustic transducerUS4342936Dec 19, 1980Aug 3, 1982Eastman Kodak CompanyHigh deflection bandwidth product polymeric piezoelectric flexure mode device and method of making sameUS4400634Dec 9, 1980Aug 23, 1983Thomson-CsfBimorph transducer made from polymer materialUS4762733Mar 26, 1986Aug 9, 1988Standard Elektrik Lorenz, A.G.Color picture tubeUS4843275Jan 19, 1988Jun 27, 1989Pennwalt CorporationAir buoyant piezoelectric polymeric film microphoneUS4885783Apr 10, 1987Dec 5, 1989The University Of British ColumbiaElastomer membrane enhanced electrostatic transducerUS4961956May 8, 1989Oct 9, 1990Lumel, Inc.Electroluminescent lamps and phosphorsUS4969197Feb 21, 1989Nov 6, 1990Murata ManufacturingPiezoelectric speakerUS5149514Feb 8, 1991Sep 22, 1992Sri InternationalLow temperature method of forming materials using one or more metal reactants and a halogen-containing reactant to form one or more reactive intermediatesUS5156885Apr 25, 1990Oct 20, 1992Minnesota Mining And Manufacturing CompanyMethod for encapsulating electroluminescent phosphor particlesUS5171734Apr 22, 1991Dec 15, 1992Sri InternationalIntroducing into fluidized bed reacaator coating sources in vaporized form, decomposing at specific temperature rangesUS5206557Nov 27, 1990Apr 27, 1993McncMicroelectromechanical transducer and fabrication methodUS5229979Dec 13, 1991Jul 20, 1993Rutgers, The State University Of New JerseyElectrostrictive driving device, process for sonic wave projection and polymer materials for use thereinUS5258201Sep 23, 1992Nov 2, 1993Munn Robin WMethod of forming a partial coating on phosphor particles by coating the phosphors in a fluidize bed for a limited time and subsequently annealing to promote ionic diffusionUS5302318Jul 30, 1991Apr 12, 1994Gte Products CorporationAdding fibrous alumina fibers to phosphor before fluidizationUS6343129Jul 19, 1999Jan 29, 2002Sri InternationalElastomeric dielectric polymer film sonic actuatorUS6806808Feb 26, 1999Oct 19, 2004Sri InternationalWireless event-recording device with identification codesUS7034432 *Jul 20, 2000Apr 25, 2006Sri InternationalElectroactive polymer generatorsUS7062055Oct 26, 2001Jun 13, 2006Sri InternationalElastomeric dielectric polymer film sonic actuatorUS20020013545Apr 25, 2001Jan 31, 2002David SoltanpourSynthetic muscle based diaphragm pump apparatusesUS20020122561 *Oct 26, 2001Sep 5, 2002Pelrine Ronald E.Elastomeric dielectric polymer film sonic actuatorUS20040232807 *Jun 29, 2004Nov 25, 2004Sri InternationalElectroactive polymer transducers and actuatorsUS20070159031 *Feb 3, 2005Jul 12, 2007Kazuo YokoyamaActuator and method for manufacturing planar electrode support for actuatorUSRE33651Oct 11, 1988Jul 30, 1991At&T Bell LaboratoriesVariable gap device and method of manufactureJP2001286162A Title not availableJPS5181120A Title not availableJPS5445593A Title not availableJPS6199499A Title not availableJPS52120840A Title not availableJPS56101788A Title not availableWO1995008905A1Sep 19, 1994Mar 30, 1995Kuopion Teknologiakeskus TekniMethod for repeating of a soundWO1999037921A1Jan 26, 1999Jul 29, 1999Massachusetts Inst TechnologyContractile actuated bellows pumpWO2001006575A1Jul 20, 2000Jan 25, 2001Stanford Res Inst IntImproved electroactive polymersWO2001006579A2Jul 20, 2000Jan 25, 2001Stanford Res Inst IntPre-strained electroactive polymersWO2001059852A2Feb 9, 2001Aug 16, 2001Joseph Stephen EckerleMonolithic electroactive polymers* Cited by examinerNon-Patent CitationsReference1Chen et al., "Active control of low-frequency sound radiation from vibrating panel using planar sound sources," Journal of Vibration and Acoustics, vol. 124, pp. 2-9, Jan. 2002.2Heydt et al., "Acoustical performance of an electrostrictive polymer film loudspeaker," Journal of the Acoustical Society of America, Vol. 107 (2), Feb. 2000.3International Search Report dated Mar. 11, 2008 in PCT Application No. PCT/US07/04602.4Khuri-Yakub et al., "Silicon micromachined ultrasonic transducers," Japan Journal of Applied Physics, vol. 39 (2000), pp. 2883-2887, Par 1, No. 5B, May 2000.5Kinsler et al., Fundmentals of Acoustics, Third Edition, John Wiley and Sons, 1982.6NXT plc, Huntingdon, UK (www.nxtsound.com), Sep. 17, 2008.7Office Action dated Apr. 1, 2008 in Japanese Application No. 10-534911.8Pelrine et al., "High-speed electrically actuated elastomers with strain greater than 100%," Science, vol. 287, pp. 836-839, Feb. 4, 2000.9Suzuki et al., "Sound radiation from convex and concave domes in infinite baffle," Journal of the Acoustical Society of America, vol. 69 (2), Jan. 1981.10Woodard, Improvements of ModalMax High-Fidelity Piezoelectric Audio Device (LAR-16321-1), NASA Tech Briefs, May 2005, p. 36.11Written Opinion dated Mar. 11, 2008 in PCT Application No. PCT/US07/04602.Referenced byCiting PatentFiling datePublication dateApplicantTitleUS7898159 *Sep 22, 2009Mar 1, 2011Sri InternationalCompliant electroactive polymer transducers for sonic applicationsUS7990022 *Mar 15, 2010Aug 2, 2011Bayer Materialscience AgHigh-performance electroactive polymer transducersUS8237325 *May 11, 2011Aug 7, 2012Pellegrini Gerald NEnergy transducer and methodUS8253300 *Jun 10, 2009Aug 28, 2012Tsinghua UniversityElectrostrictive composite and method for making the sameUS8350447Aug 20, 2009Jan 8, 2013Braun GmbhElectro-polymer motorUS8418934 *Aug 26, 2008Apr 16, 2013General Electric CompanySystem and method for miniaturization of synthetic jetsUS8740825Aug 22, 2013Jun 3, 2014Sympara Medical, Inc.Methods and devices for treating hypertensionUS8747338Aug 22, 2013Jun 10, 2014Sympara Medical, Inc.Methods and devices for treating hypertensionUS20110210648 *May 11, 2011Sep 1, 2011Pellegrini Gerald NEnergy transducer and methodUS20120193568 *Jun 10, 2009Aug 2, 2012Hon Hai Precision Industry Co., Ltd.Electrostrictive composite and method for making the sameWO2014066576A1Oct 24, 2013May 1, 2014Bayer Intellectual Property GmbhPolymer diodeWO2014089388A2Dec 6, 2013Jun 12, 2014Bayer Materialscience AgElectroactive polymer actuated aperture* Cited by examinerClassifications U.S. Classification310/317, 310/328, 310/330, 310/800International ClassificationH01L41/08Cooperative ClassificationY10S310/80, H04R19/02European ClassificationH04R19/02Legal EventsDateCodeEventDescriptionMar 7, 2013FPAYFee paymentYear of fee payment: 4Mar 27, 2009ASAssignmentOwner name: SRI INTERNATIONAL, CALIFORNIAFree format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:HEYDT, RICHARD P.;PELRINE, RONALD E.;KORNBLUH, ROY D.;AND OTHERS;REEL/FRAME:022464/0841;SIGNING DATES FROM 20070402 TO 20070511RotateOriginal ImageGoogle Home - Sitemap - USPTO Bulk Downloads - Privacy Policy - Terms of Service - About Google Patents - Send FeedbackData provided by IFI CLAIMS Patent Services©2012 Google