SOUND AND VIBRATION CONTROL WINDOWS

Abstract: A transparent vibration and sound control mechanism is disclosed. The control mechanism may include a piezoelectric material disposed between patterned electrodes. The control mechanism may be incorporated into a window so that sound waves incident on one side of the window are not reradiated on the opposite side of the window.

Description: SOTTTVn ANT) VTR ATTON CONTROT, WINDOWS BACKOKOTTND Field of the Invention The present invention relates to the control of sound and vibration transmission through the use of active materials. More specifically, this invention relates to the use of a structure incorporating a transparent piezoelectric material and electrodes which may be used in windows to reduce the transmission of sound and vibrations. Background of the Invention It is desirable in many areas to control transmission of sound and vibrations. For instance, the maintenance of: a quiet environment while traveling (e.g. , in an automobile, train, etc.); an environment conducive to learning in schools; and, an environment suitable for relaxing in a home, hotel, or hospital all depend somewhat on the elimination or reduction of unwanted noise and vibration. Past techniques used to control vibrations and sound propagation include passive or active structural vibration damping. Passive vibration damping typically involves the use of a damping material such as a passive viscoelastic layer laminated to the vibrating or sound- radiating structure, typically a panel or laminated series of panels. The amount of damping such a panel will provide typically depends on the viscoelastic material chosen and the thickness and geometry of the panel and any ∞nstraiiiing layer. Active vibration damping typically employs actuators and sensors bonded to a structural panel, beam, or other elastic element(s), and interconnected through an analog and/or digital compensator and signal conditioning electronics to provide enhanced vibration damping or sound radiation control via active feedback or feedforward control. The actuators typically consist of piezoceramic chips, piezopolymer layers, magnetostrictive or electrostrictive layers, shape memory materials, and/or electromagnetically- driven actuators such as shakers or proof mass actuators. The sensors typically comprise microphones, accelerometers, piezoelectric chips or layers, and/or strain gages. A significant drawback with respect to these damping approaches is that the materials and devices used are generally opaque. While an opaque damping panel may be suitable for some applications, a large void is left in environments where it is either necessary or desirable to have a sound and vibration control structure which transmits light (e.g. a sound and vibration control structure suitable for use in windows). SUMMARY OF THE iNVENTTON A need has arisen for a damping approach which will eliminate or reduce structural vibrations and sound radiation and still facilitate the transmission of light. An object of the present invention is to provide a structure which is transparent to visible light and capable of eliminating or reducing vibrations and sound propagation. It is another object of the present invention to provide a vibration and sound control system for incorporation into a laminated glass or plastic structure which is transparent to visible light and is capable of eliminating or reducing vibrations and sound propagation. According to one embodiment of the present invention, a transparent vibration and sound control system is disclosed. The sound and vibration control system comprises at least one transparent active layer disposed between transparent patterned electrodes and at least one transparent passive layer affixed to the at least one active layer to create a laminate structure. The system also comprises a signal conditioning network electrically connected with the electrodes. The thickness and arrangement of the at least one passive layer is such that the mechanical neutral surface of the laminate structure is not coincident with the mid-plane of the at least one active layer. In one embodiment, the active material is a transparent piezoelectric material. According to another embodiment of the present invention a window for controlling the propagation of vibrations and sounds is disclosed. The window comprises a laminated structure to be located within a window opening. The laminated structure comprises at least one layer of transparent active material, patterned electrodes disposed on opposite surfaces of each layer of transparent active material and at least one layer of transparent passive material. The active and passive layers and the patterned electrodes are bonded to each other forming the laminate structure. The window further comprises a signal conditioning network electrically connected to the patterned electrodes. The signal conditioning network may comprise a passive or active electrical network operative to dissipate a voltage differential across the electrodes. According to another embodiment of the present invention, the signal conditioning network is operative to apply an electrical signal to the electrodes. The applied electrical signal is converted into a deformation of the active material thereby causing a sound to be radiated from the laminate structure. Other embodiments will become apparent from the following Detailed Description when taken in conjunction with the drawings. RWTFF l SCKTPTTON OF THF. DRAWlr-JCTS Figure la schematically depicts a laminate structure used to control sound and vibration according to one embodiment of the present invention. Figure lb schematically depicts a sound and vibration control system incorporating the laminate structure of Figure la. Figure 2a and 2b schematically depict exemplary electrode patterns according to one embodiment of the present invention. Figure 3 schematically depicts a sound and vibration control system according to another embodiment of the present invention. Figure 4 schematically depicts a sound and vibration control system according to another embodiment of the present invention. DF Aπ-FD DESCRIPTION OF THE PREFERRED EMBODTTyraNTS According to the embodiments of the present invention, a vibration and sound control system is disclosed. The system comprises a laminate structure comprising layers of transparent active material, transparent patterned electrodes, and transparent passive material, and a signal conditioning network connected to the electrodes of the laminate structure. The system is operative to dissipate the energy present in an incident disturbance (e.g. , an incident sound wave or vibration) or to produce sound through application of a voltage to the patterned electrodes. Incident disturbance in the following description denotes any force causing a deformation of the laminate structure such as a sound wave or vibration. The laminate structure of the system is transparent and is therefore suitable for incorporation into windows and the like, to create, for example, a "quiet window." That is, a window which is controlled to actively damp sound waves and vibrations. One embodiment of a sound and vibration control system will be explained in conjunction with Figures 1 and 2. Figure la shows a laminate structure 10 which includes a layer of active material 1 disposed between electrodes 2 and a passive layer 3. Active layer 1 , is transparent to visible light and comprises a single sheet or multiple sheets of an active material. The term active material, as used in this application, is any material which responds electrically (e.g. , produces a charge) to a mechanical stimulus (e.g. , a mechanical strain), or conversely which responds mechamcally (e.g. , produces a mechanical strain) to an electrical stimulus (e.g. voltage, current or electric field). Active materials are also referred to as induced strain actuators and may be, for example, a piezoelectric material, an electrostrictive material, a shape memory material or a magnetostrictive material. In one embodiment, active layer 1 comprises a single sheet of the piezoelectric material polyvinylidene fluoride (PVDF). In another embodiment, active layer 1 comprises a single sheet of the piezoelectric material zinc oxide (ZnO). Electrodes 2 are preferably patterned on to opposite surfaces of active layer 1 , and are operative to collect charge on the suiface of, or apply a voltage to, active layer 1. Electrodes 2 are composed of any suitable transparent conductive material. In one embodiment, electrodes 2 comprise Indium Tin Oxide (ITO). Suitable techniques for applying the patterned electrodes include inter alia adhering, sputtering and spraying. Although electrodes 2 are shown in Figure 1 as sheets for ease of drawing, they are preferably applied in specific patterns. Passive layer 3 may comprise any transparent or translucent material such as glass, plastic, stained glass etc. Passive layer 3 helps enable the system to respond properly to an incident disturbance and provides protection to the underlying electrode structure. Passive layer 3 is configured so that the neutral surface C of the laminate structure (i.e. , the surface upon which the stress due to an incident disturbance will have zero magnitude), is offset from the mid¬ plane M of the active layer 1 (i.e. , the plane equidistant from opposite faces of the active layer). In this way laminate structure 10 of system 20 is given a nonzero moment arm between neutral surface C and mid-plane M of the active layer 1. Therefore an incident disturbance will give rise to a non-zero strain in active layer 1, thereby allowing active layer 1 to sense and respond to incident disturbances. The layers 1-3 form laminate structure 10 in which the individual layers are bonded together so that the structural response of passive layer 3 is coupled to the structural response of active layer 1. That is, any disturbance incident upon passive layer 3 should be commumcated to active layer 1. The bonding is accomplished using any suitable method which will provide the proper coupling of the layers. By way of example, cyanoacrylates or epoxies can be used to bond layers 1-3 together. Laminate structure 10 will generally be incorporated into a structure of a particular size and shape and having particular boundary conditions, for instance, a window or vehicle windshield. The size, shape and boundary conditions of a structure, among other variables, determine how the structure will respond to an incident disturbance. To better understand the patterning of the electrodes and the response of laminate structure 10 to an incident disturbance, a brief explanation of a structure's spatial response to a disturbance is now provided. An elastic structure's spatial response to a disturbance (for instance, an incident sound wave) is defined in terms of mode shapes. Mode shapes are the characteristic spatial deformations of a structure. The weighted collection of all mode shapes at which a particular structure will respond constitute the structure' s dynamic spatial response. Every structure (due to its size and boundary conditions) has certain mode shapes at which it is likely to respond to a disturbance. Further, certain of these mode shapes are better than others at producing or transmitting sound waves. For a structure of a known size and boundary conditions, it is possible to determine the mode shapes at which it is likely to respond and which of these mode shapes are likely to produce sound. According to one embodiment of the present invention, electrodes 2 are patterned to couple active layer 1 to those portions of the dynamic response of laminate structure 10 which conduct sound. More specifically, electrodes 2 are patterned on active layer 1 in the areas in which the mode shapes of laminate structure 10 which are conducive to the production or transmission of sound, are likely to produce significant strain. Thus, if laminate structure 10 is subjected to an incident sound wave, laminate structure 10 will likely respond by deforming in one or more of its mode shapes likely to produce sound. This deformation causes a strain in active layer 1 thereby causing a charge distribution to accumulate on the faces of active layer 1. Because electrodes 2 have been patterned in the areas where the charge distribution is likely to be greatest (that is, areas corresponding to the mode curvatures of laminate structure 10) (the second derivative of a structure's mode shapes are its mode curvatures), active layer 1 is coupled into those modes most likely to contribute to noise transmission or radiation, and the accumulated charge distribution is efficiently converted to a voltage differential across the patterned electrodes. One method of designing the patterning of electrodes 2 is to first define a set of target modal coupling coefficients, and then choose an electrode distribution that best approximates those coefficients. In particular, one can define a positive semi-definite objective function of the form: K J = ∑ [ c k (τ) - c k ^ gn (z)Y, (1) k=l where C kj ή g - are the target modal coupling coefficients, and c k are the computed modal coefficients for a particular electrode pattem with spatial parameters (e.g., locations) contained in the vector z. The electrode pattem that best approximates the target modal coupling coefficients minimizes J. A nonlinear, unconstrained optimization algorithm may be employed here, for example, the MATLAB ® function "ftnins" may be used to determine a distribution of electrodes resulting in c k which minimizes J. Other physically-motivated constraints may be imposed during the optimization process. For instance, the electrodes can not "spill over" the edges of the window, a rnini um spacing between segments may be imposed, and a minimum segment width may be defined. Figures 2a and 2b show exemplary pattems for electrode layers 2 designed using the above algorithm. Figure 2a shows an electrode pattem designed to control the (l-l)-(3-l) modes contributing to radiation and transmission of sound and vibrations in a rectangular plate with simply supported edges (an SSSS plate). Figure 2b shows an electrode pattem designed to control a broad contiguous range of modes contributing to radiation and transmission of sound and vibrations in an SSSS plate. Laminate structure 10 shown in Figure la may also be used to produce sound. One property of an active material is that it may act as an actuator as well as a sensor. Therefore, if a voltage is applied to patterned electrodes 2, that voltage will drive active layer 1 causing a deformation of the underlying structure. Further, because electrodes 2 have been patterned on areas of active layer 1 which correspond to its mode shapes likely to produce or transmit sound, the resulting deformation will correspond to one or more of those mode shapes of laminate structure 10 which produce sound. The deformation will thus produce a sound wave. The laminate structure of Figure la is used to dissipate the energy out of an incident disturbance or to transmit or retransmit the incident disturbance by connecting the structure into a system such as is shown in Figure lb. In Figure lb, like elements have the same reference numerals as in Figure la. Figure lb shows laminate stmcture 10 of Figure la incorporated into a sound and vibration control system 20. System 20 includes laminate stmcture 10 and a signal conditioning network 5 electrically connected to electrodes 2. Signal conditioning network 5 is operative to dissipate a voltage appearing across electrodes 2 in response to an incident disturbance and can be any suitable network operative to do so. Signal conditioning network 5 can operate either passively or actively. In one preferred embodiment, network 5 is a passive network comprising standard electrical elements such as resistors, inductors, capacitors and operational amplifiers. Active layer 1 (which essentially acts as a capacitor, producing a charge) is electrically connected with network 5. In one embodiment, the various circuit elements comprising network 5 convert the charge produced by active layer 1 into heat, thereby dissipating the energy out of an incident disturbance. In another embodiment, network 5 is an active feedback network. Feedback network 5 operates to dissipate the energy in an incident disturbance by applying a second voltage across electrodes 2 in response to sensing a voltage caused by the incident disturbance. The second voltage is essentially superimposed with the first voltage thereby causing a new deformation in active layer 1 , which in rum gives rise to a third voltage across electrodes 2. The difference between the applied second voltage and the third voltage is then fed back through the network to arrive at a new voltage to apply to electrodes 2. This process is repeated until the response voltage is zero which indicates the applied voltage has caused a deformation of active layer 1 wliich cancels out the deformation due to the incident disturbance. In another embodiment, network 5 is used to passively or actively detune laminate stmcture 10 so that it does not respond to incident disturbances and thus does not radiate or transmit sound. For instance, network 5 may be a passive network which sets up an impedance discontinuity in laminate stmcture 10 thus preventing the passage of energy through laminate stmcture 10. Altematively, network 5 may be an active network which employs active feedback to detune laminate stmcture 10. In another embodiment, network 5 is an active feedforward network. The feedforward network employs an extemal disturbance sensor to sense an incident disturbance. In response to an incident disturbance, the sensor generates a disturbance signal which is fed forward to signal conditioning network 5. Network 5 then produces a signal for application to electrodes 2 to cause a deformation of active layer 1 to cancel out the deformation caused by the incident disturbance. In still another embodiment, system 10 may include output device 6. Output device 6 is any device capable of further conveying the incident disturbance. In this embodiment, rather than dissipating the voltage across electrodes 2, the voltage is processed for output by signal conditioning network 5. The mode shapes causing the charge in active layer 1 , and thus the voltage across electrodes 2, are known because of the way electrodes 2 are patterned. Therefore, the network 5 can be tailored to enhance the disturbance signal (i.e., eliminate noise, boost signal, etc.). In this way, system 10 acts essentially as a microphone. Sounds are sensed by laminate stmcture 10 giving rise to a voltage across electrodes 2 and producing a disturbance signal. The resulting signal is processed by network 5 and output via output device 6. In one embodiment output device 6 is a speaker. In another embodiment, output device 6 is a txansmission circuit. In still another embodiment, output device 6 is a recording device. In still another embodiment, system 20 is used to produce sound. As explained with respect to Figure la, active layer 1 and the patterned electrodes can be used to produce sound. To produce sound, signal conditioning network 5 operates to apply an electrical signal (e.g. , voltage, current, etc.) to electrodes 2. The applied electrical signal will drive active layer 1 and cause it to deform in one of its mode shapes which produce sound. In this embodiment, system 10 is essentially being used as a speaker. Figure 3 depicts another embodiment of vibration and sound control system 30. System 30 includes active layer 1 and electrodes 2 disposed between passive layers 3 and 4. As in the embodiment of Figure 1, layers 1-4 form a laminate stmcture 10 in which the individual layers are bonded together so that the stmctural response of passive layers 3 and 4 is coupled to the stmctural response of active layer 1. That is, any disturbance to passive layers 3 and 4 is communicated to active layer 1. The configuration of the layers in Figure 3 provides proper response of laminate structure 10 to an incident vibration. Layers 1-4 are configured so that the neutral surface, C, of the laminate stmcture is offset from the mid-plane, M, of active layer 1. That is, one of layers 3 and 4 is thicker than the other. Thus, system 30 is given a nonzero moment arm between the neutral surface, C, and mid-plane, M, thereby allowing active layer 1 to be coupled into incident disturbances. Figure 4 shows an altemative embodiment of sound and vibration control system 40. In Figure 4 like elements have the same reference numerals as in Figures 1 and 3. System 40 differs from systems 20 and 30 in that laminate stmcture 10 uses two active layers 1 which are separated from each other by passive layer 3. In this way neutral surface C lies within the center of passive layer 3 and thus provides the offset to create a nonzero moment arm for laminate stmcture 10. Operation of system 40 is analogous to that of systems 20 and 30 shown in Figures 1 and 3. However, in system 40, the operation of signal conditioning network 5 is slightly modified as compared to the operation with respect to systems 20 and 30 using a single active layer. For instance, if network 5 is operating passively to dissipate energy in an incident disturbance, active layers 1 are electrically connected to each other (in series or parallel), and the electrically connected active layers are connected to dissipative network 5. Network 5 then operates to dissipate the charge produced by the electrically connected active layers as explained with respect to network 5 in Figure lb. If signal conditioning network 5 is operating as an active network to dissipate energy in an incident wave, then, typically, one of active layers 1 acts as a sensor for the incident disturbance and the other acts as an actuator. The sensing active layer feeds its signal to network 5. Network 5 receives the sensed signal and processes it to produce a cancelling signal. The cancelling signal is applied to the actuator active layer producing a deformation which will cancel the deformation caused by the incident disturbance. Modified system 40 may also be used in conjunction with an output device to retransmit the incident disturbance and as a sound source by modifying the network 5 as explained above. Although a detailed description of the present invention has been provided, it should be understood that the scope of the invention is not to be limited thereby, but is to be determined by the claims which follow. Various modifications and alternatives will be readily apparent to one of ordinary skill in the art.

Claims: ΓT ATMS I Claim: 1. A transparent vibration and sound control system comprising: at least one pair of transparent pattemed electrodes: at least one transparent active layer disposed between the transparent pattemed electrodes; at least one transparent passive layer bonded to the at least one active layer to create a laminate stmcture; and, a signal conditioning network electrically connected with the transparent pattemed electrodes; wherein the thickness and arrangement of the at least one passive layer is such that the mechanical neutral surface of the laminate stmcture is not coincident with the mid-plane of the at least one active layer. 2. The transparent vibration and sound control system of claim 1 wherein each pair of transparent pattemed electrodes are pattemed on opposite surfaces of one of the at least one transparent active layer, thereby coupling each transparent active layer into portions of the dynamic response of the laminate stmcture which transmit or radiate sound. 3. The transparent vibration and sound control system of claim 1 wherein the at least one transparent active layer comprises a layer of piezoelectric material. 4. The transparent vibration and sound control system of claim 1 wherein the at least one transparent active layer comprises a layer of zinc oxide. 5. The transparent vibration and sound control system of claim 1 wherein the at least one transparent active layer comprises a layer of polyvinylidene fluoride (PVDF). 6. The transparent vibration and sound control system of claim 1 wherein the at least one pair of transparent pattemed electrodes comprise an electrically conductive transparent material. 7. The transparent vibration and sound control system of claim 1 wherein the at least one pair of transparent pattemed electrodes comprise Indium Tin Oxide. 8. The transparent vibration and sound control system of claim 1 wherein at least one transparent active layer is operative to convert an incident sound wave into a voltage differential across a pair of transparent pattemed electrodes which it is disposed between; and, wherein the signal conditioning network is operative to sense and process the voltage differential. 9. The transparent vibration and sound control system of claim 1 wherein the signal conditioning network is operative to apply an electrical signal to the at least one pair of transparent pattemed electrodes; and, wherein the at least one active layer is operative to convert the applied electric signal into a deformation of the laminate stmcture. 10. A vibration and sound control window comprising: a laminate stmcture located within a window opening, the laminate stmcture comprising: at least one layer of transparent active material; pattemed electrodes disposed on opposite surfaces of each layer of transparent active material; at least one layer of transparent passive material, wherein the active and passive layers and the pattemed electrodes are bonded to each other forming the laminate structure; and, a signal conditioning network electrically connected to the pattemed electrodes. 11. The window of claim 10, the at least one layer of transparent passive material arranged so that the mechanical neutral suiface of the laminate stmcture is offset from the midplane of the at least one active layer. 12. The window of claim 10 wherein the pattemed electrodes are pattemed to couple each of the one or more active layers into portions of the laminate stmcture' s dynamic response which conduct sound. 13. The window of claim 10 wherein the transparent active material comprises a piezoelectric material. 14. The window of claim 10 wherein the transparent active material comprises zinc oxide. 15. The window of claim 10 wherein the transparent active material comprises polyvinylidene fluoride (PVDF). 16. The window of claim 10 wherein the electrodes comprise Indium Tin Oxide. 17. The window of claim 10 wherein the signal conditioning network comprises a passive electrical network operative to dissipate a voltage differential across the pattemed electrodes. 18. The window of claim 10 wherein the signal conditioning network comprises an active electrical network operative to drive a voltage differential across the electrodes to zero. 19. The window of claim 18 further comprising an extemal sensor which produces a disturbance signal in response to a sound wave, the disturbance signal being fed forward to the active electrical network. 20. The window of claim 10 further comprising an output device electrically connected with the signal conditioning network. 21. The window of claim 20 wherein the output device comprises a sound reproduction means. 22. The window of claim 20 wherein the output device comprises transmission means. 23. The window of claim 10 wherein the signal conditioning network is operative to apply an electrical signal to the electrodes, wherein the electrical signal is converted into a deformation of the active material thereby causing a sound to be radiated from the laminate stmcture. 24. A system for controlling vibrations and sound propagation comprising; a transparent laminate stmcture comprising one or more layers of an active material, each layer of active material disposed between electrodes, said vibration control mechanism operative to convert a force incident upon the mechanism into a first voltage differential across the electrodes; and, a signal conditioning network electrically connected with the electrodes, said signal conditioning network sensing and processing the first voltage differential between the electrodes.

Inventors: BURKE SHAWN E, BURKE, SHAWN, E.
Applicants: UNIV BOSTON, TRUSTEES OF BOSTON UNIVERSITY
Application year: 1996
Main classification: G10K11
IPC codes: G10K11, H04R17