Abstract:
A transducer assembly includes a transducer and a coupler with rheological material. A loudspeaker further includes an acoustic radiator. The coupler is mounted to the transducer and is operatively connected to the acoustic radiator. The transducer excites bending waves in the acoustic radiator to produce an acoustic output. By control of the rheological material, which may include mageto-rheological liquid or electro-rheological liquid, the transducer in various embodiments may selectively be substantially rigidly or substantially flexibly coupled to the acoustic radiator. If flexibly coupled the force experienced by the transducer when the host device is dropped, jarred, or pressured may be reduced from that experienced with a rigid connection. The acoustic radiator may be, for example, a display such as an LCD or a window mounted over a display. A mobile terminal may include such a loudspeaker in accordance with one embodiment.

Description:
BACKGROUND OF INVENTION 
     This invention relates to the field of acoustic devices, and more particularly to bending wave loudspeakers, also known as distributed mode loudspeakers (DMLs), including acoustic radiators and transducers. 
     Cellular phones, televisions, and like products often include loudspeakers having a diaphragm excited by an axially driven transducer. Such speakers are relatively large for products where space is at a premium and where there is a continual drive to reduce the size of the products. In a recently developed alternative to conventional piston-driven loudspeakers, sound may be produced by bending wave loudspeakers. Bending wave loudspeakers may use the device&#39;s display as an acoustic radiator, recognizing space savings by eliminating a relatively large conventional speaker. Further, in some cases the listening experience produced by a bending wave loudspeaker is superior to that of a conventional speaker in that the sound coming from a DML is not as localized as that produced by traditional receivers. 
     Bending wave loudspeakers include an acoustic radiator that is capable of supporting bending wave vibration and an electromechanical transducer mounted to the acoustic radiator. Bending wave energy may be transmitted to the acoustic radiator by a transducer, or exciter, to generate bending waves in the radiator, which may be a panel, and produce an acoustic output. The exciter is mounted to the panel, and may be a dynamic exciter such as an electromechanical moving coil or other inertial exciter, a piezoelectric exciter, or the like. A piezoelectric exciter is often preferable as compared to other types of exciters because it is generally smaller (and in particular thinner) and lighter. Piezoelectric materials, however, are also relatively brittle and fragile. Electronic acoustic devices, and particularly handheld ones, are susceptible to being dropped or otherwise jarred, and the piezoelectric material, rigidly mounted to the acoustic radiator, is subjected to impact force and possible breakage. 
     SUMMARY OF INVENTION 
     In accordance with an embodiment of the present invention, a transducer assembly includes a transducer and a coupler. The transducer is for exciting bending waves in an acoustic radiator to produce an acoustic output. The coupler includes rheological material and is mounted to the transducer. The coupler is further adapted to be operatively connected to the acoustic radiator to transmit bending wave energy from the transducer to the acoustic radiator. Accordingly, by control of the rheological material, when installed in a device the transducer may selectively be substantially rigidly or substantially flexibly coupled to the acoustic radiator, and if substantially flexibly coupled the force experienced by the transducer when the device is dropped, jarred, or pressured may be reduced from that experienced with a substantially rigid connection. 
     In accordance with another embodiment of the present invention, a transducer assembly includes a piezoelectric transducer to excite bending waves in an acoustic radiator to produce an acoustic output. The magneto-rheological fluid has a controllable viscosity that increases in response to the magnetic field, such that the coupler is substantially flexible in the absence of the magnetic field and is substantially rigid in the presence of the magnetic field. A coupler including foam impregnated with a magneto-rheological fluid is mounted to the transducer. The coupler is also adapted to be operatively connected to the acoustic radiator to transmit bending wave energy from the transducer to the acoustic radiator. The transducer assembly also includes a magnet for generating a magnetic field through the coupler. 
     In accordance with another embodiment of the present invention, a loudspeaker includes an acoustic radiator adapted to support bending wave vibration. A transducer is provided to excite bending waves in the acoustic radiator to produce an acoustic output. A coupler including rheological material is operatively connected to the acoustic radiator and the transducer to transmit bending wave energy from the transducer to the acoustic radiator. 
     In accordance with another embodiment of the present invention, a loudspeaker includes an acoustic radiator adapted to support bending wave vibration, and may be a display or a window mounted over a display. A piezoelectric transducer is provided to excite bending waves in the acoustic radiator to produce an acoustic output. A coupler including foam impregnated with rheological material is operatively connected to the acoustic radiator and the transducer to transmit bending wave energy from the transducer to the acoustic radiator. The loudspeaker also includes means for generating an energy field through the coupler. The rheological material has a controllable viscosity that increases in response to the energy field, such that the coupler is substantially flexible in the absence of the energy field and is substantially rigid in the presence of the energy field. 
     In accordance with another embodiment of the present invention, a mobile terminal comprises a housing and a loudspeaker mounted to the housing. The loudspeaker includes an acoustic radiator adapted to support bending wave vibration, and may be a display or a window mounted over a display. A transducer is provided to excite bending waves in the acoustic radiator to produce an acoustic output. A coupler including rheological material is operatively connected to the acoustic radiator and the transducer to transmit bending wave energy from the transducer to the acoustic radiator. 
     In accordance with another embodiment of the present invention, a mobile terminal comprises a housing and a loudspeaker mounted to the housing. The loudspeaker includes an acoustic radiator adapted to support bending wave vibration, and may be a display or a window mounted over a display. A piezoelectric transducer is provided to excite bending waves in the acoustic radiator to produce an acoustic output. A coupler including foam impregnated with rheological material is operatively connected to the acoustic radiator and the transducer to transmit bending wave energy from the transducer to the acoustic radiator. The loudspeaker also includes means for generating an energy field through the coupler. The rheological material has a controllable viscosity that increases in response to the energy field, such that the coupler is substantially flexible in the absence of the energy field and is substantially rigid in the presence of the energy field. 
     In accordance with another embodiment of the present invention, a method of making a loudspeaker includes providing an acoustic radiator adapted to support bending wave vibration. A transducer is provided to excite bending waves in the acoustic radiator to produce an acoustic output. A coupler including rheological material is operatively connected to the acoustic radiator and to the transducer to transmit bending wave energy from the transducer to the acoustic radiator. Means are provided for generating an energy field through the coupler, and wherein the rheological material has a controllable viscosity that increases in response to the energy field, such that the coupler is substantially flexible in the absence of the energy field and is substantially rigid in the presence of the energy field. 
     In accordance with another embodiment of the present invention, a method of producing sound with a device includes sending an electrical audio signal to a transducer to create bending wave energy. An energy field is generated to cause a coupler including rheological material to become substantially rigid. Bending wave energy is transmitted from the transducer through the coupler to an acoustic radiator to excite bending waves to produce an acoustic output. The method may further include reducing the strength of the energy field to cause the coupler to become substantially flexible. 
     Features and advantages of the present invention will become more apparent in light of the following detailed description of some embodiments thereof, as illustrated in the accompanying figures. As will be realized, the invention is capable of modifications in various respects, all without departing from the invention. Accordingly, the drawings and the description are to be regarded as illustrative in nature, and not as restrictive. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIGS. 1-2  are side views of loudspeakers including magneto-rheological material in accordance with embodiments of the present invention. 
         FIG. 3  is a side view of a loudspeaker including electro-rheological material in accordance with embodiments of the present invention. 
         FIGS. 4-10  are side views of loudspeakers including rheological material in accordance with additional embodiments of the present invention. 
         FIG. 11  is a perspective view of a mobile terminal in accordance with another embodiment of the present invention. 
         FIG. 12  is a section view of the mobile terminal of  FIG. 11  taken along line  12 - 12  of  FIG. 11 . 
     
    
    
     DETAILED DESCRIPTION 
       FIGS. 1-3  each illustrate a transducer assembly  20 ,  22 ,  24  and loudspeaker  26 ,  28 ,  30  in accordance with embodiments of the present invention. Specifically, these figures show loudspeakers  26 ,  28 ,  30  each including a transducer  32 ,  34 ,  36  mounted to an acoustic radiator  38 ,  40 ,  42  via a coupler  44 ,  46 ,  48 . The transducer assemblies  20 ,  22 ,  24  each include the transducer  32 ,  34 ,  36  and the coupler  44 ,  46 ,  48 . The transducers  32 ,  34 ,  36  have an intended operative frequency range and include a resonant element having a distribution of modes in the operative frequency range. The resonant element may be active, such as a piezoelectric transducer. Alternatively, the transducer  32 ,  34 ,  36  may be passive, with the transducer  32 ,  34 ,  36  further including an active transducer such as an inertial or grounded vibration transducer, for example, a moving coil transducer. 
     For the purposes of illustration herein the resonant elements are shown as piezoelectric transducers  32 ,  34 ,  36 . The piezoelectric transducers  32 ,  34 ,  36  may be various shapes, including but not limited to beams, plates, and disks. The piezoelectric transducers  32 ,  34 ,  36  may be opaque or, for example, transparent material such as PZLT used with thin film electrodes. As known in the art, voltage across the piezoelectric transducers  32 ,  34 ,  36  applied through electric leads  50  attached to the electrodes on each side of the transducers  32 ,  34 ,  36  control the direction and magnitude of bending. Alternating the positive and ground terminals causes bending in alternate directions, and may be selected as desired for a particular application. 
     The acoustic radiator  38 ,  40 ,  42  may be a panel that is capable of supporting bending wave energy from the transducer  32 ,  34 ,  36  that is transmitted through the coupler  44 ,  46 ,  48 . The panel may be a distributed mode panel, may be at least in part transparent, and may be a display. Plates made of glass, polycarbonate, acrylic, and plastic, as well as liquid crystal displays (LCDs), and LCDs incorporating thin film transistors are examples of materials that may serve as acoustic radiators  38 ,  40 ,  42 . The acoustic radiator  38 ,  40 ,  42  may be a window mounted over a display. The scope of the invention is not intended to be limited by materials listed herein, but may be carried out using any materials that allow the construction and operation of the present invention. Materials and dimensions depend on the particular application. 
     The coupler  44 ,  46 ,  48  is shown in the form of a stub and may be mounted to the transducer  32 ,  34 ,  36  and acoustic radiator  38 ,  40 ,  42  with an adhesive such as an epoxy or similar material. Examples of materials used for conventional stubs as known in the art include rigid foam plastics or other hard plastics, or metal having suitable insulating layers to prevent electrical short circuits. Known stubs generally remain stiff at all times. The coupler  44 ,  46 ,  48  of the present invention includes rheological material. The term “rheological material” as used herein refers to both magneto-rheological materials and electro-rheological materials. As known to one of skill in the art, a rheological material exhibits a significant change in its ability to flow or shear upon the application of an appropriate energy field. A rheological material having a controllable viscosity may be disposed within the coupler  44 ,  46 ,  48 . The viscosity of the rheological material increases in response to an energy field. Accordingly, the coupler  44 ,  46 ,  48  is substantially flexible in the absence of the energy field or if the energy field is too weak to make the coupler  44 ,  46 ,  48  rigid, and is substantially rigid in the presence of an energy field of sufficient strength to cause such a result. The coupler  44 ,  46 ,  48  is substantially flexible when lacking sufficient rigidity to transfer bending wave energy to an acoustic radiator to produce audible sound. Conversely, the coupler  44 ,  46 ,  48  is substantially rigid when having sufficient rigidity to transfer bending wave energy to an acoustic radiator to produce audible sound. The coupler  44 ,  46 ,  48  may be, for example, closed-cell foam impregnated with rheological material, a compliant vessel made of material such as rubber and containing rheological material, or the like. 
       FIGS. 1-3  also illustrate example energy field sources. In  FIG. 1  the rheological material is magneto-rheological fluid, and the energy field is a magnetic field  52  produced by an electromagnet  54 . Similarly, in  FIG. 2  the rheological material is magneto-rheological fluid, but with the magnetic field  56  produced by a permanent magnet  58 . The permanent magnet  58  may move between at least two positions: one in proximity to the coupler  46  that subjects the coupler  46  to the magnetic field  56 , and another farther away from the coupler  46  where the coupler  46  is substantially out of range of the magnetic field  56 . A solenoid  60  or the like may control the position of the magnet  58  as shown by the arrow  62 . Magneto-rheological fluids are responsive to the presence of a magnetic field  52 ,  56  for changing their ability to flow or shear. Magneto-rheological fluids are typically suspensions of micron sized magnetizable particles in a liquid such as oil. In the absence of a magnetic field, a magneto-rheological fluid is a free-flowing liquid that may have a consistency similar to motor oil. When exposed to a magnetic field of sufficient strength, the magnetizable particles align and reduce the ability of the magneto-rheological fluid to flow. The shear resistance of the magneto-rheological fluid is a function of the magnitude of the applied magnetic field. One example of a magneto-rheological material may be available from Lord Corporation in Cary, N.C. under the name of RHEONETIC™ magnetic fluids. 
     In  FIG. 3  the rheological material is electro-rheological fluid, and the energy field is an electric field  64  produced by applying a voltage across the coupler  48 . The electric field  64  may be generated by either directly connecting electric leads  65  to the coupler  48  or by placing an electrode and ground proximate to the coupler  48 . Electro-rheological fluids are responsive to the presence of an electric field for changing their ability to flow or shear. In the absence of an electric field, an electro-rheological fluid is a free-flowing liquid. When exposed to an electric field of sufficient strength, fibrous structures form and align, reducing the ability of the electro-rheological fluid to flow. The shear resistance of the electro-rheological fluid is a function of the magnitude of the applied electric field. Lithium polymethacrylate is one example of an electro-rheological fluid. 
     As is apparent from the above description, when an energy field is generated through a coupler, the coupler is substantially rigid and bending wave energy may be transmitted to the acoustic radiator. When the energy field is not present or is not of sufficient strength to make the coupler substantially rigid, the coupler is substantially flexible. This flexibility may be able to be enhanced by impregnating fluid in closed-cell foam gaskets and the like. This type of implementation may be preferable in high-speed impact situations, as the time of reaction in the impact case may not be fast enough with free-flowing fluid. In cases where the loading force is slower, such as a massive object being placed on the acoustic radiator (causing large deflections) a flowing fluid may be more likely to function as desired. Flexibility in the coupler may be advantageous in situations where the device in which the loudspeaker resides is not in use. For example, when a mobile terminal such as a cellular phone is not in on a call (i.e. receiving or transmitting radio signals), it may be particularly subject to being dropped, jarred, or pressured. The phone may be configured to not generate an energy field at those times, and the flexibility in the coupler may help to avoid breakage of the transducer that may result from impact force transmitted through the acoustic radiator. 
     Although the embodiments of  FIGS. 1-3  show a single coupler  44 ,  46 ,  48  being mounted to the proximate surface of the acoustic radiator  38 ,  40 ,  42 , other mounting configurations are possible. Examples of other embodiments are shown in  FIGS. 4-10 . In the embodiments of  FIGS. 1-10 , for example, it should be understood that as known by one of skill in the art that mass, such as plastic material or the like, may be added to the embodiments described herein at selected locations on the piezoelectric transducers in order to increase the magnitude of or control the vibration imparted to the respective acoustic radiators. Locations for such mass, for example, may be on the edges or periphery of centrally mounted transducers as discussed below for  FIG. 4 , or at a central point on transducers that are edge mounted as discussed below for  FIGS. 6 and 7 . In the embodiments of  FIGS. 4-10  one or more couplers including rheological material in the form of stubs are used. A magnetic field  66  is shown as the energy field on each figure; it should be understood that the field could instead be an electric field through the coupler, and that the magnetic field source, also not shown, may include an electromagnet, permanent magnet, or the like. 
       FIG. 4  shows a piezoelectric transducer  68  mounted at its center to a coupler  70  including rheological material in accordance with an embodiment of a loudspeaker  72  according to the present invention. The coupler  70  extends into an aperture  74  in an acoustic radiator  76  and is mounted to the inside surface  78  of the side of the radiator  76  distal from the transducer  68 . A mass  80  may be mounted to the ends of the transducer  68  if the transducer  68  is a beam, or to the periphery as an annular ring if the transducer  68  is a disk as shown. 
       FIG. 5  shows a beam-type transducer  82  mounted an acoustic radiator  84  in accordance with an embodiment of a loudspeaker  86  according to the present invention. Two couplers  88 ,  90  including rheological material are used to couple the transducer  82  to the acoustic radiator  84 . One coupler  90  is located towards one end of the transducer  82  and the other  88  is located towards the center of the transducer  82 . 
       FIG. 6  shows a disk-type transducer  94  coupled along its periphery to the surface of an acoustic radiator  96  by an annular-shaped coupler  98  in accordance with an embodiment of a loudspeaker  100  according to the present invention. Again, the coupler  98  includes rheological material. The central portion of the transducer  94  is suspended over a cavity  102  in the radiator  96 . A mass  104  may be provided with a damping pad  106  of resilient material such as an elastic polymer interposed between the mass  104  and the transducer  94 .  FIG. 7  is an embodiment of a loudspeaker  108  similar to that of  FIG. 6 , with a mirror-image transducer  110  added to the single transducer  112 , mounted to the opposite sides of a cavity  114  in the radiator  96 , and may operate in push/pull mode. Annular shaped couplers  115 ,  117  are interposed between the transducers  110 ,  112  and the radiator  96 . The transducers  110 ,  112  are coupled to a common mass  116 , with a damping pad  118 ,  120  between each transducer  110 ,  112  and the mass  116 . 
       FIG. 8  shows a piezoelectric transducer  122  within an acoustic radiator  124  in accordance with an embodiment of a loudspeaker  126  according to the present invention. Couplers  128 ,  130  including rheological material are disposed on each side of the transducer  122  to transmit vibration to each of the skins  132 ,  134  of the radiator  124 . 
       FIG. 9  shows stacked elements  136 ,  138  in accordance with an embodiment of a loudspeaker  140  according to the present invention. The elements  136 ,  138  may both be active, such as piezoelectric transducers, or one may be active and the other passive. Couplers  142 ,  144  may both include rheological material, but only one coupler  142 ,  144  in between an acoustic radiator  146  and the piezoelectric transducer need include rheological material. An energy field (not shown) may be applied to any coupler  142 ,  144  that includes rheological material. The couplers  142 ,  144  may be located off-center as shown. 
       FIG. 10  shows a grounded transducer  148  in accordance with an embodiment of a loudspeaker  150  according to the present invention. A transducer is grounded when it is coupled to a supporting structure of the assembly. A supporting structure  152  provides a reaction force against the edges of the transducer  148 , making the displacement of the transducer  148  be fully applied to an acoustic radiator  154 . A coupler  155  is disposed between the transducer  148  and the acoustic radiator  154 . If the transducer  148  is a beam, two couplers  156 ,  158  including rheological material may be used as shown, with one at each end of the beam. If the transducer  148  is disk-shaped a coupler including rheological material may be annular for mounting the periphery of the disk to the supporting structure  152 . 
       FIGS. 11 and 12  show a mobile terminal  160  in accordance with an embodiment according to the present invention. As used herein, the term “mobile terminal” may include, among other things, a cellular radiotelephone with or without a multi-line display, a Personal Communications System (PCS) terminal that may combine a cellular radiotelephone with data processing, facsimile and data communications capabilities; a PDA that can include a radiotelephone, pager, Internet/intranet access, Web browser, organizer, calendar and/or a global positioning system (GPS) receiver; a conventional laptop and/or palmtop receiver or other appliance that includes a radiotelephone transceiver; and a personal music playback system such as for CDs, minidisks, MP-3 files, memory sticks, or the like. The mobile terminal  160  includes a back part  162  and a front part  164  that supports a microphone  166 , keypad  168 , and a display window  170 . The display window  170  has an opaque surrounding portion  172 . A display  174  ( FIG. 12 ) is supported on the front part  164  by a suspension  176  that is fitted around the periphery of the display  174 , which may be, for example, an LCD display. The display window  170  is similarly mounted to the front part  164  with a suspension  178 . In the section view of  FIG. 12  a transducer  180  is shown mounted to the display window  170  that is mounted over the display  174 . The transducer  180  is mounted with a coupler  182  including rheological material to the opaque area  172  of the display window  170  to shield the transducer  180  from view. 
     One of ordinary skill in the acoustic arts will quickly recognize that the invention has other applications in other environments. It will also be understood by someone of ordinary skill in the art that the mounting geometries of the transducers to acoustic radiators discussed and illustrated herein are not necessarily the most efficient or desirable to create a desired acoustic output. In fact, many embodiments and implementations are possible. For example, the mounting location of a transducer and coupler on an acoustic radiator and the mounting location of a coupler on a transducer may be varied from those discussed without departing from the scope of the present invention. Various types of transducers, couplers, and acoustic radiators may be used. The following claims are in no way intended to limit the scope of the invention to the specific embodiments described. It should be understood by those skilled in the art that the foregoing modifications as well as various other changes, omissions and additions may be made without parting from the spirit and scope of the present invention.