Abstract:
A damper includes at least one matrix and at least one carbon nanotube structure disposed on at least one surface of the at least one matrix. A loudspeaker using the damper is also disclosed. The loudspeaker includes a frame, a diaphragm secured on the frame, a bobbin having a voice coil, and a damper. The bobbin is secured to the diaphragm. The damper has a first engaging surface engaged with the frame and a second engaging surface engaged with the bobbin.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims all benefits accruing under 35 U.S.C. §119 from China Patent Application No. 200910190211.5, filed on Sep.15, 2009, in the China Intellectual Property Office, the disclosure of which is incorporated herein by reference. 
       BACKGROUND 
       [0002]    1. Technical Field 
         [0003]    The present disclosure relates to a damper based on carbon nanotubes, and a loudspeaker using the same. 
         [0004]    2. Description of Related Art 
         [0005]    A loudspeaker is an acoustic device transforming received electric signals into sounds. The electric signals have enough power to make the sounds audible to humans. There are different types of loudspeakers that can be categorized by their working principle, such as electro-dynamic loudspeakers, electromagnetic loudspeakers, electrostatic loudspeakers, and piezoelectric loudspeakers. Among the various types, electro-dynamic loudspeakers have simple structures, good sound quality, and low cost, thus it is most widely used. 
         [0006]    Electro-dynamic loudspeakers typically include a diaphragm, a bobbin, a voice coil, a damper, a magnet, and a frame. The voice coil is an electrical conductor placed in the magnetic field of the magnet. By applying an electrical current to the voice coil, a mechanical vibration of the diaphragm is produced due to the interaction between the electromagnetic field produced by the voice coil and the magnetic field of the magnets, to produce sound waves. 
         [0007]    The damper can support the voice coil so that the voice coil can move up and down without moving laterally. Also, the damper can slow the vibration of the diaphragm and protect the diaphragm from being damaged. However, the material of the damper is usually polymer, metal, or non-carbon nanotube paper, and therefore has relatively low strength in the radial or lateral direction, low elasticity in the axial direction, and low endurance strength. 
         [0008]    What is needed, therefore, is to provide a damper with improved strength in the radial direction, elasticity in axial direction, and endurance, and a loudspeaker using the same. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    Many aspects of the embodiments can be better understood with reference to the following drawings. The components in the drawings are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the embodiments. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views. 
           [0010]      FIG. 1  is a schematic structural view of an embodiment of a damper. 
           [0011]      FIG. 2  is a cross-sectional view of the damper of  FIG. 1 , taken along line II-II. 
           [0012]      FIG. 3  shows a Scanning Electron Microscope (SEM) image of a drawn carbon nanotube film. 
           [0013]      FIG. 4  is a schematic, enlarged view of a carbon nanotube segment in the drawn carbon nanotube film of  FIG. 3 . 
           [0014]      FIG. 5  shows an SEM image of a flocculated carbon nanotube film. 
           [0015]      FIG. 6  shows an SEM image of a pressed carbon nanotube film. 
           [0016]      FIG. 7  is a schematic structural view of another embodiment of a damper. 
           [0017]      FIG. 8  is an SEM image of an untwisted carbon nanotube wire. 
           [0018]      FIG. 9  is an SEM image of a twisted carbon nanotube wire. 
           [0019]      FIG. 10  is a schematic, exploded view of still another embodiment of a damper. 
           [0020]      FIG. 11  is a schematic, cross-sectional view of still another embodiment of a damper. 
           [0021]      FIG. 12  is a schematic, cross-sectional view of yet another embodiment of a damper. 
           [0022]      FIG. 13  is a schematic, exploded view of an embodiment of a loudspeaker. 
           [0023]      FIG. 14  is a schematic, cross-sectional view of the loudspeaker of  FIG. 13  after being assembled. 
       
    
    
     DETAILED DESCRIPTION 
       [0024]    The disclosure is illustrated by way of example and not by way of limitation in the figures of the accompanying drawings in which like references indicate similar elements. It should be noted that references to “an” or “one” embodiment in this disclosure are not necessarily to the same embodiment, and such references mean at least one. 
         [0025]    Referring to  FIG. 1 , an embodiment of a damper  10  is shown. The shape and size of the damper  10  is not limited. The damper  10  can be fabricated into a sheet shape, or other shapes to adapt to the actual needs of a desired loudspeaker design. In the embodiment shown in  FIG. 1 , the damper  10  is in the form of an annular disk with a corrugated cutaway section as shown in  FIG. 2 . The damper  10  forms a plurality of alternating concentric peaks  10   a  and valleys  10   b , thereby presenting the corrugated configuration. 
         [0026]    The damper  10  comprises a matrix  12  and two layer-shaped carbon nanotube structures  14 . The matrix  12  is interposed between the two layer-shaped carbon nanotube structures  14 , thereby forming a multi-layer structure. A central hole  16  is defined through the matrix  12  and the two layer-shaped carbon nanotube structures  14 . The shape and size of the central hole  16  corresponds to the shape and size of a bobbin or a voice coil of a loudspeaker, so that the damper  10  can be installed on the bobbin or the voice coil through the central hole  16 . 
         [0027]    The matrix  12  has good elasticity and high specific strength. The matrix  12  can be made of cloth, paper, cellulose membrane, or polymer film. For example, the matrix  12  can be a glass fiber cloth, kraft paper, polyethylene terephthalate membrane, polyimide membrane, polyphenylene ether acid membrane, polypropylene membrane, polystyrene membrane, polyvinyl chloride membrane, or polyether sulfone membrane. 
         [0028]    Each of the layer-shaped carbon nanotube structures  14  can comprise at least one layer of carbon nanotube film disposed or wrapped around surfaces of the matrix  12  so as to form the damper  10 . The carbon nanotube film can include a plurality of carbon nanotubes distributed therein, and the carbon nanotubes therein can be combined by van der Waals attractive force therebetween. 
         [0029]    The carbon nanotubes in the carbon nanotube film can be orderly or disorderly arranged. The term ‘disordered carbon nanotube structure’ includes, but is not limited to, a structure where the carbon nanotubes are arranged along many different directions, such that the number of carbon nanotubes arranged along each different direction can be almost the same (e.g. uniformly disordered); and/or entangled with each other. ‘Ordered carbon nanotube structure’ includes, but is not limited to, a structure where the carbon nanotubes are arranged in a systematic manner, e.g., the carbon nanotubes are arranged approximately along a same direction and or have two or more sections within each of which the carbon nanotubes are arranged approximately along a same direction (different sections can have different directions). The carbon nanotubes in the carbon nanotube structure  14  can be single-walled, double-walled, and/or multi-walled carbon nanotubes. Diameters of the single-walled carbon nanotubes range from about 0.5 nanometers to about 50 nanometers. The diameters of the double-walled carbon nanotubes can range from about 1 nanometer to about 50 nanometers. The diameters of the multi-walled carbon nanotubes can range from about 1.5 nanometers to about 50 nanometers. The carbon nanotube film can be a drawn carbon nanotube film, a flocculated carbon nanotube film, or a pressed carbon nanotube film. 
       Drawn Carbon Nanotube Film 
       [0030]    In one embodiment, the carbon nanotube structure  14  can include at least one drawn carbon nanotube film. Examples of a drawn carbon nanotube film are taught by U.S. Pat. No. 7,045,108 to Jiang et al., and WO 2007015710 to Zhang et al. The drawn carbon nanotube film includes a plurality of successive and oriented carbon nanotubes joined end-to-end by van der Waals attractive force therebetween. The carbon nanotubes in the carbon nanotube film can be substantially aligned in a single direction. The drawn carbon nanotube film can be formed by drawing a film from a carbon nanotube array capable of having a film drawn therefrom. Referring to  FIGS. 3 and 4 , each drawn carbon nanotube film includes a plurality of successively oriented carbon nanotube segments  143  joined end-to-end by van der Waals attractive force therebetween. Each carbon nanotube segment  143  includes a plurality of carbon nanotubes  145  substantially parallel to each other, and combined by van der Waals attractive force therebetween. As can be seen in  FIG. 3 , some variations can occur in the drawn carbon nanotube film. The carbon nanotubes  145  in the drawn carbon nanotube film are also oriented along a preferred orientation. 
         [0031]    The carbon nanotube structure  14  can also include at least two stacked drawn carbon nanotube films. In other embodiments, the carbon nanotube structure  14  can include two or more coplanar drawn carbon nanotube films. Coplanar drawn carbon nanotube films can also be stacked upon other coplanar films. Additionally, an angle can exist between the orientation of carbon nanotubes in adjacent drawn films, stacked and/or coplanar. Adjacent drawn carbon nanotube films can be combined by only the van der Waals attractive force therebetween without the need of an additional adhesive. An angle between the aligned directions of the carbon nanotubes in the two adjacent drawn carbon nanotube films can range from about 0 degrees to about 90 degrees. If the angle between the aligned directions of the carbon nanotubes in adjacent drawn carbon nanotube films is larger than 0 degrees, a microporous structure is defined by the carbon nanotubes. The carbon nanotube structure  14  in one embodiment employing these films will have a plurality of micropores. The sizes of the micropores can be less than about 10 μm. 
       Flocculated Carbon Nanotube Film 
       [0032]    In other embodiments, the carbon nanotube structure  14  can include a flocculated carbon nanotube film. Referring to  FIG. 5 , the flocculated carbon nanotube film can include a plurality of long, curved, disordered carbon nanotubes entangled with each other. Further, the flocculated carbon nanotube film can be isotropic. The carbon nanotubes can be substantially uniformly dispersed in the carbon nanotube film. Adjacent carbon nanotubes are acted upon by van der Waals attractive force to obtain an entangled structure with micropores defined therein. It is understood that the flocculated carbon nanotube film is very porous. The sizes of the micropores can be less than about 10 μm. The porous nature of the flocculated carbon nanotube film will increase the specific surface area of the carbon nanotube structure. Because the carbon nanotubes in the carbon nanotube structure  14  are entangled with each other, the carbon nanotube structure  14  employing the flocculated carbon nanotube film has excellent durability, and can be fashioned into desired shapes with a low risk to the integrity of the carbon nanotube structure  14 . The thickness of the flocculated carbon nanotube film can range from about 1 μm to about 1 mm. 
       Pressed Carbon Nanotube Film 
       [0033]    In other embodiments, the carbon nanotube structure  14  can include at least a pressed carbon nanotube film. Referring to  FIG. 6 , the pressed carbon nanotube film can be a free-standing carbon nanotube film. The carbon nanotubes in the pressed carbon nanotube film can be arranged along a same direction or along different directions. The carbon nanotubes in the pressed carbon nanotube film can rest upon each other. Adjacent carbon nanotubes are attracted to each other and combined by van der Waals attractive force. An angle between a primary alignment direction of the carbon nanotubes and a surface of the pressed carbon nanotube film is about 0 degrees to approximately 15 degrees. The greater the pressure applied, the smaller the angle obtained. If the carbon nanotubes in the pressed carbon nanotube film are arranged along different directions, the carbon nanotube structure  14  can be isotropic. Here, “isotropic” means the carbon nanotube film has properties identical in all directions parallel to a surface of the carbon nanotube film. The thickness of the pressed carbon nanotube film can range from about 0.5 nm to about 1 mm. Examples of a pressed carbon nanotube film are taught by US PGPub. 20080299031A1 to Liu et al. 
         [0034]    The carbon nanotube structures  14  and the matrix  12  can be combined together with adhesives or by hot pressing to form a three-layer structure. If the matrix  12  is made of metal, the adhesives can be silver glue. If the carbon nanotube structures  14  and the matrix  12  are combined together by hot pressing, at least some of the carbon nanotubes of the carbon nanotube structures  14  infiltrate into opposites surfaces of the matrix  12 , and this can strengthen the bonding force between each of the carbon nanotube structures  14  and the matrix  12 . 
         [0035]    In one embodiment, if one of the two carbon nanotube structures  14  is omitted, then only one carbon nanotube structure  14  is disposed on one surface of the matrix  12 . As a result, a two-layer structure is formed. 
         [0036]      FIG. 7  shows a schematic structural view of another embodiment of a damper  20  comprising a central hole  26 , a matrix  22 , and a carbon nanotube structure  24 . The damper  20  is similar to the damper  10 , except that the carbon nanotube structure  24  comprises at least one linear carbon nanotube structure arranged on the matrix  22 . 
         [0037]    In one embodiment, as shown in  FIG. 7 , the carbon nanotube structure  24  is a single linear carbon nanotube structure wound around the matrix  22  many times by extending the single linear carbon nanotube structure through the central hole  26  many times. On one surface of the matrix  22  shown in  FIG. 7 , the single linear carbon nanotube structure forms a plurality of sub-portions extending radially from the central hole  26  towards an outer periphery of the matrix  22 . 
         [0038]    In one embodiment, the carbon nanotube structure  24  comprises a plurality of linear carbon nanotube structures and the linear carbon nanotube structures are arranged radially on the matrix in the same or similar manner as that shown in the  FIG. 7 . 
       Linear Carbon Nanotube Structure 
       [0039]    The linear carbon nanotube structure can include one or more carbon nanotube wires. The carbon nanotube wires in the linear carbon nanotube structure can be substantially parallel to each other to form a bundle-like structure or twisted with each other to form a twisted structure. 
         [0040]    The carbon nanotube wire can be an untwisted carbon nanotube wire or a twisted carbon nanotube wire. An untwisted carbon nanotube wire is formed by treating a carbon nanotube film with an organic solvent.  FIG. 8  shows an untwisted carbon nanotube wire including a plurality of successive carbon nanotubes substantially oriented along the linear direction of the untwisted carbon nanotube wire and joined end-to-end by van der Waals attraction force therebetween. The untwisted carbon nanotube wire can have a diameter ranging from about 0.5 nm to about 100 μm. 
         [0041]    A twisted carbon nanotube wire is formed by twisting a carbon nanotube film by using a mechanical force.  FIG. 9  shows a twisted carbon nanotube wire including a plurality of carbon nanotubes oriented around an axial direction of the twisted carbon nanotube wire. The length of the twisted carbon nanotube wire can be set as desired and the diameter of the carbon nanotube wire can range from about 0.5 nanometers to about 100 micrometers. The twisted carbon nanotube wire can be treated with an organic solvent before or after twisting. 
         [0042]    In the embodiment shown in  FIG. 7 , the linear carbon nanotube structure comprises three carbon nanotube wires twisted with each other to form a twisted structure. 
         [0043]    It is noteworthy that the carbon nanotube structure  24  can include a plurality of carbon nanotube wires and a plurality of wires made of other materials. The plurality of carbon nanotube wires and the plurality of wires made of other materials can be crossed with each other or woven together. The other materials include polymer, paper, fiber, cloth, and metal. 
         [0044]      FIG. 10  shows a schematic structural view of another embodiment of a damper  30  comprising a matrix  32  and a carbon nanotube structure  34  disposed on a surface of the matrix  32 . The damper  30  is similar to the damper  10 , except that the damper  30  is a two-layer structure. The carbon nanotube structure  34  includes a plurality of linear carbon nanotube structures  342  substantially parallel with each other (not shown), crossed with each other, or woven together to obtain a layer-shaped carbon nanotube structure  34 . The layer-shaped carbon nanotube structure  34  can be disposed on a surface of the matrix  32  with adhesives or by hot pressing. In the embodiment shown in  FIG. 10 , the linear carbon nanotube structures  342  are woven together and form a network which resembles the outer configuration of the matrix  32 . 
         [0045]    It is noteworthy that the carbon nanotube structure  34  can include a plurality of linear carbon nanotube structures  342  and a plurality of wires made of other materials. The plurality of linear carbon nanotube structures  342  and the plurality of wires made of other materials can be crossed with each other or woven together. The other materials include polymer, paper, fiber, cloth, and metal. It is also noteworthy that the damper  30  can further comprise another carbon nanotube structure  34  and the matrix  32  can be disposed between the two carbon nanotube structures  34 . 
         [0046]      FIG. 11  shows a schematic structural view of another embodiment of a damper  40  comprising a matrix  42  and a carbon nanotube structure  44 . The damper  40  is similar to the damper  10 , except that the damper  40  further comprises an enhancement layer  48 , and the carbon nanotube structure  44  is sandwiched between the matrix  42  and the enhancement layer  48 . 
         [0047]    The carbon nanotube structure  44  can include at least one carbon nanotube film or at least one linear carbon nanotube structure discussed above. The carbon nanotube structure  44  can also be a combination of the at least one carbon nanotube film and the at least one linear carbon nanotube structure disposed on a surface of the at least one carbon nanotube film with adhesives or by hot pressing. 
         [0048]    The enhancement layer  48  can be made of metal, paper, polymer, diamond, boron carbide, or ceramics. The enhancement layer  48  can be formed on one surface of the carbon nanotube structure  44  via a coating or depositing method. The enhancement layer  48  can enhance the bonding strength between the carbon nanotube structure  44  and the matrix  42 . Materials of the enhancement layer  48  can be selected to have good binding ability with the matrix  42 . For example, if the matrix  42  is made of metal, the enhancement layer  48  can be made of the same metal. 
         [0049]      FIG. 12  shows a schematic structural view of another embodiment of a damper  50 . The damper  50  is similar to the damper  10 , except that the damper  50  comprises two matrixes  52  and a carbon nanotube structure  54 . The carbon nanotube structure  54  is sandwiched between the two matrixes  52  to form a three-layer structure. 
         [0050]    It is noteworthy that the damper  50  can include a plurality of matrixes and a plurality of carbon nanotube structures. The plurality of matrixes and the plurality of carbon nanotube structures can be stacked alternately, one on top of the other to form a multi-layer structure. It is also noteworthy that the damper  50  can further comprise an enhancement layer disposed on the carbon nanotube structure in the same or similar manner as that of the damper  40 . 
         [0051]    Referring to  FIGS. 13 and 14 , a loudspeaker  100  of one embodiment is shown. The loudspeaker  100  includes a frame  110 , a magnetic circuit  120 , a voice coil  130 , a voice coil bobbin  140 , a diaphragm  150  and a damper  160 . The damper  160  can be one of the above dampers  10 ,  20 ,  30 ,  40 ,  50 . 
         [0052]    The frame  110  has a structure of a truncated cone with an opening (not labeled) on one end. The frame  110  has a bottom  112  and a hollow cavity  111 . The hollow cavity  111  receives the diaphragm  150  and the damper  160 . The bottom  112  has a center hole  113 . The bottom  112  of the frame  110  is fixed to the magnetic circuit  120 . 
         [0053]    The magnetic circuit  120  includes a lower plate  121 , an upper plate  122 , a magnet  123 , and a magnet core  124 . The magnet  123  is disposed between the upper plate  122  and the lower plate  121 . The upper plate  122  and the magnet  123  are both substantially ring shaped, and define a substantially cylindrical shaped magnetic gap  125  in the magnetic circuit  120 . The magnet core  124  is fixed on the lower plate  121 , is received in the magnetic gap  125 , and goes through the center hole  113  of the bottom  112 . The magnetic circuit  120  is fixed on the bottom  112  via the upper plate  122 . The upper plate  122  can be combined with the bottom  112  via adhesive or mechanical force. In one embodiment according to  FIG. 13 , the upper plate  122  is fixed on the bottom  112  by screws (not shown) via screw holes  126 . 
         [0054]    The diaphragm  150  is a sound producing member of the loudspeaker  100 . The diaphragm  150  can have a cone shape if used in a large sized loudspeaker  100 . If the loudspeaker  100  has a smaller size, the diaphragm  150  can have a planar circular shape or a planar rectangular shape. A material of the diaphragm  150  can be aluminum alloy, magnesium alloy, ceramic, fiber, or cloth. In one embodiment according to  FIG. 13 , the diaphragm  150  has a conical shape. The diaphragm  150  includes an outer rim (not labeled) and an inner rim (not labeled). The outer rim of the diaphragm  150  is fixed to the opening end of the frame  110 , and the inner rim of the diaphragm  150  is fixed to the voice coil bobbin  140 . Furthermore, an external input terminal (not shown) can be attached to the frame  110 . A dust cap can be fixed over and above a joint portion of the diaphragm  150  and the voice coil bobbin  140 . 
         [0055]    The damper  160  holds the diaphragm  150  mechanically. The damper  160  is fixed to the bottom  112  of the frame  110 . An inner rim of the damper  160  is connected with the voice coil bobbin  140 . The damper  160  has a relatively high rigidity along the radial direction thereof, and a relatively low rigidity along the axial direction thereof, thus the voice coil bobbin  140  can freely move up and down but not radially. 
         [0056]    The voice coil  130  is a driving member of the loudspeaker  100 . The voice coil  130  is disposed around an outer surface of the bobbin  140 . When an electric signal is inputted into the voice coil  130 , a magnetic field is formed by the voice coil  130  as the variation of the electric signals. The interaction of the magnetic field caused by the voice coil  130  and the magnetic circuit  120  produces the vibration of the voice coil  130 . The vibration of the voice coil  130  would make the voice coil bobbin  140  vibrate, and accordingly the diaphragm  150  fixed on the voice coil bobbin  140  will vibrate. The vibration of the diaphragm  150  causes the loudspeaker  100  to produce sound. 
         [0057]    According to the above descriptions, the damper of present disclosure has following advantages. 
         [0058]    (1) Because the carbon nanotubes provided in the damper have good strength and elasticity, the carbon nanotube structure provided in the damper can improve the strength and the elasticity of the damper. The damper can prevent the voice coil from making unfavorable movement, even if excessive vibration is applied to the voice coil. Therefore, the sound volume of the loudspeaker using the damper can be increased. 
         [0059]    (2) The carbon nanotube structure decreases the weight of the damper under the same volume. 
         [0060]    It is to be understood that the above-described embodiments are intended to illustrate rather than limit the disclosure. Any elements described in accordance with any embodiments is understood that they can be used in addition or substituted in other embodiments. Embodiments can also be used together. Variations may be made to the embodiments without departing from the spirit of the disclosure. The above-described embodiments illustrate the scope of the disclosure but do not restrict the scope of the disclosure.