Abstract:
The coaxial connector includes a plug and a receptacle. The plug contains a spring-loaded central contact and a fixed shield contact. The receptacle contains a fixed central contact and a spring-loaded shield contact. When the plug and the receptacle are joined, each of the spring-loaded contacts is compressed to positively engage the respective fixed contact to facilitate an electrical connection. Mating edges of the plug and receptacle are chamfered to facilitate concentric alignment and to reduce the required insertion force between the plug and receptacle. The contacts of both the plug and the receptacle are recessed below the mating surface to prevent a person or another conductive surface from making inadvertent contact with an electrically conductive member of the connector.

Description:
BACKGROUND OF THE INVENTION 
     The subject matter disclosed herein relates to a coaxial connector. More specifically, the subject matter relates to a coaxial connector requiring a low insertion/extraction force designed to withstand a high number of mating cycles. 
     As is known to those skilled in the art, coaxial cables are electrical conductors configured to conduct high frequency electrical signals. Typically, a coaxial cable includes a central conductor carrying the high frequency signal about which an insulating layer, a ground shield, typically of braided, metallic construction, and an outer jacket that encloses the entire cable are sequentially wrapped. Coaxial cables are used in many applications requiring the ability to removably connect the cable to a piece of equipment, for example, cable television, electronic test equipment, and medical imaging. 
     An exemplary application that utilizes coaxial cables is a Magnetic Resonance Imaging (MRI) system. An MRI system requires transmission of high frequency resonance signals between imaging coils and the MRI scanner. The imaging coils typically include multiple channels, each channel transmitting a signal along a separate coaxial cable. It is desirable to include each of the signals from the multiple channels on a single connector. Consequently, multiple coaxial cables are typically connected using a single, gang connector. Because the insertion and extraction force required for a gang connector is proportional to the number of coaxial cables being connected by the gang connector, it would be desirable for the individual coaxial connectors used in the gang connector to require a low insertion/extraction force. In addition, the imaging coils are typically customized for the anatomical region being imaged. Consequently, individual coils are frequently connected to and disconnected from the MRI scanner. It would, therefore, also be desirable to have a coaxial connector rated for a high number of mating cycles. 
     SUMMARY OF THE INVENTION 
     Consistent with the foregoing and in accordance with the subject matter as embodied and broadly described herein, a high mating cycle coaxial connector requiring a low insertion force is described in suitable detail to enable one of ordinary skill in the art to make and use the invention. 
     The coaxial connector includes a plug and a receptacle. The plug contains a spring-loaded central contact and a fixed shield contact. The receptacle contains a fixed central contact and a spring-loaded shield contact. When the plug and the receptacle are joined, each of the spring-loaded contacts is compressed to positively engage the respective fixed contact to facilitate an electrical connection. Mating edges of the plug and receptacle are chamfered to facilitate concentric alignment and to reduce the required insertion force between the plug and receptacle. The contacts of both the plug and the receptacle are recessed below the mating surface to prevent inadvertent contact with an electrically conductive member of the connector. 
     In one embodiment of the invention, a connector for coupling a first and a second coaxial cable, each coaxial cable having a central conductor and a shield conductor is disclosed. The connector includes an inner contact electrically connected to the central conductor of one of the cables and a dielectric member having an opening extending longitudinally therethrough to receive the inner contact. The connector also has an outer contact electrically connected to the shield conductor of the cable. The outer contact has a generally hollow interior for receiving the dielectric member and the inner contact. The connector further includes a housing and a spring. The housing defines a cavity in communication with a first opening and a second opening wherein the inner contact, dielectric, and outer contact are movably mounted within the cavity. The first opening is configured to receive a mating connector, and the inner contact and the outer contact are electrically connected to the coaxial cable through the second opening. The spring biases at least the outer contact toward the first opening. 
     As another aspect of the invention, the connector may further include a rim disposed about at least a portion of the periphery of the outer contact and at the end of the outer contact nearest the first opening. The outer surface of the rim is beveled and the inner surface of the rim is configured to seat a first end of the spring. The housing includes a lip extending around at least a portion of the second opening, and the second end of the spring is seated against the lip. The first opening of the housing is preferably disposed in a front surface of the housing, and the second opening is preferably disposed in a rear surface of the housing. A portion of the outer contact may extend through the second opening and receive a retainer connected to the portion of the outer contact outside of the housing. The retainer is preferably biased against the rear surface of the housing by the spring. 
     In another embodiment of the connector, a connector for coupling a first and a second coaxial cable includes a plug and a receptacle. The plug includes a first inner contact electrically connected to the central conductor of the first coaxial cable at a fixed end. A first spring is preferably enclosed within the first inner contact to bias a movable end of the first inner contact in a direction opposite of the fixed end. The plug further includes a first dielectric member having an opening extending longitudinally therethrough to receive the first inner contact and a first outer contact electrically connected to the shield conductor of the first cable. The first outer contact has a generally open interior for receiving the first dielectric member and the first inner contact. 
     The receptacle includes a second inner contact electrically connected to the central conductor of the second coaxial cable and a second dielectric member having an opening extending longitudinally therethrough to receive the second inner contact. The receptacle also has a second outer contact electrically connected to the shield conductor of the second coaxial cable having a generally open interior for receiving the second dielectric member and the second inner contact. The receptacle further includes a housing and a spring. The housing defines a cavity in communication with a first opening and a second opening wherein the second inner contact, dielectric, and outer contact are movably mounted within the cavity. The first opening is configured to receive the plug, and the inner contact and the outer contact are electrically connected to the second coaxial cable through the second opening. The spring biases at least the second outer contact toward the first opening. 
     As another aspect of the invention, an edge of the first outer contact, defined by a mating face and an outer surface of the first outer contact, is chamfered and an edge of the second outer contact, defined by a mating face and an inner wall of the second outer contact, is complementarily chamfered to receive a portion of the first outer contact. Preferably, the second outer contact further includes a lip extending around the periphery of the opening between the chamfered surface and the inner wall to provide a stop for receiving the mating face of the first outer contact. 
     As another aspect of the invention, the connector further includes a second housing having a cavity for receiving a plug and at least one opening for receiving a threaded connector extending therethrough. The threaded connector engages the second housing and protrudes beyond a mating surface of the second housing. The receptacle housing has at least one opening extending at least partly through the receptacle housing which has a threaded portion to receive the threaded connector protruding beyond the mating surface of the second housing. The connector may further include multiple plugs and multiple cavities in the second housing, and each plug is mounted in one of the cavities. The connector may also include a plurality of receptacles wherein each of the receptacle housings is integrally connected to form a single housing and each receptacle is configured to receive one of the plugs. 
     These and other objects, advantages, and features of the invention will become apparent to those skilled in the art from the detailed description and the accompanying drawings. It should be understood, however, that the detailed description and accompanying drawings, while indicating preferred embodiments of the present invention, are given by way of illustration and not of limitation. Many changes and modifications may be made within the scope of the present invention without departing from the spirit thereof, and the invention includes all such modifications. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING(S) 
       Preferred exemplary embodiments of the subject matter disclosed herein are illustrated in the accompanying drawings in which like reference numerals represent like parts throughout, and in which: 
         FIG. 1  is a perspective view of the connector according to one embodiment of the invention; 
         FIG. 2  is a cross-sectional view of the connector of  FIG. 1 ; 
         FIG. 3  is an exploded view of the connector of  FIG. 1 ; 
         FIG. 4  is a cross-sectional view of a plug according to another embodiment of the invention; 
         FIG. 5  is a cross-sectional view of the receptacle taken at  4 - 4  as shown in  FIG. 1 ; 
         FIG. 6  is a perspective view of a plug incorporating multiple connectors according to another embodiment of the invention; and 
         FIG. 7  is another perspective view of the plug of  FIG. 6 ; 
     
    
    
     In describing the preferred embodiments of the invention which are illustrated in the drawings, specific terminology will be resorted to for the sake of clarity. However, it is not intended that the invention be limited to the specific terms so selected and it is understood that each specific term includes all technical equivalents which operate in a similar manner to accomplish a similar purpose. For example, the word “connected,” “attached,” or terms similar thereto are often used. They are not limited to direct connection but include connection through other elements where such connection is recognized as being equivalent by those skilled in the art. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The various features and advantageous details of the subject matter disclosed herein are explained more fully with reference to the non-limiting embodiments described in detail in the following description. 
     Referring to  FIGS. 1-3 , one embodiment of a connector for connecting two coaxial cables according to the present invention is illustrated. The connector is preferably a two-part connector, including a plug  10  and a receptacle  100 . A first coaxial cable is electrically connected to either the plug  10  or the receptacle  100 , and a second coaxial cable is electrically connected to the other of the plug  10  or the receptacle  100 . The plug  10  and receptacle  100  are complementarily configured such that joining the plug  10  and receptacle  100  establish an electrical connection between a central conductor and a ground shield in each of the two coaxial cables. The plug  10  is illustrated as a straight, board mount package and the receptacle  100  is illustrated as a straight, crimp package. It is contemplated that the mounting package of either the plug  10  or the receptacle  100  may be straight or right-angled, board mount or crimped, or any other suitable configuration for establishing electrical connection between the connector and the coaxial cable. 
     Referring to  FIG. 4 , another embodiment of the plug  10  is disclosed. The plug  10  includes an inner contact  12 , an outer contact  16 , and a non-conductive material, such as a dielectric member  14 , separating the inner  12  and outer  16  contacts. The inner contact  12  is preferably elongated and has a connection member  20  connected to a base  22  at a first end of the inner contact  12 . A mating end  24  of the inner contact  12  is slidably connected to the base  22 . Preferably, the connection member  20 , the base  22 , and the mating end  24  are generally cylindrical in shape. Optionally, any suitable shape may be used. A first spring  26  may be housed within the inner contact  12 . A first end of the spring  26  is seated within the base  22  and a second end of the spring  26  is seated against the mating end  24  of the inner contact  12 . The mating end  24  includes a mating surface  25  that is preferably generally rounded and configured to engage a complementarily curved mating surface  125  of an inner contact  112  of the receptacle  100 . Optionally, the mating surface  25  may be flat, conical, pyramidal, or of any other suitable geometry and the mating surface  125  of the receptacle  100  may be configured in a complementary geometry to engage the mating surface  25  of the plug  10 . 
     The inner contact  12  is preferably positioned adjacent to a central member  28  which has a longitudinally extending central aperture  30 . The connection member  20  of the inner contact  12  extends into a first end  31  of the aperture  30  and a ferrule, or contact,  32  extends into a second end  33  of the aperture  30 . The contact  32  is soldered or crimped to the central conductor of a coaxial cable prior to inserting the contact  32  into the aperture  30 . The contact  32  engages the connection member  20  to establish an electrical connection between the central conductor and the connection member  20  of the inner contact  12 . 
     A dielectric member  14  is positioned around the inner contact  12 . The dielectric member  14  is preferably cylindrical, but may be any suitable shape. The dielectric member  14  has an aperture  36  extending longitudinally therethrough and configured to receive the inner contact  12 . A first end of the dielectric member  14  is at least partly positioned against the central member  28  and a second end of the dielectric member  14  extends beyond the mating surface  25  of the inner contact  12  and forms, in part, a mating surface  38  of the plug. The periphery  40  of the aperture  36  is preferably chamfered, defining a slope from the mating surface  38  into the aperture  36  to facilitate receiving an inner contact  112  of a receptacle  100 . 
     The central member  28  and dielectric member  14  are inserted into an outer contact  16 . The outer contact  16  is electrically connected to the shield of the coaxial cable and may define, in part, the outer surface of the plug  10 . The outer contact  16  has an inner passage  42  extending longitudinally therethrough. The outer contact  16  is generally cylindrical and the radius of the inner passage  42  and an outer surface  44  may alternately be uniform or vary along the length of the outer contact  16 . Optionally, the outer contact  16  may be of any suitable shape. The outer contact  16  may also be a single member or may include multiple members,  16   a  and  16   b , that are each electrically connected. The inner passage  42  is configured to receive the central member  28  and the dielectric member  14 . The periphery  46  of the outer contact  16   a  at the mating surface  38  is preferably chamfered, defining a slope from the mating surface  38  towards the outer surface  44   a  to facilitate insertion of the plug  10  into a receptacle  100 . The periphery  48  of the outer contact  16   b  at the end opposite the mating surface  38  is also preferably chamfered to facilitate insertion of the coaxial cable. The central conductor and the insulating layer of the coaxial cable are inserted into the inner passage  42  and the ground shield extends over the outer surface  44   b  of the outer contact  16   b . A sleeve  50 , previously positioned over the outer jacket of the coaxial cable, is slidably positioned to cover the exposed ground shield and at least a portion of the outer jacket of the coaxial cable. The sleeve  50  is then connected to the ground shield, for example by soldering or crimping. 
     The receptacle  100  includes an inner contact  112 , an outer contact  116 , and a non-conductive material, such as a dielectric member  114 , separating the inner  112  and outer  116  contacts. The inner contact  112  is electrically connected to the central conductor of a coaxial cable. The inner contact  112  is preferably cylindrical in shape. Optionally, any suitable shape may be used. The inner contact  112  is preferably elongated and may be of single or multiple piece construction. The radius of the inner contact  112  may alternately be uniform or vary along the length of the inner contact  112 . The inner contact  112  has a connection member  120  at a first end of the inner contact  112  with an opening  121  to receive the central conductor of the coaxial cable. The central conductor may be directly inserted into the opening  121 . Optionally, a ferrule, or contact may first be soldered or crimped to the central conductor, and then the ferrule or contact is inserted into the opening  121 . The second end of the inner contact  112  defines a mating surface  125  complementarily configured to the mating surface  25  for the inner contact  12  of the plug  10 . Additionally, the periphery  123  of the mating surface  125  is preferably chamfered, defining a slope from the mating surface  125  toward the outer surface  127  of the inner contact  112  to facilitate insertion of the inner contact  112  into the dielectric member  14  of the plug  10 . 
     The dielectric member  114  separates the inner contact  112  and the outer contact  116 . Preferably, the dielectric member  114  is cylindrical, but may be any suitable shape. The dielectric member  114  has a longitudinally extending aperture  136  configured to receive the inner contact  112 . The length of the dielectric member  114  is less than the length of the inner contact  112 , and the inner contact  112  is inserted into the dielectric member  114  such that a first end of the dielectric member  114  is generally even with the first end of the inner contact  112  and the mating surface  125  of the inner contact  112  extends beyond a mating surface  138  of the dielectric member  114 . The dielectric member  114  is then inserted into an outer contact  116 . 
     The outer contact  116  of the receptacle  100  is complementarily configured to receive the outer contact  16  of the plug  10 . Preferably, the outer contact  116  has a longitudinally extending inner passage  142  configured to receive the dielectric member  114 . The outer contact  116  is generally cylindrical and the radius of the inner passage  142  and an outer surface  146  may alternately be uniform or vary along the length of the outer contact  116 . Optionally, the outer contact  116  may be of any suitable shape. The outer contact  116  includes a lip  148  generally coplanar and adjacent to the mating surface  138  of the dielectric member  114 . The outer contact  116  further includes a rim  150  extending around the outer periphery  146  that includes a beveled surface  147  defining a slope extending inward from the outer edge  151  of the rim  150  to the lip  148 . An outer surface  152  of the rim  150  is generally parallel to the outer periphery  146  of the outer contact  116  and extends for a distance along the outer periphery of the outer contact  116 . A rear surface  154  of the rim  150  faces toward the opposite end of the outer contact  116  and extends from the outer surface  152  of the rim  150  to the outer periphery  146  of the outer contact  116 . The rear surface  154  is preferably longitudinally positioned near the mating end  138  of the outer contact  116 . 
     The outer contact  116  is electrically connected to the ground shield of the coaxial cable. The periphery  180  of the outer contact  116  at end opposite the mating surface  138  is preferably chamfered to facilitate insertion of the coaxial cable. The central conductor and the insulating layer of the coaxial cable are inserted into the inner passage  142  and the ground shield extends over the outer surface  146  of the outer contact  116 . A sleeve  166 , previously positioned over the outer jacket of the coaxial cable, is slidably positioned to cover the exposed ground shield and at least a portion of the outer jacket of the coaxial cable. The sleeve  166  is then connected to the ground shield, for example by soldering or crimping. 
     The receptacle  100  further includes a housing  160  and a spring  162 . The housing  160  has mating surface  169  and a rear surface  171 . The housing further defines a cavity  170  extending longitudinally through the housing  160 . The cavity  170  is in communication with a first opening  173  in the mating surface  169  and a second opening  175  in the rear surface  171 . The cavity  170 , along with the periphery of the first opening  173 , is configured to slidably receive a rim  150  of the outer contact  116 . The second opening  175  is configured to slidably receive the outer periphery  146  of the outer contact  116 . Because the diameter of the rim  150  at the mating surface of the outer contact  116  is greater than the diameter of the outer periphery  146  of the outer contact  115 , a lip  174  extends around the periphery of the second opening  175  that faces and is generally the same width as the rear surface  154  of the rim  150 . 
     The spring  162  biases the outer contact towards the mating surface  169  of the housing  160 . Prior to inserting the outer contact  116  into the cavity  170  the spring  162  is slidably engaged around the outer periphery  146 . A first end of the spring  162  is seated against the rear surface  154  of the rim. The spring  162  and the outer contact  116  may then be inserted into the cavity  170 . At least a portion of the outer contact  116  extends through the second opening  175 , and the second end of the spring  162  is seated against the lip  174  of the housing. 
     A retainer  164  keeps the outer edge  151  of the outer contact  116  longitudinally disposed within the housing  160 . The retainer  164  is connected to the portion of the outer contact  116  extending through the second opening  175 . The retainer  164  may be secured to the outer contact  116  by any suitable means, such as a press-fit, an adhesive, or a threaded connection. In an uncompressed state, the spring  162  biases the outer contact  116  and, consequently, the towards the mating surface  169  of the housing  160 . The retainer  164  engages the rear surface  171  of the housing  160 , providing a limit to the expansion of the spring  162 . 
     The connector also includes a method to secure the plug  10  and receptacle  100  together in opposition to the force of the compressed springs. In one embodiment, the outer surface  44  of the outer contact  16  for the plug  10  slidably engages the first opening  173  of the housing  160  of the receptacle  100  by a friction fit. Optionally, at least one fastening member retains the plug  10  in connection with the receptacle  100 . Preferably, the plug  10  includes a housing  17  having a cavity for receiving the outer contact  16  of the plug. The housing  17  also includes at least one opening  190  for receiving a threaded connector extending through the housing. The opening  190  may alternately have a smooth inner surface, a threaded inner surface, or a combination thereof. The threaded connector may alternately engage the threaded inner surface, the outer surface of the housing, a rim extending around the inner surface of the opening  190 , or be captive within the opening  190 . The threaded connector extends beyond the second housing and engages an opening  192 , having a threaded portion, in the housing  160  for the receptacle  100 . Optionally, other suitable methods of maintaining connection between the plug  10  and receptacle  100  may be used, such as a press-fit, snap-fit, clamp, or any other suitable connecting method. 
     Optionally, as shown in  FIGS. 6 and 7 , multiple plugs  10  and receptacles  100  may be included in a single connector. The housing  17  of the plug  10  and the housing  160  of the receptacle  100  may each have multiple cavities to receive multiple plugs  10  and receptacles  100 . The plugs  10  and receptacles  100  are complementarily positioned such that each plug  10  engages one of the receptacles  100  when the connector is joined. 
     The connector may be made of any material suitable for the application. In one embodiment, the connector may be used within a strong magnetic field. Consequently, the connector is preferably constructed of materials having low magnetic susceptibility. For example, the contacts may be constructed of beryllium copper, phosphur bronze, or certified non-magnetic brass, and the housings may be constructed of a molded plastic. Preferably, the relative magnetic permeability, μ R , of the connector is less than 1.0005 where relative permeability is the ratio of the permeability of a specific material to the permeability of free space. 
     The connector is also constructed to maintain proper transmission impedance. Preferably, the connector has a fifty ohm impedance. Alternately, the connector may have a seventy-five ohm impedance. The impedance of the connector is determined based on the relative dielectric constant, E r , and the thickness of the dielectric member,  14  or  114 , between the inner contact,  12  or  112 , and the outer contact,  16  or  116 , of the plug  10  or receptacle  100 , respectively. 
     In operation, a first coaxial cable is electrically connected to either the plug  10  or the receptacle  100 , and a second coaxial cable is electrically connected to the other of the plug  10  or the receptacle  100 . The central conductors of each coaxial cable are connected to the inner contacts,  12  and  112 , and the shield conductors of each coaxial cable are connected to the outer contacts,  16  and  116 . The plug  10  and the receptacle  100  are joined, typically by a press-fit, such that the inner contact  12  of the plug  10  engages the inner contact  112  of the receptacle  100  and the outer contact  16  of the plug  10  engages the outer contact  116  of the receptacle  100 . 
     The chamfered surfaces facilitate concentric alignment of the plug  10  and the receptacle  100  during a mating cycle. As the plug  10  and the receptacle  100  are joined, the chamfered periphery  123  of the mating surface  125  of the inner contact  112  for the receptacle  100  may engage the chamfered periphery  40  of the aperture  36  in the dielectric member  14  for the plug  10 . Similarly, the chamfered periphery  46  of the mating surface  38  for the plug  10  may engage the chamfered periphery  147  of the rim  150  of the outer contact  116  for the receptacle  100 . The chamfered surfaces help align the inner and outer contacts as the plug  10  and receptacle  100  are joined. Optionally, it is contemplated that other geometries may similarly be used to facilitate alignment between the plug  10  and the receptacle  100 . Suitable geometries may include, but are not limited to: a concave mating surface on one connector and a convex mating surface on the other connector; outer peripheries that are oval, square, triangular, or other suitable shapes; or alignment tabs on one connector and corresponding recesses on the other connector. 
     The springs,  26  and  162 , significantly reduce the friction present during a mating cycle. As the plug  10  and receptacle  100  are joined, the mating surface  25  of the inner contact  12  for the plug  10  engages the mating surface  125  of the inner contact  12  for the receptacle  100 . Similarly, the mating surface  38  of the dielectric member  14  and the outer contact  16  for the plug  10  engages the mating surface  138  of the dielectric member  114  and the outer contact  116  for the receptacle  100 . However, the plug  10  and receptacle  100  are not fully joined when the corresponding mating surfaces initially contact each other. Additional pressure must be applied, moving the plug  10  further into the receptacle  100  and causing the spring  26  in the inner contact  12  of the plug  10  and the spring  162  around the outer contact  116  of the receptacle to compress. The compressed springs,  26  and  162 , positively maintain engagement of the inner,  12  and  112 , and outer,  16  and  116 , contacts of the plug  10  and receptacle  100 , respectively, without requiring a friction fit between the corresponding contacts. Eliminating the need for a friction fit between the plug  10  and receptacle  100  contacts significantly reduces the insertion and extraction force required for the connector. The reduced friction also reduces wear on the connector, increasing the expected number of mating cycles for the connector. 
     After joining the plug  10  and receptacle  100 , a threaded connector may be used to positively maintain connection. The threaded connector may also be used to draw the plug  10  and receptacle  100  completely together as the threaded connector engages the threaded portion of the receptacle. Alternately, other clamping or securing means may be fastened to positively retain connection between the plug  10  and receptacle  100  during connection. 
     It should be understood that the invention is not limited in its application to the details of construction and arrangements of the components set forth herein. The invention is capable of other embodiments and of being practiced or carried out in various ways. Variations and modifications of the foregoing are within the scope of the present invention. It also being understood that the invention disclosed and defined herein extends to all alternative combinations of two or more of the individual features mentioned or evident from the text and/or drawings. All of these different combinations constitute various alternative aspects of the present invention. The embodiments described herein explain the best modes known for practicing the invention and will enable others skilled in the art to utilize the invention