Abstract:
An electromechanical relay ( 10 ) that includes a frame ( 52 ) and a header assembly ( 20 ) having a plurality of contacts ( 24, 26, 28 ). The relay ( 10 ) also includes a core assembly ( 62 ) having an end engaging the frame ( 52 ). The relay ( 10 ) further includes an armature assembly ( 64 ) pivotally connected to the core assembly ( 62 ). The armature assembly ( 64 ) has at least one actuator ( 76, 77 ) engaging one of the contacts ( 24, 26 ). The relay ( 10 ) also includes a shield ( 16 ) connected to the header assembly ( 20 ) and defining a cavity ( 84 ) in which the contacts ( 24, 26, 28 ) are disposed.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention is directed generally to an electromechanical relay and, more particularly, to an ultraminiature electromechanical relay. 
     2. Description of Background 
     Ultraminature electromechanical relays are used in various applications, such as instrumentation, telecommunications, automatic test systems, wireless technologies, automotive and medical electronics, as well as commercial and general aviation and aerospace applications. Many of these applications, and others, operate in very high frequency ranges, such as 100 MHz to 10 GHz, and even beyond. General purpose ultraminiature electromechanical relays are typically not designed to handle such high frequencies. They are typically limited to applications below 4 GHz. Above this range, the signal fidelity of prior relays is typically diminished. 
     Accordingly, there exists a need for an electromechanical relay which can operate in the frequency ranges demanded by many high frequency applications without diminishing signal fidelity. 
     BRIEF SUMMARY OF INVENTION 
     The present invention is directed to an electromechanical relay. The relay includes a frame and a header assembly having a plurality of contacts. The relay also includes a core assembly having an end engaging the frame. The relay further includes an armature assembly pivotally connected to the core assembly. The armature assembly has an armature and at least one actuator engaging one of the contacts. The relay also includes a shield connected to the header assembly which defines a cavity in which the contacts are disposed. The contacts are disposed in the cavity of the shield. 
     The present invention represents a substantial advance over prior art relays. The present invention has the advantage that it is operable at very high frequencies without diminishing signal fidelity. The present invention also has the advantage that it prevents leakage and radiation of high frequency signals transmitting through the relay. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
     For the present invention to be clearly understood and readily practiced, the present invention will be described in conjunction with the following figures, wherein: 
     FIG. 1 is a diagram illustrating an exploded view of a relay according to the present invention; 
     FIG. 2 is a diagram illustrating an exploded view of a motor assembly of the relay of FIG. 1; 
     FIG. 3 is a diagram illustrating a top-view of the shield of the relay of FIG. 1; 
     FIG. 4 is a diagram illustrating a cross-sectional side-view of the shield of the relay of FIG. 1; 
     FIG. 5 is diagram illustrating a cross-sectional side-view of the relay of FIG. 1 in the de-energized state; 
     FIG. 6 is a diagram modeling equivalent electrical circuit connections between the signal and voltage terminals of the relay of FIG. 1 in the de-energized state; 
     FIG. 7 is a diagram illustrating a cross-sectional side-view of the relay of FIG. 1 in the energized state; 
     FIG. 8 is a diagram modeling equivalent electrical circuit connections between the signal and voltage terminals of the relay of FIG. 1 in the energized state; 
     FIG. 9 is a diagram illustrating a top-view of the shield and header assembly of the relay of FIG. 1; 
     FIG. 10 is a diagram illustrating a cross-sectional side-view of the shield and header assembly of the relay of FIG. 1; 
     FIG. 11 is a graph of the insertion loss of a relay constructed according to the teachings of the present invention and the combined best data of Teledyne Relays RF 100 Series and the Teledyne Relays RF 300 Series relays; 
     FIG. 12 is a graph of the isolation loss of a relay constructed according to the teachings of the present invention and combined best data of Teledyne Relays RF 100 Series and the Teledyne Relays RF 300 Series relays; and 
     FIG. 13 is a graph of the return loss of a relay constructed according to the teachings of the present invention and combined best data of Teledyne Relays RF 100 Series and the Teledyne Relays RF 300 Series relays. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 is a diagram illustrating an exploded view of a relay  10  according to the present invention. The relay  10  includes a cover  12 , a motor assembly  14 , a shield  16 , and a header assembly  20 . The cover  12  may be constructed of any material which protects the relay  10  from electromagnetic interference such as, for example, metal. 
     The header assembly  20  includes a header blank  22 . The header blank  22  may be constructed of a conductive material such as, for example, a gold-plated alloyed metal sold under the trade name Kovar®, a registered trademark of Westinghouse Electric &amp; Manufacturing Co., aluminum, steel, copper, nickel, and other metal alloys. The header blank  22  may be connected to electrical ground. In the embodiment of the relay  10  illustrated in FIG. 1, the header assembly  20  includes a normally open (NO) moving contact  24 , a normally closed (NC) moving contact  26 , and a lower stationary contact  28  mounted to a top side of the header blank  22 . The contacts  24 ,  26 ,  28  may be constructed of any material which ensures reliable switching such as, for example, a gold-plated precious metal alloy. 
     The header assembly  20  also includes three signal terminals  30 ,  32 ,  34 . The normally open moving contact  24  is connected at one end to the signal terminal  30 ; the NC moving contact  26  is connected at one end to the signal terminal  34 ; and the lower stationary contact  28  is connected to signal terminal  32 . The moving contacts  24 ,  26  may have a preset load, such as by a mechanical spring action, forcing the end of the moving contacts  24 ,  26  not connected to the signal terminals  32 ,  34  away from the header blank  22  and toward the motor assembly  14 . The header assembly  20  also includes two voltage terminals  36 ,  38  and two lead posts  40 ,  42 . The lead posts  40 ,  42  are portions of the voltage terminals  36 ,  38 , respectively, which extend through the header blank  22 . The connections between the contacts  24 ,  26 ,  28  and the signal terminals  30 ,  34 ,  32  are electrically insulated from the header blank  22  by seals  44 , as are the connections between the lead posts  40 ,  42  and the voltage terminals  36 ,  38 . The seals  44  may be made from an insulative material such as, for example, glass. 
     The embodiment illustrated in FIG. 1 is utilized in a single pole/double throw (SPDT) relay  10 . In another embodiment of the present invention, a different number of contacts  24 ,  26 ,  28  may be employed, such as two pairs of moving contacts  24 ,  26  and a pair of upper stationary contacts  28 , with a concomitant number of signal terminals  30 ,  32 ,  34 . This would correspond to a double pole/double throw (DPDT) relay. A different number of voltage terminals  36 ,  38  may also be used. 
     FIG. 2 is a diagram illustrating an exploded view of the motor assembly  14  of the relay  10  of FIG.  1 . The motor assembly  14  includes a mounting bracket  50 , a frame  52  with a permanent magnet  54 , a coil  56  with coil leads  58 , a spring washer  60 , a core assembly  62 , and an armature assembly  64 . The mounting bracket  50  and the frame  52  may be constructed of a material which provides high magnetic efficiency and mechanical rigidity to the relay  10  such as, for example, metal. The frame  52  includes opposing depending ends, one of which may be connected to the permanent magnet  54  and the other may define a pole face  66 . The core assembly  62  includes a core shank  68 , a core head  70 , and a clip pivot  72 . The clip pivot  72  may include a pair of opposed depending legs  73 . The armature assembly  64  includes an armature  74  and a number of actuators  76 ,  77 . In the illustrated embodiment, the armature  74  is bent at substantially the center of the armature  74  at an obtuse angle. Other embodiments of the present invention contemplate the use of differently shaped armatures  74 . The actuators  76 ,  77  have heads  80  made of an insulative material such as, for example, glass. In the embodiment of the motor assembly  14  illustrated in FIG. 2, the armature  74  has two actuators  76 ,  77 , although a different number of actuators  76 ,  77  may be utilized. The armature  74  also includes a hinge pin  82  to connect the armature  74  to the core assembly  62 , as described hereinbelow. 
     To complete the description of the motor assembly  14 , the core shank  68  is mounted to the core head  70 . The clip pivot  72 , the spring washer  60 , the coil  56 , the frame  52 , and the mounting bracket  50  all have openings for receiving the core shank  68 . The depending legs  73  of the clip pivot  72  extend away from the core shank  68  and toward the armature assembly  64 . The hinge pin  82  of the armature  74  is pivotally connected to the depending legs  73  of the clip pivot  72  such that the armature  74  is capable of rotational movement relative to the core assembly  62 . Other embodiments of the present invention contemplate different manners in which to pivotally connect the armature  74 . The cover  12  may be hermetically sealed to the header blank  22  of the header assembly  20 . In addition, the coil leads  58  of the coil  56  are connected to the lead posts  40 ,  42 . The shield  16  is mounted to the header blank  22 , as described hereinbelow. 
     FIGS. 3 and 4 are diagrams illustrating the shield  16  of the relay  10  of FIG.  1 . FIG. 3 is a top-view of the shield  16  and FIG. 4 is a cross-sectional side-view of the shield  16 . The shield  16  may be constructed from a conductive material, such as, for example, a Kovar® metal alloy with gold plating, aluminum, steel, copper, nickel, and other metal alloys. The shield  16  defines a substantially V-shaped cavity  84  with side walls  88 , and is connected to the header blank  22  such that the moving contacts  24 ,  26  and the lower stationary contact  28  are disposed in the cavity  84 . The moving contacts  24 ,  26  are disposed respectively in the channels  85 ,  86  of the cavity  84 , and the lower stationary contact  28  is disposed in the vertex channel  87  of the cavity  84 . In other embodiments of the present invention, the cavity  84  and the shield  16  may be shaped differently in order that various configurations of contacts  24 ,  26 ,  28  may be disposed in the cavity  84 . The cavity  84  is precisely sized, as described hereinbelow with reference to FIGS. 9-10, to provide impedance matching for the relay  10  for transmitting and receiving high frequency signals. 
     The shield also includes an upper stationary contact  90 , which may be constructed of a conductive material, such as metal. The upper stationary contact  90  may be substantially V-shaped, and is connected to a top-side of the shield  16  such that each end  91 ,  92  of the upper stationary contact  90  is adjacent one channel  85 ,  86  of the cavity  84 . The vertex portion  93  of the upper stationary contact  90  may be connected to a center portion  96  of the shield  16 . The upper stationary contact  90  may be connected to the shield  16  in various manners, such as, for example, by resistance welding, laser welding, and epoxy bonding. In other embodiments of the present invention, the upper stationary contact  90  may assume different geometrical shapes, particularly if a differently shaped cavity  84  is provided in the shield  16 . In addition, in other embodiments of the present invention, a different number of upper stationary contacts  90  may be utilized. 
     The center portion  96  of the shield  16  may be bent relative to the shield  16  such that it is deflected toward the header blank  22  to assure positive contact between the center portion  96  of the shield  16  and the header blank  22 . This feature ensures proper grounding of the shield  16 , and prevents high frequency leakage between the signal paths. 
     The operation of the relay  10  is now described with reference to FIGS. 5-8. When no voltage is applied across the voltage terminals  36 ,  38 , no electrical current flows through the coil  56 . This corresponds to the de-energized state of the relay  10 . FIG. 5 is a cross-sectional side-view of the relay  10  of FIG. 1 in the de-energized state. In the de-energized state, the permanent magnet  54  retains the armature in the de-energized position by virtue of the attractive force of magnetic flux path D from the permanent magnet  54 . In other embodiments of the present invention, the armature  74  may be retained in the de-energized position by a biasing spring, such as a leaf spring. With the armature  74  in the de-energized position, the insulative head  80  of the actuator  77  is forced against the NC moving contact  26 , and is disposed in the channel  86  of the cavity  84 , such that the NC moving contact  26  is forced against the lower stationary contact  28 . Still in the de-energized position, the actuator  76  is not forced against the NO moving contact  24 , which is disposed in the channel  85 , allowing the NO moving contact  24  to be forced against the end  91  of the upper stationary contact  90  by virtue of the mechanical spring action of the NO moving contact  24 . 
     FIG. 6 is a diagram modeling equivalent electrical circuit connections of the relay  10  in the de-energized state. In the de-energized state, because the NC moving contact  26  is connected to the signal terminal  34  (A 3 ) and because the lower stationary contact  28  is connected to the signal terminal  32  (A 2 ), a signal path is created between the signal terminal  32  (A 2 ) and the signal terminal  34  (A 3 ). In addition, because the upper stationary contact  90  is connected to electrical ground (via the shield  16  and the header blank  22 ), and because the NO moving contact  24  is connected to the signal terminal  30  (A 1 ), a signal path is created between the signal terminal  30  (A 1 ) and electrical ground. In the de-energized state, i.e., when there is no voltage across the voltage terminals  36 ,  38 , the signal terminal  30  (A 1 ) is connected to electrical ground and the signal terminal  32  (A 2 ) is connected to signal terminal  34  (A 3 ). 
     When a voltage is applied across the voltage terminals  36 ,  38  electrical current flows in the coil  56 . This corresponds to the energized state of the relay  10 . FIG. 7 is a cross-sectional view of the relay  10  in the energized state. The current in the coil  56  induces a magnetic flux in flux path E which is in a direction opposite to flux path D. As the current in the coil  56  increases, the holding force of the armature  74  against the permanent magnet  54  decreases by virtue of the decreasing net magnetic flux. The mechanical force of the NC moving contact  26  against the actuator  77  in conjunction with the electromagnetic attractive force between the armature  74  and the pole face  66  of the frame  52  from flux path E eventually creates a net torque in the counter-clockwise (CCW) direction, relative to FIG. 7, causing the armature  74  to rotate in the CCW direction into the energized position. With the armature  74  in the energized position, the head  80  of the actuator  76  forces the NO moving contact  24  against the lower stationary contact  28 , thus creating a signal path between the signal terminal  30  (A 1 ) and the signal terminal  32  (A 2 ). With the armature  74  still in the energized state, the other actuator  77  is not forced against the NC moving contact  26 , allowing the NC moving contact  26  to be forced against the end  92  of the upper stationary contact  90  by virtue of the mechanical spring action of the NC moving contact  26 . Thus, a signal path is created between the signal terminal  34  (A 3 ) and electrical ground. This is illustrated in FIG. 8, which models equivalent electrical circuit connections of the relay  10  in the energized state. 
     When the voltage is removed from the voltage terminals  36 ,  38 , current stops flowing through the coil  56 , which eventually reduces the magnetic flux of flux path E to substantially zero. With no induced flux in flux path E, there is minimal attractive force between the armature  74  and the pole face  66  of the frame  52 . The mechanical force of the NO moving contact  24  against the actuator  76  in conjunction with the electromagnetic attractive force between the armature  74  and the permanent magnet  54  creates a net torque in the clockwise (CW) direction, relative to FIG. 7, causing the armature  74  to rotate in the CW direction into the de-energized position. With the armature in the de-energized position, the signal terminal  32  (A 2 ) is connected to the signal terminal  34  (A 3 ), and the signal terminal  30  (A 1 ) is connected to ground, as described hereinbefore. 
     FIGS. 9 and 10 are diagrams illustrating the shield  16  and the header assembly  20  of the relay  10  of FIG.  1 . FIG. 9 is a top view of the shield  16  and the header assembly  20  and FIG. 10 is a cross-sectional side-view of the shield  16  and the header assembly  20 . Signal fidelity is achieved by matching the impedance of the signal path along the contacts  24 ,  26 ,  28  with that of the signal source. Impedance matching of the signal path through the contacts  24 ,  26 ,  28  is achieved where the edges of the contacts  24 ,  26 ,  28  are in close proximity to the side walls  88  of the shield  16  such that the contacts  24 ,  26 ,  28  are strongly coupled to the shield  16 . The separation distance, denoted as D S , between the edges of the moving contacts  24 ,  26  and the side walls  88  of the shield  16  characterizes the impedance of the signal path through the moving contacts  24 ,  26 . Because both the contacts  24 ,  26 ,  28  and the shield  16  are made of electrically conductive materials, the signal transmitting through the relay  10  is capacitively coupled between the contacts  24 ,  26 ,  28  and the shield  16 . The degree of signal coupling is a function of the signal frequency and the capacitance between the contacts  24 ,  26 ,  28  and the shield  16 . The amount of capacitance between the contacts  24 ,  26 ,  28  and the shield  16  is a function of their separation distance, the thickness of the contacts  24 ,  26 ,  28 , and the thickness of the shield  16 . Thus, the impedance of the signal path may be varied by varying the separation distance, D S , between the moving contacts  24 ,  26  and the side walls  88  of the shield  16 . In other words, the impedance may be represented by a ratio aspect relationship between the width of the moving contacts  24 ,  26 , denoted by D MC , and the width of the channels  85 ,  86  of the cavity  84 , denoted by D C , in which the moving contacts  24 ,  26  are disposed. Experimental and numerical modeling has shown that when this ratio (D MC /D C ) approaches 0.84, the impedance of the signal path is approximately 50Ω, a system impedance widely used in high frequency applications. Reducing the ratio, which corresponds to a greater separation distance, D S , between the moving contacts  24 ,  26  and the shield  16 , results in a greater signal path impedance, although the relationship is non-linear. Because the contacts  24 ,  26 ,  28  are in close proximity to the side walls  88  of the shield  16 , the coupling between the contacts  24 ,  26 ,  28  and the shield  16  is greater than the coupling between the contacts  24 ,  26 ,  28  and other ground sources, such as the armature  74  and the header blank  22 . Accordingly, the side walls  88  function as a protective barrier against leakage and radiation of high frequency signals transmitting through the relay  10 . 
     Signal fidelity may also be enhanced by matching the impedance of the signal path through the signal terminals  30 ,  32 ,  34  with that of the signal source. Impedance matching of the signal terminals  30 ,  32 ,  34  is achieved by proper sizing of the seals  44  with respect to the diameter of the signal terminals  30 ,  32 ,  34  and the dielectric constant of the insulative material of which the seals  44  are made, as described hereinbefore. It should be noted that the sizing of the seals  44  insulating the voltage terminals  36 ,  38  from the header blank  22  have a negligible affect on signal fidelity. 
     The superior RF characteristics of the relay  10  according to the present invention are depicted graphically in FIGS. 11-13. FIGS. 11-13 show the frequency response for three key RF parameters for the relay  10  of the present invention and for the combined best data of two relays from the relevant art, the Teledyne Relays RF 100 Series and the Teledyne Relays RF 300 Series. FIG. 11 is a graph of the insertion loss of the relay  10  of the present invention and the relevant art relays. The insertion loss as a function of frequency of the relay  10  of the present invention is illustrated in FIG. 11 as  101 . The combined best insertion loss of the Teledyne Relays RF 100 Series and the Teledyne Relays RF 300 Series relays is illustrated in FIG. 11 as  102 . The typical insertion loss limit for an RF relay is 1.0 dB. Any relay with insertion loss exceeding 1.0 dB is considered impractical to use. The relay  10  of the present invention has an insertion loss of less than 1.0 dB up to approximately 13.0 GHz, while the relevant art relays have an insertion loss less than 1.0 dB only up to approximately 4.2 GHz. 
     FIG. 12 is a graph of the isolation loss of the relay  10  constructed according to the teachings of the present invention and the relevant art relays. The isolation loss as a function of the frequency of the relay  10  of the present invention is illustrated in FIG. 12 as  103 . The combined best insertion loss of the Teledyne Relays RF 100 Series and the Teledyne Relays RF 300 Series relays is illustrated in FIG. 12 as  104 . For high frequency applications, the isolation loss is typically required to be 40 dB or greater. The relay  10  of the present invention exhibits better than 40 dB isolation loss up to 13 GHz, while the relevant art relays only provide 40 dB or better isolation loss up to 2 GHz. 
     FIG. 13 is a graph of the return loss of the relay  10  constructed according to the teachings of the present invention and the relevant art relays. The return loss as a function of frequency of the relay  10  of the present invention is illustrated in FIG. 13 as  105 . The best combined return loss of the Teledyne Relays RF 100 Series and the Teledyne Relays RF 300 Series relays is illustrated in FIG. 13 as  106 . The return loss of an RF relay is typically required to be 15 db or higher. The relay  10  of the present invention exhibits a return loss better than 15 dB up to approximately 12 GHz, while the prior art relays exhibit a return loss better than 15 dB only up to 5 GHz. 
     The present invention is also directed to a method of matching the impedance of the relay  10  with the impedance of a signal source. The method includes disposing a number of contacts  24 ,  26 ,  28  of the relay  10  in the cavity  84  of the shield  16 , such that the edges of the contacts  24 ,  26 ,  28  are in close proximity to the side walls  88  of the shield  16 , such that the contacts  24 ,  26 ,  28  are strongly coupled to the shield  16  and weakly coupled to other ground sources, such as the armature  74  and header blank  22 . 
     Those of ordinary skill in the art will recognize that many modifications and variations of the present invention may be implemented. The foregoing description and the following claims are intended to cover all such modifications and variations. Furthermore, the materials and processes disclosed are illustrative, but are not exhaustive. Other materials and processes may also be used to make devices embodying the present invention.