Abstract:
Electrical switches are described. In one aspect, an electrical switch includes a closed-loop fluid channel, multiple electrodes, and a pressure control system. The closed-loop fluid channel contains an electrically-conductive fluid and an electrically-insulating fluid. Each of the electrodes is in contact with fluid within the fluid channel at a respective location. The pressure control system is operable to change relative fluid pressure within the fluid channel at locations between adjacent electrodes to control splitting of a contiguous region of electrically-conductive fluid electrically connecting a pair of adjacent electrodes and merging of split regions of electrically-conductive fluid.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
         [0001]    Under 35 U.S.C. §119 this application claims the benefit of co-pending Japanese Patent Application No. 2001-321594, which was filed Oct. 19, 2001, and is incorporated herein by reference.  
         BACKGROUND  
         [0002]    A wide variety of different electrical switches has been proposed. In a reed relay switch, a miniature glass vessel contains an inert gas and two magnetic alloy leads. A coil of an electromagnetic drive is wound around the reed relay. In a typical configuration, when the coil is not energized, the ends of the leads repel each other so that the switch is open. When the coil is energized, the ends of the leads attract each other to close the switch. A reed relay may be implemented as a dry reed relay or a wet reed relay. Dry reed relays typically have high contact resistance and relatively low reliability because of considerable wear at the lead contacts. In a wet reed relay, the contact surfaces of the leads are covered with mercury, which decreases the friction-based wear of the lead contacts.  
           [0003]    Another type of electrical switch includes a plurality of electrodes that are disposed for fluid contact at specific locations along the inner walls of an electrically-insulating sealed channel that is filled with a small volume of an electrically-conductive liquid. Two electrodes are connected together electrically when the electrically-conductive liquid forms a continuous, electrically-conductive path between the pair of electrodes. The electrical connection between the electrodes is broken when the continuous, electrically-conductive path between the pair of electrodes is broken. A continuous volume of the electrically-conductive liquid may be moved into and out of contact with the pair of electrodes by creating a pressure differential across the liquid column in the channel. The pressure differential may be created by varying the volume of a gas supplied from a compartment located on one side of the liquid column, such as with a diaphragm or by heating the gas in the gas compartment.  
           [0004]    To avoid the risk that the electrode surfaces might be corroded by components of the gas inside the channel, U.S. Pat. No. 6,323,447 (assigned to Agilent Technologies, Inc.) has proposed an electrical switch in which the electrodes are covered by electrically-conductive fluid at all times. This electrical switch has a cavity, two solid electrodes, an electrically-conductive fluid, and a form modification unit. The solid electrodes are separated from each other within the cavity containing the electrically-conductive fluid. The electrodes are in a “closed” state when the conductive fluid is in a contiguous form and in an “open” state when the conductive fluid is in a non-contiguous form.  
         SUMMARY  
         [0005]    The invention enables multiple electrode pairs to be switched in an electrical switch having a compact form factor. The invention also features electrical switches that are characterized by low distortion, low insertion loss, and broadband frequency response at high frequencies (e.g., microwave and milliwave wavelength regions).  
           [0006]    In one aspect, the invention features an electrical switch that includes a closed-loop fluid channel, multiple electrodes, and a pressure control system. The closed-loop fluid channel contains an electrically-conductive fluid and an electrically-insulating fluid. Each of the electrodes is in contact with fluid within the fluid channel at a respective location. The pressure control system is operable to change relative fluid pressure within the fluid channel at locations between adjacent electrodes to control splitting of a contiguous region of electrically-conductive fluid electrically connecting a pair of adjacent electrodes and merging of split regions of electrically-conductive fluid.  
           [0007]    Other features and advantages of the invention will become apparent from the following description, including the drawings and the claims. 
       
    
    
     DESCRIPTION OF DRAWINGS  
       [0008]    [0008]FIG. 1A is diagrammatic view of an electrical switch in a first switch state.  
         [0009]    [0009]FIG. 1B is a circuit diagram of the electrical switch of FIG. 1A.  
         [0010]    [0010]FIG. 2A is a diagrammatic view of the electrical switch of FIG. 1A in a second switch state.  
         [0011]    [0011]FIG. 2B is a circuit diagram of the electrical switch of FIG. 2A.  
         [0012]    [0012]FIG. 3A is a diagrammatic view of an electrical switch in a first switch state.  
         [0013]    [0013]FIG. 3B is a diagrammatic view of the electrical switch of FIG. 3A in a second switch state. 
     
    
     DETAILED DESCRIPTION  
       [0014]    In the following description, like reference numbers are used to identify like elements. Furthermore, the drawings are intended to illustrate major features of exemplary embodiments in a diagrammatic manner. The drawings are not intended to depict every feature of actual embodiments nor relative dimensions of the depicted elements, and are not drawn to scale.  
         [0015]    Referring to FIGS. 1A, 1B,  2 A, and  2 B, in one embodiment that is operable as a double-pole changeover switch, an electrical switch  10  includes a closed-loop fluid channel  12 , multiple electrodes  14 ,  16 ,  18 ,  20 , and a pressure control system that includes a pair of reservoirs  22 ,  24 .  
         [0016]    Fluid channel  12  is defined in a base  26 , which is made of electrically-insulating material. In some embodiments, base  26  is made by laminating together two electrically-insulating substrates with the fluid channel being defined by matching, opposed grooves or channels in the substrates. The resulting structure is sealed to prevent leakage of fluid from fluid channel  12 . The two substrates may be made of the same material or different materials. For example, in some embodiments the substrates may be made of different materials, such as a ceramic substrate and a glass substrate. Fluid channel  12  contains an electrically-conductive fluid that is split into two volumes  28 ,  30  (shown hatched); an electrically-insulating fluid  32  (shown in white) fills the remaing areas of fluid channel  12 . The electrically-conductive fluid may be formed of a liquid metal (e.g., mercury, gallium, or sodium-potassium). The electrically-insulating fluid  32  may be an inert gas (e.g., a gas containing one or more of nitrogen, argon, and helium) or a vaporizable liquid (e.g., a liquid including one or more of a fluorocarbon, an oil, an alcohol, and water).  
         [0017]    In the illustrated embodiment, the fluid channel  12  is substantially square, and the electrodes  14 - 20  are provided at the substantially L-shaped corners of fluid channel  12 . Each electrode  14 - 20  has a respective contact point that is disposed for contact with the electrically-conducting fluid at a respective location within the fluid channel  12 . The electrodes  14 - 20  preferably are formed from a material (e.g., a metal including one or more of tungsten, molybdenum, chromium, titanium, tantalum, iron, nickel, palladium, and platinum) that has good wettability with respect to the electrically-conductive fluid. As described in detail below, in operation, when the electrically-insulating fluid  32  is moved or deformed, the wettability of electrodes  14 - 20  with respect to the electrically-conducting fluid protects the electrodes  14 - 20  against damage or corrosion that otherwise might occur from exposure to electrically-insulating fluid  32  because the electrode surfaces are covered by electrically-conductive fluid at all times during switching operations. In addition, the wettability of electrodes  14 - 20  with respect to the electrically-conducting fluid and the surface tension of the electrically-conductive fluid cooperate to latch the electrical switch  10  in an open- or closed-state.  
         [0018]    Reservoirs  22 ,  24  of the pressure control system are defined by cavities in base  26 . In the illustrated embodiment, reservoir  22  is located outside of fluid channel  12  and reservoir  24  is circumscribed by fluid channel  12 . Reservoir  22  is coupled to fluid channel  12  through two fluid ports  34 ,  36  that are located respectively between contact points of two pairs ( 16 ,  20  and  14 ,  18 ) of adjacent electrodes, with no electrode in common between the electrode pairs. Similarly, reservoir  24  is coupled to fluid channel  12  through two fluid ports  38 ,  40  that are located respectively between contact points of two pairs ( 14 ,  16  and  18 ,  20 ) of adjacent electrodes, with no electrode in common between the electrode pairs. In the illustrated embodiment, the dimensions of ports  34 - 40  are small enough to prevent electrically-conducting fluid from flowing out of channel  12  through ports  34 - 40 . Reservoirs  22 ,  24  each contain a respective heating element  42 ,  44  that may be operated independently to heat the electrically-insulating fluid contained within the reservoirs  22 ,  24  and change the state of the switch.  
         [0019]    Referring to FIGS. 1A and 1B, in one state of electrical switch  10 , the circuits defined by electrode pair  14 ,  18  and electrode pair  16 ,  20  are closed by electrically-conductive fluid volumes  36 ,  34 , respectively, whereas the circuits defined by electrode pair  14 ,  16  and  18 ,  20  are open as a result of the presence of electrically-insulating fluid between the electrodes of each electrode pair  14 ,  16  and  18 ,  20 .  
         [0020]    Referring to FIGS. 2A and 2B, when a bias is applied to heater  42 , the resulting thermal energy causes non-conductive fluid inside reservoir  22  to expand or to undergo a transition from the liquid phase to the vapor phase, producing a positive pressure with respect to reservoir  24 . This positive pressure acts on the electrically-conductive fluid volumes  28 ,  30  through ports  34 ,  36 , causing each of the electrically-conductive fluid volumes  28 ,  30  to split into two substantially equal parts in fluid channel  12 . The split portions of the electrically-conductive fluid volumes  28 ,  30  are moved and deformed, forcing electrically-insulating fluid located between electrodes  14 ,  16  and electrodes  18 ,  20  into reservoir  24 . The resulting split portions of the electrically-conductive fluid volumes  28 ,  30  merge to form two continuous electrically-conductive fluid volumes  46 ,  48 . In this second state of electrical switch  10 , the circuits defined by electrode pair  14 ,  16  and electrode pair  18 ,  20  are closed by electrically-conductive fluid volumes  46 ,  48 , respectively, whereas the circuits defined by electrode pair  14 ,  18  and electrode pair  16 ,  20  are open as a result of the presence of electrically-insulating fluid between the electrodes of each electrode pair  14 ,  18  and  16 ,  20 . Reservoirs  22 ,  24  are designed so that even after the bias has been removed from the heater  42 , the surface tension of the electrically-conductive fluid volumes  46 ,  48  overcomes the pressure exerted by the gas inside reservoir  24 .  
         [0021]    The electrical switch  10  is switched back to the state of FIGS. 1A and 1B, as follows. When a bias is applied to heater  44 , electrically-insulating fluid inside reservoir  24  expands or undergoes a transition from the liquid phase to the vapor phase, producing a positive pressure with respect to reservoir  22 . This positive pressure acts on the electrically-conductive fluid volumes  46 ,  48  through ports  38 ,  40 , causing each of the electrically-conductive fluid volumes  46 ,  48  to split into two substantially equal parts in fluid channel  12 . The split portions of the electrically-conductive fluid volumes  46 ,  48  are moved and deformed, forcing electrically-insulating fluid located between electrodes  14 ,  18  and electrodes  16 ,  20  into reservoir  22 . The resulting split portions of the electrically-conductive fluid volumes  46 ,  48  merge to form the original continuous electrically-conductive fluid volumes  28 ,  30  (see FIG. 1A).  
         [0022]    As shown in FIGS. 1A and 2A, in the illustrated embodiment, the electrically-conductive fluid preferably has a volume that substantially matches the volume needed to form continuous, electrically-conductive paths between two pairs of electrodes. In this way, when an electrical path is opened or closed by the movement of electrically-conductive fluid, the conduction path physically disappears with respect to the open circuit paths, and only physically appears in the required size in the closed circuit paths. This eliminates the parasitic inductance that otherwise would be present in the open circuit paths as a result of residual electrically-conductive fluid operating as open stubs. This feature improves the frequency response of electrical switch  10 . For example, this feature makes it possible to achieve a flat frequency response even at high frequencies (e.g., microwave and milliwave frequencies) In addition, the distances between the electrode pairs and the volume of the electrically-conducting fluid are selected so that the electrode contact points remain covered by electrically-conducting fluid at all times during the switching operations. This feature protects the electrode contact point surfaces against possible corrosion or damage that otherwise might result from exposure to the electrically-insulating fluid.  
         [0023]    Referring to FIGS. 3A and 3B, in an embodiment that is operable as a power merger/splitter switch, an electrical switch  50  includes a closed-loop fluid channel  12 , multiple electrodes  14 ,  16 ,  18 ,  20 , and a pressure control system that includes a pair of reservoirs  22 ,  24 . Each of the elements of electrical switch  50  may be implemented in the same way as the corresponding elements of electrical switch  10 , except for the configuration of the pressure control system, the arrangement of the electrodes  14 - 20 , and the inclusion of a resistor  52  that is coupled between electrodes  16  and  20 , as explained in detail below.  
         [0024]    Reservoir  22  is coupled to fluid channel  12  through two fluid ports  54 ,  56  that are located respectively between contact points of two pairs ( 14 ,  16  and  14 ,  20 ) of adjacent electrodes that share a common electrode (i.e., electrode  14 ). Similarly, reservoir  24  is coupled to fluid channel  12  through two fluid ports  58 ,  60  that are located respectively between contact points of two pairs ( 16 ,  18  and  18 ,  20 ) of adjacent electrodes that share a common electrode (i.e., electrode  18 ).  
         [0025]    In the illustrated embodiment, each of the electrodes  16 ,  20  is spaced from electrode  18  by a distance of one-quarter the wavelength (λ 1 ) corresponding to a target signal frequency f 1 , and the width and height of the channel  12  is selected so that the characteristic impedance of the electrical path produced by the electrically-conductive fluid volume  62  is Z 0 . The electrodes  16 ,  20  are electrically connected together by resistor  52 , which has a resistance value of {square root}{square root over (2)}Z 0 . The resulting structure operates as a Wilkinson divider that provides a uniform power splitter/merger function with isolation characteristics between the electrodes  16 ,  20 .  
         [0026]    In the illustrated embodiment, each of the electrodes  16 ,  20  is spaced from electrode  14  by a distance of one-quarter the wavelength (λ 2 ) corresponding to a target signal frequency f 2 , creating another Wilkinson divider that may be used with a different signal frequency f 2 . In this configuration, electrical switch  50  may be incorporated in a circuit in which signal sources of different frequencies are selected, while the power of these signals is divided in two before being outputted.  
         [0027]    Referring to FIG. 3A, in one state of electrical switch  50 , the circuits that are defined by electrode pair  14 ,  16  and electrode pair  14 ,  20  are closed by electrically-conductive fluid volume  62 , whereas the circuits defined by electrode pair  16 ,  18  and  18 ,  20  are open as a result of the presence of electrically-insulating fluid between the electrodes of each electrode pair  16 ,  18  and  18 ,  20 .  
         [0028]    Referring to FIGS. 3A and 3B, when a bias is applied to heater  42 , the resulting thermal energy causes non-conductive fluid inside reservoir  22  to expand or to undergo a transition from the liquid phase to the vapor phase, producing a positive pressure with respect to reservoir  24 . This positive pressure acts on the electrically-conductive fluid volume  62  through ports  54 ,  56 , causing each of the electrically-conductive fluid volume  62  to split into three volumes: two substantially equal parts and a residual part that remains at electrode  14  to protect electrode  14  against exposure to electrically-insulating fluid. The substantially equal split portions of the electrically-conductive fluid volume  62  are moved and deformed, forcing electrically-insulating fluid located between electrodes  16 ,  18  and electrodes  18 ,  20  into reservoir  24 . The substantially equal split portions of the electrically-conductive fluid volume  62  merge through the residual volume of electrically-conductive fluid held in contact with electrode  18  to form a continuous electrically-conductive fluid volume  64 . The distances between the electrode pairs and the volume of the electrically-conducting fluid are selected so that the contact points of electrodes  16 ,  20  remain covered by electrically-conducting fluid at all times during the switching operations. This feature protects the contact point surfaces of electrodes  16 ,  20  against possible corrosion or damage that otherwise might result from exposure to the electrically-insulating fluid. In this second state of electrical switch  50 , the circuits defined by electrode pair  16 ,  18  and electrode pair  18 ,  20  are closed by electrically-conductive fluid volume  64 , whereas the circuits defined by electrode pair  14 ,  16  and electrode pair  14 ,  20  are open as a result of the presence of electrically-insulating fluid between the electrodes of each electrode pair  14 ,  16  and  14 ,  20 . Reservoirs  22 ,  24  are designed so that even after the bias has been removed from the heater  42 , the surface tension of the electrically-conductive fluid volume  64  overcomes the pressure exerted by the gas inside the reservoir  24 .  
         [0029]    The electrical switch  50  may be switched back to the state of FIG. 3A, as follows. When a bias is applied to heater  44 , electrically-insulating fluid inside reservoir  24  expands or undergoes a transition from the liquid phase to the vapor phase, producing a positive pressure with respect to reservoir  22 . This positive pressure acts on the electrically-conductive fluid volume  64  through ports  58 ,  60 , causing the electrically-conductive fluid volume  64  to split into three volumes: two substantially equal parts and a residual part that remains at electrode  18  to protect electrode  18  against exposure to electrically-insulating fluid. The split portions of the electrically-conductive fluid volume  64  are moved and deformed, forcing electrically-insulating fluid located between electrodes  14 ,  16  and electrodes  14 ,  20  into reservoir  22 . The resulting split portions of the electrically-conductive fluid volume  64  merge through the residual volume of electrically-conductive fluid held in contact with electrode  14  to form the original continuous electrically-conductive fluid volume  62 .  
         [0030]    As shown in FIGS. 3A and 3B, in the illustrated embodiment, the quarter-wavelength electrical path produced by the electrically-conductive fluid volume  62  completely disappears due to the movement of the electrically-conductive fluid when the switch state changes to that of FIG. 3B. Similarly, the quarter-wavelength electrical path produced by the electrically-conductive fluid volume  64  completely disappears due to the movement of the electrically-conductive fluid when the state changes to that of FIG. 3A. This feature provides a Wilkinson divider of nearly ideal form, in which there is no capacitance component, extra open stubs, or the like near the electrodes  16 ,  20 . Also, just as in the embodiment of FIGS.  1 A- 2 B, the open or closed state of the switch is maintained by the surface tension of the conductive fluid even after the bias is removed from the heaters  42 ,  44 .  
         [0031]    In each of the above-described embodiments, the physical shape of the fluid channel  12  containing the electrically-conductive fluid volumes may be tailored so that the electrically-conductive fluid volumes have desired transmission line characteristics.  
         [0032]    Other embodiments are within the scope of the claims. For example, although the above embodiments were described in connection with specific electrical switch configurations, these embodiments readily may be incorporated in different switch configurations (e.g., a single-pole, double-throw switch and a single-pole, single-throw switch).