Patent Publication Number: US-2006017532-A1

Title: Metallic contact electrical switch incorporating lorentz actuator

Description:
BACKGROUND  
      Many electronic devices include one or more switches that control electronic signals, voltages or currents, which, to simplify the following description, will collectively be referred to as signals. In many cases, transistors are used to switch relatively low-power, low-frequency signals. However, in other cases, especially those in which the signal power is high and/or the signal frequency is high, or in cases in which great precision is needed, it is often desirable to switch a signal using metallic contacts, rather than using a transistor, because a transistor can alter, distort or degrade the signal, or may impose a limitation on the signal power, or may leak in its open state or may attenuate the signal in its closed state.  
      A reed relay is a typical example of a conventional miniature metallic contact switch. A reed relay has two reeds made of a magnetic alloy sealed together with an inert gas in a glass envelope. The envelope is surrounded by an electromagnetic driver coil. In the OFF state of the switch, no current flows through the driver coil and the reeds are biased to break contact between the tips of the reeds. In the ON state of the switch, current flowing through the coil causes the reeds to attract each other and to move into contact with each other. This establishes an electrical circuit between the reeds.  
      The reed relay has problems related to its relatively large size and relatively short service life. As to the first problem, the reeds and magnetic coil are physically large compared with a transistor, for example. Moreover, the large size and relatively slow electromagnetic response of the reeds impairs the performance of the reed relay when a high switching rate is required. As to the second problem, the flexing of the reeds as they switch causes mechanical fatigue, which can lead to breakage of the reeds after extended use.  
      In some applications, the reeds are tipped with contacts of rhodium (Rh) or tungsten (W), or are plated with rhodium (Rh) or gold (Au), to provide a high electrical conductivity and an ability to withstand electrical arcing during switching. However, contacts of these materials will typically fail over time. A type of reed relay called a “wet” relay has a longer service life than a conventional reed relay. In a wet relay, a liquid metal, such as mercury (Hg) provides the electrical contact between the reeds. This solves the problem of contact failure, but the problem of mechanical fatigue of the reeds remains unsolved.  
      Liquid metal switches have a thread of liquid metal in a channel and switch electrodes spaced apart along the length of the channel. A liquid metal switch is described in U.S. Pat. No. 6,323,447 of Kondoh et al., assigned to the assignee of this disclosure, and incorporated into this disclosure by reference. The liquid metal electrically connects the switch electrodes when the switch is in its ON state. An insulating fluid separates the liquid metal at a point between the switch electrodes when the switch is in its OFF state. The insulating fluid is typically high-purity nitrogen (N) or another such inert gas.  
      Liquid metal switches solve many of the problems of conventional reed relays. Liquid metal switches are substantially smaller than conventional reed relays. Also, the liquid metal switch has a longer service life and higher reliability. Finally, the liquid metal switches can be made using conventional wafer-scale fabrication methods and are therefore relatively inexpensive. However, liquid metal switches are actuated by heating the insulating fluid. This actuation method is relatively slow, can be difficult control and can have relatively high power consumption.  
      Thus, what is needed is a miniature metallic contact electrical switch that lacks the disadvantages of the conventional heat-actuated liquid metal switch.  
     SUMMARY OF THE INVENTION  
      The invention provides a metallic contact switch that comprises a housing defining a cavity, a conductive switching liquid in the cavity, switch contacts located in the cavity in electrical contact with the switching liquid in at least one switching state of the switch and a Lorentz actuator comprising conductive actuating liquid located in the cavity and capable of movement in the cavity. The Lorentz actuator is mechanically coupled to the switching liquid to change the switching state of the switch.  
      The Lorentz actuator typically has a faster response time, consumes less power and is easier to control than the heated insulating fluid actuators referred to above. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is an isometric view of a liquid metal pump that demonstrates the principles of a Lorentz actuator.  
       FIGS. 2A and 2B  are respectively a plan view and a side elevation of a first embodiment of a metallic contact electrical switch in accordance with the invention.  
       FIG. 2C  is a cut-away plan view of the embodiment of the switch shown in  FIGS. 2A and 2B  showing its internal structure.  
       FIGS. 3A and 3B  are cross-sectional views along the section line  3 A- 3 A in  FIG. 2C  of the embodiment of the switch shown in  FIGS. 2A and 2B  in its two switching states.  
       FIGS. 4A and 4B  are plan views of first substrate and second substrate, respectively, of the embodiment of the switch shown in  FIGS. 2A and 2B .  
       FIGS. 5A and 5B  are cut-away plan views showing the internal structure of a second embodiment of a metallic contact switch in accordance with the invention in each of its switching states.  
       FIG. 5C  is a cut-away plan view showing the internal structure of an embodiment of a double-pole, double-throw metallic contact switch in accordance with the invention in one of its switching states.  
       FIGS. 6A and 6B  are cut-away plan views showing the internal structure of a third embodiment of a metallic contact switch in accordance with the invention in each of its switching states.  
       FIG. 7A  is a cut-away plan view showing the internal structure of a fourth embodiment of a metallic contact switch in accordance with the invention one of its switching states.  
       FIG. 7B  is a cut-away plan view of a variation on the embodiment of the switch in accordance with the invention shown in  FIG. 7A .  
       FIGS. 8A-8D  are cut-way plan views illustrating the operation of the embodiment shown in  FIG. 7A  of the switch in accordance with the invention.  
       FIGS. 9A and 9B  are cut-away plan views showing the internal structure of a fifth embodiment of a metallic contact switch in accordance with the invention in each of its switching states.  
       FIG. 9C  is a cross-sectional view along the section line  9 C- 9 C in  FIG. 9A  of the embodiment of the switch shown in  FIGS. 9A and 9B .  
       FIGS. 9D and 9E  are plan views of the first and second substrates, respectively, of the embodiment of the switch shown in  FIGS. 9A and 9B .  
       FIGS. 10A and 10B  are cut-away views showing the internal structure of a sixth embodiment of a metallic contact switch in accordance with the invention.  
       FIGS. 11A and 11B  are enlarged cut-away plan views showing part of a seventh embodiment of a metallic contact switch in accordance with the invention in which the structure of the cavity is modified to increase the stability of the switching states of the switch.  
       FIG. 11C  is an enlarged cut-away plan view showing an alternative cavity structure that increases the stability of the switching states of embodiments of the switch in accordance with the invention.  
       FIGS. 12A and 12B  are respectively a plan view and a cross-sectional view of an eighth embodiment of a metallic contact switch in accordance with the invention.  
       FIG. 12C  is a cross-sectional view of a variation on the embodiment of the switch in accordance with the invention shown in  FIGS. 12A and 12B .  
       FIGS. 13A, 13B  and  13 C are respectively two cut-away plan views and a cross-sectional view of a ninth embodiment of a metallic contact switch in accordance with the invention.  
       FIGS. 13D and 13E  are plan views of the first and second substrates, respectively, of the embodiment of the switch in accordance with the invention shown in  FIGS. 13A and 13B .  
    
    
     DETAILED DESCRIPTION  
      The invention is based on the inventor&#39;s realization that a Lorentz actuator can be used to generate the motive force needed actuate a liquid metal switch.  
       FIG. 1  is an isometric view of a liquid metal pump  10  that can be found on display in many science museums to demonstrate the Lorentz force. Pump  10  employs the Lorentz force to electromagnetically pump the liquid metal mercury. The Lorentz force is generated when an electric current flows in a direction non-parallel to a magnetic field.  
      In pump  10 , an enclosed reservoir  20  holds a supply of mercury  30 . The reservoir is made of an electrically non-conducting material such as glass. Opposed electrodes  60  and  62  extend through the walls of the reservoir part-way along its length into contact with the mercury. A riser tube  40  extends between one end of reservoir  20  and the upper end of an inclined open channel  22 . A return tube  42  extends between the lower end of channel  22  and the other end of reservoir  20 . A power supply (not shown) is connected to electrodes  60  and  62  by wires (not shown) to provide an electric current that flows through the portion of the mercury  30  located between the electrodes. The current flows through the mercury in the −z-direction shown in  FIG. 1 . A magnet (not shown) applies a magnetic field represented by an arrow  70  across the reservoir in the vicinity of the electrodes. The magnetic field is oriented in the +y-direction, orthogonal to the direction of the current flow through the mercury.  
      The Lorentz force is exerted on a charged object moving through a magnetic field. The electrons in the mercury that conduct the current between the electrodes  60  and  62  are charged objects. The direction of the Lorentz force is mutually orthogonal to the directions of the electric and magnetic fields. Thus, the Lorentz force is oriented in the −x-direction shown along the length of reservoir  20 , i.e., in the −x-direction shown. The Lorentz force therefore the mercury along the length of reservoir  20  in the −x-direction. The pumped mercury flows up through riser tube  40  into channel  22 . The mercury flows down channel  22 , where its flow can be observed. The mercury returns to enclosure  20  by flowing down return tube  42 . Arrows  50  indicate the mercury flow.  
       FIGS. 2A and 2B  are respectively a plan view and a side elevation of a first embodiment  100  of a metallic contact electrical switch in accordance with the invention.  FIG. 2C  is a cut-away plan view of switch  100  showing its internal structure. In switch  100 , a Lorentz actuator generates a motive force that is used to control the position of a conducting switching liquid relative to a pair of electrical switch contacts. The Lorentz actuator generates the motive force by a control current passing through a conducting actuating liquid located in a magnetic field supplied by a magnet. The control current is applied to the actuating liquid through opposed control electrodes.  
      Switch  100  has a housing  110  that defines a cavity  120  in which is located conducting switching liquid  130 . Switch contacts  140  and  141  are also located in cavity  120  in electrical contact with switching liquid  130  in at least one of the switching states of switch  100 . A Lorentz actuator  150  that comprises conducting actuating liquid  152  located in cavity  120  and is capable of movement in the cavity is mechanically coupled to the switching liquid  130  to change the switching state of switch  100 .  
      In switch  100 , cavity  120  is elongate and linear and has a switching portion  122  and an actuating portion  124 . Switch contacts  140  and  141  are located in the switching portion  122  of cavity  120 . Lorentz actuator  150  is composed of conducting actuating liquid  152  located in the actuating portion  124  of cavity  120 ; opposed control electrodes  160  and  162  located in the actuating portion  124  of cavity  120  in electrical contact with actuating liquid  152  in at least one of the switching states of switch  100 , and a magnet  170  located adjacent the actuating portion  124  of cavity  120 . The actuating portion  124  of cavity  120 , control electrodes  160  and  162 , and magnet  170  are arranged such that the direction of current flow through actuating liquid  152  between control electrodes  160  and  162 , the direction of the magnetic field applied by magnet  170  to actuating liquid  152  and direction in which actuating liquid  152  is capable of moving in the actuating portion  124  of cavity  120  are mutually orthogonal.  
      Actuating liquid  152  is coupled to switching liquid  130  by an insulating fluid  154 . Insulating fluid  154  electrically isolates switching liquid  130 , and, hence, switch contacts  140  and  141 , from actuating liquid  152  and from the electrical circuit formed in part by control electrodes  160  and  162  and actuating liquid  152 . In applications in which it is acceptable to have a fluctuating DC voltage imposed on the signal switched by switch contacts  140  and  141 , insulating fluid  154  may be omitted. In such embodiment, a single body of conducting liquid constitutes actuating liquid  152  and switching liquid  130 . Switching liquid  130 , actuating liquid  152  and, if present, insulating fluid  154  collectively constitute a moving element  158 .  
      The terms conducting and insulating are used in this disclosure in a relative sense. A material described as conducting has a greater electrical conductivity than a material described as insulating. The ratio of the electrical conductivities of the conducting material and the insulating material depends on the application in which the switch will be used. A greater ratio is needed in applications that need the switch have a large ratio of OFF to ON resistance than in applications in which the switch having a smaller ratio of OFF to ON resistance are acceptable.  
      The example of magnet  170  is a permanent magnet. In other embodiments, magnet  170  is an electromagnet. The location of magnet  170  is indicated by a broken line in  FIG. 2C .  
      In the example shown in  FIGS. 2A-2C , the portions of cavity  120  not occupied by moving element  158  are evacuated to enable the moving element to move freely in the x-direction in cavity  120  when the switching state of switch  100  changes. In other embodiments, cavity  120  additionally comprises a pressure equalizing portion that extends between the remote end of switching portion  122  and the remote end of actuating portion  124 . The remote end of switching portion  122  is the end of switching portion  122  remote from actuating portion  124  and the remote end of actuating portion  124  is the end of actuating portion  124  remote from switching portion  122 . The pressure equalizing portion allows moving element  158  to move freely in the x-direction in cavity  120  by enabling fluid filling the portions of cavity  120  not occupied by the moving element to flow back and forth between the remote end of switching portion  122  and the remote end of actuating portion  124  when the switching state of switch  100  changes. The pressure equalizing portion of cavity  120  will be described in more detail below with reference to  FIG. 4B .  
       FIGS. 3A and 3B  are cross-sectional views along the section line  3 A- 3 A in  FIG. 2C  of switch  100  in its two switching states.  FIGS. 3A and 3B  show the direction of the magnetic field B that magnet  170  applies to actuating liquid  152  in Lorentz actuator  150 .  FIG. 3A  shows the result of applying a control voltage between control electrode  162  and control electrode  160  ( FIG. 2C ). The control voltage causes a control current to flow through actuating liquid  152  in the +y-direction from control electrode  162  to control electrode  160 . Interaction of the control current and magnetic field B applies a motive force F in the −x-direction to actuating liquid  152 . Motive force F moves actuating liquid  152  in the −x-direction in the actuating portion  124  of cavity  120 . Switching liquid  130  is coupled to actuating liquid  152  by insulating fluid  154 . Thus, motive force F moves moving element  158  composed of switching liquid  130 , insulating fluid  154  and actuating liquid  152  in the −x-direction to a position in the switching portion  122  of cavity  120  in which switching liquid  130  electrically connects switch contacts  140  and  141 .  
       FIG. 3B  shows the result of applying a control voltage between control electrode  160  and control electrode  162 . The control voltage causes a control current to flow through actuating liquid  152  in the −y-direction from control electrode  160  to control electrode  162 . Interaction of the control current and magnetic field B applies a motive force F′ in the +x-direction to actuating liquid  152 . Motive force F′ moves moving element  158  in the +x-direction in cavity  120  to a position in which the electrical connection between switch contacts  140  and  141  provided by switching liquid  130  is broken.  
      The distance that moving element  158  moves in the x-direction depends on the temporal duration of the control voltage and the dynamics of the moving element in cavity  120 . The control voltage is timed to move the moving element over a distance that alternately puts switching liquid  130  in contact with and out of contact with switch contacts  140  and  141 . The distance through which the moving element moves can alternatively be defined by the amount of electrical charge that passes between control electrodes  160  and  162  and vice versa. Other ways of defining the distance through which moving element  158  moves in cavity  120  are described below.  
      As shown in  FIGS. 3A and 3B , housing  110  is composed of a first substrate  112  and a second substrate  114 . Second substrate  114  is bonded to first substrate  112 . First substrate  112  and second substrate  114  are shown in more detail in  FIGS. 4A and 4B , respectively.  
       FIG. 4A  is a plan view of first substrate  112 . Broken lines show the locations of second substrate  114  on the first substrate and of cavity  120  in the second substrate. First substrate  112  has a planar major surface  113  (also shown in  FIG. 3A ) on which switch contacts  140  and  141  and control electrodes  160  and  162  are located.  
      Second substrate  114  has a planar major surface  115  that is juxtaposed with surface  113  of first substrate  112  in switch  100 .  FIG. 4B  is a view of the major surface  115  of second substrate  114 . Cavity  120 , composed of switching portion  122  and actuating portion  124 , is defined in substrate  114 . In the example shown, the width, i.e., dimension in the y-direction, of actuating portion  124  is greater than that of switching portion  122 . Accordingly, actuating portion  124  is greater in cross-sectional area than switching portion  122 . Alternatively, switching portion  122  and actuating portion  124  are equal in either or both of width and cross-sectional area.  
      Cavity  120  is located in substrate  114  such that, when substrates  112  and  114  are assembled to form switch  100 , part of each of the switch contacts  140  and  141  is located inside the switching portion  122  of cavity  120  in contact with switching liquid  130  and part of each of the control electrodes  160  and  162  is located inside the actuating portion  124  of cavity  120  in contact with actuating liquid  152 .  
       FIG. 4B  also shows switching liquid  130  occupying part of switching portion  122  of cavity  120 , actuating liquid  152  occupying parts of switching portion  122  and actuating portion  124 , and insulating fluid  154  occupying part of switching portion  122  between the parts occupied by switching liquid  130  and actuating liquid  152 .  
       FIG. 4B  also shows an embodiment of cavity  120  additionally having the above-mentioned optional pressure equalizing portion  126  defined in substrate  114 . Pressure equalizing portion  126  extends between the remote end of the switching portion  122  and the remote end of actuating portion  124 . The portion of cavity  120  not occupied by moving element  158  is filled with an insulating fluid  155 . Pressure equalizing portion  126  allows insulating fluid  155  to flow back and forth between the remote end of switching portion  122  and the remote end of actuating portion  124  to equalize pressure across moving element  158  as switch  100  changes state. The material of insulating fluid  155  may be the same as, or different from, that of insulating fluid  154 .  
      The cross-sectional area and length of the pressure equalizing portion  126  of cavity  120  and the physical properties of insulating fluid  155  influence the dynamic switching properties of switch  100 . In some embodiments, pressure equalizing portion  126  is dimensioned and insulating fluid  155  is chosen to provide switch  100  with specific dynamic switching properties. In other embodiments, pressure equalizing portion  126  is dimensioned and insulating fluid  155  is chosen to impart a negligible change on the dynamic switching properties on switch  100 . Pressure equalizing portion  126  may alternatively be defined at least in part in first substrate  112  ( FIG. 4A ).  
      Switch  100  is a single-pole, single-throw, i.e., ON-OFF, switch. Other embodiments of a switch in accordance with the invention provide additional poles and additional throws.  
       FIGS. 5A and 5B  are cut-away plan views showing the internal structure of a second embodiment  200  of a metallic contact switch in accordance with the invention in each of its switching states. Switch  200  is a single-pole, double-throw switch, i.e., a two-way switch. Elements of switch  200  that correspond to elements of above-described switch  100  are indicated by the same reference numerals and will not be described again here.  
      Switch  200  has a third switch contact  142  located on the major surface  113  of substrate  112 . Switch contact  142  is located in and extends from the switching portion  122  of cavity  120  and is in electrical contact with switching liquid  130  in one of the switching states of switch  200 . In this embodiment, switch contacts  140 ,  141  and  142  are arrayed in order in the x-direction along the length of switching portion  122 . In this disclosure, the term length used in connection with an element, such as cavity  120 , denotes the dimension of the element in the x-direction. Switch contacts  140 ,  141  and  142  have a nominally uniform pitch, i.e., switch contacts  140 ,  141  and  142  are separated in the x-direction by nominally-equal distances. However, a functioning switch will be obtained with some deviation from a uniform pitch.  
      In the example shown, switch contact  141  is located on the opposite side of switching portion  122  from switch contacts  140  and  142 , i.e., common switch contact  141  extends in the +y-direction from switching portion  122 , whereas switch contacts  140  and  142  extend in the −y-direction from switching portion  122 . This arrangement reduces capacitance between common switch contact  141  and switch contacts  140  and  142 . In other embodiments, switch contacts  140 ,  141  and  142  are all located on the same side of switching portion  122 , i.e., all three switch contacts extend from switching portion  122  in the same direction.  
      To provide double-throw switching, the length of switching liquid  130  in the switching portion  122  of cavity  120  is greater than the distance between switch contacts  140  and  141 , but less than the distance between the adjacent edges of switch contacts  140  and  142 .  FIG. 5A  shows switch  200  in one of its switching states in which switching liquid  130  contacts switch contacts  140  and  141 , and switch contact  142  contacts insulating fluid  154 . In this switching state, switching liquid  130  electrically connects switch contact  140  to switch contact  141 , and switch contact  142  is electrically isolated.  
       FIG. 5B  shows switch  200  after a control current has passed from control electrode  160  to control electrode  162  to generate a motive force in the +x-direction.  
      The motive force has moved actuating liquid  152  in the +x-direction and the actuating liquid has moved switching liquid  130  in the +x-direction by a distance approximately equal to the pitch of switch contacts  140 ,  141  and  142 . The movement of switching liquid  130  has put switching liquid  130  in contact with switch contacts  141  and  142 . In this switching state, switching liquid  130  electrically connects switch contact  142  to switch contact  141 , and switch contact  140  is electrically isolated. Switch  200  is returned to its switching state shown in  FIG. 5A  by passing a control current from control electrode  162  to control electrode  160 .  
       FIG. 5C  is a cut-away plan view showing the internal structure of an embodiment  202  of a double-pole, double-throw switch in one of its switching states. Switch  202  is based on single-pole, double-throw, switch  200  described above with reference to  FIGS. 5A  and SB. Elements of switch  202  that correspond to elements of the switches described above with reference to  FIGS. 2A, 2B ,  5 A and  5 B are indicated by the same reference numerals and will not be described again here.  
      In switch  202 , switch contacts  240 ,  241  and  242  are arrayed in the x-direction on major surface  213  of first substrate  212  next to switch contacts  140 ,  141  and  142 . Switch contacts  240 ,  241  and  242  have the same pitch as switch contacts  140 ,  141  and  142 . Switch contact  242  is separated from switch contact  140  by a distance different from the pitch of the switch contacts. In another embodiment, switch contact  242  is separated from switch contact  140  by a distance equal to the pitch of the switch contacts.  
      Defined in second substrate  214  is a cavity  220  similar to cavity  120  shown in  FIG. 5A . Cavity  220  has a switching portion  222  and an actuating portion  224 . Relative to switching portion  122  of cavity  120  ( FIG. 5A ), switching portion  222  is extended in the −x-direction to accommodate switch contacts  240 ,  241  and  242  in addition to switch contacts  140 ,  141  and  142 . Switching liquid  230  and insulating fluid  254  are disposed in tandem with switching liquid  130  and insulating fluid  154  in switching portion  222 . The length of switching liquid  230  and the length of switching liquid  130  in the switching portion  222  of cavity  220  are approximately equal. The length of insulating fluid  254  in switching portion  222  is approximately equal to the distance between switch contacts  140  and  242 .  
       FIG. 5C  shows switch  202  in the one of its switching states corresponding to the switching state shown in  FIG. 5A . Switching liquid  130  electrically contacts switch contacts  140  and  141 , switch contact  142  contacts insulating fluid  154 , switching liquid  230  electrically contacts switch contacts  240  and  241 , and switch contact  242  contacts insulating fluid  254 . In this switching state, switching liquid  130  electrically connects switch contact  140  to switch contact  141 , switch contact  142  is electrically isolated, switching liquid  230  electrically connects switch contact  240  to switch contact  241 , and switch contact  242  is electrically isolated.  
      In the switching state (not shown) of switch  202  corresponding to that shown in  FIG. 5B , switching liquid  130  contacts switch contacts  141  and  142 , switch contact  140  contacts insulating fluid  254 , switching liquid  230  contacts switch contacts  241  and  242 , and switch contact  240  is electrically isolated. In this switching state, switching liquid  130  electrically connects switch contact  141  to switch contact  142 , switch contact  140  is electrically isolated, switching liquid  230  electrically connects switch contact  241  to switch contact  242 , and switch contact  240  is electrically isolated.  
       FIGS. 6A and 6B  are cut-away plan views showing the internal structure of a third embodiment  300  of a metallic contact switch in accordance with the invention in each of its switching states. Switch  300  is a double-pole, double-throw switch. Elements of switch  300  that correspond to elements of the switches described above are indicated by the same reference numerals and will not be described again here.  
      Defined in second substrate  314  is cavity  320  having a switching portion  122 , an actuating portion  324  and a switching portion  322  arranged in tandem in the x-direction. Located in switching portion  122  is part of actuating liquid  152 , insulating fluid  154  and switching liquid  130  in an arrangement similar to that of actuating liquid  152 , insulating fluid  154  and switching liquid  130  in the switching portion  122  of cavity  120  described above with reference to  FIGS. 2A-2C . Actuating liquid  152  additionally fills actuating portion  324  of cavity  320  and part of switching portion  322 . Switching portion  322  additionally accommodates insulating fluid  354  and switching liquid  330  arranged in tandem in an arrangement that is a mirror image of the arrangement of insulating fluid  154  and switching liquid  130  in switching portion  322 .  
      Switch  300  has three switch contacts  140 ,  141  and  142  located on the major surface  313  of substrate  312 . Switch contacts  140 ,  141  and  142  are located in and extend from switching portion  122  of cavity  320  in a manner similar to that described above with reference to  FIG. 5A . Switch  300  additionally has three switch contacts  340 ,  341  and  342  located on major surface  313  of substrate  312 . Switch contacts  340 ,  341  and  342  are located in and extend from the switching portion  322  of cavity  320 . Switch contacts  340 ,  341  and  342  are arrayed in order in the −x-direction along the length of switching portion  322 . Switch contacts  340 ,  341  and  342  have a nominally uniform pitch as described above, but a functioning switch will be obtained even with some deviation from uniformity. All the switch contacts  140 - 142 ,  340 - 342  have the same pitch. In the example shown, switch contact  341  extends from switching portion  322  in the opposite direction to switch contacts  340  and  342 , but may alternatively extend from switching portion  322  in the same direction as switch contacts  340  and  342 .  
      The length of switching liquid  130  in switching portion  122  of cavity  320  is greater than the distance between switch contacts  140  and  141 , but less than the distance between the adjacent edges of switch contacts  140  and  142  as described above. The length of switching liquid  330  in switching portion  322  is greater than the distance between switch contacts  340  and  341 , but less than the distance between the adjacent edges of switch contacts  340  and  342 .  
       FIG. 6A  shows switch  300  in one of its switching states in which switching liquid  130  makes contact with switch contacts  140  and  141 , switch contact  142  contacts insulating fluid  154 , switching liquid  330  makes contact with switch contacts  340  and  341  and switch contact  342  is electrically isolated. Thus, switching liquid  130  electrically connects switch contact  140  to switch contact  141 , switch contact  142  is electrically isolated, switching liquid  330  electrically connects switch contact  340  to switch contact  341 , and switch contact  342  is electrically isolated.  
       FIG. 6B  shows switch  300  after a control current has passed from control electrode  160  to control electrode  162  to generate a motive force that has moved actuator liquid  152  in the +x-direction. Actuator liquid moving the +x-direction has moved moving element  358 , composed of switching liquid  130 , insulating fluid  154 , actuating liquid  152 , insulating fluid  354  and switching liquid  330 , in the +x-direction. Switching liquid  130  and switching liquid  330  have moved through a distance equal to the pitch of the switch contacts. The movement of moving element  358  puts switching liquid  130  in contact with switch contacts  141  and  142 , switching liquid  330  in contact with switch contacts  341  and  342  and insulating fluid  354  in contact with switch contact  340 . Thus, switching liquid  130  electrically connects switch contact  141  to switch contact  142 , switch contact  140  is electrically isolated, switching liquid  330  electrically connects switch contact  341  to switch contact  342 , and switch contact  340  is electrically isolated.  
      A double-pole, single-throw switch can be made based on the embodiment shown in  FIGS. 6A and 6B  by omitting switch contact  140  or switch contact  142  and by omitting switch contact  340  or switch contact  342 . The identity of the omitted switch contacts determines whether the poles of the switch are ON (or OFF) simultaneously or alternately. Similarly, double-pole, single-throw switch can be made based on the embodiment shown in  FIG. 5C  by omitting switch contact  140  or switch contact  142  and by omitting switch contact  240  or switch contact  242 . The identity of the omitted switch contacts determines whether the poles of the switch are ON (or OFF) simultaneously or alternately.  
       FIG. 7A  is a cut-away plan view showing the internal structure of a fourth embodiment  400  of a metallic contact switch in accordance with the invention one of its switching states. Elements of switch  400  that correspond to elements of the switches described above are indicated by the same reference numerals and will not be described again here. Switch  400  is a single-pole, single-throw switch in which Lorentz actuator  450  is configured to define the travel of actuating liquid  152  in the actuating portion  124  of cavity  120 . The defined travel of actuating liquid  152  in turn defines the travel of switching liquid  130  in the switching portion  122  of cavity  120  relative to switch contacts  140  and  141 . The other switch embodiments described herein may be similarly modified to incorporate a Lorentz actuator in which the actuating liquid has a defined travel.  
      In switch  400 , control electrodes  160 ,  462  and  464  are located in actuating portion  124  of cavity  120 . Control electrode  160  is located on one side of actuating portion  124  and, in the example shown, is elongate in the x-direction. Control electrodes  462  and  464  are located opposite control electrode  160  on the other side of actuating portion  124 , and are separated from one another in the x-direction and from control electrode  160  in the y-direction. Each of the control electrodes  462  and  464  is smaller in length than control electrode  160 . Alternatively, with proper positioning of control electrode  160 , electrodes  160 ,  462  and  464  may all be approximately equal in length.  
      Actuating liquid  152  occupies part of the length of the actuating portion  124  of cavity  120 . Insulating fluid  154  occupies part of the actuating portion  124  and part of the switching portion  122  of cavity  120  between actuating liquid  152  and switching liquid  130 .  
      Denote the desired travel of switching liquid  130  by t 1 , the cross-sectional area of the switching portion  122  of cavity  120  by A 1  and the cross-sectional area of the actuating portion  124  of cavity  120  by A 2 . To move switching liquid  130  a distance of t 1  requires that the travel t 2  of actuating liquid  152  be t 2 =t 1 ×A 1 /A 2 . The difference between the length l of actuating liquid  152  in actuating portion  124  and the distance d between adjacent edges of control electrodes  462  and  464  defines the travel t 2  of actuating liquid  152 , i.e., t 2 =l−d. Thus, difference between the length l of actuating liquid  152  and the distance d between adjacent edges of control electrodes  462  and  464  is given by: 
 
 l−d=t   1   ×A   1   /A   2 . 
 
       FIG. 7A  shows switch  400  in an exemplary initial switching state in which switching liquid  130  electrically connects switch contacts  140  and  141  and actuating liquid  152  is in electrical contact with control electrode  462  and control electrode  160 , but does not make electrical contact with control electrode  464 .  
       FIGS. 8A-8D  illustrate the operation of switch  400  starting at the exemplary initial switching state shown in  FIG. 7A . To change the switching state of switch  400  from the initial switching state shown in  FIG. 7A , a negative control voltage is applied between control electrode  160  (nominally ground) and control electrode  462 , as shown in  FIG. 8A . Consequently, a control current, represented by arrow  480 , flows in the −y-direction from control electrode  160  to control electrode  462 . Control current  480  and magnetic field B (see  FIG. 3A ) generate a motive force, represented by an arrow  481 , in the +x-direction. Motive force  481  moves actuating liquid  152  and, hence, moving element  158 , composed of actuating liquid  152 , insulating fluid  154  and switching liquid  130 , in the +x-direction. As a result of this motion, actuating liquid  152  moves into contact with control electrode  464  and switching liquid  130  moves out of contact with switch contact  140 . The loss of contact between switching liquid  130  and switch contact  140  breaks the electrical circuit between switch contacts  140  and  141 .  
      Further motion of actuating liquid  152  in the x-direction in response to motive force  481  causes the actuating liquid to break contact with control electrode  462 , as shown in  FIG. 8B . This stops the flow of the control current through the actuating liquid, and, as a result, Lorentz actuator  450  generates no more motive force. With no motive force applied, moving element  158  decelerates to a stop with actuating liquid  152  in contact with control electrodes  160  and  464  and switching liquid  130  in contact only with switch contact  141 . The control voltage is then removed from control electrode  462 .  
      Switch  400  remains in the switching state shown in  FIG. 8B  until a positive control voltage is applied between control electrode  160  (nominally ground) and control electrode  464 , as shown in  FIG. 8C . A control current, represented by arrow  482 , flows in the +y-direction from control electrode  464  to control electrode  160 . Control current  482  and magnetic field B (see  FIG. 3A ) generate a motive force, represented by an arrow  483 , in the −x-direction. Motive force  483  moves actuating liquid  152  and, hence, moving element  158 , in the −x-direction. As a result of this motion, actuating liquid  152  moves back into contact with control electrode  462  and switching liquid  130  moves into contact with switch contact  140 . The contact between switching liquid  130  and switch contact  140  re-establishes the electrical circuit between switch contacts  140  and  141 .  
      Further motion of actuating liquid  152  in the −x-direction in response to motive force  483  causes the actuating liquid to break contact with control electrode  464 , as shown in  FIG. 8D . This stops the flow of the control current through the actuating liquid, and, as a result, Lorentz actuator  450  generates no more motive force. With no motive force applied, moving element  158  decelerates to a stop with the actuating liquid in contact with control electrodes  160  and  462  and switching liquid  130  in contact with switch contact  140  and switch contact  141 . The control voltage is then removed from control electrode  160 . Switch  400  has returned to its exemplary initial switching state shown in  FIG. 7A .  
       FIG. 7B  is a cut-away plan view of a variation  402  on switch  400  shown in  FIG. 7A  in which the need for a bipolar control voltage is eliminated. In the embodiment shown in  FIG. 7B , control electrode  160  is replaced by a control electrode  460  located in actuating portion  124  opposite control electrode  462  and a control electrode  466  located in actuating portion  124  opposite control electrode  464 . Control electrodes  460  and  466  are typically mirror images of control electrodes  462  and  464 , respectively.  
      In operation, a control voltage is applied between control electrode  462  (nominally ground) and control electrode  460  (high) to generate a motive force in the +x-direction to change switch  402  from the switching state shown in  FIG. 7B  to a switching state similar to that shown in  FIG. 8B . In this switching state, the movement of actuating liquid  152  in the +x-direction breaks the electrical circuit shown in  FIG. 7B  between control electrodes  460  and  462  and establishes an electrical circuit between control electrodes  464  and  466 . Switch  402  is returned to its switching state shown in  FIG. 7B  by applying a control voltage between control electrode  466  (nominally ground) and control electrode  464  (high) to generate a motive force in the −x-direction. The motion of the actuating liquid in the −x-direction re-establishes the electrical circuit between control electrodes  460  and  462  and breaks the electrical circuit between control electrodes  464  and  466 .  
       FIGS. 9A and 9B  are cut-away plan views showing the internal structure of a fifth embodiment  500  of a metallic contact switch in accordance with the invention in each of its switching states. Switch  500  has a toroidal cavity.  FIG. 9C  is a cross-sectional view along the section line  9 C- 9 C in  FIG. 9A .  FIGS. 9D and 9E  are plan views of the first and second substrates, respectively, of switch  500 . The example of switch  500  shown is a double-pole, double-throw switch. Other examples have different numbers of poles and/or throws. Elements of switch  500  that correspond to elements of the switches described above with reference to  FIGS. 2A, 2B ,  5 A, SB,  6 A and  6 B are indicated by the same reference numerals and will not be described again here.  
      Switch  500  is composed of a housing  510  that defines a toroidal cavity  520 ;  
      conducting switching liquid  130  located in cavity  520 ; switch contacts  140 ,  141  and  142  located in cavity  520  in electrical contact with switching liquid  130  in at least one of the switching states of switch  500 ; and a Lorentz actuator  550  mechanically coupled to switching liquid  130  to change the switching state of the switch. Switching liquid  130  is located in a switching portion  522  of cavity  520 . Switch  500  also has conducting switching liquid  530  located in a switching portion  526  of cavity  520 , and switch contacts  540 ,  541  and  542  located in switching portion  526  of cavity  520  in electrical contact with switching liquid  530  in at least one of the switching states of switch  500 .  
      Lorentz actuator  550  is composed of conducting actuating liquid  152  located in an actuating portion  524  of cavity  520 , control electrodes  560  and  562  located in actuating portion  524  of cavity  520  in electrical contact with actuating liquid  152  and a magnet  570  located adjacent actuating portion  524  of cavity  520 . The actuating portion  524  of cavity  520 , control electrodes  560  and  562 , and magnet  570  are arranged such that the direction of current flow through actuating liquid  152  between control electrodes  560  and  562 , the direction of the magnetic field applied by magnet  570  to actuating liquid  152  and the resulting direction of motion of actuating liquid  152  in cavity  520  are mutually orthogonal.  
      In the example of Lorentz actuator  550  shown, control electrodes  560  and  562  are in electrical contact with actuating liquid  152  in one of the switching states of switch  500 . Lorentz actuator  550  additionally has opposed control electrodes  564  and  566  located in actuating portion  524  of cavity  520  in electrical contact with actuating liquid  152  in the other of the switching states of switch  500 . Together with control electrodes  560  and  562 , control electrodes  564  and  566  define the travel of actuating liquid  152 , and, hence, switching liquid portions  130  and  530 , in cavity  520  in a manner similar to that described above with reference to  FIG. 7B .  
      Insulating fluid portions  154  and  554  mechanically couple actuating liquid  152  of Lorentz actuator  550  to switching liquid  130  and switching liquid  530 , respectively. Additionally insulating fluid portion  556  mechanically couples switching liquid  130  and to switching liquid  530 .  
      In the example of switch  500  shown  FIGS. 9A-9C , housing  510  is composed of a first substrate  512  and a second substrate  514  bonded to first substrate  512 .  FIG. 9E  shows the major surface  515  of second substrate  514  that faces first substrate  512 . Toroidal cavity  520  extends into second substrate  514  from major surface  515 . Also shown in  FIG. 9E  are switching portion  522 , actuating portion  524  and switching portion  526  of cavity  520 . Switching portion  522 , actuating portion  524  and switching portion  526  are arranged in tandem. In the example shown, switching portion  522 , actuating portion  524  and switching portion  526  are simply circumferential regions of cavity  520  and do not differ from one another structurally. In other embodiments, switching portion  522 , actuating portion  524  and switching portion  526  differ from one another structurally. For example, in one embodiment, actuating portion  524  differs in cross-sectional area from switching portions  522  and  526 . In another embodiment, one or more of the portions of cavity  520  between switching portion  522 , actuating portion  524  and switching portion  526  differ in cross-sectional area from switching portion  522 , actuating portion  524  and switching portion  526  to impose specific dynamic switching properties on switch  500 .  
       FIG. 9E  also shows switching liquid  130 , actuating liquid  152  and switching liquid  530  located in switching portion  522 , actuating portion  524  and switching portion  526 , respectively, of cavity  520 , and insulating fluid portions  154 ,  556  and  554  occupying the portions of cavity  520  not occupied by switching liquid  130 , actuating liquid  152  and switching liquid  556 .  
       FIG. 9D  shows the major surface  513  of first substrate  512  that faces second substrate  514 . The positions on first substrate  512  of second substrate  514  and of toroidal cavity  520  in the second substrate are indicated in  FIG. 9D  by broken lines. Located on major surface  513  are three switch contacts  140 ,  141  and  142  located in and extending radially from the switching portion  522  of cavity  520 .  
      Additionally, three switch contacts  540 ,  541  and  542  are located on major surface  513  circumferentially offset in the clockwise direction from switch contacts  140 ,  141  and  142 . Switch contacts  540 - 542  are located in and extend radially from the switching portion  526  of cavity  520 . Switch contacts  140 - 142  are circumferentially arrayed in counterclockwise order along switching portion  522  and switch contacts  540 - 542  are circumferentially arrayed in counterclockwise order along switching portion  526 . Switch contacts  140 - 142  have nominally uniform angular separations, but a functioning switch will be obtained even with some deviation from uniformity. Switch contacts  540 - 542  have nominally uniform angular separations equal to those of switch contacts  140 - 142 , but a functioning switch will be obtained even with some deviation from uniformity and equality.  
      Referring additionally to  FIGS. 9A-9B , the circumferential distance between the ends of switching liquid  130  in the switching portion  522  of cavity  520  is greater than the circumferential distance between switch contacts  140  and  141 , but less than the circumferential distance between the adjacent edges of switch contacts  140  and  142 . The circumferential distance between the ends of switching liquid  530  in switching portion  526  is greater than the circumferential distance between switch contacts  540  and  541 , but less than the circumferential distance between the adjacent edges of switch contacts  540  and  542 .  
      Control electrodes  560 ,  562 ,  564  and  566  are also located on the major surface  513  of first substrate  512 . Control electrodes  560  and  562  are located radially opposite one another on opposite sides of the actuating portion  524  of cavity  520  and extend radially outwardly and inwardly, respectively, from the actuating portion. Control electrodes  566  and  564  are located radially opposite one another on opposite sides of the actuating portion  524  of cavity  520 , are circumferentially offset in the counterclockwise direction from control electrodes  560  and  562 , respectively, and extend radially outwardly and inwardly, respectively, from the actuating portion.  
      The angle through which the actuating liquid  152  of Lorentz actuator  550  rotates about the center  528  of toroidal cavity  520  is given by the difference between the angle subtended at center  528  by actuating liquid  152  and the angle subtended at center  528  by the adjacent edges of control electrodes  562  and  564 .  
       FIG. 9A  shows switch  500  in one of its switching states in which switching liquid  130  is in electrical contact with switch contacts  140  and  141 , and switch contact  142  contacts insulating fluid  154 , and switching liquid  530  is in electrical contact with switch contacts  540  and  541  and switch contact  542  contacts insulating fluid  556 . Thus, switching liquid  130  electrically connects switch contact  140  to switch contact  141 , switch contact  142  is electrically isolated, switching liquid  530  electrically connects switch contact  540  to switch contact  541 , and switch contact  542  is electrically isolated. Moreover, control electrodes  560  and  562  are in electrical contact with actuating liquid  152  whereas control electrodes  564  and  566  are in contact with insulating fluid  554 .  
       FIG. 9B  shows switch  500  after a control voltage has been applied between control electrode  560  and control electrode  562 . A control current flowing through actuating liquid  152  generates a motive force that moves actuating liquid  152  clockwise until the electrical contact between actuating liquid  152  and control electrodes  560  and  562  breaks. The counterclockwise motion of actuating liquid  152  moves moving element  558 , composed of actuating liquid  152 , insulating fluid  154 , switching liquid  130 , insulating fluid  556 , switching liquid  530  and insulating fluid  554 , counterclockwise through an angle about center  528  approximately equal to the angular pitch of the switch contacts. The movement of moving element  558  puts insulating fluid  556  in contact with switch contact  140 , switching liquid  130  in contact with switch contacts  141  and  142 , insulating fluid  554  in contact with switch contact  540  and switching liquid  530  in contact with switch contacts  541  and  542 . Thus, switch contact  140  is electrically isolated, switching liquid  130  electrically connects switch contact  141  to switch contact  142 , switch contact  540  is electrically isolated and switching liquid  530  electrically connects switch contact  541  to switch contact  542 . Finally, the counterclockwise movement of actuating liquid  152  puts actuating liquid  152  in contact with control electrodes  564  and  566 .  
      To return switch  500  to its switching state shown in  FIG. 9A , a control voltage is applied control electrodes  564  and  566 . The resulting control current flowing through actuating liquid  152  generates a motive force that moves actuating liquid  152  clockwise until the electrical contact between actuating liquid  152  and control electrodes  564  and  566  breaks. The clockwise motion of actuating liquid  152  moves moving element  558  clockwise through an angle about center  528  approximately equal to the angular pitch of the switch contacts. This restores switch  500  it its switching state described above with reference to  FIG. 9A .  
      A double-pole, single-throw switch can be made based on the double-pole-double-throw example shown in  FIGS. 9A and 9B  by omitting switch contact  140  or switch contact  142  and by omitting switch contact  540  or switch contact  542 . The identity of the omitted switch contacts determines whether the poles of the switch are ON (or OFF) simultaneously or alternately.  
      More poles can be incorporated into the switch  500  described above with reference to  FIGS. 9A and 9B  by increasing the number of portions of switching liquid in cavity  520 . The portions of switching liquid are circumferentially spaced from one another and from switching liquid  130 , switching liquid  530  and actuating liquid  152 . Portions of insulating fluid fill the portions of cavity  520  not occupied by the switching liquid portions and the actuating liquid. Additional sets of switch contacts are located on the major surface  513  of first substrate  512  in locations corresponding to the locations of the additional switching liquid portions.  
       FIGS. 10A and 10B  are cut-away views showing the internal structure of a sixth embodiment  600  of a metallic contact switch in accordance with the invention. In switch  600 , a Lorentz actuator is used to control the electrical continuity of a conducting switching liquid relative to a set of switch contacts. In this embodiment, the switch contacts remain in continuous electrical contact with the switching liquid. The Lorentz actuator generates an actuation force by passing a control current through a conducting actuating liquid located in a magnetic field. The control current is provided to the actuating liquid via opposed control electrodes.  
      Switch  600  is composed of a housing  610  that defines a cavity  620 ; conducting switching liquid  130  located in cavity  620 ; switch contacts  140 ,  141  and  142  located in cavity  620  in electrical contact with switching liquid  130  in both of the switching states of switch  600 ; and a Lorentz actuator  650  mechanically coupled to switching liquid  130  to change the switching state of the switch.  
      Cavity  620  is composed of a switching portion  622 , an actuating portion  624  and coupling portions  626  and  628 . Actuating portion  624  is substantially parallel to switching cavity  622  and is offset from switching cavity  622  in the y-direction. Coupling portions  626  and  628  extend from opposite ends of actuating portion  624  to switching portion  622  and join switching portion  622  at points offset from one another along the length of the switching portion.  
      Switching liquid  130  occupies most of switching portion  622  of cavity  620 . Actuating liquid  152  occupies actuating portion  624 , part of coupling portion  626  and part of coupling portion  628 . Insulating fluid  154  occupies the remainder of coupling portion  626  and, in the switching state shown in  FIG. 10A , the remainder of switching portion  622 . Insulating fluid  654  occupies the remainder of coupling portion  628 .  
      Switch contacts  140 ,  141  and  142  are located in and extend from switching portion  622  of cavity  620 . Switch contacts  140 ,  141  and  142  are arrayed in the x-direction along the length of switching portion  622  and are interleaved with coupling portions  626  and  628 . Switch contact  141  is located between coupling portions  626  and  628 , switch contact  140  is located in switching portion  622  on the opposite side of coupling portion  626  from switch contact  141  and switch contact  142  is located in switching portion  622  on the opposite side of coupling portion  628  from switch contact  141 .  
      Lorentz actuator  650  is composed of conducting actuating liquid  152  located in the actuating portion  624  of cavity  620 , opposed control electrodes  160  and  162  located in and extending from actuating portion  624  in electrical contact with actuating liquid  152  and a magnet  170  located adjacent actuating portion  624 . Actuating portion  624 , control electrodes  160  and  162 , and magnet  170  are arranged such that the direction of current flow through actuating liquid  152  between control electrodes  160  and  162 , the direction of the magnetic field applied by magnet  170  to actuating liquid  152  and the resulting direction of motion of actuating liquid  152  in actuating portion  624  are mutually orthogonal.  
      In the switching state of switch  600  shown in  FIG. 10A , insulating fluid  154  occupies part of switching portion  622  of cavity  620  in addition to part of coupling portion  626 . The portion of insulating fluid  154  occupying part of switching portion  622  divides switching liquid  130  into a switching liquid portion  632  in electrical contact only with switch contact  140  and a switching liquid  634  portion in electrical contact with switch contacts  141  and  142 . Thus, switching liquid portion  634  electrically connects switch contacts  141  and  142 , but insulating fluid  154  electrically insulates switch contact  140  from the other two switch contacts.  
       FIG. 10B  shows the switching state of switch  600  after a control voltage has been applied between control electrode  160  and control electrode  162 . The motive force generated by the interaction of the resulting control current passing through actuating liquid  152  and the magnetic field generated by magnet  170  moves actuating liquid  152  in the +x-direction. The movement of actuating liquid  152  in the +x-direction drives insulating fluid  654  through the coupling portion  628  of cavity  620  into switching portion  622 , where insulating fluid  654  divides switching liquid portion  634  into switching liquid portion  636  that remains in electrical contact only with switch contact  142  and a switching liquid portion that moves in the −x-direction in the switching portion  622  of cavity  620 . The moving switching liquid portion expels insulating fluid  154  from the switching portion, which allows the moving switching liquid portion to join with switching liquid portion  632  to form switching liquid portion  638 . Switching liquid portion  638  is in electrical contact with switch contacts  140  and  141 . Thus, switching liquid portion  638  electrically connects switch contacts  140  and  141 , but insulating fluid  654  electrically isolates switch contact  142  from the other two switch contacts.  
      To restore switch  600  to the switching state shown in  FIG. 10A , a control voltage is applied between control electrode  162  and control electrode  160 . The motive force generated by the interaction of the resulting control current passing through actuating liquid  152  and the magnetic field generated by magnet  170  moves actuating liquid  152  in the −x-direction. The movement of actuating liquid  152  in the −x-direction drives insulating fluid  154  through the coupling portion  626  of cavity  620  into switching portion  622 , where insulating fluid  154  divides switching liquid portion  638  into switching liquid portion  632  that remains in electrical contact only with switch contact  142 , as described above, and a switching liquid portion that moves in the +x-direction in the switching portion  622  of cavity  620 . The moving switching liquid portion expels insulating fluid  654  from the switching portion, which allows the moving switching liquid portion to join with switching liquid  636  to re-form switching liquid portion  634 , described above.  
      In a double-pole version (not shown) of switch  600 , cavity  620  has an additional switching portion with switch contacts arrayed along its length in an arrangement similar to that of switching portion  622  described above. The switch contacts are interleaved with two additional coupling portions that extend to the opposite ends of actuating portion  624 .  
      The switching states of the above-described metallic contact switch embodiments are metastable. Referring to  FIGS. 2A-2C , for example, when the control current stops flowing between the control electrodes  160  and  162  of Lorentz actuator  150 , moving element  158 , composed of switching liquid  130 , insulating fluid  154  and actuating liquid  152 , stops moving in cavity  120  and remains in the position to which it has moved until a control current flows once again. However, an external stimulus, such as a mechanical shock or vibration, can cause moving element  158  to move in the cavity. Sufficient movement of the moving element can result in an undesired change the switching state of the switch.  
       FIGS. 11A and 11B  are enlarged cut-away plan views showing part of a seventh embodiment  700  of a switch in which the structure of the cavity is modified to increase the stability of the switching states of the switch. The modified structure of the cavity reduces the ability of an external stimulus, such as a mechanical shock or vibration, to move the moving element in the cavity and, hence, to change the switching state of the switch. The modified cavity structure will be described with reference to the cavity of a single-pole, double-throw switch similar to that shown in  FIGS. 5A and 5B . The cavities of the other embodiments of the switch described herein may be similarly modified. Elements of the switch shown in  FIGS. 11A and 11B  that correspond to elements of the switches described above are indicated using the same reference numerals and will not be described again in detail.  
       FIGS. 11A and 11B  show the switching portion  722  of the cavity  720  of switch  700 . The remainder of switch  700  is not shown to simplify the drawing, but is similar to switch  200  described above with reference to  FIGS. 5A and 5B . Switch contacts  140 ,  141  and  142  are located in and extend from the switching portion  722  of cavity  720 . Switch contacts  140 ,  141  and  142  are arrayed in the x-direction along the length of switching portion  722  in a manner similar to that described above. Only the parts of switch contacts  140 ,  141  and  142  in and immediately adjacent switching portion  722  are shown to simplify the drawing.  
      Switching portion  722  has constrictions  780 ,  781 ,  782  and  783  arrayed in the x-direction along its length. Constrictions  780 - 783  are interleaved with switch contacts  140 - 142 . In each of constrictions  780 - 783 , the cross-sectional area of switching portion  722  is less than that of the remainder of switching portion  722 , e.g., less than that of the part of switching portion in which switch contact  140  is located. Constrictions  780  and  782  are separated in the x-direction and constrictions  781  and  783  are separated in the x-direction by respective distances approximately equal to, but not less than, the length of switching liquid  130  in switching portion  722 .  
      In the switching state shown in  FIG. 11A , the moving element composed of switching liquid  130 , insulating fluid  154  and actuating liquid  152  is free to move over a short distance in both the +x- and −x-directions. Electrical contact between switching liquid  130  and switch electrodes  140  and  141  is maintained over this range of movement. However, as the moving element moves further in the −x-direction, before switching liquid  130  loses contact with switch contact  141 , the end surface  131  of switching liquid  130  encounters constriction  780 . The encounter decreases the radius of curvature of end surface  131 , which generates a force in the +x-direction. The force resists further motion of the moving element in the −x-direction, and helps maintain contact between switching liquid  130  and switch contact  141 . Additionally, the end surface  153  of actuating liquid  152  encountering constriction  783  generates a force with a component in the +x-direction that additionally resists movement of the moving element in the −x-direction.  
      As the moving element moves in the +x-direction, before switching liquid  130  loses contact with switch contact  140 , the end surface  133  of switching liquid  130  encounters constriction  782 . The resulting decrease in the radius of curvature of end surface  133  generates a force in the −x-direction. The force resists further motion of the moving element in the +x-direction, and helps maintain contact between switching liquid  130  and switch contact  140 .  
       FIG. 11B  shows switch  700  in its other switching state. The Lorentz actuator (not shown) of switch  700  generates a substantially greater motive force in the x-direction than the Lorentz actuator of switch  200  described above with reference to  FIGS. 5A and 5B . The additional motive force is needed to drive the end surface  133  of switching liquid  130  through constriction  782  and to drive the end surface  131  of the switching liquid through constriction  781 . Once switch  700  is in its switching state shown in  FIG. 11B , interaction between the end surface  131  of switching liquid  130  and constriction  781  resists motion of the moving element in the +x-direction and helps maintain contact between the switching liquid and switch contact  141 . Moreover, interaction between the end surface  133  of switching liquid  130  and constriction  783  resists motion of the moving element in the −x-direction and helps maintain contact between the switching liquid and switch contact  142 .  
      Also shown in  FIGS. 11A and 11B  is an optional constriction  784  in switching portion  722 . Constriction  784  is offset in the +x-direction relative to adjacent constriction  783 . Interaction between the end surface  153  of actuating liquid  152  and constriction  784  resists further motion of the actuating liquid in the −x-direction, and, hence, helps maintain contact between switching liquid  130  and switch contact  142  in the switching state shown in  FIG. 11B .  
      Additional constrictions (not shown) may be located in the actuating portion (not shown) of cavity  720  to control the positioning of actuating liquid  152  in the actuating portion. Moreover, in embodiments with more than one switching portion, additional constrictions may be located in each switching portion.  
       FIG. 11C  is an enlarged cut-away plan view showing an alternative switching portion  723  of the cavity  720  of switch  700  that increases the stability of the switching states of the switch. Alternative switching portion  723  reduces the ability of an external stimulus, such as a mechanical shock or vibration, to move the moving element lengthways in the cavity and, hence, to change the switching state of the switch. The alternative switching portion will be described with reference to the cavity of a single-pole, double-throw switch similar to that shown in  FIGS. 5A and 5B . The cavities of the other embodiments of the switch described herein may be similarly modified.  
      Switching portion  723  has an internal wall comprising alternate regions having a low wettability and a high wettability with respect to switching liquid  130 . In this disclosure, the terms high wettability and low wettability are used in a relative rather than an absolute sense. Thus, a material having a low wettability with respect to the switching liquid has a lower wettability with respect to the switching liquid and a material having a high wettability with respect to the switching liquid, and a material having a high wettability with respect to the switching liquid has a higher wettability with respect to the switching liquid and a material having a low wettability with respect to the switching liquid. In the example shown, switching portion  723  is defined in second substrate  114  ( FIG. 2A , for example) with its internal wall  725  of a material having a high wettability with respect to switching liquid  130 . Arrayed along switching portion  723  are bands  785 ,  786 ,  787  and  788  of a material having a low wettability with respect to switching liquid  130 . Bands  785 - 788  are interleaved with switch contacts  140 - 142 . Bands  785  and  787  are separated in the x-direction and bands  786  and  788  are separated in the x-direction by a distance approximately equal to, but not less than, the length of switching liquid  130  in switching portion  723 .  
      In an embodiment in which switching liquid  130  is mercury, metals have a high wettability with respect to mercury and typical substrate materials have a low wettability with respect to mercury. However many metals form amalgams with mercury. In an exemplary embodiment, the material of second substrate  114  has a low wettability with respect to mercury, and the wall  725  of the switching portion  722  of cavity  720  outside bands  785 ,  786 ,  787  and  788  is coated with a high wettability material, and the substrate material is exposed in bands  785 ,  786 ,  787  and  788 . In an exemplary embodiment, the wall outside bands  785 ,  786 ,  787  and  788  is coated with an adhesion layer of chromium (Cr) and a layer of a metal such as platinum (Pt) or iron (Fe) that is not dissolved by mercury to form an amalgam. In an alternative embodiment, the high-wettability material is rhodium (Rh). In embodiments in which the material of second substrate  114  has a relatively high wettability with respect to switching liquid  130 , or in embodiments in which an especially high wettability contrast between the regions of low wettability and high wettability is desired, wall  725  is coated in bands  785 ,  786 ,  787  and  788  with a material having a low wettability with respect to the switching liquid. Glass and many plastics have a low wettability with respect to mercury.  
      In the switching state shown in  FIG. 11C , the moving element composed of switching liquid  130 , insulating fluid  154  and actuating liquid  152  is free to move over a short distance in both the +x- and −x-directions in contact with switch electrodes  140  and  141 . Electrical contact between switching liquid  130  and switch electrodes  140  and  141  is maintained over this range of movement. The end surface  131  of switching liquid  130  is in contact with wall  725  of high wettability material and therefore has a relatively large radius of curvature. However, as the moving element moves further in the −x-direction, before switching liquid  130  loses contact with switch contact  141 , the end surface  131  of switching liquid  130  encounters band  785  of low wettability material. The encounter decreases the radius of curvature of end surface  131 , which generates a force in the +x-direction. This force resists further motion of the moving element in the −x-direction, and helps maintain contact between switching liquid  130  and switch contact  141 .  
      As the moving element moves in the +x-direction, before switching liquid  130  loses contact with switch contact  140 , the end surface  133  of switching liquid  130  encounters band  787  of low wettability material. The resulting decrease in the radius of curvature of end surface  133  generates a force in the −x-direction. The force resists further motion of the moving element in the +x-direction, and helps maintain contact between switching liquid  130  and switch contact  140 .  
      In an embodiment in which band  788  additionally has a low wettability with respect to actuating liquid  152 , the decrease in the radius of curvature of the end surface  153  of actuating liquid  152  resulting from end surface  153  encountering band  788  generates a force in the +x-direction that additionally resists movement of the moving element in the −x-direction in the switching state shown in  FIG. 11C .  
      In the other switching state (not shown) of embodiment of switch  700  shown in  FIG. 11C , interaction between the end surface  131  of switching liquid  130  and band  786  of low wettability material resists motion of switching liquid  130  in the +x-direction, and interaction between end surface  133  and band  788  resists motion of switching liquid  130  in the −x-direction.  
      Also shown in  FIG. 11C  is an optional band  789  of a material having a low wettability with respect to actuating liquid  152 . Band  789  is located in the +x-direction relative to adjacent band  788 . Interaction between the end surface  153  of actuating liquid  152  and band  789  resists motion of actuating liquid  152  in the −x-direction, and, hence, helps maintain contact between switching liquid  130  and switch contact  142  in the other switching state.  
      Additional bands (not shown) of low-wettability material may be located in the actuating portion (not shown) of cavity  720  to control the positioning of actuating liquid  152  in the actuating portion. Moreover, a combination of the bands of low-wettability material shown in  FIG. 11C  and the constrictions shown in  FIGS. 11A and 11B  may be used in combination to control the position of the moving element in the cavity.  
      As an alternative to defining alternate regions having a low wettability and a high wettability with respect to switching liquid  130  by means of bands  785 - 780  of low-wettability material applied to a substrate of high-wettability material as shown in  FIG. 11C , the material of substrate  114  may have a low wettability with respect to switching liquid  130 . In this case, the wall  725  of switching portion  723  is covered in regions corresponding to those between the bands  785 - 788  shown in  FIG. 11C  with bands of a material having a high wettability with respect to switching liquid  130 . Such bands are shaped to expose switch contacts  140 - 142  to switching liquid  130 .  
      The structures described above with reference to  FIGS. 11A-11C  also serve to define the positions in which switching liquid stops relative to switch contacts  140  and  141  and relative to switch contacts  141  and  142  when the switching state of switch  700  is changed.  
       FIGS. 12A and 12B  are respectively a plan view and a cross-sectional view of an eighth embodiment  800  of a metallic contact switch in accordance with the invention in which the magnitude of the control current needed for the Lorentz actuator to generate a given motive force is reduced. Switch  800  will be described with reference to a single-pole, single-throw switch similar to that described above with reference to  FIGS. 2A-2B . Elements of switch  800  that correspond to elements of the switch described above with reference to  FIGS. 2A-2C  are indicated by the same reference numerals and will not be described again here. Lorentz actuators similar to those to be described next may be incorporated into the other embodiments of the switch described herein.  
      In the Lorentz actuator  850  of switch  800 , a magnet assembly  870  incorporating magnet  170  applies the magnetic field to actuating liquid  152 . For a given strength of magnet  170 , magnet assembly  870  applies a substantially greater magnetic field to actuating liquid  152  than the arrangement described with reference to  FIGS. 2A-2C  in which the magnetic field is applied by magnet  170  affixed to second substrate  114  adjacent the actuating portion of the cavity.  
      Magnet assembly  870  is composed of magnet  170  and ferromagnetic pole pieces  874  and  876 . Magnet  170  is located adjacent one side of housing  110  with its polar axis orthogonal to the major surface  113  of first substrate  112 . Pole piece  874  extends across second substrate  114  from magnet  170  to the region of substrate  114  in which the actuation portion  124  of cavity  120  is defined. The locations of cavity  120 , and, in particular, the actuation portion  124  thereof, relative to pole piece  874  are shown by broken lines in  FIG. 12A .  
      Referring now to  FIG. 12B , pole piece  876  extends across first substrate  112  from magnet  170  to the region of substrate  112  aligned with the actuation portion  124  of cavity  120  defined in substrate  114 . The locations of cavity  120 , and, in particular, the actuation portion  124  thereof, relative to pole pieces  874  and  876  are shown in  FIG. 12B . In switch  800 , actuating liquid  152  is located in the high-intensity magnetic field that exists in a gap in the magnetic circuit formed by magnet  170  and pole pieces  874  and  876 .  
       FIG. 12C  is a cross-sectional view showing a variation  802  on switching device  800  in which first substrate  812  defines a recess  816  that accommodates pole piece  876 . Pole piece  876  extends from magnet  170  to the region of substrate  812  aligned with the actuation portion  124  of cavity  820  defined in second substrate  114 . The location of cavity  120 , and, in particular, actuation portion  124 , relative to pole pieces  874  and  876  is shown in  FIG. 12C . Locating pole piece  876  in recess  816  in first substrate  812  reduces the distance between pole pieces  874  and  876 , which increases the strength of the magnetic field in the gap in the magnetic circuit in which actuating liquid  152  is located.  
       FIGS. 13A, 13B  and  13 C are respectively two cut-away plan views and a cross-sectional view of a ninth embodiment  900  of a metallic contact switch in accordance with the invention in which the magnitude of the control current needed for the Lorentz actuator to generate a given motive force is further reduced, and which the resistance of the Lorentz actuator is increased.  FIGS. 13D and 13E  are plan views of the first and second substrates, respectively, of switch  900 . Switch  900  will be described with reference to a single-pole, double-throw switch similar to that shown in  FIGS. 5A and 5B . Elements of switch  900  that correspond to elements of the switches described above are indicated by the same reference numerals and will not be described again here. Lorentz actuators similar to that to be described next may be incorporated into the other embodiments of the switch described herein.  
      In switch  900 , cavity  920  is composed of a switching portion  122  and an actuating portion  924  in tandem in an arrangement similar to that described above. The length of actuating portion  924  is increased to accommodate part of insulating fluid  154 , switching liquid  152 , insulating fluid  954  and switching liquid  952  arranged in tandem in order in the x-direction. Additionally located in actuating portion  924  are opposed control electrodes  960  and  964  in electrical contact with switching liquid  152  and opposed control electrodes  966  and  962  in electrical contact with switching liquid  952 . Control electrodes  960  and  962  extend from switching portion  924  to allow them to be connected to a control circuit (not shown). Control electrodes  964  and  966  are internally connected in series by a trace  961  ( FIG. 13D ) that extends across actuating portion  924  in the y-direction. Trace  961  is insulated from switching liquid portions  152  and  952  located in actuating portion  924 . Alternatively, control electrodes  964  and  966  are similar in shape to control electrodes  960  and  962  and are externally connected in series.  
      Magnet  970  is shaped to apply a magnetic field to actuating liquid  152  and actuating liquid  952  over their full range of travel in the actuating portion  924  of cavity  920 . Alternatively, separate magnets may be used to apply respective magnetic fields to switching liquid  152  and switching liquid  952 . As a further alternative, an arrangement of pole pieces similar to that described above with reference to  FIGS. 12A-12C  may be used to apply a magnetic field to actuating liquid  152  and actuating liquid  952  collectively or individually.  
      Insulating fluid  954  mechanically couples the motive force generated by passing a control current through switching liquid  952  to the motive force generated by additionally passing the control current through switching liquid  152 . Thus, each of the actuating liquids  152  and  952  need generate only one-half of the motive force that Lorentz actuator  950  is required to generate to move moving element  958 , composed of switching liquid  130 , insulating fluid  154 , actuating liquid  152 , insulating fluid  954  and actuating liquid  952 , in the +x- or −x-direction. The additional mass of insulating fluid  954  and actuating liquid  952  is less than that of switching liquid  130 , insulating fluid  154  and actuating liquid  152 , so that the control current through each of actuating liquid  152  and actuating liquid  952  is less than of a Lorentz actuator such as that shown in  FIGS. 2A-2C  having a single portion of actuating liquid. Control electrodes  964  and  966  are connected in series, so that a control voltage applied between control electrodes  960  and  962  or vice versa causes the same control current to pass through both actuating liquid  152  and actuating liquid  952 .  
      Lorentz actuators have a low electrical resistance: electrically connecting two Lorentz actuators in series as just described provides a Lorentz actuator with an increased electrical resistance that has a better impedance match with a typical control circuit.  
      The cross-sectional view of  FIG. 13C  shows details of the internal series connection between electrodes  964  and  966  ( FIG. 13A ). First substrate  913  is composed of a base  916  having electrically-conducting trace  961  located on its major surface. The remainder of the major surface of the base is covered by a planarizing layer  917 . A layer  918  of an electrically-insulating material covers the planarizing layer and the trace. Switch contacts  140 - 142  and control electrodes  960 ,  962 ,  964  and  966  are located on the major surface of insulating layer  918 . Referring additionally to  FIG. 13D , apertures in insulating layer  918  at both ends of trace  961  accommodate vias  963  and  965  electrically connected to the trace. Control electrode  964  is electrically connected to the end of via  963  remote from trace  961 . Control electrode  966  is electrically connected to the end of via  966  remote from trace  961 . Thus, vias  963  and  965  and trace  961  form an circuit that electrically connects control electrode  964  to control electrode  966 .  
      In the example shown in  FIGS. 13A-13C , two portions of actuating liquid and respective pairs of opposed control electrodes are located in actuating portion  924 . In other embodiments, the number of portions of actuating liquid and respective opposed electrodes located in actuating portion  924  is greater than two. Additional traces, similar to trace  961 , are provided to connect the electrodes contacting the portions of actuating liquid in series. Moreover, in further embodiments, the travel of the moving element of the Lorentz actuator is defined in a manner similar to that described above with reference to  FIG. 7B . In such embodiments, two pair of opposed electrodes, are located to make contact with each portion of actuating liquid in actuating portion  924 . The electrodes for imparting forward motion and those for imparting reverse motion are separately connected in series. In embodiments in which the series connections are internal, traces similar to trace  961  are provided at different levels in substrate  912  to provide the forward and reverse interconnections, respectively.  
      Fabrication of an embodiment of a switch in accordance with the invention will be described next with reference to an exemplary fabrication of switch  100  described above with reference to  FIGS. 2A-2C ,  3 A,  3 B,  4 A and  4 B. Fabrication of the other embodiments described herein is similar.  
      Although embodiments of a metallic contact switch in accordance with the invention can be individually fabricated, the switches are typically fabricated by wafer-scale processing in which wafers containing the respective substrates of hundreds or thousands of switches are processed and assembled. The assembled wafers are then singulated into individual switches or are divided into small arrays of switches.  
      Switch  100  is fabricated as follows. Referring first to  FIG. 4A , a first wafer of which first substrate  112  forms part is provided. Examples of suitable materials for the first wafer are silicon, glass, ceramic and plastic. A metal substrate with an insulating layer on its major surface may alternatively be used. The switch contacts  140  and  141  and the control electrodes  160  and  162  of each switch are defined in a conducting material on one major surface of the first wafer. In an embodiment, a conducting layer, such as a layer of Pt or Fe, is deposited on the major surface of the wafer of which substrate  112  forms part. The conducting layer is patterned by etching or a lift-off process to define switch contacts  140  and  141  and control electrodes  160  and  162 . In other embodiments, the switch contacts and control electrodes are deposited on the major surface of the wafer by such processes as screen printing and lamination. In some embodiments, the switch contacts and the control electrodes are of different materials.  
      In some embodiments, either or both of the switch contacts  140  and  141  and the control electrodes  160  and  162  are composed of layers of more than one material. In an example, the switch contacts and control electrodes are composed of a thin adhesion layer, a thick conduction layer of a high-conductivity material, and a thin contact layer of a material having a relatively high wettability with respect to switching liquid  130  and actuating liquid  152 . Additionally, the material of the contact layer is one that is insoluble in, and is not otherwise eroded by, the switching liquid and the actuating liquid. For example, the material of the adhesion layer is titanium, the material of the conduction layer is gold and the material of the contact layer is rhodium. In another example, the adhesion layer is chromium and a combined conduction layer and contact layer is platinum, rhodium or iron.  
      The first wafer may optionally be subject to processing similar to that to be described below to define at least part of cavity  120  therein.  
      Referring now to  FIG. 4B , a second wafer of which second substrate  114  forms part is provided. Examples of suitable materials for the second wafer are silicon, glass, ceramic and plastic. The second wafer is processed to define the shapes of the individual second substrates. The second substrates are shaped to expose the bonding pads that form part of the switch contacts and control electrodes in the assembled switch. Exemplary processes that can be used to define the shapes of the individual second substrates are selective etching or selective ablation applied to a silicon, glass or fired ceramic second wafer, and molding applied to a green ceramic or plastic second wafer. Prior to the shape-defining processing, the second wafer may be attached to a handle wafer to maintain its structural integrity during subsequent processing.  
      As part of the shape-defining processing or separately, the cavity  120  of each switching device  100  is defined in the second wafer. Processes similar to those described above for shape defining or other processes may be used. In embodiments, in which cavity  120  is wholly defined in first substrate  112 , the processing of the second wafer to define cavity  120  is omitted.  
      The second wafer of which second substrate  114  forms part is oriented with the major surface  115  of substrate  114  facing up. A measured quantity of switching liquid  130  is placed in the switching portion  122  of the cavity  120  of each second substrate and a measured portion of actuating liquid  152  is placed in the actuating portion  124  of the cavity of each second substrate. In embodiments in which the insulating fluid is a liquid, a measured quantity of insulating fluid  154  is placed in the cavity  120  of each second substrate between the switching liquid and the actuating liquid. Techniques for dispensing measured quantities of liquid metals are described by Fazzio in U.S. patent application Ser. No. 10/826,249, filed on 16 Apr. 2004, entitled Liquid Metal Processing and Dispensing for Liquid Metal Devices, assigned to the assignee of this disclosure and incorporated herein by reference. Materials useable as the switching liquid and the actuating liquid include mercury (Hg), gallium (Ga), an alloy comprising gallium and indium, an alloy comprising gallium, indium and tin, and a slurry of conducting particles in a carrier liquid. Materials useable as the insulating fluid include a gas, an inert gas, nitrogen (N 2 ), argon (Ar), a liquid, a low-viscosity liquid, methanol (CH 3 OH), ethanol (C 2 H 5 OH) and a transformer oil.  
      The major surface of the second wafer of which second substrate  114  forms part is coated with a thin layer of a bonding material, such as an adhesive. The first wafer of which substrate  112  forms part is then inverted and is placed on the second wafer in the appropriate alignment. The first and second wafers typically carry reference marks to ensure the accuracy of the alignment between the wafers. The bonding material is then cured to bond the wafers together. The assembled wafers are then singulated into individual switches. The switches may be tested prior to singulation.  
      In some embodiments, the first wafer of which first substrate  112  forms part is attached to the second wafer of which second substrate  114  forms part in vacuo, or at least under reduced pressure, to avoid Lorentz actuator  150  having to compress air trapped at the end of the switching portion  122  of cavity  120  remote from actuating portion  124  and at the end of actuating portion  124  remote from switching portion  122  during operation of switch  100 . In embodiments in which insulating fluid  154  is a gas, the first wafer is attached to the second wafer in an atmosphere of the insulating fluid. In such embodiments, insulating fluid is additionally located at the remote ends of switching portion  122  and actuating portion  124  of cavity  120 , and cavity  120  typically incorporates a pressure equalizing portion  126  as shown in  FIG. 4B .  
      This disclosure describes the invention in detail using illustrative embodiments. However, the invention defined by the appended claims is not limited to the precise embodiments described.