Micro-electromechanical system power relay

Abstract

The power relay has an actuator comprising a micro-electromechanical system stator assembly and a plunger assembly that moves along a central longitudinal axis between a first position and a second position, the plunger assembly comprising a plunger including a pair of ferromagnetic plates between which a magnet is located, the first of the pair of ferromagnetic plates being located between a first ferromagnetic layer and a second ferromagnetic layer of the stator assembly, and the second of the pair of ferromagnetic plates being located between a second ferromagnetic layer and a third ferromagnetic layer of the stator assembly. The contacts formed by the ferromagnetic plates and ferromagnetic layers may include an array of micro-machined bends or stabilized liquid-solid electrical contacts.

Description

[Technical Field]

[0001] background Technical field This disclosure relates to a device for managing power, and more specifically to a power relay constructed with a micro-electromechanical (MEMS) structure. [Background technology]

[0002] Explanation of related technologies Controlling electricity is crucial in many areas of today's electrified world. Smarter power grids can enable utilities to manage power very locally, allowing power providers or customers to switch off selected devices during peak demand. This can allow suppliers to avoid deploying rolling blackouts to prevent grid failures. Instead, high-current loads such as washing machines and air conditioners can be disabled until the peak load subsides.

[0003] To provide this level of control, utility companies require remotely addressable switches in the form of relays. Existing relays are large and inefficient, generating sufficient heat at the required current level, which necessitates large heat sinks. Thus, these relays are too large to fit into existing circuit breakers, requiring upgrades to load centers to support their installation. To address this problem, small, low-contact-resistance relays are needed.

[0004] Another application of such small relays lies in data processing centers, which may house hundreds of thousands of servers. Operators require the ability to remotely cycle power on each server individually, and / or provide this capability (as a cloud service). Power distribution units (PDUs) used for this purpose often have individual circuit breakers and separate relays for each outlet. By moving the relays within the circuit breakers (only possible with very small relays that do not require heat sinks for the required current levels) and shrinking the circuit breakers, PDUs can be significantly reduced in size, which is an important metric for high-density, modern data centers. [Overview of the Initiative] [Means for solving the problem]

[0005] Brief Overview This disclosure relates to a power relay constructed using a micro-electromechanical (MEMS) structure. The relay utilizes three novel MEMS structures individually or in combination thereof.

[0006] According to one aspect of the present disclosure, a power relay is provided that utilizes an actuator having a stator assembly having a chamber that penetrates and is partially defined along a central longitudinal axis, the stator assembly comprising a nonconductive substrate having a top surface, one or more layers comprising components with which a load mechanically or electrically interacts, a first ferromagnetic layer adjacent to a spacer, a first plurality of coils adjacent to the first ferromagnetic layer, a second ferromagnetic layer adjacent to the first plurality of coils, a second plurality of coils adjacent to the second ferromagnetic layer, and a third ferromagnetic layer adjacent to the second plurality of coils, the bottom surface of the third ferromagnetic layer defining the upper end of the chamber.

[0007] The power relay is located within a chamber of the stator assembly and further includes a plunger assembly that, when in operation, moves along a central longitudinal axis between a first position and a second position, the plunger assembly including a plunger which includes a pair of ferromagnetic plates in which a magnet is located. The first ferromagnetic plate of the pair of ferromagnetic plates is located between the first and second ferromagnetic layers of the stator assembly, and (ii) the second ferromagnetic plate of the pair of ferromagnetic plates is located between the second and third ferromagnetic layers of the stator assembly.

[0008] According to another aspect of the present disclosure, the power relay described above utilizes contacts, the contacts comprising, in a first alternative embodiment, a first contact member having an exposed surface, the exposed surface having irregularities forming one or more high and low points on the exposed surface, and a second contact member having a contact surface and a plurality of conductive bends extending from the contact surface, wherein the first contact member and the second contact member are movable relative to each other to provide distinct open and closed positions, and further, when the first contact member is positioned adjacent to the second contact member in a closed position in which the contact surface of the second contact member is not electrically in contact with one or more high points on the exposed surface of the first contact member, each bend of the plurality of conductive bends is electrically in contact with the exposed surface of the first contact member.

[0009] According to another embodiment of the contacts of the present disclosure, all of the plurality of conductive bends extending from the contact surface of the second contact member have the same height above the contact surface of the first contact member, and the height is greater than the sum of the first distance between the high and low points on the exposed surface of the first contact member and the separation distance between the exposed surface of the first contact member and the high points on the contact surface of the second contact member when the first contact member is in the closed position.

[0010] Alternatively, according to a further aspect of the present disclosure, the power relay having the actuator described above includes a contact, the contact being a first contact member having a base having an exposed surface, the base having a first pocket opening to the exposed surface, the first pocket having an external side wall and a bottom wall defining the interior of the first pocket; a first metal layer on the bottom wall of the first pocket having an upper surface below the exposed surface of the first contact member; a liquid metal layer having only the upper surface of the first metal layer and extending above the exposed surface of the first contact member; and a second contact member having a contact surface, the second contact member being positioned adjacent to the first contact member in an open position, and movable to a closed position such that the contact surface of the second contact member contacts and compresses the liquid metal layer and the first metal layer until the contact surface of the second contact member abuts the exposed surface of the first contact member.

[0011] According to another embodiment of the power relay contact described above, the contact includes a second pocket formed on the exposed surface of a first contact member, the second pocket having a bottom wall that is tangent to the first pocket and is below the exposed surface of the first contact member and above the bottom wall of the first pocket, the second pocket further comprising tangent side walls and a bottom wall that define the interior of the second pocket, a portion of the interior of the second pocket overlapping with the interior of the first pocket.

[0012] According to a further embodiment of the aforementioned contact of the present disclosure, the liquid metal layer is formed from a compliant material that is displaced by pressure applied by a second contact member in a closed position and returns to its original shape in response to the second contact member moving to an open position.

[0013] In yet another aspect of the present disclosure, a power relay is provided which includes the actuator described above in combination with a contact, the contact comprising a first contact member having an exposed surface, the exposed surface having irregularities forming one or more high and low points on the exposed surface, and a second contact member having a contact surface and a plurality of conductive bends extending from the contact surface, wherein the first contact member and the second contact member are movable relative to each other to provide distinct open and closed positions, and further, when the first contact member is positioned adjacent to the second contact member in a closed position in which the contact surface of the second contact member is not electrically in contact with one or more high points on the exposed surface of the first contact member, each bend of the plurality of conductive bends is electrically in contact with the exposed surface of the first contact member.

[0014] A further aspect of the present disclosure provides a power relay including the actuator described above in combination with a contact, the contact comprising: a first contact member having a base having an exposed surface, the base having a first pocket opening to the exposed surface, the first pocket having an external side wall and a bottom wall defining the interior of the first pocket; a first metal layer on the bottom wall of the first pocket, the first metal layer having an upper surface below the exposed surface of the first contact member; a liquid metal layer having only the upper surface of the first metal layer and extending above the exposed surface of the first contact member; and a second contact member having a contact surface, the second contact member being positioned adjacent to the first contact member in an open position, and movable to a closed position in which the contact surface of the second contact member contacts and compresses the liquid metal layer and the first metal layer until the contact surface of the second contact member abuts the exposed surface of the first contact member.

[0015] According to another aspect of the power relay contact described above, the contact includes a second pocket formed on the exposed surface of the first contact member. The second pocket circumscribes the first pocket and has a bottom wall that is below the exposed surface of the first contact member and above the bottom wall of the first pocket. The second pocket further includes a circumferential side wall and a bottom wall that define the interior of the second pocket, and a portion of the interior of the second pocket overlaps with the interior of the first pocket.

[0016] According to a further aspect of the contacts described above of the present disclosure, the liquid metal layer is formed from a compliant material that is displaced by the pressure applied by the second contact member in the closed position and returns to its original shape in response to the second contact member moving to the open position.

[0017] According to a further aspect of the contacts described above of the present disclosure, the first metal layer and the liquid metal layer may be placed directly on the upper flat surface of the first contact member without the presence of the first or second pocket.

Brief Description of the Drawings

[0018] Brief Description of Some of the Drawings The foregoing and other features and advantages of the present disclosure will be better understood and will be more readily understood from the following detailed description in conjunction with the accompanying drawings.

[0019] [Figure 1] FIG. 1 includes a schematic diagram of a solenoid or actuator having a conventional electromagnetic form.

[0020] [[ID=2B]] ) [Figure 2A] FIG. 2A includes a cross-sectional view of various layers of an actuator according to various embodiments of the present disclosure.

[0021] [Figure 2B]Figures 2B and 2C show how the various layers of the electromechanical actuator shown in Figure 2A generally correspond to one of two "stacks", namely a static stack (also called a "stator assembly") or an actuatable stack (also called a "rotor assembly" or a "plunger assembly"). [Figure 2C] Figures 2B and 2C show how the various layers of the electromechanical actuator shown in Figure 2A generally correspond to one of two "stacks", namely a static stack (also called a "stator assembly") or an actuatable stack (also called a "rotor assembly" or a "plunger assembly").

[0022] [Figure 3] Figure 3 includes a schematic diagram of the latching behavior of the electromechanical actuator caused by the magnetic circuit in the "open position" and the "closed position".

[0023] [Figure 4] Figure 4 includes a schematic diagram showing how passing a current through the coil results in a substantially constant magnetic force applied to the plunger.

[0024] [Figure 5-1] Figures 5A - 5E show the magnetic flux within the plunger assembly moving from a first position to a second position and then back to the first position.<​​​​​​​​​​​​​Figure 7 includes schematic cross-sectional views of the plunger assembly, contact assembly, and stator assembly.

[0027] [Figure 8] Figure 8 includes a cross-sectional view of the electromechanical actuator, as well as a schematic diagram of possible assembly sequences.

[0028] [Figure 9] Figure 9 includes a high-level diagram of the process for manufacturing an electromechanical actuator.

[0029] [Figure 10] Figures 10A and 10B are diagrams of contact arrays formed in accordance with this disclosure.

[0030] [Figure 11] Figures 11A and 11B illustrate the operation of a conventional contact.

[0031] [Figure 12] Figures 12A and 12B illustrate, respectively, the construction and operation of the contacts using the contact array of Figure 10B according to this disclosure.

[0032] [Figure 13] Figure 13 shows an array of bent portions formed according to this disclosure.

[0033] [Figure 14] Figure 14 shows an array of the bends in Figure 13, including the external hardstop feature according to this disclosure.

[0034] [Figure 15] Figures 15A and 15B are cross-sectional views along line 15B-15B in Figure 15A, showing a contact member formed according to one embodiment of the present disclosure.

[0035] [Figure 16] Figure 16 shows the wetting of the tantalum layer in the contact members of Figures 15A and 15B.

[0036] [Figure 17] Figure 17 shows the contact in the open state according to this disclosure.

[0037] [Figure 18] Figure 18 shows the contacts in the closed state according to this disclosure.

[0038] [Figure 19] Figure 19 shows a pair of contacts according to this disclosure in which neither contact is machined into a pocket.

[0039] [Figure 20A] Figure 20A is an isometric projection view of a means for assembling a contact point by stacking multiple layers.

[0040] [Figure 20B] Figure 20B is a cross-sectional view along line BB in Figure 20A.

[0041] [Figure 21A] Figure 21A is an unequal projection view of a liquid metal droplet in an open junction with a dendritic channel.

[0042] [Figure 21B] Figure 21B is a magnified and detailed view of a portion of Figure 21A.

[0043] [Figure 22A] Figure 22A is an unequal projection view of a liquid metal droplet in closed contact with a metal object pushed into a channel.

[0044] [Figure 22B] Figure 22B is a magnified and detailed view of a portion of Figure 22A.

[0045] [Figure 22C] Figure 22C is an enlarged top view of a portion of Figure 22A.

[0046] [Figure 23] Figures 23A and 23B show the relay in the open and closed states, respectively, according to this disclosure.

[0047] [Figure 24] Figure 24 illustrates the use of a liquid layer on a contact point according to this disclosure.

[0048] [Figure 25] Figures 25A and 25B show a bipolar relay formed in accordance with this disclosure.

[0049] [Figure 26] Figure 26 is a top view of a bipolar relay formed in accordance with this disclosure. [Modes for carrying out the invention]

[0050] Detailed explanation The following description includes specific details to provide a complete understanding of the various disclosed implementations. However, those skilled in the art will recognize that implementations may be carried out without using one or more of these specific details, or using other methods, components, materials, etc. In other examples, well-known structures related to circuit breakers, relays, coils, and typical electrical components are not illustrated or described in detail to avoid unnecessarily obscuring the description of the implementations.

[0051] Unless the context requires otherwise, the word “comprise” and its variations, such as “comprises” and “comprising,” throughout the specification and the following claims should be interpreted in an open and inclusive sense, that is, “inclusive but not limited.”

[0052] The terms “connected” and “coupled,” and any variations thereof, are intended to include any connection or combination between two or more elements, whether direct or indirect. The connection or combination may be physical, logical, or a combination thereof. For example, objects may be electrically or communicatively connected to one another without sharing a physical connection.

[0053] Throughout this specification, any reference to “one implementation” or “implementation” means that a particular feature, structure, or characteristic described in relation to an implementation is included in at least one implementation. Therefore, the appearance of the expression “in one implementation” or “in an implementation” in various parts of this specification does not necessarily all refer to the same implementation. Furthermore, a particular feature, structure, or characteristic may be combined in any suitable manner in one or more implementations. For simplicity and clarity of explanation, it will be understood that reference numbers may be repeated between drawings to indicate corresponding or similar elements or steps, where appropriate.

[0054] The headings and summaries of the disclosures provided herein are for convenience only and do not constitute an interpretation of the scope or meaning of the implementations.

[0055] Operating principle overview How to use This device is driven by a predetermined current pulse passing through a coil. A positive current pulse opens the relay, and a negative pulse (i.e., a pulse in the opposite direction) closes the relay.

[0056] Magnetic latch To avoid requiring a continuous drive current to keep it open or closed, this implementation is designed to "latch" in place each time it is switched. This is achieved by designing the actuator to be magnetically bistable.

[0057] low resistance contacts For relays to be practical in low space volume and high current applications, they must have extremely low contact resistance. Two different methods are employed to achieve contact resistance of less than 100 microohms, as will be explained in more detail below. These two methods utilize liquid metal wetting and arrays of microfabricated bends. Other methods may also be suitable for meeting the low resistance requirements of such MEMS relay designs.

[0058] liquid metal contacts A thin layer of liquid metal should fill the gap between the contact surface and the crossbar surface caused by roughness and misalignment, and should be as thin as possible while still performing this function. The liquid metal and contact material should be selected for high conductivity, sufficient surface adhesion, and sufficient lifespan at operating temperatures (limited by diffusion).

[0059] As will be described in more detail below, the preferred implementation currently uses a gallium-indium-tin eutectic or near-eutectic alloy on a tungsten base contact, along with a tantalum adhesive layer. Other substrate materials include copper and molybdenum. Suitable liquid contact layers include cesium-potassium-sodium, elemental gallium and other gallium-based alloys (e.g., indium, tin, zinc, and / or bismuth), mercury, sodium-potassium alloy (NaK), cesium, rubidium, and francium. Adding other components to the liquid metal mixture may provide improved properties, such as adding cesium to NaK to lower its freezing point to -78°C, or adding lithium to NaK to improve its ability to bond to copper or other metals. The base contact material may be treated to form a thin layer of intermetallic material to prevent diffusion of the liquid metal into or out of the base contact, or to promote adhesion of the liquid metal to the base contact.

[0060] Micro-machined bent contact points Contact resistance is generally inversely proportional to the square root of the force applied to press a pair of contacts together. Having an array of small flexible contacts allows for many small contacts with relatively little force. This is important for enabling the small physical size of MEMS relays. Since the resistance is inversely proportional to the square root of the number of flexible contacts, contact with 100 micro-bends on its surface exhibits one-tenth the resistance of a single solid contact.

[0061] Package and internal environment In the case of wet junctions, the package must be sufficiently airtight, and the internal environment must be sufficiently free of water and oxygen to prevent the destruction of the wet junctions due to oxidation.

[0062] The package is filled with a chemically inert, electrically insulating gas at a pressure exceeding 1 atmosphere to provide sufficient dielectric standoff for a given stroke length. Using a pressure above 1 atmosphere also applies a pressure bias across any leakage paths through the package, preventing the inflow or outflow of air.

[0063] A preferred implementation uses a gas consisting primarily of or entirely of nitrogen, but may be mixed with other insulating gases to improve arc resistance. One such gas to be mixed with nitrogen is helium, which is commonly used for leak detection and can therefore help verify the hermetically sealed relay package. Other possible implementations may use insulating liquids (e.g., hexamethyldisiloxane, low molecular weight silicone oil).

[0064] A more detailed description of the aforementioned microfabricated structures follows. These microfabricated structures can be used individually or in specific combinations as described herein to form the power relays of this disclosure.

[0065] Microelectromechanical System (MEMS) Actuator with Magnetic Latch, Method for Manufacturing and Using the Same Figure 1 includes a schematic diagram of a solenoid or actuator 100 having a conventional electromagnetic configuration. The conventional electromagnet configuration includes a control coil 102 wound around a ferromagnetic core 104. The application of current through the control coil 102 generates a magnetic field having an orientation substantially parallel to the axis of the control coil 102. This magnetic field attracts the upper of two contacts 108. The upper contact moves downward until it contacts the lower contact 108. This closes the switch, allowing current to flow from the power source to the load. When the current through the control coil 102 is interrupted by opening the control switch 106, the upper contact 108 is returned to its neutral open position by spring force.

[0066] Typically, conventional electromechanical actuators are at least a few centimeters in both length and width. Their construction requires a coil of windings that must be formed using a bobbin winding machine. The winding of the coil increases the complexity, and therefore the cost, of manufacturing such actuators. In contrast, the electromechanical actuator introduced here allows for the use of planar circuits, reducing the complexity of forming the coil and enabling the resulting device to be much smaller, with dimensions of 1 mm × 6 mm × 6 mm or less. This makes it possible for the resulting device to be used in applications requiring miniaturization.

[0067] Conventional solenoid actuators typically do not latch into a fixed position at the end of their stroke, and even in implementations where latching is possible, the latch is typically achieved using mechanical means. Mechanical latching adds a moving part to the design, increasing its cost and reducing its reliability. The electromechanical actuator introduced here provides magnetic latches at each end of the stroke, depending on its design, and requires no additional components. The magnetic latch is entirely passive and does not require external energy to hold the plunger at both ends of the stroke.

[0068] Overview of Electromechanical Actuators At a high level, the electromechanical actuators described herein are generally laminated devices manufactured by cutting thin sheets of material and then joining those thin sheets together in a stack, as will be further described below. Through continuous cut / bond iterations, structures comprising electromechanical actuators collectively can be arranged in plane relative to each other in almost any configuration.

[0069] Figure 2A includes cross-sectional views of various layers of the electromechanical actuator 200 according to various embodiments of the present disclosure. Figures 2B–2C, on the other hand, show how the various layers of the electromechanical actuator 200 generally correspond to one of two “stacks,” namely the static stack 232 (also called the “static assembly,” “stator assembly,” or simply the “stator”) or the actuatable stack 234 (also called the “actuatable assembly,” “rotor assembly,” “plunger assembly,” or simply the “plunger”). As will be further described below, the plunger assembly 234 can be vertically displaced within the stator assembly 232 to controllably move a load 218 positioned below the spacer 220.

[0070] Referring again to Figure 2A, the stator assembly 232 represents a collection of layers having chambers 236 partially defined along a central longitudinal axis 238. The central longitudinal axis 238 may substantially bisect the width of the electromechanical actuator 200. The substrate 202 may be the bottom layer of the stator assembly 232. The substrate 202 may be a small block of insulating material on which functional components (e.g., relays or valves) are fabricated to complete the electromechanical device. The insulating material may be, for example, ceramic or glass. Insulation is not necessarily required (e.g., insulation may be useful if the electromechanical actuator 200 forms part of an electrical switch). Therefore, the substrate 202 may alternatively consist of a non-insulating material on which functional components are fabricated to complete the electromechanical device. Some embodiments may not include the substrate 202 at all, in which case the load stop sections 204A-204B may be the bottom layer of the electromechanical actuator 200.

[0071] Regarding the "footprint," it is generally desirable to make the electromechanical actuator 200 as small as possible within the limits set by the current density. Cost and magnetic performance tend to increase favorably as the size decreases. For example, the actuation force may be proportional to the square root of the movable magnet mass of the electromechanical actuator 200 and the square root of the power consumed. Generally, the substrate 202 may be less than 4 mm thick (and preferably less than 3 mm thick). The thickness of the substrate 202 may be fundamental to the operation of the electromechanical device and therefore may not depend much on the intended application of the electromechanical actuator 200. The shape, length, and width of the substrate 202 may vary depending on the intended application of the electromechanical actuator 200. However, in some embodiments, the length may not exceed 10 mm, 20 mm, 25 mm, or 50 mm, and the width may not exceed 10 mm, 20 mm, 25 mm, or 50 mm. Therefore, the surface area of ​​the substrate 202 may be 100 mm². 2 (i.e., 10mm x 10mm), 400mm 2(i.e., 20mm x 20mm), 625mm 2 (i.e., 25mm x 25mm), or 2,500mm 2 (i.e., it may be less than 50mm x 50mm). In other embodiments, since there are no basic size constraints on the electromechanical actuator 200, the length and / or width may exceed 50mm, and therefore the surface area of ​​the substrate 202 is 625mm². 2 It is acceptable to exceed this limit.

[0072] The stator assembly 232 and the plunger assembly 234 can be connected to each other by one or more bends intended to control, restrain, or limit the lateral movement of the plunger assembly and the inclination of the plunger assembly 234 as it moves vertically within the chamber of the stator assembly 232, as shown in Figure 2B. Specifically, the bends may be designed to provide a desired axial force when the plunger assembly 234 is latched, thereby allowing and supporting faster movement of the plunger assembly 234 when current is applied to the coils in the stator assembly 232, as the axial force provided by the bends counteracts the latching force. In some embodiments, multiple bends are used to restrain torsional movement ("inclination") and lateral movement of the plunger assembly 234, while in other embodiments, a single bend is used to restrain the lateral movement of the plunger assembly 234 with generally lower torsional constraints.

[0073] The bends 208 and 222 are compliant mechanisms that require a relatively small force to deflect in the operating direction (i.e., along the central longitudinal axis 238), but a much larger force to deflect in any other direction. As will be further described below, the bends 208 and 222 may represent different parts of the same bend that flexibly connect the stator assembly 232 and the plunger assembly 234. This characteristic greatly restricts the plunger assembly 234 to take the same path through the center of the stator assembly 232 with each actuation. Furthermore, this characteristic eliminates little to no friction between the stator assembly 232 and the plunger assembly 234 and limits the rotation of the plunger assembly 234 within the chamber 236 of the stator assembly 232. In the embodiment shown in Figure 2A, the bends 208 and 222, which may represent different components of a single bend, can apply a “biasing force” to the plunger assembly 234 in either direction, which allows for a higher initial actuation force (and thus a faster displacement) during actuation. Generally, the bent portions 208 and 222 are made of metal, metal alloy, or polymer.

[0074] As shown in Figure 2A, the stator assembly may include a series of ferromagnetic layers with coils positioned between them. During operation, as will be further described below, an electric current is applied to the coils to magnetically polarize the series of ferromagnetic layers. In the embodiment shown in Figure 2A, the stator assembly 232 includes a triptych of ferromagnetic layers, namely, a first ferromagnetic layer 210 (also called the “lower ferromagnetic layer”), a second ferromagnetic layer 214 (also called the “intermediate ferromagnetic layer”), and a third ferromagnetic layer 216 (also called the “upper ferromagnetic layer”). Generally, the lower and intermediate ferromagnetic layers 210, 214 may extend circumferentially around the chamber 236 and thus have an annular shape. On the other hand, the upper ferromagnetic layer 216 may extend across the entire width of the stator assembly 232 such that its bottom surface defines the upper end of the chamber 236. Although the upper ferromagnetic layer 216 shown in Figure 2A has a disc shape, the upper ferromagnetic layer 216 can have an annular shape similar to the intermediate and lower ferromagnetic layers 214, 210. In such embodiments, the opening in the upper ferromagnetic layer 216 may allow observation and / or measurement of the movement of the plunger assembly 234, and / or connection of an additional load to the top of the plunger. It should be noted that the opening may be sized such that its diameter is smaller than the diameter of the upper ferromagnetic plate 230, to ensure that the plunger assembly 234 remains completely constrained within the chamber of the stator assembly 232.

[0075] The lower, middle, and upper ferromagnetic layers 210, 214, and 216 are generally only the thickness necessary to prevent magnetic saturation while the plunger assembly 234 is operating within the chamber 236 of the stator assembly 232. Generally, the thickness of the lower, middle, and upper ferromagnetic layers 210, 214, and 216 is 0.4 mm or less (preferably 0.3 mm). Most of the other layers included in the stator assembly 232 are less constrained and may be determined based on the intended use of the electromechanical actuator 200. For example, the thickness of the "coil stack" may vary depending on the number of coils, and the thickness of the spacer 206 may depend on the plunger assembly 234, as the bottom of the plunger assembly 234 must be able to move between the upper surfaces of the load stop sections 204A-204B and the lower surface of the lower ferromagnetic layer 210 within the chamber 236. The load stop sections 204A-204B are the surfaces to which the load contacts at the "closed" end of its stroke. The load stop sections 204A to 204B may serve different purposes depending on the device in which the actuator is incorporated. In a relay, for example, the load stop sections 204A to 204B may be conductive elements that are short-circuited by the load 218 when the load 218 is in the closed position. In a MEMS valve, the load stop sections 204A to 204B (or a single load stop section) may be a valve seat. In this situation, the load 218 becomes the valve itself, sealing against the valve seat in the closed position. Therefore, the load stop sections 204A to 204B are shown in Figure 2A to show the surface in contact with the plunger. Note that various intermediate layers (e.g., bends and spacers) are not shown in Figure 2A for the sake of simplification. These various intermediate layers generally have a thickness of 25 to 375 micrometers (μm) and a width of 1.5 to 6 mm. Generally, all the layers shown in Figure 2A have a thickness of 25–375 μm and a width of 1.5–6 mm, although the dimensions may depend on the intended application of the electromechanical actuator 200.

[0076] One or more coils can be positioned between each set of ferromagnetic layers. In the embodiment shown in Figure 2A, for example, the first set of coils is positioned between the lower ferromagnetic layer 210 and the intermediate ferromagnetic layer 214, and the second set of coils is positioned between the intermediate ferromagnetic layer 214 and the upper ferromagnetic layer 216. With such a design, the lower ferromagnetic layer 210 is positioned adjacent to the load stop sections 204A-204B, the first set of coils is positioned adjacent to the lower ferromagnetic layer 210, the intermediate ferromagnetic layer 214 is positioned adjacent to the first set of coils, the second set of coils is positioned adjacent to the intermediate ferromagnetic layer 214, and the upper ferromagnetic layer 216 is positioned adjacent to the second set of coils. It should be noted that the term “adjacent” as used herein can generally be used to refer to the spatial relationship between two components. The first component may be “adjacent” to the second component without each side being adjacent to the other. Thus, one or more intermediate components may exist between components that are “adjacent” to each other. Conversely, the term “directly adjacent” is generally used to refer to components that are adjacent to each other without any intermediate components in between, except for adhesives or other materials that may be required to join them.

[0077] In the embodiment shown in Figure 2A, the first plurality of coils includes a pair of coils 212A-B, and the second plurality of coils also includes a pair of coils 212C-D. In Figure 2A, the first and second plurality of coils include the same number of coils, but the first and second plurality of coils can include different numbers of coils. For example, a single coil can be located between a pair of ferromagnetic layers. The required number of coils may depend on the force required to actuate, given the latch force, the desired drive voltage and current, and the acceleration required to satisfy the desired open time and / or closed time requirements.

[0078] During operation, current is applied to coils 212A-D, as further described below. When this occurs, coils 212A-D generate magnetic fields in opposite directions, and the lower, middle, and upper ferromagnetic layers 210, 214, and 216 of the stator assembly 232 have inner poles in a north-south-north ("NSN") or south-north-south ("SNS") configuration from top to bottom, depending on the direction of the current. Note that the term "inner pole" is used to refer to the radial end of each ferromagnetic layer located closest to the plunger assembly 234. Since the plunger assembly 234 has two fixed poles (i.e., either an NS configuration or an SN configuration, which is determined during the manufacture of the plunger assembly 234 by the orientation of the permanent magnet 228), all adjacent poles between the stator assembly 232 and the plunger assembly 234 will push or pull in the same direction, and reversing the direction of the current will reverse the direction in which the stator assembly 232 and the plunger assembly 234 are pushed or pulled.

[0079] The plunger assembly 234 is located within the chamber 236 of the stator assembly 232 and represents another set of layers that move along the central longitudinal axis 238 between a first position and a second position during operation.

[0080] As described above, the stator assembly 232 and the plunger assembly 234 can be connected to each other by one or more bends. In the embodiment shown in Figure 2A, diagram features 208 and 222 represent different regions of a single bend layer. Thus, the inner bend region 222 may be directly connected to the outer bend region 208, and the inner bend region 222 may move vertically with the plunger assembly 234 due to the elastic deformation of the bend layer, while the outer bend region 208 may remain stationary embedded in the layer of the stator assembly 232 despite being connected to the inner bend region 222. The bends may be designed to allow vertical displacements between 0 and 25 microns, between 25 and 100 microns, between 100 and 150 microns, between 150 and 200 microns, between 200 and 250 microns, or greater than 250 microns. The bends can have various forms. For example, the bend may be in the form of a disc with a circular ring, or the bend may have a central circular portion and a hexagonal ring connected by three interconnecting segments (also called "arms") that bend. In Figure 2A, the outer bend region 208 is the hexagonal ring, and the inner bend region 222 is the central circular portion. Thus, the outer bend region 208 and the inner bend region 222 are part of the same layer. In embodiments in which the electromechanical actuator 200 includes multiple bends, the bends may be arranged at different heights along a "stack". Having multiple bends provides better (i.e., stiffer) angular control of the movement of the plunger assembly 234 and prevents "tilting" as the plunger assembly 234 moves vertically. Additional bends may also allow stress to be distributed between them, enabling a longer fatigue life and / or additional material options.

[0081] The spacer 224 may be positioned along the upper surface of the bend 222 such that the bottom of the spacer 224 is horizontally aligned with the lower ferromagnetic layer 210 of the stator assembly 232 when the plunger assembly 234 is positioned in a first position, as shown in Figure 2A. When the plunger assembly 234 is positioned in a second position, the top of the spacer 224 may be horizontally aligned with the lower ferromagnetic layer 210 of the stator assembly 232. At high levels, the thickness of the spacer 224 may be selected to accommodate the controlled movement of the plunger assembly 234.

[0082] A plunger element (or simply "plunger") may be positioned along the upper surface of the spacer 224. The plunger element may include a permanent magnet 228 having ferromagnetic plates bonded, laminated, or otherwise fixed along its upper and lower poles. Specifically, the lower ferromagnetic plate 226 may be connected along the lower pole of the permanent magnet 228, or the upper ferromagnetic plate 230 may be connected along the upper pole of the permanent magnet 228. As shown in Figure 2A, the upper and lower ferromagnetic plates 226, 230 may be seated between the ferromagnetic layers in the stator assembly 232. Specifically, the lower ferromagnetic plate 226 may be positioned between the lower ferromagnetic layer 210 and the intermediate ferromagnetic layer 214, or the upper ferromagnetic plate 230 may be positioned between the intermediate ferromagnetic layer 214 and the upper ferromagnetic layer 216. During operation, the upper and lower ferromagnetic plates 226, 230 can couple the permanent magnet 228 to the lower, middle, and upper ferromagnetic layers 210, 214, 216 by providing a low-reluctance path for the magnetic field generated by the coils 212A~D to follow.

[0083] Therefore, the plunger assembly 234 may include (i) a load 218 which is a component driven by an actuator that performs some function when moving, (ii) a bend 222 for controlling vertical movement along the central longitudinal axis 238, (iii) a spacer 224, and (iv) a permanent magnet 228 having upper and lower ferromagnetic plates 230, 226 fixed along its poles. The upper ferromagnetic plate 230 may be located between the upper ferromagnetic layer 216 and the intermediate ferromagnetic layer 214 of the stator assembly 232, and the lower ferromagnetic plate 226 may be located between the intermediate ferromagnetic layer 214 and the lower ferromagnetic layer 210.

[0084] The thickness of the permanent magnet 228 is generally maximized within constraints set by the surrounding layers and the application of the electromechanical actuator 200, both mechanically and magnetically. For example, the thickness of the magnet may be selected so as not to exceed the saturation magnetic flux density of the ferromagnetic plates 226, 230. Similarly, the thickness of the magnet may also be selected so that the total magnetic flux is sufficient to generate a suitable latch force for the intended application of a particular embodiment. Mechanical constraints on the thickness of the magnet may include ensuring that the vertical distance between the upper surface of the lower ferromagnetic plate 226 and the lower surface of the upper ferromagnetic plate 230 does not exceed the difference between the thickness of the intermediate ferromagnetic layer 214 and the intended length of the stroke. The thickness of the permanent magnet 228 may typically be sized such that the lower ferromagnetic plate 226 contacts the intermediate ferromagnetic layer 214 at the top of the stroke while the upper ferromagnetic plate 230 contacts the upper ferromagnetic layer 216, and the lower ferromagnetic plate 226 contacts the lower ferromagnetic layer 210 at the bottom of the stroke while the upper ferromagnetic plate 230 contacts the intermediate ferromagnetic layer 214 (i.e., the gap is equal on both sides). This may tend to maximize the magnetic force in both latching and acting by minimizing the gap in the magnetic circuit at both ends of the stroke.

[0085] Similar to the stator assembly 232, the dimensions of the layers within the plunger assembly 234 are generally not constrained and may therefore be determined based on the intended use of the electromechanical actuator 200. However, the permanent magnet 228, the lower ferromagnetic plate 226, and the upper ferromagnetic plate 230 may be designed with the stator assembly 232 in mind. For example, the permanent magnet 228, the lower ferromagnetic plate 226, and the upper ferromagnetic plate 230 should be designed such that (i) the upper ferromagnetic plate 230 can move within the gap between the upper surface of the intermediate ferromagnetic layer 214 and the lower surface of the upper ferromagnetic layer 216, and (ii) the lower ferromagnetic plate 226 can move within the gap between the upper surface of the lower ferromagnetic layer 210 and the lower surface of the intermediate ferromagnetic layer 214.

[0086] As seen in Figures 2A to 2C, the chamber 236 does not have to be purely cylindrical. Instead, the layers of the stator assembly 232 and / or plunger assembly 234 may be sized and arranged such that the chamber 236 has structural features along its longitudinal sides that allow for improved control of the plunger assembly 234. For example, consider the embodiment shown in Figure 2A. In this embodiment, the upper ferromagnetic layer 216 extends around the entire circumference of the stator assembly 232. The intermediate and lower ferromagnetic layers 214, 210, on the other hand, have the form of annular cylinders (also called “coaxial cylinders”), with a central opening corresponding to the chamber 236. These annular cylinders are defined by an inner radius extending from the central longitudinal axis 238 to the inner circumference and an outer radius extending from the central longitudinal axis 238 to the outer circumference. Similarly, each “coil stack” may have the form of an annular cylinder. However, the inner radius of the “coil stack” does not have to be the same as the inner radius of the intermediate and lower ferromagnetic layers 214, 210. If the inner radius of the "coil stack" is greater than the inner radius of the intermediate and lower ferromagnetic layers 214, 210, structural features generally called "notches" or "shelves" are formed, and these structural features can accommodate the upper and lower ferromagnetic plates 230, 226 as described above.

[0087] Overview of the operating principle As described above, the electromechanical actuator 200 can be driven by applying a fixed pulse of current through coils 212A to 212D.

[0088] To move the plunger assembly 234 from a first position to a second position, current is applied to coils 212A~D so that the current flows in a first direction. When the plunger assembly 234 moves from the first position to the second position, downward movement may be hindered by any of the following: (i) mechanical resistance of the bends 208, 222; (ii) the upper ferromagnetic plate 230 contacting the upper surface of the intermediate ferromagnetic layer 214; (iii) the lower ferromagnetic plate 226 contacting the upper surface of the lower ferromagnetic layer 210; or (iv) the load 218 contacting the components at the end of its stroke.

[0089] To move the plunger assembly 234 from a second position to a first position, current is applied to coils 212A~D such that the current flows in a second direction opposite to the first direction. When the plunger assembly 234 moves from the second position to the first position, upward movement may be hindered by (i) the mechanical resistance of the outer and inner bent regions 208, 222, (ii) the upper ferromagnetic plate 230 contacting the bottom surface of the upper ferromagnetic layer 216, or (iii) the lower ferromagnetic plate 226 contacting the bottom surface of the intermediate ferromagnetic layer 214. Thus, upward movement may be hindered by the bent portion reaching its limit of elongation so that its restoring force prevents further axial movement, or by the upper ferromagnetic plate 230 or the intermediate ferromagnetic layer acting as a physical barrier.

[0090] Therefore, in order to actuate the plunger assembly 234, a fixed current pulse obtained from a power source (not shown) can be applied to the coils 212A-D of the stator assembly 232, such action magnetically polarizes the upper, middle, and lower ferromagnetic layers 216, 214, and 210. A positive current may move the plunger assembly 234 to a first position, thereby moving the load 218 to the "open" position. Conversely, a negative current may move the actuator assembly 234 to a second position, thereby moving the load 218 to the "closed" position. Figure 3 includes a simplified diagram of the latching behavior of the electromechanical actuator caused by the magnetic circuits in the "open" and "closed" positions. In Figure 3, dashed lines indicate magnetic flux in one magnetic circuit, and dotted lines indicate magnetic flux in another magnetic circuit. Magnetic flux in one direction, indicated by the dashed lines, causes the electromechanical actuator to "open," and magnetic flux in the opposite direction, indicated by the dotted lines, causes the electromechanical actuator to "close." Note that Figure 3 shows a portion of the plunger assembly.

[0091] The load 218 may be described as being in an "open" position or a "closed" position, but a person skilled in the art will recognize that these positions may simply be opposite end positions. Thus, the "open" position may also be called the "first end position" or simply the "first position," and the "closed" position may also be called the "second end position" or simply the "second position."

[0092] A. Magnetic latch A key aspect of electromechanical actuators is their approach to operation. Conventional electromechanical actuators may require a continuous current to be applied to maintain a given state (e.g., closed). To avoid the need to continuously apply current for an electromechanical actuator to remain open or closed, the actuator can instead be designed to "latch" in place each time the state changes. This is achieved by designing the actuator to be magnetically bistable.

[0093] Referring to Figure 2A, the spacing between the upper ferromagnetic layer 216, the intermediate ferromagnetic layer 214, and the lower ferromagnetic layer 210 in the stator assembly 232 can be matched with the spacing between the upper ferromagnetic plate 230 and the lower ferromagnetic plate 226, as well as the permanent magnet 228 and spacer 224, in the plunger assembly 234. The distance over which the magnetic field lines generated by coils 212A-D pass through the non-ferrous material is minimized when the plunger is at its highest and lowest positions, and this effect is maximized when the spacing is matched. This creates two minimums of magnetoresistance (and therefore potential energy) at these positions, causing the plunger to "latch" at its highest and lowest positions, and the magnetic "latching force" is maximum when the spacing is matched.

[0094] The size of the permanent magnet 228, the thickness of the upper and lower ferromagnetic plates 230, 226, the vertical spring constants of the outer and inner bend regions 208, 222, and the distance between the highest and lowest positions can affect the latching force. To maximize the operating speed, the net latching force (including the magnetic and bend contributions) can be minimized within a set of constraints by vibration and shock resistance. Since the operating force that should be maximized to optimize the switching speed is largely determined based on the sum of the magnetic latching force and the vertical bend force, the geometry of the bend tends to be the easiest parameter to manipulate. Therefore, selecting the bend spring constant to set the “net latching force” to an appropriate value is typically preferable to redesigning or re-selecting the permanent magnet 228 or the upper and lower ferromagnetic plates 230, 226, or to using a larger distance (also called “gap size”).

[0095] B. Magnetic operation Figure 4 includes a schematic diagram showing how passing current through coils 406A-N and 410A-N results in a constant magnetic force being applied to plunger 402. To better illustrate the magnetic force, the electromechanical actuator 400 is "decomposed" so that the various layers are separated and "enlarged" so that the various layers are not drawn to scale.

[0096] As described above, the stator assembly 420 may include triplets of ferromagnetic layers in which coils are located between them, such that (i) at least one coil is located between the lower ferromagnetic layer 404 and the intermediate ferromagnetic layer 408, and (ii) at least one coil is located between the intermediate ferromagnetic layer 408 and the upper ferromagnetic layer 412. For example, a plurality of coils 406A-N may be located between the lower ferromagnetic layer 404 and the intermediate ferromagnetic layer 408, and another plurality of coils 410A-N may be located between the intermediate ferromagnetic layer 408 and the upper ferromagnetic layer 412. The first and second plurality of coils 406A-N, 410A-N may contain the same number of coils, or the first and second plurality of coils 406A-N, 410A-N may contain different numbers of coils. Typically, each of the coils 406A-N, 410A-N contains at least two coils, but any number of coils can be located between the lower ferromagnetic layer 404 and the intermediate ferromagnetic layer 408, or between the intermediate ferromagnetic layer 408 and the upper ferromagnetic layer 412. The thickness of each "coil stack" may depend, for example, on the size of the plunger 402. The thickness of each "coil stack" tends to be proportional to the number of coils it contains.

[0097] The plunger 402 may include a permanent magnet 414 having ferromagnetic plates 416, 418 fixed along its upper and lower poles. Here, for example, the lower ferromagnetic plate 416 is connected along the lower pole (i.e., the south pole) of the permanent magnet 414, and the upper ferromagnetic plate 418 is connected along the upper pole (i.e., the north pole) of the permanent magnet 414.

[0098] The upper, middle, and lower ferromagnetic layers 412, 408, and 404 can be arranged alternately with the upper and lower ferromagnetic plates 418 and 416, as shown in Figure 4. The upper ferromagnetic plate 418 can be located between the upper ferromagnetic layer 412 and the middle ferromagnetic layer 408, and the lower ferromagnetic plate 416 can be located between the middle ferromagnetic layer 408 and the lower ferromagnetic layer 404.

[0099] As described above, when current is passed through coils 406A~N and 410A~N, a constant magnetic force is applied to the plunger 402 (more specifically, to the upper ferromagnetic plate and the lower ferromagnetic plates 418 and 416). This constant magnetic force is generally proportional to the current and the number of turns in coils 406A~N and 410A~N. When this constant magnetic force overcomes the "latch force" of the plunger 402 (more specifically, the permanent magnet 414), the plunger 402 begins to move downward (for example, towards the lower ferromagnetic layer 404) or upward (for example, towards the upper ferromagnetic layer 412).

[0100] By applying a positive current to coils 406A~N and 410A~N, movement in one direction (e.g., upward) can be achieved. Applying a negative current to coils 406A~N and 410A~N may cause movement in the other direction (e.g., downward). For example, a positive current may move the plunger 402 upward until the upper ferromagnetic plate 418 contacts the bottom surface of the upper ferromagnetic layer 412 and / or the lower ferromagnetic plate 416 contacts the bottom surface of the intermediate ferromagnetic layer 408. When the plunger 402 is in this position, the electromechanical actuator 400 may be described as "open". Conversely, a negative current may move the plunger 402 downward until the upper ferromagnetic plate 418 contacts the top surface of the intermediate ferromagnetic layer 408 and / or the lower ferromagnetic plate 416 contacts the top surface of the lower ferromagnetic layer 404. When the plunger 402 is in this position, the electromechanical actuator 400 may be described as "closed."

[0101] Various parameters can affect this constant magnetic force, as well as the speed at which the plunger 402 can move between positions. These parameters include: • The thickness and composition of the upper, middle, and lower ferromagnetic layers 412, 408, and 404. For example, the thickness of the upper ferromagnetic layer, the intermediate ferromagnetic layer, and the lower ferromagnetic layer may range from 25 μm to 325 μm. • Thickness and grade of permanent magnet 414. For example, the thickness of the permanent magnet 414 may be 0.2 to 0.5 mm. • Number of turns for coils 406A~N and 410A~N. The magnitude of the current applied to coils 406A~N and 410A~N. • Diameters of coils 406A~N, 410A~N, and permanent magnet 414. The spatial relationships affect the direction of the magnetic field gradient, including the spacing between the upper, middle, and lower ferromagnetic layers 412, 408, and 404, and the overlap between them.

[0102] During operation, current is applied to coils 406A~N and 410A~N. When this occurs, coils 406A~N and 410A~N generate magnetic fields in opposite directions, inducing poles in the upper, middle, and lower ferromagnetic layers 412, 408, and 404. Depending on the direction of the current, the inner poles of the upper, middle, and lower ferromagnetic layers 412, 408, and 404 may be in an NSN configuration or an SNS configuration. The permanent magnet 414 has two fixed poles, where the permanent magnet has, for example, an NS configuration. Thus, when the upper, middle, and lower ferromagnetic layers 412, 408, and 404 are magnetically polarized, all the inner poles of the stator assembly 420 push or pull the plunger 402 in the same direction. Reversing the direction of the current reverses the direction in which the inner poles of the stator assembly 420 push or pull the plunger 402. Figure 4 shows how applying current to coils 406A~N and 410A~N can induce magnetic polarization that applies a magnetic force to plunger 402.

[0103] Figures 5A to 5E include visualizations showing the strength and direction of the magnetic field as the plunger assembly moves between a first and a second position. Specifically, Figure 5A shows the plunger assembly in the first position. To move the plunger assembly to the second position, a fixed pulse of positive current can be applied to the coil to magnetically pull the plunger assembly downward. Figure 5B shows the plunger assembly as it moves toward the second position, and Figure 5C shows the plunger assembly in the second position. To return the plunger assembly to the first position, a fixed pulse of negative current can be applied to the coil to magnetically pull the plunger assembly upward. Figure 5D shows the plunger assembly as it moves toward the first position, and Figure 5E shows the plunger assembly returning to the first position.

[0104] C. Restricted movement and bending To keep the plunger assembly centered within the chamber of the stator assembly, bends (e.g., bends 208 and 222 in Figure 2A) can be used to ensure that the movement is nearly perpendicular, if not perfectly perpendicular, to the central longitudinal axis. Furthermore, these bends can suppress or prevent friction between the plunger assembly and the various layers of the stator assembly. To achieve this, the bends may need to have a stiffness against lateral motion equal to at least the maximum lateral magnetic force divided by the worst-case clearance within the manufacturing tolerance (assuming a worst-case scenario for the geometry within the manufacturing tolerance).

[0105] In order for the load (e.g., load 218 in Figure 2A) to be able to sit flat along the upper surface of the load stopping section (e.g., load stopping sections 204A-204B in Figure 2A), the maximum lateral asymmetry of the bending force may be smaller than the remaining closing latch force after any force applied by the bending section has been taken into account.

[0106] Figure 6 includes a perspective cross-sectional view showing how a bent portion 602 connected to the plunger assembly 604 can restrict the movement of the plunger assembly 604 relative to the stator assembly 606. To ensure that the bent portion 602 is properly positioned, the bent portion 602 may be "sandwiched" between the layers of the plunger assembly 604 and / or the stator assembly 606. For example, the bent portion 602 may be sandwiched between ceramic layers.

[0107] For simplicity, only some components of the plunger assembly and stator assemblies 604, 606 are shown in Figure 6. Specifically, Figure 6 shows how the bend 602 can ensure that the movement of the load 608 is substantially vertical or longitudinal, i.e., along the longitudinal axis 610. Although some degree of inclination may occur, the plunger assembly 604 does not undergo meaningful horizontal or lateral movement, nor does the plunger assembly 604 undergo meaningful rotation about the longitudinal axis.

[0108] As shown in Figure 6, such a method for guiding the movement of the plunger assembly 604 not only allows for highly consistent and repeatable movement, but also avoids any friction from the plunger assembly 604 contacting the inner wall of the stator assembly 606. This friction can result in insufficient and / or unreliable performance, and therefore, it is important to avoid this friction.

[0109] Packaging and internal environment The implementation of the electromechanical actuator may benefit from being sealed to prevent the inflow or outflow of fluids (e.g., gases and liquids) from the ambient environment into or from the chamber of the stator assembly to the ambient environment.

[0110] In addition to being hermetically sealed, embodiments of electromechanical actuators may be evacuated or filled with or injected with insulating fluid. For example, a chamber defined within a stator assembly may be filled with a chemically inert electrical insulating gas at a pressure above or below 1 atmosphere, or the chamber may be filled with a chemically inert electrical insulating liquid at a pressure above or below 1 atmosphere. When used in an electromechanical relay, the chamber may be filled with insulating fluid to provide sufficient dielectric standoff for a given stroke length of the plunger assembly. Having atmospheric pressure above 1 atmosphere also results in a pressure bias being applied across any leakage paths through the hermetically sealed envelope, thereby blocking or preventing the entry or exit of air into or from the chamber of the stator assembly to the ambient environment. The liquid in the chamber may be electrically insulating or conductive, depending on the application. The liquid may function as a means of transmitting liquid pressure or as a means of providing dielectric breakdown resistance.

[0111] Generally, insulating fluids are chemically inert electrical insulating gases composed entirely or primarily of nitrogen. However, nitrogen can be mixed with one or more other electrical insulating gases to improve arc resistance, for example (so that it may be useful in electromechanical relays). However, other fluids can also be used. For example, the insulating fluid may be another chemically inert electrical insulating gas such as argon, or the insulating fluid may be a chemically inert electrical insulating liquid such as hexamethyldisiloxane or octamethyltrisiloxane, which are low molecular weight, low viscosity silicones.

[0112] Design selection Since the actuation force is proportional to acceleration, the sum of the initial forces at the start of the "stroke" disproportionately determines the time required to switch from one state to another. The sum of the initial forces can be roughly characterized by the sum of the latch force, actuation force, and bending force. To maximize the force at the start of the "stroke," the bending section can be used like a spring to counteract the latch force. If the latch force is partially, if not completely, counteracted, the sum of the initial forces can instead be characterized by the sum of the actuation force and bending force.

[0113] Design and manufacturing methods for electromechanical actuators To design an electromechanical actuator according to the embodiments disclosed herein, it is most convenient to consider the electromechanical actuator as a combination of two components: (i) a stator assembly having a chamber partially defined along a central longitudinal axis, and (ii) a plunger assembly located within the chamber of the stator assembly and moving along the central longitudinal axis between a first position and a second position during operation. At a high level, the stator assembly includes two subcomponents: (i) a contact assembly and (ii) a drive electromagnetic assembly. Figure 7 includes a schematic diagram of the plunger assembly 702 and the stator assembly 708 of relay 704. As described above, the stator assembly 708 facilitates the operation of the plunger assembly 702 by generating a magnetic field when current is applied. The operation of the plunger assembly 702 results in its lowest surface engaging with or disengaging from the load stop section 706, which is a contact in the relay.

[0114] The manufacture of an electromechanical actuator requires the separate manufacture of its subcomponents. Figure 8 includes a diagram of a set of steps that can be used to assemble the relay 200 as a collection of layers. Note that for convenience, the components described may be referred to with reference to Figures 2A and 2B. The order of assembly is important because the bent layers, represented by bent regions 208 and 222, which are part of the same bend, are included in both subassemblies. Furthermore, the manner in which the ferromagnetic layers are connected requires that the plunger assembly be assembled in place, since the plunger assembly 234 cannot be inserted through the opening in the intermediate ferromagnetic layer 214 after it has been assembled. For illustrative purposes, one possible order of assembly as shown in Figure 8 is as follows:

[0115] Step 1: Begin with spacer 1 (220 in Figure 2A) which is securely connected between plunger assembly 234 and stator assembly 232 by a removable tab marked with an "x".

[0116] Step 2: Load 2 is stacked on spacer 1.

[0117] Step 3: The lower ferromagnetic layer 210 is laminated onto the assembly fabricated in Step 2.

[0118] Step 4: The spacer 224, lower ferromagnetic plate 226, and permanent magnet 228 of the plunger assembly 234 are stacked in the opening left inside the lower ferromagnetic layer 210.

[0119] Step 5: The first set of coils 212A-B and the intermediate ferromagnetic layer 214 are stacked onto the assembly fabricated in Step 4.

[0120] Step 6: The upper ferromagnetic plate 230 is stacked on top of the permanent magnet 228.

[0121] Step 7: The second set of coils 212C-D and the upper ferromagnetic layer 216 are laminated on top of the assembly fabricated in Step 6.

[0122] Step 8: The spacer layer 206 is stacked on the bottom of the assembly fabricated in Step 7. Next, the tabs (x) connecting the inner and outer portions of the spacer 220 applied in Step 1 are removed, releasing the movement of the plunger assembly 234, which was constrained by the bends (collectively represented by 208 and 222).

[0123] Step 9: The assembly prepared in Step 8 is placed on top of the load stoppers 204A-204B. The load stoppers 204A-204B may be stacked or clamped in appropriate places below the assembly.

[0124] Those skilled in the art will recognize that other assembly sequences are possible and, in some embodiments, may be desirable based on the speed or precision at which the electromechanical actuator 200 is assembled.

[0125] Figure 9 includes a high-level diagram of process 900 for fabricating an electromechanical actuator according to another aspect of the present disclosure. Note that, again, components described with reference to Figure 2A may be referenced. However, Figure 9 is specific to the design of an electromechanical actuator that does not include a bend connecting the stator assembly and the plunger assembly. First, the manufacturer can fabricate the upper ferromagnetic layer by cutting a single layer from, for example, a piece of ferromagnetic material (e.g., steel) (step 901). Next, the manufacturer can fabricate the plunger (step 902). For example, the manufacturer can create or obtain a permanent magnet and then stack ferromagnetic plates along its upper and lower poles. These ferromagnetic plates may be called the “upper ferromagnetic plate” and the “lower ferromagnetic plate,” respectively. The manufacturer can then fabricate the plunger assembly by laminating, bonding, or otherwise connecting spacers and loads to the lower ferromagnetic plate (step 903). Note that additional layers may be included in the plunger assembly.

[0126] To fabricate the stator assembly, the manufacturer obtains a substrate (step 904), bonds the components that the load interacts with to the top surface of the substrate (step 905), and then alternately laminates ferromagnetic layers and coils onto the top surface of a pair of contacts (step 906). Generally, the ferromagnetic layers and coils are laminated such that the resulting electromechanical actuator includes triplets of ferromagnetic layers, each having one or more coils located between the first and second ferromagnetic layers and another one or more coils located between the second and third ferromagnetic layers. In some embodiments, the bottom ferromagnetic layer is laminated directly adjacent to the pair of contacts, while in other embodiments, there are one or more intervening layers, as shown in Figure 2A.

[0127] To create an electromechanical actuator, the manufacturer can position the plunger assembly within a defined cavity through the stator assembly, and then bond the upper ferromagnetic layer to the stator assembly (step 907). By bonding the upper ferromagnetic layer to the stator assembly, a fully enclosed chamber is defined inside the stator assembly. As described above, during operation, the plunger assembly can move between different positions within the fully enclosed chamber.

[0128] It should be understood that the aforementioned actuator can be used alone or in combination with any of the following alternative microfabricated contacts provided herein. The first contact mounting configuration utilizes an array of microfabricated bends on one of the contact members, and the second contact mounting configuration utilizes a liquid-solid interface between the contact members. These will be described below in this order.

[0129] Electrical contacts using an array of microfabricated bent sections Another aspect of the present disclosure provides a structure for minimizing the force required for a switch contact to achieve a desired (low) contact resistance. Inelastic deformation that brings two surfaces together requires, by definition, a higher force than elastic deformation, since the inelastic deformation yield point always exceeds the elastic deformation limit.

[0130] By using a number of elastic spring bends ("finger") to form a composite contact, each individual contact can fit into the mating side without lifting the surrounding fingers off the surface, thus allowing all or at least most of the fingers to make contact.

[0131] The available contact force is divided across the entire finger based on the amount of displacement each finger needs to adapt to. A desirable improvement to this system would be to make the force on each spring element constant, or at least nonlinear, to better equalize the force on each spring element.

[0132] Multifinger contacts may be fabricated using microfabrication techniques, including wire electrical discharge machining (EDM) and laser microfabrication using femtosecond lasers. The contacts may be fabricated from metallic materials, including copper, beryllium copper, and other conductive materials.

[0133] Multiple conductive bends may be formed by a laser microfabrication process. Alternatively, multiple conductive bends may be formed by an additive manufacturing process, or multiple conductive bends may be formed from carbon nanotubes grown on a base surface.

[0134] The flexible cantilever finger structure is cut at an angle to the contact base surface. The fingers may be cut in a rectangular array or a linear array, or in other patterns such as a hexagonal or circular array at the bend. Figures 10A and 10B illustrate an array of 13 × 20 = 260 fingers, with only 21 fingers 20 shown. Figure 10A shows a pair of vertical cuts (gaps 22) made by the machining tool. Figure 10B shows angled fingers 20 formed by a pair of orthogonal cuts (gaps 22) made at a 45-degree angle. The result is an array 50 which can consist of 260 fingers 24, as shown in Figure 13. Each finger 20, 24, when micro-machined, has preferred dimensions in the range of 3 microns × 3 microns to 100 microns × 100 microns, and has gaps 22, 26 between each row of fingers 20, 24 ranging from 10 microns to 200 microns. When fingers 20 and 24 are formed by growing carbon nanotubes, the preferred dimensions are in the range of 0.4 nanometers to 100 nanometers in diameter and 1 nanometer to 10 nanometers in spacing between fingers.

[0135] As the size of the electromechanical relay decreases, the volume of the magnetic material and current-carrying conductors in the electromagnetic actuator decreases, thus reducing the force available to press the contacts against each other. The available force is divided among all the contacts in the array. It can be shown that the electrical resistance of an array of N bends with a given total vertical force and a given total contact area is proportional to 1 / (square root N). Thus, contact with an array of 10 × 10 fingers has 100 contacts and 1 / 10 the resistance of a single contact compressed with the same total force. For the mathematical derivation of this result, see "Mathematical Analysis of Contact Bend Array Scaling" below.

[0136] Figures 11A to 11B show a conventional contact structure, and Figures 12A to 12B show how the contact structure of this disclosure functions. Each of the four figures in Figures 11A to 11B and Figures 12A to 12B shows the same rigid lower contact member 28 having a undulating upper surface 30 that forms a valley 32 between two protrusions 34 or high points. For illustrative purposes, the surface undulations are exaggerated in the figures. Note that the undulations in the figures represent unintended artifacts left by the fabrication or wear of the contact material, rather than representing an intentional feature of the contact. In Figures 11A to 11B, the conventional solid contact 38 is shown in the open and closed states, respectively.

[0137] During operation, the solid movable upper contact member 38, shown in Figure 11A and positioned above the lower contact member 28, contacts the lower contact member 28 as shown in Figure 11B, but only at two protrusions 34 or high points on the lower contact member 28. This limits the surface area available for electrical contact and the resulting conduction. In conventional relays or switches, the solution to this problem is to apply a greater force to the upper contact member 38. When the appropriate force is applied, the upper or lower contact member 38 or 28 plastically deforms, providing greater surface contact with the lower contact member 28 and thus lower resistance.

[0138] Next, referring to Figures 12A and 12B, a novel flexible contact array device 40 formed according to this disclosure is shown. The aforementioned lower contact member 28 is positioned and shown below the upper contact member 42 formed according to this disclosure. In Figure 12A, the upper contact member 42 is in the open position, and in Figure 12B, the upper contact member 42 is in the closed position. The upper contact member 42 has a number of bends extending from the lower surface 46, which are also referred to herein as fingers 44. As shown in Figure 3A, the fingers 44 are in a relaxed, straight position and are not in contact with the lower contact member 28.

[0139] When the contact 40 is closed by moving the upper contact member 42 toward the lower contact member 28 to the closed position, the fingers 44 bend as they move to contact the upper surface 30 of the lower contact member 28. When the fingers 44 contact the highest bump 34 on the lower contact member 28 and bend the most compared to the fingers 44 contacting the lowest point in the valley 32, the total force required to bend the fingers 44 is much lower than the total force required to plastically deform the upper contact member 38 in a typical contact design. Here, the number of contacts when the contact 40 is in the closed position shown in Figure 12B is equal to the number of fingers 44 in contact with the lower contact member 28. In this closed position, the lower surface 46 of the upper contact member 42 is positioned at a first distance from the lowest point 32 of the upper surface 30 of the lower contact member 28. This first distance includes the distance between the highest bump 34 and the lower surface 46 of the upper contact member 42, and this distance is shorter than the first distance.

[0140] Ideally, all of the conductive fingers 44 extending from the upper contact member 42 are at the same height or distance from the contact base surface (lower surface 46) of the upper contact member 42. This distance is greater than the sum of the first distance between the high point 34 and the low point 32 on the exposed upper surface 30 of the lower contact member 28 when the upper contact member 42 is in the closed position, and the separation distance between the lower surface 46 of the upper contact member 42 and the highest point of one or more high points 34 on the upper surface 30 of the lower contact member 28.

[0141] The reduced contact force requirements of this bent array design are a key enablement for using small, relatively weak electromagnetic actuators to achieve low-resistance contacts.

[0142] Microfabrication (laser) or EDM (electrical discharge machining) can be used to create arrays of inclined cantilever spring bends from a solid conductor. This allows the use of substrates of any thickness with the best possible conductive path, as no additional bonding is required. The spring geometry and material can be optimized to provide the lowest contact resistance for a given set of perpendicular forces and compliance range (surface heterogeneity). The springs or fingers 44 can be coated after machining to provide other beneficial properties, such as providing a soft material at the tip to improve oxidation resistance, reduce friction at the contact surface, or increase the degree of plastic deformation in which the bend contacts the opposing contact. The spring bends may be formed in a variety of shapes other than simple inclined cantilevers, including S-shaped springs, helical springs, buckling springs, or structures of any shape that elastically deform under forces perpendicular to the main contact surface. Such bends may be formed using a variety of processes, including 3D printing using metal or plated polymers, photochemical etching, reactive ion etching, or deposition or growth of carbon nanotube structures.

[0143] As can be easily understood from the above, this disclosure provides a contact structure that provides the formation of a low-resistance contact member when only low vertical force is available. This is of particular interest in small relays or general relays that need to be optimized for low power in coil drive devices.

[0144] If the fingers are excessively bent by excessive pressure, the fingers may be damaged. The geometry of the contacts may be modified to provide a hard stop that controls the maximum degree of bending of the fingers. This hard stop may be formed on either of the two contact members, or to some extent on both contact members. The hard stop may take the form of a wall 52 surrounding the array 50 of fingers 24, as shown in Figure 14, but may be shorter in overall height than the fingers 24. The hard stop may also be formed as a discontinuous set of rigid structures. The height of the hard stop may be optimized to allow an ideal degree of deformation of the bent portion.

[0145] Mathematical analysis of array scaling of contact point bending section Scaling analysis of the upper limit of CFA resistor pairs

[0146] Assumption:

[0147] 1. The equal load distribution of the total contact array force ("F") across all ("n") contact bends results in a force of F / n per individual contact.

[0148] 2. An array of n contact points (bends) distributed over a certain area (footprint) "A".

[0149] 3. The effective conductor area is a certain percentage (f) of the footprint area (A / n). a )

[0150] 4. The actual electrical contact area of ​​each bend is controlled by Hertz's elastic contact mechanics or the plastic deformation area versus force approximation [2].

[0151] 5. Each contact point is arranged parallel to the others.

[0152] CFA Resistor Calculation Individual contact spread resistance [1]:

number

[0153] Here,

[0154] R s , the electrical resistance of the flexure joint area

[0155] ρ, the flexure resistivity

[0156] a, the effective flexure cross-sectional radius

[0157] b, the effective contact radius [[ID=2l]]

[0158] c i , the fitting constant

[0159] f a , the flexure cross-sectional shape factor relating the area to the effective radius

[0160] A, the total area (footprint) of the flexure array

[0161] n, the number of flexures

[0162] P, the asperity contact force - area exponent (= 1 / 3 for elastic asperities, = 1 / 2 for plastic asperities)

[0163] F, the total force on the flexure array

[0164] H p , the elastic or plastic asperity parameter

[0165] For the most significant case of plastically deformed asperities, the total contact resistance of the array (excluding the bulk resistance of the individual flexures) scales as the reciprocal of the square root of the number of flexures

Equation

[0166] Stabilized liquid - solid electrical contacts It has been found that surface contact can be improved with minimal force by wetting one or both switch contacts with a conductive fluid. Depending on the surface energy (or surface tension) of liquid-solid, liquid-vapor, and solid-vapor interfaces, the liquid-solid contact interface may support a liquid film of finite static thickness (repulsive or non-wetting), or tend to have zero thickness at a finite number of interface points (attractive or wetting). Both phenomena can be utilized to obtain favorable electrical contact properties. However, existing solutions for liquid contacts have their own problems. The liquid should ideally have both high thermal and electrical conductivity, be preferentially metallically bonded, and operate over a wide temperature range, including room temperature. This can be achieved by using liquid metals. Other classes of conductive fluids, such as ionic liquids, do not meet some of these requirements, including having significantly lower conductivity than liquid metals. Mercury is a liquid metal at room temperature and was used as a switch in thermostats until its toxicity became apparent.

[0167] Other liquid metals such as sodium-potassium (NaK), gallium, and gallium alloys are less toxic but are not always reliable as wet junctions because they can react with most metals. "Galinstan®" is a specific near-eutectic alloy of gallium, indium, and tin with a freezing point of -19°C and a boiling point of 1300°C. Gallium is known to react with a wide range of metals to form intermetallic phases, which threatens the stability of solid metal electrode surfaces. For example, copper is a common electrode material due to its excellent conductivity, but it forms intermetallic crystals with gallium at temperatures slightly above room temperature. This persistent reactivity endangers the contact interface because (a) gallium is depleted from the Galinstan alloy, changing its chemical composition and raising its liquidus temperature (e.g., "slushy," semi-solid vs. liquid), and (b) intermetallic crystal growth increases surface roughness and unevenness.

[0168] This disclosure uses a stabilized interface between a liquid and a solid to pair one of several liquid metals with a solid contact material, thereby promoting adhesion of the liquid metal to the solid contact while limiting the reaction between the liquid metal and the solid metal. This disclosure includes a configuration in which this interface is fabricated within a concave cavity to eliminate the detrimental contribution of intermetallic crystalline irregularities during repeated opening and closing (i.e., switching) of the contact surface. Switch contacts formed according to this disclosure have been tested and they exhibit electrical resistances of less than 100 microohms, which are 10 to 100 times lower than the several milliohms for solid relays or the tens of milliohms for conventional electromechanical contacts.

[0169] Liquid metals, including gallin-stan alloys, have been used as fluid bridges between two stationary electrodes. Some of these studies have used them to demonstrate the potential of stabilizing the electrode surfaces before exposing the electrodes to the gallin-stan alloy. U.S. Patent No. 6,570,110 describes the use of liquid gallium or gallium alloys to bridge the space between two stationary electrodes.

[0170] In this disclosure, a multilayer material interface is provided within a fabricated topographic shape on one or both solid contact surfaces. In summary, the designed system includes one or more of the following key functional features: (1) a liquid metal that maximizes both mechanical compliance and current-conducting surface area; (2) a rationally designed and intentionally reacted intermetallic layer (which may be crystalline, quasicrystalline, or amorphous) that establishes chemical stability between the liquid metal and the adjacent substrate material and thus also promotes adhesion between the liquid metal and the solid contact surface; (3) an adjacent diffusion barrier layer that prevents atomic transport and chemical reactions between the liquid metal and the substrate material; (4) a primary base contact material layer that forms the majority of the current path; and (5) (a) solid-solid contact interaction in a closed state (e.g., providing a "hard stop"). (b) a fabricated topographic shape (e.g., recesses and / or irregularities) within the base contact layer that helps to align and level the base contact layer, (c) a fabricated topographic shape (e.g., recesses and / or irregularities) within the base contact layer that helps to align and level the base contact layer, (b) a fabricated topographic shape (e.g., recesses and / or irregularities) within the base contact layer that may have nano- to micro-scale topographic structural features naturally / accidentally or intentionally generated from the solid-solid contact interface, thus limiting the possibility of electric arc discharge, and (c) a fabricated topographic shape (e.g., recesses and / or irregularities) within the base contact layer that helps to protect the intermetallic layer and / or barrier layer from repeated mechanical shocks and potential deformation during switch closing operation, and (6) a second contact formed from a conductor that is robust against reaction with liquid metal but does not readily wet with liquid metal, and may or may not wet with liquid metal itself.

[0171] Each of the key technical and functional features is described in more detail below.

[0172] Liquid metal: Gallium alloys (nominal, 68.5% gallium, 21.5% indium, 10.0% tin by weight) are used in thin film form or droplet form, continuously across the contact surface, or in a select area that can be defined by lithographic patterning of the underlying intermetallic bonding layer and / or physical topographic shape (e.g., physical confinement). The underlying intermetallic bonding layer and the liquid metal are applied to one (preferably) or both sides of the opposing contact surfaces using a liquid dispenser. It should be understood that these metals may also be deposited by colloidal suspension or physical vapor deposition (e.g., sputtering, thermal or electron beam deposition) and possibly subsequently annealed to homogenize the alloy. Other suitable conductive liquids at or near room temperature may include elemental gallium and other gallium alloys (e.g., indium, tin, zinc, and / or bismuth), mercury, sodium potassium alloy (NaK), cesium, rubidium, and francium. Adding other components to a liquid metal mixture can provide improved properties, such as adding cesium to NaK to lower its freezing point to -78°C, or adding lithium to NaK to improve its ability to adhere to copper or other metals.

[0173] Intermetallic layer: A tantalum-gallium two-phase intermetallic crystal is used as the interface between the liquid metal and its substrate material. Tantalum works well because of its low solubility in gallium (e.g., ≤0.1 wt%) at 600°C) compared to most other metals, and the most prominent phases on the gallium-rich side of the phase diagram (TaGa2, TaGa3) are stable in the presence of gallium up to at least 520°C; therefore, tantalum is selected for one implementation configuration. Tests and experiments confirm that no detectable intermetallic formation reactions occur between tantalum and indium or between tantalum and tin. Tantalum is deposited by magnetron sputtering to achieve a film thickness of approximately 500–1000 nanometers (but can range from 1 nanometer to 1 millimeter), and its thickness is important to overcome the surface roughness of the substrate (e.g., one implementation configuration uses tungsten with a root mean square roughness value of 400–1200 nanometers). Other methods for depositing tantalum include electron beam deposition, thermal deposition, chemical vapor deposition, electrochemical deposition, and colloidal film casting.

[0174] During the junction formation process, gallium or a gallium-based alloy is deposited on the tantalum film (see above), and the material is annealed in an inert atmosphere at temperatures ranging from 200 to 650°C for residence times from 10 minutes to 70 hours. Typically, this is carried out at 550°C for 2 hours in argon at atmospheric pressure (≤0.2 ppm O2, ≤0.5 ppm H2O), and then cooled to room temperature without quenching or removing excess liquid metal. This process may also be accelerated by rapid thermal annealing using a radiant heater at temperatures below 1060°C (the melting point of TaGa2). During this annealing process, tantalum reacts with gallium to form Ta-Ga crystals ranging from 0.1 to 15 micrometers, which energy-dispersive X-ray spectroscopy (EDS) analysis shows to be primarily TaGa2 and TaGa3. To maintain the eutectic stoichiometry in the bulk liquid for subsequent contact operation, excess liquid metal may be removed (e.g., physically using a pressurized gas stream or chemically using hydrochloric anhydride in ethanol) and replaced with fresh galinstan alloy. Other useful metals that can react to form an intermetallic interface layer in this application include titanium, vanadium, chromium, iron, zirconium, niobium, ruthenium, molybdenum, tungsten, and rhenium.

[0175] Diffusion Barrier: The diffusion layer should be non-porous and continuous with minimal vacancy defects that allow the liquid metal to diffuse into the pure solid metal within the base contact. It must be thick enough to prevent undesirable interactions, but thin enough to maintain low electrical resistance. The thickness of this barrier may be between 10 nanometers and 10,000 nanometers, depending on the application. In one implementation configuration, such a diffusion barrier layer may have a thickness between 10 and 200 nanometers. In other implementation configurations, the thickness may be between 200 and 500 nanometers, between 500 and 1000 nanometers, between 1000 and 5000 nanometers, or between 5000 and 10,000 nanometers. Two implementation configurations of the diffusion barrier are described herein. One implementation configuration utilizes a highly stable intermetallic phase between the in-situ formed liquid metal and the base contact metal, and thus limits further reactions between the two materials. There may be one or more intermetallic phases acting as both adhesion promoters and diffusion barriers. In one implementation configuration, highly stable γ-phase Cu4Ga9 was used on a copper base contact having a less stable θ-phase CuGa2 on top (as verified by cross-sectional SEM / EDS) at the interface with the liquid metal galinstan alloy.

[0176] Other implementations of diffusion barriers involve depositing a third material positioned within a stack between the intermetallic material and the base contact material. In one implementation, tungsten is used because it is known to be an excellent barrier against copper diffusion, and tests and experiments have shown that it remains stable in the presence of gallium without degradation up to high temperatures of 650°C. Tungsten can be deposited on the copper base contact material by magnetron sputtering, chemical vapor deposition, electrochemical vapor deposition, or simultaneous sputtering of copper and tungsten, causing a stepwise transition from copper to tungsten to mitigate thermal mismatch effects, or by performing diffusion bonding of two foils of copper and tungsten. Other diffusion barrier materials may include ruthenium, titanium, tantalum, titanium nitride, tantalum nitride, tungsten nitride, niobium nitride, molybdenum nitride, titanium-tungsten alloys, tantalum carbide, cerium oxide, and graphene.

[0177] Base contacts: Copper contacts can provide low on-resistance in switch devices. The implementation of the diffusion barrier described above allows the use of copper with liquid metals that would otherwise react with and corrode the copper base contacts. Other low-conductivity base contact materials, including tungsten, molybdenum, tantalum, and niobium, may be chosen instead of copper, at the cost of better chemical compatibility and stability with liquid metals and other materials in multilayer systems.

[0178] Topographic shape: In this mounting configuration, a secure stop for contact is formed by machining one or more pockets into at least one of the electrodes. The non-wetted counter electrode mechanically contacts the top of the pocket wall, providing a clearly defined gap and volume in which liquid metal can remain. The pocket may be formed in two parts having different depths, as described in the following representative mounting configuration and shown in the accompanying drawings.

[0179] Referring to Figures 15A and 15B, a typical first contact 60 is shown, which has a centrally located circular pocket 62 having a wall 63 (shown in Figure 16) surrounded by a shallower circumscribing pocket 64. Both pockets are surrounded by a larger ring surface area 69 that acts as a stop. It will be understood that the pockets 62, 64 can be formed in other geometric planar shapes, including ellipses. The pockets 62, 64 may be formed using any acceptable technique known to those skilled in the art, including but not limited to milling, laser processing using pulsed or continuous wave lasers, photochemical etching, electrical discharge machining (EDM), reactive ion etching, or any other technique suitable for producing pockets of the desired geometric shape.

[0180] These pockets 62, 64 of varying areas or shapes may be formed by stacking and laminating layers of planar material. Each size and shape of the opening may then be completely cut through the material using a saw, laser, waterjet, or other cutting technique. The layers may be joined by adhesive, welding, soldering, or the use of any other technique. This means of forming pockets is shown in Figures 20A and 20B. As an example, pocket 62 may be formed by joining a layer 602 with a circle cut out on the surface of a holeless layer 601. Pocket 64 may then be formed by joining a layer 603 having a larger diameter hole on top of layer 602.

[0181] Alternative geometric shapes can achieve the same objective: to first contain the liquid metal, and then allow the movable contacts to spread the liquid metal when pressure is applied. This technique is shown in Figures 21A, 21B and 22A-22C. A complex shape is cut, consisting of central pockets 2101, 2201 and one or more arms or "dendrites" 2102, 2202 radiating from this shape. Figures 21A and 21B show open contacts where the liquid metal 2103 is not compressed. The stationary liquid metal 2103 naturally accumulates in the central pockets 2101 for two reasons. Firstly, the bottom surface of this central pocket 2101 may have a different surface that wets or attracts the liquid metal, while the bottom surface of the dendrite may be treated to repel the liquid metal. Secondly, as will be discussed later, surface tension makes the liquid prefer a shape that does not extend within the arms.

[0182] Figures 22A and 22C show closed junctions (with the upper junction not shown). In Figures 22A and 22B, the liquid metal 2203 is pushed into the dendrite 202. Its surface area increases. Surface tension then exerts a restoring force that pulls the metal back into the central cavity. The geometry of the dendrite 2202 can affect this restoring force. If the dendrite 2202 is too wide, the restoring force will be weak because the surface area will not be maximized. If the dendrite 2202 is too narrow, the liquid metal may not be able to enter the dendrite 2202 in sufficient quantity. If the dendrite 2202 is elongated, some of the liquid metal may form spherical or nearly spherical satellites within the dendrite cavity, and this metal may dissociate from the bulk of the liquid metal.

[0183] The ideal width of a dendrite or arm can be calculated by considering the pressure on the liquid metal and the surface tension resulting from driving it into the arm. For example, with a given working force available to compress the material, the increase in pressure within the liquid metal is limited. In one design, this pressure can be 9.4 pounds per square inch (PSI). This pressure must balance the resistance pressure caused by the curvature of the liquid metal surface as it bends into the arm. Pressure and radius of curvature are inversely proportional, as described by Laplace's law. A pressure of 9.4 PSI balances the curvature, which depends on the surface tension of the liquid metal. Literature values ​​for the surface tension of eutectic galinstan range from 534 to 718 mN / m (millineutons / meter). This gives a minimum radius of curvature between 0.017 and 0.022 mm. This radius of curvature of 2204 is shown in Figure 22C. Using the value of the lower surface tension, calculations show that with an arm width of 0.034 mm, liquid metal can be completely pushed into the arm at a pressure of 9.4 PSI. If the arm is narrower than twice the minimum radius of curvature mentioned above, the liquid will only partially enter the arm, forming a dome-shaped projection with the minimum radius. This results in much less available movement of the liquid metal. If the arm is significantly wider than twice the minimum radius, the restoring force decreases due to the larger radius of the liquid metal pushed into the arm.

[0184] The volume available through one or more arms is the sum of the volumes accessible through each arm at a given pressure. The number of arms may also be calculated by determining the volume of liquid metal extending over the hard stop of the second contact. This volume must be displaced within the small reservoir formed by the arms. Calculating the accessible volume of each arm and dividing it by the volume above the hard stop minus the available volume of the main reservoir provides the minimum number of arms required to prevent the liquid metal from leaking out of the reservoir or pushing up the hard stop.

[0185] This alternative geometry using arms may be more advantageous than the aforementioned method using pockets with stepped diameters. When pockets are formed by stacking layers, dendritic pockets are formed of only two layers, one of which is solid and the other of which has dendritic arms and a main reservoir, whereas the stepped method requires three layers: a first layer to provide the bottom of the hole and second and third layers to provide two stepped pockets of different diameters.

[0186] Another implementation of the present disclosure uses a simple first pocket, where only a portion of its floor is treated to wet the liquid metal. When the liquid metal is compressed, it flows outward onto the non-wetted surface. When the pressure is released, the liquid metal returns to its resting position due to the force resulting from surface tension and repulsion from the untreated portion of the pocket floor.

[0187] The dimensions described below are representative for illustrative purposes. Other dimensions may work just as well depending on the application. The shallower pocket 64 in Figures 15A and 15B has a diameter of 400 micrometers and a depth of 10 micrometers in one typical mounting configuration. At the center of this pocket 64 is a deeper portion or pocket 62, which has a diameter of 200 micrometers and a total depth of 35 micrometers in one typical mounting configuration. The bottom 66 of the deeper pocket 62 is 65 micrometers below the bottom 68 of the larger, shallower pocket 64 in one typical mounting configuration. The bottom exposed surfaces 66 and 68 of each pocket 62 and 64 may each have a deliberately designed surface finish. For example, each bottom surface 66 and 68 may be polished, or finished with a matte texture, or with a patterned and / or tuned structure. In a sputter coater, a mask is used to prevent coating of the bottom surface 68 of the larger pocket 64 or the top surface 69 of the first contact 60.

[0188] Figure 16 shows an exaggerated tantalum layer 72 on the bottom surface 66 of a deeper pocket 62. Typically, this layer 72 is very thin. It may be deposited as a monolayer of atoms having a minimum thickness of 4 angstroms, which is the diameter of a single atom. This layer 72 may be continuous or may have some voids or pinholes. Its thickness may range from 4 angstroms to 100 angstroms, or 1 nanometer to 10 nanometers, or 10 nanometers to 1 micron, or 1 micron to 100 microns, or 100 to 1000 microns. The liquid metal coating 74 is formed by droplets of galinstan dispensed onto the tantalum layer 72. The first contact point 60 is treated as described above to drive the reaction between the tantalum layer 72 and the galinstan liquid metal coating 74 to a stable point. The liquid metal coating 74 is applied in a volume sufficient to form a convex meniscus that rises above the upper surface 69 of the first contact point 60, as shown in Figure 16. Therefore, when the metal contact 60 is in contact with a movable plate electrode such as the second contact 76 as shown in Figure 18, which will be described later, no intermetallic layer on the surface of the tantalum layer 72 is in contact with the movable plate electrode or the second contact 76.

[0189] More specifically, Figure 17 shows a second contact 76 positioned above the first contact 60 in the open position, and Figure 18 shows contact between the liquid metal coating 74 and the opposing second contact 76 in the closed position. Ideally, this second contact 76 fits within the boundary of a larger, shallower outer pocket 64. A secure stop for the two contacts 60, 76 is provided by metal-to-metal contact at the bottom surface 68 around the shallower outer pocket 64. The liquid metal coating 74 is flattened by the contact pressure from the second contact 76. The liquid metal coating 74 is mechanically held by the sidewall 63 of the deeper pocket 62 and further held in the desired position by chemical attraction to the tantalum layer 72 on the bottom 66 of the pocket 62 and capillary repulsion from bare metal (e.g., tungsten) elsewhere. The excess liquid metal displaced by the pressure from the opposing second contact 76 flows into the shallower pocket 64. When the contact 76 opens, the liquid metal coating 74 is pushed back into a meniscus shape by the repulsive force between the metal (e.g., tungsten) of the first contact 60 and the liquid metal coating 74, as well as the surface tension of the liquid metal coating 74.

[0190] Figure 19 shows a contact pair 71 in which no pockets are machined into either contact. In this case, the first contact, or base contact 73, is composed of several materials. The base contact 73 has a flat, planar upper surface 75 which is first coated with a bonding layer 77. Then, a liquid metal layer 78 is deposited on top of the bonding layer 77. The second contact 79 has a flat lower surface 70. In Figure 19, this contact pair 71 is shown in the open position. In the closed position, the second contact 79 is pressed against the liquid metal layer 78 and makes electrical contact. The liquid metal layer 78 is included in this case by attraction to the bonding layer 77. From the above, it will be further understood that one advantage achieved by this disclosure is the addition of a pocket for accommodating a galinstan alloy, thereby preventing mechanical damage to the wettable intermetallic layer and improving the durability of the contact. Furthermore, by coating the metal contact (e.g., tungsten) with a thin layer of tantalum, wetting by liquid metals such as galinstan alloys becomes possible, and tungsten can be used as a bulk material. Tungsten is tantalum (1.3 & 10 -7 Resistivity lower than ohms (5.6 × 10⁻¹⁰) -8 It has an ohm-meter value and therefore provides low resistance to the device.

[0191] Power relay circuit design options The aforementioned actuator and contact mounting configurations may be combined to provide a power relay circuit, as will be described more fully below.

[0192] Relay structure A MEMS relay is an assembly of a MEMS actuator and one or more sets of contacts. The aforementioned MEMS actuator is constructed using a set of microfabricated layers, and the two aforementioned methods for forming very low-resistance contacts are components of the relay. This low contact resistance is crucial for constructing small, high-current relays, as it allows the relay to operate without a large heatsink to dissipate the energy that would otherwise be converted into heat in conventional contact sets.

[0193] Dielectric breakdown voltage (standoff) When a relay is in its open state, it must be able to prevent arc discharge between its input and output contacts. The relationship between the voltage applied between the two contacts and the distance the arc travels between the two contacts is described by the Paschen curve for a particular gas at a given pressure. Other factors, including the type and pressure of any gas or liquid filling the gap between the contacts, also apply. For a given contact configuration, the maximum voltage that can be applied without generating an arc is called the dielectric breakdown voltage. The rating of a relay is the dielectric breakdown voltage between the contacts. A typical commercial relay designed to operate at 120VAC has a dielectric breakdown voltage of 750 volts or 1000 volts.

[0194] Geometric shape of the contact point The geometry of the contacts plays a crucial role in the function of a power relay. The resistance of a metal structure is inversely proportional to the cross-sectional area through which the current flows and linearly proportional to the length of the current path through the metal. In MEMS devices, the cross-sectional area is inherently limited by the small size of the device. To minimize resistance, the length of the current path through the entire relay must also be minimized. The design in question achieves this by using the crossbar method. One variation of this design is shown in Figures 23A and 23B. Figure 23A shows the relay 80 in its open state. Figure 23B shows the relay 80 in its closed or conducting state. The input contact 81 and output contact 82 are arranged at the same height as each other across a gap 83. The gap 83 is sized to provide adequate isolation to prevent arc discharge at the relay's rated voltage. This gap size is calculated based on the voltage required for the relay to withstand and the dielectric value and pressure of the gas or liquid filling the space within the gap.

[0195] The relay includes a movable contact 84 in addition to fixed contacts 81 and 82. This contact is connected to a magnetic rotor 85. The rotor 85 is set in an opening of one or more coils (not shown in this figure) which, when current flows through the coils, can apply an axial force to the rotor 85 and, therefore, to the movable contact 84.

[0196] As shown in Figure 23A, when the movable contact 84 is in the open position, the relay 80 is in an open state, and current cannot flow from the input contact 81 to the output contact 82.

[0197] Figure 23B shows the same relay 80 with a set of contacts 81, 82 and rotor 85 in the closed position. In this state, a movable contact 84 in the form of a crossbar makes physical and electrical contact with the input contact 81 and the output contact 82. Current can now flow through the relay 80 in the opposite direction, from the input contact 81 through the movable contact 84 or the crossbar to the output contact 82, or from contact 82 through the movable contact 84 to the other contact 81.

[0198] Actuator considerations Since the actuation force is proportional to the acceleration, the sum of the initial forces at the start of the stroke (the sum of dynamic resistances caused by latching, actuation, adhesion of the liquid metal, hydrodynamics, and bending forces) disproportionately determines the time required to switch. To maximize the force at the start of the stroke, the bending section can be used like a spring or preload. In this application, the bending section can be designed to be in the opposite direction to the latching force and to provide a smaller release force. This release force from the bending section, combined with the force caused by the magnet in the magnetic field from the coil, increases the acceleration as the plunger moves away from the latched position.

[0199] The actuator must provide sufficient travel distance to open an appropriate gap between the crossbar and the contact pair. This distance must be at least half of the required dielectric breakdown distance. The gap 86 between the input contact 81 and the movable contact 84 or the crossbar, and the associated gap between the movable contact 84 and the output contact 82 are electrically in series. Therefore, the dielectric breakdown of the two gaps may be added together. Since the gap sizes are equal by the design of the crossbar and contacts, each gap must support an equal portion of the total dielectric breakdown. The gap supported by the MEMS actuator is 200 micrometers. Other gap distances that provide a useful standoff voltage are 100–150 micrometers, 150–200 micrometers, or 200–250 micrometers or more.

[0200] Contact point considerations One of the most important attributes of a relay is its contact resistance. When electricity flows through a relay, some of the energy is converted into heat. The amount of energy released (watts) is the product of the resistance and the square of the current. When two rigid surfaces are placed in contact, they only make contact at a few points on the surface that are the highest points of the irregularities. If more force is applied to press the contacts against each other, the irregularities deform and become flat, increasing the surface contact area and consequently decreasing the electrical resistance. In small relays, it is difficult to generate a large contact force due to the small physical size of the magnet and coil. In a standard small relay, the contact resistance is typically in the range of 30 to 50 milliohms. A novel solution to this contact resistance problem in this invention is to incorporate one of two options for low-resistance, low-contact-force contacts. These techniques, which are described separately elsewhere, are microfabricated arrays of stabilized liquid-solid contacts and flexible contacts.

[0201] For either the stabilized liquid-solid contact or the microfabricated array of the flexible contact solutions described above, the specialized contact material may be applied to either the fixed contact or the movable contact, or both. In Figure 24, the wetted surface 74 of the liquid-solid contact may be applied to the surfaces of both fixed contacts 81, 82 closest to the movable contact 84, or to the surface of the movable contact 84 closest to the fixed contacts 81, 82.

[0202] In the case of the aforementioned array of micro-machined flexible contacts, the flexible contacts are machined onto one of the contact surfaces of each contact pair. Thus, the surfaces of the input contact 81 and output contact 82 closest to the movable contact 84 may have an array of micro-machined contacts, or the surface of the movable contact 84 closest to the two contacts 81, 82 may be covered with such an array.

[0203] Other contact arrangements Conventional relays are available in multiple circuit configurations or "forms." Each form specifies the number of poles and throws. Poles refer to the number of parallel switches controlled by the relay. Poles can be any number, but are often 1 to 3. Throws refer to the number of positions the relay can conduct. Typically, throws are either 1 or 2 and are often called single-throw or double-throw. For example, a relay incorporating multiple switching switches may be described as single-pole, double-pole, or triple-pole, with each pole referring to an individual switch. A double-pole double-throw relay has two separate switches, each with a common terminal that can be connected to one of two switching terminals. In a non-latching relay, one of the two switching terminals is generally called normally open (NO), and the other terminal is generally called normally closed (NC). The terms NC and NO do not apply to latching relays, as they are stable with no power applied in either the open or closed state.

[0204] Multithrow array The MEMS relays described herein can also be configured to support multiple poles and multiple throws. Figures 25A and 25B show configurations that support both normally open (NO) and normally closed (NC) contacts. In Figure 25A, the relay 87 includes two crossbars 88, 89 arranged at both ends of the rotor 90 and mounted at both ends. The relay 87 also includes two pairs of fixed contacts: an upper pair 91, 92 and a lower pair 93, 94. In Figure 25A, the contact pair 93, 94 is open, and the upper contact pair 91, 92 is closed. Since the crossbar 89 is not in contact with these contacts 93, 94, current cannot flow from contact 93 to contact 94. Current can flow from contact 91 to 92 via the upper crossbar 88.

[0205] Figure 25B shows an alternate state of relay 87. The rotor 90 is electromagnetically driven to the lower position in the figure. Here, current can flow from contact 93 to contact 94 via the crossbar 89. The upper contacts 91 and 92 are now separated from the upper crossbar 88, and as a result, the upper set of contacts 91 and 92 is in the open state.

[0206] Multi-pole array MEMS relays may be assembled with more complex arrangements of crossbars and contacts. Figure 26 shows a top view of a two-pole relay design 95. Device 95 includes two crossbars 96, 97 that are parallel to each other and mounted on a common rotor. Each of the two crossbars is positioned above a pair of fixed contacts. The left crossbar 96 is positioned above fixed contact 98, and the crossbar 97 is positioned above fixed contact 99. All four fixed contacts 98, 99 are arranged so that their top surfaces are coplanar. When the rotor presses the crossbars 96, 97 against the fixed contacts 98, 99, two separate circuits are closed. When the rotor pulls the crossbars 96, 97 away from the fixed contacts 98, 99, both circuits open.

[0207] It can be seen that three or more poles can be formed by adding additional crossbars and sets of contacts. Arrays of liquid-solid contacts or micro-machined contacts provide the necessary compliance to enable connection at all contact surfaces, even in situations where the fixed contact surfaces are not perfectly coplanar.

[0208] Multi-throw, multi-pole array Those skilled in the art of relay design will understand that a multi-throw, multi-pole relay can be formed by combining the two concepts shown in Figures 25A, 25B, and 26.

[0209] Dielectric filling material The standoff voltage between a set of contacts is affected by the medium filling the gap between the contacts. Various gases and liquids can provide significantly higher standoff voltages than air for a given distance between contacts. The relationship between pressure, distance, and standoff voltage is described by Paschen's law, which allows for the prediction of the standoff voltage. Relay design involves enclosing it in an hermetically sealed package. The package may be filled with a gas or liquid having a high dielectric constant to increase the standoff voltage. Further increases are possible by increasing the pressure of the gas in the package. Suitable gases for this use include nitrogen, argon, and sulfur hexafluoride (SF6). Suitable liquids include hexamethyldisiloxane or octamethyltrisiloxane.

[0210] Extended implementation form Multiple crossbars and contact sets for N-pole M-throw switching

[0211] Displacement of electrode by liquid (hexamethyldisiloxane)

[0212] Replacement of the bent portion by the bearing surface

[0213] Replacement of wet junctions by cantilevered microarrays

[0214] Replacement of lamination adhesive by welding

[0215] It should be understood that various modifications can be made to this disclosure to enhance its usefulness. Further embodiments can be provided by combining the various embodiments described above. The aspects of the embodiments can be modified to use concepts from various patents, applications, and publications to provide further embodiments, as needed.

[0216] This application claims priority to U.S. Patent Application No. 63 / 508,748, filed on 16 June 2023, which is incorporated herein by reference in its entirety.

Claims

1. An electrical relay circuit for use with a load, A stator assembly having a chamber that penetrates and is partially defined along a central longitudinal axis, the stator assembly comprising: a non-conductive substrate having a top surface; one or more layers containing components with which the load interacts mechanically or electrically; a first ferromagnetic layer adjacent to a spacer; a first plurality of coils adjacent to the first ferromagnetic layer; a second ferromagnetic layer adjacent to the first plurality of coils; a second plurality of coils adjacent to the second ferromagnetic layer; and a third ferromagnetic layer adjacent to the second plurality of coils, the bottom surface of the third ferromagnetic layer defining the upper end of the chamber, A plunger assembly located within the chamber of the stator assembly, which moves along the central longitudinal axis between a first position and a second position during operation, the plunger assembly includes a plunger comprising a pair of ferromagnetic plates in which a magnet is located, wherein (i) the first ferromagnetic plate of the pair of ferromagnetic plates is located between the first and second ferromagnetic layers, and (ii) the second ferromagnetic plate of the pair of ferromagnetic plates is located between the second and third ferromagnetic layers, and An electrical relay circuit equipped with this.

2. The pair of ferromagnetic plates and the first, second, and third ferromagnetic layers further cooperate to drive at least one contact, and each contact is A first contact member having an exposed surface, wherein the exposed surface has irregularities that form one or more high and low points on the exposed surface, A second contact member having a base surface and a plurality of conductive bends extending from the base surface. Includes, The first contact member and the second contact member are movable relative to each other to provide distinct open and closed positions. The electric relay circuit according to claim 1, wherein when the first contact member is positioned adjacent to the second contact member in a closed position in which the base surface of the second contact member is not in electrical contact with one or more high points on the exposed surface of the first contact member, each of the plurality of conductive bends is in electrical contact with the exposed surface of the first contact member.

3. The pair of ferromagnetic plates and the first, second, and third ferromagnetic layers further cooperate to drive at least one contact, and each contact is A first contact member having a base with an exposed surface, wherein the base has a first pocket opening to the exposed surface, and the first pocket has an outer side wall and a bottom wall defining the interior of the first pocket, A first metal layer located on the bottom wall of the first pocket, the first metal layer having an upper surface below the exposed surface of the first contact member, A liquid metal layer located only on the upper surface of the first metal layer and extending above the exposed surface of the first contact member, A second contact member having a contact surface, wherein the second contact member is positioned adjacent to the first contact member in an open position, and is movable to a closed position in which the contact surface of the second contact member contacts and compresses the liquid metal layer and the first metal layer until the contact surface of the second contact member abuts against the exposed surface of the first contact member. The electrical relay circuit according to claim 1, including the following:

4. The electric relay circuit according to claim 1, comprising a cavity in which the stator assembly and plunger are formed, wherein the cavity is filled with a dielectric gas.

5. The electrical relay circuit according to claim 1, comprising a cavity in which the stator assembly and plunger are formed, wherein the cavity is filled with a dielectric liquid.

6. The electrical relay circuit according to claim 1, wherein the electrical relay circuit is structured to provide a double-throw type.

7. The electrical relay circuit according to claim 2, wherein the electrical relay circuit is structured to provide a double-throw type.

8. The electrical relay circuit according to claim 3, wherein the first pocket includes one or more arms extending from the main pocket, the arms being slender compared to the size of the first pocket, and the arms having a bottom surface and sides.

9. The electrical relay circuit according to claim 8, wherein the surface bottom wall of the first pocket is treated to attract the liquid metal, and the bottom and side surfaces of the arm are treated to repel the liquid metal.

10. The electrical relay circuit according to claim 9, wherein the bottom surface of the first pocket is treated by applying a coating of a material that wets the liquid metal.

11. The electrical relay circuit according to claim 3, wherein only a portion of the bottom of the first pocket is treated such that the portion of the bottom wall of the first pocket attracts the liquid metal.

12. The electrical relay circuit according to claim 11, wherein the portion of the bottom wall of the first pocket is treated by applying a coating of a material that wets the liquid metal.

13. An electrical relay circuit for use with a load, A stator assembly having a chamber that penetrates and is partially defined along a central longitudinal axis, the stator assembly comprising: a non-conductive substrate having a top surface; one or more layers containing components with which the load interacts mechanically or electrically; a first ferromagnetic layer adjacent to a spacer; a first plurality of coils adjacent to the first ferromagnetic layer; a second ferromagnetic layer adjacent to the first plurality of coils; a second plurality of coils adjacent to the second ferromagnetic layer; and a third ferromagnetic layer adjacent to the second plurality of coils, the bottom surface of the third ferromagnetic layer defining the upper end of the chamber, A plunger assembly located within the chamber of the stator assembly, which moves along the central longitudinal axis between a first position and a second position during operation, wherein the plunger assembly includes a plunger comprising a pair of ferromagnetic plates in which a magnet is located, (i) the first ferromagnetic plate of the pair of ferromagnetic plates is located between the first and second ferromagnetic layers, and (ii) the second ferromagnetic plate of the pair of ferromagnetic plates is located between the second and third ferromagnetic layers, The pair of ferromagnetic plates and the first, second, and third ferromagnetic layers further cooperate to drive two or more contacts. Equipped with, Each contact point is A first contact member having an exposed surface, wherein the exposed surface has irregularities that form one or more high and low points on the exposed surface, A second contact member having a contact surface and a plurality of conductive bends extending from the contact surface. Includes, The first contact member and the second contact member are movable relative to each other to provide distinct open and closed positions. An electrical relay circuit in which, when the first contact member is positioned adjacent to the second contact member in a closed position in which the contact surface of the second contact member is not electrically in contact with one or more high points on the exposed surface of the first contact member, each of the plurality of conductive bends electrically contacts the exposed surface of the first contact member.

14. The electrical relay circuit according to claim 13, wherein all of the plurality of conductive bends extending from the contact surface of the second contact member have the same height above the contact surface of the first contact member, and the height is greater than the sum of a first distance between the high point and the low point on the exposed surface of the first contact member and the separation distance between the exposed surface of the first contact member and one or more high points on the contact surface of the second contact member when the first contact member is in the closed position.

15. The electrical relay circuit according to claim 13, wherein the plurality of conductive bent portions are formed at less than a right angle to the contact surface of the second contact member.

16. The electrical relay circuit according to claim 13, wherein each of the plurality of conductive bends has a planar geometric profile with dimensions of 10 to 50 microns in one direction and 10 to 50 microns in a dimension perpendicular to the one direction, and further includes a gap of 20 to 200 microns between adjacent bends.

17. An electrical relay circuit for use with a load, A stator assembly having a chamber that penetrates and is partially defined along a central longitudinal axis, the stator assembly comprising: a non-conductive substrate having a top surface; one or more layers containing components with which the load interacts mechanically or electrically; a first ferromagnetic layer adjacent to a spacer; a first plurality of coils adjacent to the first ferromagnetic layer; a second ferromagnetic layer adjacent to the first plurality of coils; a second plurality of coils adjacent to the second ferromagnetic layer; and a third ferromagnetic layer adjacent to the second plurality of coils, the bottom surface of the third ferromagnetic layer defining the upper end of the chamber, A plunger assembly located within the chamber of the stator assembly, which moves along the central longitudinal axis between a first position and a second position during operation, wherein the plunger assembly includes a plunger comprising a pair of ferromagnetic plates in which a magnet is located, (i) the first ferromagnetic plate of the pair of ferromagnetic plates is located between the first and second ferromagnetic layers, and (ii) the second ferromagnetic plate of the pair of ferromagnetic plates is located between the second and third ferromagnetic layers, The pair of ferromagnetic plates and the first, second, and third ferromagnetic layers further cooperate to drive at least one contact. Equipped with, The aforementioned at least one contact is A first contact member having a base with an exposed surface, wherein the base has a first pocket opening to the exposed surface, and the first pocket has an outer side wall and a bottom wall defining the interior of the first pocket, A first metal layer located on the bottom wall of the first pocket, the first metal layer having an upper surface below the exposed surface of the first contact member, A liquid metal layer located only on the upper surface of the first metal layer and extending above the exposed surface of the first contact member, A second contact member having a contact surface, wherein the second contact member is positioned adjacent to the first contact member in an open position, and is movable to a closed position in which the contact surface of the second contact member contacts and compresses the liquid metal layer and the first metal layer until the contact surface of the second contact member abuts against the exposed surface of the first contact member. An electrical relay circuit, including one.

18. The electrical relay circuit according to claim 17, further comprising a second pocket formed on the exposed surface of the first contact member, the second pocket having a bottom wall that is tangent to the first pocket and is located below the exposed surface of the first contact member and above the bottom wall of the first pocket, the second pocket further comprising an external side wall and a bottom wall that define the interior of the second pocket, and a portion of the interior of the second pocket overlaps with the interior of the first pocket.

19. The electrical relay circuit according to claim 17, wherein the liquid metal layer is formed from a compliant material that is displaced by the pressure applied by the second contact member in the closed position and returns to its original shape in response to the second contact member moving to the open position.

20. The electrical relay circuit according to claim 18, wherein the excess material from the liquid metal layer is displaced into the second pocket in response to the pressure from the second contact member moving to the closed position, and when the second contact member moves to the open position, the excess material from the liquid metal layer is driven to return to its original shape as a meniscus in response to the repulsive force generated between the material forming the first contact member and the material forming the liquid metal layer.

21. The electrical relay circuit according to claim 20, wherein the repulsive force is further generated by the surface tension in the liquid metal layer.

22. An electrical relay circuit for use with a load, A stator assembly having a chamber that penetrates and is partially defined along a central longitudinal axis, the stator assembly comprising: a non-conductive substrate having a top surface; one or more layers containing components with which the load interacts mechanically or electrically; a first ferromagnetic layer adjacent to a spacer; a first plurality of coils adjacent to the first ferromagnetic layer; a second ferromagnetic layer adjacent to the first plurality of coils; a second plurality of coils adjacent to the second ferromagnetic layer; and a third ferromagnetic layer adjacent to the second plurality of coils, the bottom surface of the third ferromagnetic layer defining the upper end of the chamber, A plunger assembly located within the chamber of the stator assembly, which moves along the central longitudinal axis between a first position and a second position during operation, wherein the plunger assembly includes a plunger comprising a pair of ferromagnetic plates in which a magnet is located, (i) the first ferromagnetic plate of the pair of ferromagnetic plates is located between the first and second ferromagnetic layers, and (ii) the second ferromagnetic plate of the pair of ferromagnetic plates is located between the second and third ferromagnetic layers, The pair of ferromagnetic plates and the first, second, and third ferromagnetic layers further cooperate to drive at least one contact. Equipped with, The aforementioned at least one contact is A first contact member having a base with an exposed surface, The first metal layer on the upper surface, A liquid metal layer located only on the upper surface of the first metal layer and extending above the exposed surface of the first contact member, A second contact member having a contact surface, wherein the second contact member is positioned adjacent to the first contact member in an open position, and is movable to a closed position in which the contact surface of the second contact member contacts and compresses the liquid metal layer and the first metal layer until the contact surface of the second contact member abuts against the surface of the first contact member. An electrical relay circuit, including one.

23. The electrical relay circuit according to claim 22, wherein the liquid metal layer is formed from a compliant material that is displaced by the pressure applied by the second contact member in the closed position and returns to its original shape in response to the second contact member moving to the open position.

24. The circuit according to claim 23, wherein tungsten is located within the first contact member, a galinstan alloy is located within the liquid metal layer, and the liquid metal layer has a meniscus shape when not under pressure, the meniscus shape of the liquid metal layer is compressed into a compressed shape in response to pressure applied by the second contact member to the liquid metal layer, and in response to further pressure from the second contact member, excess material from the liquid metal layer is displaced into a pocket within the first contact member, and when the second contact member moves to the open position, the excess material from the liquid metal layer returns to the meniscus shape in response to the repulsive force between the tungsten in the first contact member and the galinstan alloy in the liquid metal layer.

25. The electrical relay circuit according to claim 24, wherein the repulsive force includes the surface tension in the liquid metal layer.

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