Electrically controllable privacy glazing with energy recovery booster

Abstract

A drive for an electrically dynamic structure can store and release energy during the polarity cycle to improve the energy efficiency of operation. In some examples, the drive includes an energy storage element. In operation, the drive can charge an electrically controllable optically active material to a first operating voltage in a first polarity and then discharge the optically active material during polarity reversal. The drive can store the energy released from the optically active material during discharge and subsequently release the energy to charge the optically active material to a second operating voltage with a second polarity different from the first.

Description

This application claims the benefit of U.S. provisional patent application No. 62 / 669,005, filed on May 9, 2018, the full content of which is incorporated herein by reference. TECHNICAL FIELD OF THE INVENTION This disclosure relates to structures that include an electrically controllable optically active material and, more particularly, to drives for controlling the electrically controllable optically active material. BACKGROUND OF THE INVENTION Windows, doors, partition walls, and other structures with controllable light modulation have been gaining popularity in the market. These structures are commonly known as “smart” or “privacy” structures because of their ability to transform from a transparent state, where a user can see through the structure, to a private state where visibility is blocked. For example, smart windows are used in luxury cars and homes, and smart partition walls are used in office spaces to provide controlled privacy and visual obscuration. A variety of different technologies can be used to provide controlled optical transmission to a smart structure. For example, electrochromic, photochromic, thermochromic, suspended particle, and liquid crystal technologies are used in different smart structure applications to provide controllable privacy. These technologies generally use a power source, such as electricity, to transform from a transparent state to a private state and vice versa. In practice, an electrical driver can be used to control or "drive" the optically active material. The driver can apply or stop applying electrical energy to the optically active material to transition it between a transparent state and a privacy state, or vice versa. Additionally, the driver can apply an electrical signal to the optically active material once it has transitioned to a particular state to help maintain that state. For example, the driver can apply an electrical signal of alternating polarity to the optically active material to transition it between states and / or maintain it in a transition state.When configured in this way, the process of changing the structure's polarity from one polarity to the other may require discharging the structure from a falling voltage to zero and then charging it from zero volts to an operating voltage in the opposite polarity. This consumes electrical energy, which affects the structure's overall energy efficiency. BRIEF DESCRIPTION OF THE INVENTION In general, this disclosure relates to privacy structures that incorporate an electrically controllable, optically active material providing controllable privacy. Privacy structures can be implemented in the form of a window, door, skylight, interior partition wall, or other structure where controllable visible transmittance is desired. In any case, the privacy structure can be fabricated from multiple panels of transparent material with an electrically controllable medium between them. Each panel of transparent material can carry a layer of electrodes, which can be implemented as a layer of electrically conductive, optically transparent material deposited on the panel.The optically active material can be controlled, for example, by an electrically coupled driver connected to the electrode layers, by controlling the application and / or removal of electrical energy to the optically active material. For instance, the driver can control the application and / or removal of electrical energy from the optically active material, thereby causing it to transition from a dispersed state, where visibility through the structure is inhibited, to a transparent state, where visibility through the structure is relatively clear. The electrical driver, which may also be called a controller, can be designed to receive power from a power source, such as a rechargeable and / or replaceable battery and / or a wall or mains power supply. The electrical driver can condition the electricity received from the power source, for example, by changing the frequency, amplitude, waveform, and / or other characteristics of the electricity received from the power source. The electrical driver can supply the conditioned electrical signal to electrodes that are electrically coupled to the optically active material. Furthermore, in response to user input or other control information, the electrical driver can change the conditioned electrical signal supplied to the electrodes and / or stop supplying electricity to the electrodes.Consequently, the electrical driver can control the electrical signal supplied to the optically active material, thereby controlling the material to maintain a specific optical state or to transition from one state (e.g., a transparent or dispersive state) to another state. In some configurations according to this disclosure, an electrical drive is configured to recover the energy released when the polarity of the electrically controllable optically active material is changed, for example, instead of discharging the released energy to ground. For example, the drive may include one or more energy storage elements. In operation, the drive may charge the electrically controllable optically active material to a first polarity or charging stage, for example, in which a first layer of electrodes functions as the anode and a second layer of electrodes functions as the cathode.To alternate the polarity, the driver can discharge the electrically controllable optically active material and then recharge the electrically controllable optically active material to a second polarity or charging stage, for example, in which the first electrode layer functions as the cathode and the second electrode layer functions as the anode. To improve the energy efficiency of the drive, it can store the energy released from the electrically controllable optically active material (ECA) during the discharge process in one or more energy storage elements. The drive can then use this stored energy, for example, in addition to energy supplied by a separate power source, to deliver electricity at an operating voltage to the ECA at a polarity opposite to the polarity to which the ECA was originally driven. In this way, the drive can recover and reuse energy during the polarity change, reducing the energy requirements of the privacy structure. In one example, the structure of an electrically dynamic window is described. The structure includes a first panel of transparent material, a second panel of transparent material, and an electrically controllable optically active material located between the first and second transparent panels. The electrically controllable optically active material is positioned between a first and a second electrode layer. The structure also includes a drive electrically connected to the first and second electrode layers. The drive is electrically connected to a power supply and configured to provide a pulse signal to the first and second electrode layers to control the electrically controllable optically active material.In the example, the drive includes an Ln / nznz / E / YiAi energy storage element and is configured to: charge the electrically controllable optically active material to a first charge state, then discharge the electrically controllable optically active material in a first discharge process, which includes storing energy in the energy storage element released from the electrically controllable optically active material during the first discharge process, and then charge the electrically controllable optically active material to a second charge state, opposite to the first charge state. In another example, an electric drive is described for driving an electrically dynamic window structure. The drive includes a power supply and a switching network. The switching network includes first, second, third, and fourth switching mechanisms. The first switching mechanism is coupled between a first side of a privacy structure and ground, where the privacy structure includes an electrically controllable optically active material located between a first electrode carried by a first panel of transparent material and a second electrode carried by the second panel of transparent material. The second switching mechanism is coupled between a second side of the privacy structure and ground. The third switching mechanism is coupled between the power supply and the first side of the privacy structure.The fourth switching mechanism is coupled between the power supply and the second side of the privacy structure. The example specifies that the switching network is arranged in an H-bridge configuration to provide bidirectional power to the privacy structure. The example drive also includes a first energy storage element and a second energy storage element. The second energy storage element is coupled between the first side of the privacy structure and the first and third switching mechanisms. The drive also includes a third energy storage element coupled between the second side of the privacy structure and the second and fourth switching mechanisms.Furthermore, the example drive includes a controller in communication with the switching network and configured to selectively switch the first, second, third, and fourth switching mechanism so that energy is transferred from the power supply to the electrically controllable optically active material to charge the electrically controllable optically active material in a first polarity, energy is transferred from the electrically controllable optically active material to the second energy storage element and / or the third energy storage element, and energy is transferred from the second energy storage element and / or the third energy storage element to the first energy storage element. In another example, a method is described for supplying electrical power to a privacy structure and recapturing energy to a first energy storage element from the privacy structure by adjusting a switching network configuration. The example method is carried out with a switching network that includes a first switching mechanism, a second switching mechanism, a third switching mechanism, and a fourth switching mechanism arranged in an H-bridge configuration, where the privacy structure includes an electrically controllable optically active material located between a first electrode layer and a second electrode layer.The method includes closing the third switching mechanism and the second switching mechanism to cause current to flow from an energy source, through a second energy storage element, through the privacy structure in a first direction, and to a third energy storage element to energize the second and third energy storage elements and / or the privacy structure. The method further includes opening the third switching mechanism and closing the first switching mechanism to cause current Ln / nznz / E / YiAi to flow in a loop through the privacy structure in the first direction, the third energy storage element, and the second energy storage element, so that energy is transferred from the second and third energy storage elements to the privacy structure.The method further involves eliminating the second current path by opening the first switching mechanism. The method also involves closing the first switching mechanism to cause current to flow through the privacy structure in a second direction opposite to the first, the second energy storage element, and the third energy storage element, thereby transferring energy from the privacy structure to the second and third energy storage elements.Furthermore, the method involves opening the first switching mechanism and closing the third switching mechanism to cause current to flow through the third energy storage element, through the privacy structure in the second direction, through the second energy storage element and to the first energy storage element so that energy is transferred from the privacy structure, the second energy storage element and / or the third energy storage element to the first energy storage element. In another example, a method is described for supplying electrical power to a privacy structure and recapturing energy to a first energy storage element from the privacy structure. The example method is carried out in a privacy structure that includes an electrically controllable optically active material located between a first electrode layer and a second electrode layer. The method involves arranging a plurality of switching mechanisms in a first load configuration such that a current flows in a first current path from a power source to the first electrode layer of the privacy structure in a first direction.The method involves arranging the plurality of switching mechanisms in a second load configuration, where the second load configuration creates a second current path that includes the privacy structure and a second energy storage element such that current flows through the privacy structure in the first direction. The method also involves arranging the plurality of switching mechanisms in a third load configuration, where the third load configuration eliminates the current flow paths to and from the privacy structure and maintains the privacy structure in a first load state.The method further includes arranging the plurality of switching mechanisms in a first discharge configuration such that the current flows through the second energy storage element and the privacy structure in a second direction opposite to the first direction. Additionally, the method includes arranging the plurality of switching mechanisms in a second discharge configuration such that the current flows through the privacy structure in the second direction to the first energy storage element. In another example, a drive for an electrically dynamic window structure is described. The drive includes a power supply, a switching network comprising a plurality of switching elements, a first energy storage element, and a controller.The controller is configured to adjust the plurality of switching elements for the purpose of: (a) charging the electrically dynamic window structure to a first charged state, (b) discharging the electrically dynamic window structure to a discharged state while storing the discharged energy from the dynamic window structure in the first energy storage element, (c) charging the electrically dynamic window structure to a first reverse charged state, where the first reverse charged state is opposite to the first charged state, (d) discharging the electrically dynamic window structure to a discharged state while storing energy discharged from the electrically dynamic window structure in the first energy storage element, and (e) repeating steps (a)-(d) at a predetermined frequency. Details of one or more examples are described in the accompanying drawings and in the description below. Other features, objects, and advantages will be apparent from the description, the drawings, and the claims. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a side view of an example privacy glazing structure. Figure 2 is a side view of the example privacy glazing structure of Figure 1 incorporated into a multi-pane insulating glazing unit. Figure 3 is an example schematic illustration showing an example connection arrangement of a driver to electrode layers of a privacy structure. Figure 4 shows an example driver signal applied between a first layer of electrodes and a second layer of electrodes over time. Figures 5A-5C illustrate an example of a switching network in the form of an H-bridge configuration for applying a reversible polarity voltage to a load. Figure 6 shows an example driver configuration that includes a switching network and a plurality of energy storage devices in communication with it. Figures 7A-7D illustrate an example charging process for charging a load through an impeller as shown in Figure 6. Figures 8A-8D illustrate an example discharge process for discharging a charge through an impeller like the one shown in Figure 6. Figures 9A-9D illustrate an example reverse charging process for charging a load in an opposite polarity with respect to the charging process of Figures 7A-7D using a driver as shown in Figure 6. Figures 10A-10D illustrate an example reverse discharge process for discharging a reverse-charged load through an impeller like the one shown in Figure 6. Figure 11 shows an example graph of voltage versus time signals from a driver for two different optical states for an optically active material. Figure 12 is a process flow diagram illustrating an example control process for operating an optically active material, such as in an electrically dynamic window. DETAILED DESCRIPTION OF THE INVENTION In general, this disclosure is directed to electrical control systems, devices, and methods for controlling optical structures that have controllable light modulation. For example, an optical structure may include an electrically controllable optically active material that provides a controlled transition between a privacy or scattering state and a visible or transmittance state. An electrical controller, or driver, may be electrically coupled to the optically active material through electrode layers that delimit the material. The electrical driver may be powered by a power source and may condition the electricity received from the power source, for example, by changing the frequency, amplitude, waveform, and / or other characteristics of the electricity received from the power source. The electrical driver may then send the conditioned electrical signal to the electrodes.Furthermore, in response to user input or other control information, the electrical driver can change the conditioned electrical signal supplied to the electrodes and / or stop supplying electricity to the electrodes. Consequently, the electrical driver can control the electrical signal supplied to the optically active material, thereby controlling the material to maintain a specific optical state or to transition from one state (e.g., a transparent or dispersive state) to another. As discussed in more detail below, an electrical drive, according to the disclosure, can periodically change the polarity of the electricity supplied to the privacy structure. When the electrically controllable optically active layer is implemented as a liquid crystal material, this periodic polarity reversal can help prevent ions within the optically active material from preferentially migrating toward an electrode layer, a phenomenon sometimes referred to as ion deposition. In some examples, the drive includes hardware and / or software to recover and reuse the energy released during the polarity change and / or the transition between optical states. For example, the drive may include multiple switching mechanisms, each configured to open and / or close during operation to establish different electrical charging and / or discharging pathways.The drive may also include an energy storage element. In operation, the drive can control switching mechanisms to electrically couple and decouple the energy storage element from the electrically controllable optically active material. Consequently, the energy storage element can capture and store the energy released when the electrically controllable optically active material is discharging and subsequently return the stored electrical energy to the optically active material during subsequent charging. Example electric drive configurations and electrical control features are described in more detail in Figures 3-10. However, Figures 1 and 2 first describe example privacy structures that can use an electric drive arrangement as described herein. Figure 1 is a side view of an example privacy glazing structure comprising a first transparent material panel 14 and a second transparent material panel 16, with an optically active material layer 18 sandwiched between the two transparent panels. The privacy glazing structure 12 also includes a first electrode layer 20 and a second electrode layer 22. The first electrode layer 20 is carried by the first transparent material panel 14, while the second electrode layer 22 is carried by the second transparent material panel. In operation, electricity supplied through the first and second electrode layers 20 and 22 can control the optically active material 18 to regulate visibility through the privacy glazing structure. The privacy glazing structure 12 can utilize any suitable privacy material for the optically active material layer 18. Furthermore, although the optically active material 18 is generally illustrated and described as a single material layer, it should be appreciated that a structure conforming to the disclosure may have one or more layers of optically active material with the same or different thicknesses. In general, the optically active material 18 is configured to provide controllable and reversible optical darkening and lightening. The optically active material 18 may be an electrically controllable optically active material that changes the direct visible transmittance in response to changes in the electrical energy applied to the material. In one example, optically active material 18 is formed from an electrochromic material that changes its opacity, and therefore its light transmission properties, in response to changes in voltage applied to the material. Typical examples of electrochromic materials are WO3 and MoOs, which are generally colorless when applied to a substrate in thin layers. An electrochromic layer can change its optical properties through oxidation or reduction processes. For example, in the case of tungsten oxide, protons can move within the electrochromic layer in response to a change in voltage, reducing the tungsten oxide to blue tungsten bronze. The intensity of the coloration varies depending on the magnitude of the charge applied to the layer. In another example, the optically active material 18 is a liquid crystal material. Different types of liquid crystal materials that can be used as optically active material 18 include polymer-dispersed liquid crystals (PDLCs) and polymer-stabilized cholesteric texture materials (PSCTs). Polymer-dispersed liquid crystals typically involve the phase separation of a nematic liquid crystal from a homogeneous liquid crystal containing a quantity of polymer sandwiched between electrode layers 20 and 22. When the electric field is switched off, the liquid crystals can be randomly dispersed. This scatters the light penetrating the liquid crystal and dissipates the light transmitted through the material.When a certain voltage is applied between the two electrode layers, the liquid crystals can align homeotropically and the optical transparency of the liquid crystals is increased, allowing light to be transmitted through the crystals. In the case of polymer-stabilized cholesteric texture (PSCT) materials, the material can be either a normal-mode polymer-stabilized cholesteric texture material or an inverse-mode polymer-stabilized cholesteric texture material. In a normal-mode polymer-stabilized cholesteric texture material, light is scattered when no electric field is applied. If an electric field is applied to the liquid crystal, it transitions to a homeotropic state, causing the liquid crystals to reorient themselves parallel to the direction of the electric field. This increases the optical transparency of the liquid crystals and allows light to be transmitted through the liquid crystal layer.In a polymer-stabilized inverse-mode cholesteric texture material, the liquid crystals are transparent in the absence of an electric field (e.g., a zero electric field), but opaque and light is scattered when an electric field is applied. In an example where the optically active material 18 layer is implemented using liquid crystals, the optically active material includes liquid crystals and a dichroic dye to provide a host-liquid crystal operating mode. When configured in this way, the dichroic dye can function as a guest compound within the liquid crystal host. The dichroic dye can be selected so that the orientation of the dye molecules follows the orientation of the liquid crystal molecules. In some instances, when an electric field is applied to the optically active material 18, there is little or no absorption along the short axis of the dye molecule, and when the electric field is removed from the optically active material, the dye molecules absorb along the long axis.As a result, the dichroic dye molecules can absorb light when the optically active material enters a dispersed state. When configured in this way, the optically active material can absorb incident light, preventing an observer on one side of the privacy glazing structure 12 from clearly seeing activity occurring on the opposite side. When the optically active material 18 is implemented using liquid crystals, the optically active material may include liquid crystal molecules within a polymer matrix. The polymer matrix may or may not be cured, resulting in a solid or liquid polymer medium surrounding the liquid crystal molecules. Furthermore, in some examples, the optically active material 18 may contain spacer microspheres (e.g., microspheres), having an average diameter of 3 to 40 micrometers, to maintain the separation between the first panel of transparent material 14 and the second panel of transparent material 16. In another example where the optically active material layer 18 is implemented using a liquid crystal material, the liquid crystal material l / ol Ln / nznz / E / YiAi becomes opaque when switched to the privacy state. Such a material can scatter the light incident upon it, preventing an observer on one side of the privacy glazing structure 12 from clearly observing the activity occurring on the opposite side. This material can significantly reduce the regular visible transmittance through the material (also known as direct visible transmittance), while only minimally reducing the total visible transmittance in the privacy state compared to the light-transmitting state.When these materials are used, the amount of scattered visible light transmitted through the material can increase in the privacy state compared to the light transmission state, thus compensating for the reduction in regular visible transmittance through the material. Regular or direct visible transmittance can be considered the transmitted visible light that is neither scattered nor redirected through the optically active material.18 Another type of material that can be used as an optically active material layer 18 is a suspended particle material. Suspended particle materials are typically dark or opaque in an unactivated state but become transparent when a voltage is applied. Other types of electrically controllable optically active materials can be used as optically active material 18, and disclosure is not limited in this respect. Regardless of the specific type of materials used for the optically active material layer 18, the material can switch from a light-transmitting state, in which the privacy glazing structure 12 is intended to be transparent, to a privacy state, in which visibility through the insulating glazing unit is intended to be blocked. The optically active material 18 can exhibit a progressive decrease in direct visible transmittance when transitioning from a state of maximum light transmission to a state of maximum privacy. Similarly, the optically active material 18 can exhibit a progressive increase in direct visible transmittance when transitioning from a state of maximum privacy to a state of maximum transmission.The rate at which the optically active material 18 transitions from a generally transparent transmission state to a generally opaque privacy state can be determined by a variety of factors, including the specific type of material selected for the optically active material 18, the temperature of the material, the electrical voltage applied to the material, and the like. To electrically control the optically active material 18, the privacy glazing structure 12 in the example in Figure 1 includes the first electrode layer 20 and the second electrode layer 22. Each electrode layer can be in the form of an electrically conductive coating deposited on or over the surface of each respective panel facing the optically active material 18. For example, the first panel of transparent material 14 can define an inner surface 24A and an outer surface 24B on an opposite side of the panel. Similarly, the second panel of transparent material 16 can define an inner surface 26A and an outer surface 26B on an opposite side of the panel. The first electrode layer 20 can be deposited on the inner surface 24A of the first panel, while the second electrode layer 22 can be deposited on the inner surface 26A of the second panel.The first and second electrode layers 20, 22 can be deposited directly onto the inner surface of a respective panel or one or more intermediate layers, such as a blocking layer, and deposited between the inner surface of the panel and the electrode layer. Each electrode layer 20, 22 can be an electrically conductive coating that is a transparent conductive oxide coating (“TCO”), such as aluminum-doped zinc oxide and / or tin-doped indium oxide. In some examples, the transparent conductive coatings forming the electrode layers 20, 22 define wall surfaces of a cavity between the first panel of transparent material 14 and the second panel of transparent material 16 with which the optically active material 18 comes into contact. In other examples, one or more different coatings can cover the first and / or second electrode layers 20, 22, such as a dielectric coating (e.g., silicon oxynitride).In any case, the first transparent material panel 14 and the second transparent material panel 16, as well as any coating on the inner faces 24A, 26A of the panels, can form a cavity or chamber containing the optically active material 18. The transparent material panels form the privacy glazing structure 12, which includes the first panel 14 and the second panel 16, and can be made of any suitable material. Each transparent material panel can be made of the same material, or at least one of the transparent material panels can be made of a different material than at least one other transparent material panel. In some examples, at least one of (and optionally all of) the panels of the privacy glazing structure 12 are made of glass. In other examples, at least one of (and optionally all of) the privacy glazing structures 12 are made of plastic, such as, for example, a fluorocarbon plastic, polypropylene, polyethylene, or polyester. When glass is used, the glass can be aluminum borosilicate glass, soda-lime glass (for example, sodium silicate-lime glass), or another type of glass.Furthermore, glass can be transparent or colored, depending on the application. Although glass can be manufactured using different techniques, in some examples it is produced on a float glass line where molten glass is poured into a bath of molten tin to shape and solidify the glass. Such glass may be called float glass. In some examples, the first panel 14 and / or the second panel 16 can be formed from multiple different types of materials. For example, the substrates can be formed from laminated glass, which may include two panels of Ln / nznz / E / YiAi glass bonded together with a polymer, such as polyvinyl butyral. Additional details regarding the privacy glazing substrate arrangements that may be used in this disclosure can be found in U.S. Patent Publication No. 2018 / 0307111, entitled “HIGH PERFORMANCE PRIVACY GLAZING STRUCTURES,” published on October 25, 2018, the full contents of which are incorporated herein by reference. The privacy glazing structure 12 can be used in any desired application, including in a door, window, wall (e.g., a partition door), skylight in a residential or commercial building, or other applications. To facilitate installation of the privacy glazing structure 12, the structure may include a frame 30 that surrounds the outer perimeter of the structure. In different examples, the frame 30 may be made from wood, metal, or a plastic material such as vinyl. The frame 30 may define a channel 32 that receives and supports the outer perimeter edge of the structure 12. The line of sight through the privacy glazing structure 12 is generally established as the location where the frame 30 ends and visibility through the privacy glazing structure 12 begins. In the example in Figure 1, the privacy glazing structure 12 is illustrated as a privacy cell formed by two panels of transparent material that enclose the optically active material 18. In other configurations, the privacy glazing structure 12 can be incorporated into a multi-panel glazing structure that includes a privacy cell having one or more additional panels separated by one or more gaps between panels. Figure 2 is a side view of an example configuration in which the privacy glazing structure 12 of Figure 1 is incorporated into a multi-panel insulating glazing unit having a gap between panels. As shown in the illustrated example in Figure 2, a multi-panel privacy glazing structure 50 can include a privacy glazing structure 12 separated from a panel (e.g., a third panel) of additional transparent material 52, for example, by a gap between panels 54 and a spacer 56. The spacer 56 can extend around the entire perimeter of the multi-panel privacy glazing structure 50 to hermetically seal the gap between panels 54 from gas exchange with the surrounding environment. To minimize heat exchange through the multi-panel privacy glazing structure 50, the gap between panels 54 can be filled with an insulating gas or even evacuated. For example, the gap between panels 54 can be filled with an insulating gas such as argon, krypton, or xenon.In such applications, the insulating gas can be mixed with dry air to provide a desired air-to-insulating gas ratio, such as 10 percent air and 90 percent insulating gas. In other examples, the space between panels 54 can be evacuated so that the space between panels is at a vacuum pressure relative to the pressure of an environment surrounding the multi-panel privacy glazing structure 50. Spacer 56 can be any structure that maintains opposing substrates in a spaced relationship throughout the service life of the multi-panel privacy glazing structure 50 and seals the interpane space 54 between opposing material panels, for example, to inhibit or eliminate gas exchange between the interpane space and the environment surrounding the unit. An example of a spacer that can be used as spacer 56 is a tubular spacer placed between the first transparent material panel 14 and the third transparent material panel 52. The tubular spacer can define a lumen or hollow tube, which, in some examples, is filled with a desiccant.The tubular spacer may have a first lateral surface that adheres (by means of a first microsphere of sealant) to the outer surface 24B of the first transparent material panel 14 and a second lateral surface that adheres (by means of a second microsphere of sealant) to the third transparent material panel 52. A top surface of the tubular spacer may be exposed to the space between panels 54 and, in some examples, includes openings that allow the gas within the space between panels to communicate with the desiccant material inside the spacer. Such a spacer may be manufactured from aluminum, stainless steel, a thermoplastic, or any other suitable material. Another example of a spacer that can be used as spacer 56 is a spacer formed from a corrugated metal reinforcing sheet surrounded by a sealant composition. The corrugated metal reinforcing sheet can be a rigid structural component that keeps the first panel of clear material 14 separated from the third panel of clear material 52. In yet another example, spacer 56 can be formed from a foam material surrounded by a metal sheet on all sides except one side that faces the gap between panels. As another example, spacer 56 can be a thermoplastic (TPS) spacer formed by placing a primary sealant (e.g., adhesive) between the first panel of clear material 14 and the third panel of clear material 52, followed, optionally, by a secondary sealant applied around the defined perimeter between the substrates and the primary sealant.Spacer 56 can have other configurations, as people of mid-level skill will appreciate. Depending on the application, the first transparent material panel 14, the second transparent material panel 16, and / or the third transparent material panel 52 (when included) can be coated with one or more functional coatings to modify the performance of the privacy structure. Examples of functional coatings include, but are not limited to, low-emissivity coatings, solar control coatings, and photocatalytic coatings. In general, a low-emissivity coating is designed to allow visible and near-infrared light to pass through a panel while substantially preventing far-infrared and mid-infrared radiation from passing through. A low-emissivity coating may include one or more layers of infrared reflective film sandwiched between two or more layers of transparent dielectric film.Infrared reflective film may include a conductive metal such as silver, gold, or copper. A photocatalytic coating, on the other hand, may be a coating that includes a photocatalyst, such as titanium dioxide. In practice, the photocatalyst may exhibit photoactivity that can aid in self-cleaning or reduce panel maintenance. The electrode layers 20 and 22 of the privacy glazing structure 12, whether implemented individually or as a multi-panel structure with a gap between panels, can be electrically connected to a driver. The driver can provide power and / or control signals to control the optically active material 18. In some configurations, wiring is used to establish an electrical connection between the driver and each respective electrode layer. A first wire can provide electrical communication between the driver and the first electrode layer 20, and a second wire can provide electrical communication between the driver and the second electrode layer 22.In general, the term wiring refers to any flexible electrical conductor, such as a metal wire optionally covered with an insulating coating, a flexible printed circuit board, a bus bar, or other electrical connector that facilitates electrical connection to the electrode layers. Figure 3 is a schematic illustration showing an example connection arrangement between a driver and electrode layers of a privacy structure. In the illustrated example, wires 40 and 42 electrically couple the driver 60 to the first electrode layer 20 and the second electrode layer 22, respectively. In some examples, wire 40 and / or wire 42 can be connected to their respective electrode layers through a conduit or hole in the transparent panel adjacent to the electrode layer. In other configurations, wire 40 and / or wire 42 can make contact with their respective electrode layers at the edge of the privacy structure 12 without requiring wire 40 and / or wire 42 to extend through other sections (e.g., transparent panels 14, 16) to reach the respective electrode layers.In any case, the impeller 60 can be electrically coupled to each of the electrode layers 20 and 22. In operation, the driver 60 can apply a voltage difference between the electrode layers 20 and 22, which creates an electric field across the optically active material 18. The optical properties of the optically active material 18 can be adjusted by applying and / or adjusting the voltage across the layer. In some embodiments, the effect of the voltage on the optically active material 18 is independent of the polarity of the applied voltage. For example, in some instances where the optically active material 18 comprises liquid crystals that align with an electric field between the electrode layers 20 and 22, the optical result of the crystal alignment is independent of the electric field's polarity. For instance, the liquid crystals can align with an electric field in one polarity and can rotate approximately 180° if the polarity is reversed.However, the optical state of liquid crystals (e.g., opacity) in any orientation can be approximately the same. Figure 4 shows an example of an alternating current trigger signal that can be applied between the first electrode layer 20 and the second electrode layer 22 over time. It will be appreciated that the signal in Figure 4 is an example and is used for illustrative purposes, and that any variety of signals applied from the driver can be used. In the example in Figure 4, a voltage signal between the first and second electrode layers produced by the driver varies with time between the applied voltages Va and -VA. In other words, in the illustrated example, a voltage of magnitude Va is applied between the first and second electrode layers, and the polarity of the applied voltage changes back and forth in time.The optical state (e.g., transparent or opaque) of the optically active material 18 can remain substantially unchanged while a voltage is applied to the optically active layer, even if the applied voltage varies over time. This is because the naked human eye cannot detect changes in the optically active material 18 in response to alternating current polarity. However, the optically active material 18 can change state (e.g., from transparent to opaque) if the driver stops supplying power to the optically active layer. As shown in the example in Figure 4, the voltage does not immediately reverse the polarity from Va to -Va. Instead, the voltage changes polarity over a transition time of 70 (shaded). In some examples, a sufficiently long transition time can generate an observable transition of the optically active material between polarities. For example, in one embodiment, liquid crystals in an optically active material can align with an electric field to create a substantially transparent structure and become substantially opaque when the electric field is removed. Therefore, when transitioning from Va (transparent) to -Va (transparent), a sufficiently slow transition between Va and Va can generate an observable optical state (e.g., opaque or partially opaque) when -VA < V < Va (e.g., when |V| ≤ Va).On the other hand, a sufficiently rapid transition between polarities (e.g., from Va to -Va) may appear to an observer (e.g., to the naked eye in real time) to produce no apparent change in the optical state of the optically active material. In some examples, if a particular optical state (e.g., a transparent state) is to be maintained, switching between the polarities corresponding to that optical state (e.g., between +Va and -Va) can prevent damage to the optically active material. For example, in some cases, a DC or static voltage applied to an optically active material can cause ionic coating within the structure, resulting in optical defects. To prevent this optical deterioration, a drive for an optically active material (e.g., in an electrically dynamic window such as a privacy structure) can be configured to continuously switch between the applied polarities of an applied voltage (e.g., Va) in order to maintain the desired optical state. One technique for applying a voltage of opposite polarity to a load (for example, an optically active material) is through a switching network, such as an H-bridge configuration. Figures 5A–5C illustrate an example of a switching network in the form of an H-bridge configuration for applying a voltage of reversible polarity to a load. As shown, the switching network 100 includes four switches, SW1, SW2, SW3, and SW4, arranged between a voltage source +V, a load 80, and ground. Figure 5A shows a general H-bridge configuration where switches SW1, SW2, SW3, and SW4 are all in a closed state. In the example in Figure 5B, switches SW3 and SW2 are closed, while switches SW4 and SW1 are open, placing a voltage of +V on the left side of load 80 and ground on the right side of load 80. Figure 5C shows another switching configuration, where switches SW4 and SW1 are closed and switches SW2 and SW3 are open, placing a voltage of +V on the right side of load 80 and ground on the left side of load 80. Thus, a voltage V is applied across load 80 in one polarity in the configuration of Figure 5B, and in the opposite polarity in the configuration of Figure 5C. In a traditional H-bridge switching network, repeatedly applying a voltage of one polarity to a load and then applying a voltage of the opposite polarity to the load can be inefficient. For example, with respect to a capacitive load, applying a voltage of one polarity can charge the capacitive load to the first voltage. However, applying the voltage of the second polarity requires first discharging the capacitive load from the first voltage to zero volts, and then charging the capacitive load to the first voltage in the opposite direction. This results in a loss of energy during each polarity reversal. According to some examples in this disclosure, a driver may include one or more energy storage elements combined with a switching network to capture stray energy from the load, for example, when the load is discharged, by applying a reverse polarity voltage to the load. Figure 6 shows an example driver configuration that includes a switching network and a plurality of energy storage devices communicating with the switching network. In the illustrated example, the driver 200 includes a power supply 210 shown applying a voltage Va, a ground 220, and a switching network 230 used to drive the load 240, for example, in opposite polarities. The switching network 230 may include one or more switching mechanisms capable of selectively electrically connecting and disconnecting components on either side of the switching mechanism.In various embodiments, the switching mechanisms may include transistors, such as metal-oxide-semiconductor field-effect transistors (MOSFETs) or similar. The power supply 210 may be a DC power supply (e.g., a battery), an AC power supply (e.g., a wall or mains electricity), or another suitable power source. The driving load 240 may be an electrically controllable optically active material 18 together with the first and second electrode layers 20, 22. In the example in Figure 6, the switching network 230 includes a first switching mechanism SW1 coupled between a first side 235 of a load 240 and ground 220, and a second switching mechanism SW2 coupled between a second side 245 of the load 240 and ground 220. In some examples, an isolating component 224 may selectively prevent or permit current flow from switching mechanisms SW1 and SW2 to ground 220. The switching network 230 further includes a third switching mechanism SW3 coupled between the first side 235 of the load 240 and the power supply 210, and a fourth switching mechanism SW4 coupled between the second side 245 of the load 240 and the power supply 210. It will be appreciated that, as used herein, being “coupled to” or “coupled between” components implies at least one electrical connection. indirect.However, unless otherwise stated, the expressions “coupled to” or “coupled between” do not require that the “coupled” components be directly connected to each other. The drive 200 in Figure 6 includes the first energy storage element SE1, which is shown in electrical communication with the third and fourth switching mechanisms, SW3 and SW4, respectively, and the power supply 210 on one side, and ground 220 on the other side. The insulating component 212 is shown positioned to selectively enable or disable current flow between the power supply 210 and other drive 200 components, such as the first energy storage element SE1 or the third and fourth switching mechanisms. The impeller 200 further includes a second energy storage element SE2 coupled to the first side 235 of the load 240 and coupled between the third switching mechanism SW3 and the first switching mechanism SW1. Similarly, the impeller includes a third energy storage element SE3 coupled to the second side 245 of the load 240 and coupled between the fourth switching mechanism SW4 and the second switching mechanism SW2. In various embodiments, the energy storage elements may be electrical energy storage elements, such as inductive energy storage elements, capacitive energy storage elements, one or more batteries, or the like. In some examples, the storage elements SE1, SE2, and SE3 are identical. In other examples, at least one of SE1, SE2, and SE3 differs from the others. In some embodiments, SE1 comprises a capacitive energy storage element, and SE2 and SE3 comprise inductive energy storage elements. In some such embodiments, SE2 and SE3 comprise paired inductive energy storage elements. The drive unit 200 in Figure 6 also includes a controller 260 in communication with the switching network 230. In the illustrated example, the controller 260 is in communication with each of the switching mechanisms (SW1, SW2, SW3, SW4). The controller 260 can be configured to control the switching operation of the switching mechanisms, for example, by opening and closing the switching mechanisms to selectively connect or disconnect electrically components on each side of each switching mechanism. In various embodiments, the controller 260 can be configured to control the switching mechanisms in series and / or in parallel (e.g., simultaneous switching). In some examples, the controller 260 is configured to control the switching mechanisms in order to provide a voltage (for example, from the power supply 210) to the load 240, such as an optically active material in an electrically dynamic window. Furthermore, in some embodiments, the controller 260 can be configured to control the switching mechanisms in order to periodically change the polarity of the voltage applied to the load 240. In some of these examples, the operation of the switching network can be implemented such that at least some of the energy discharged from the load (for example, by changing polarities) can be recovered and stored in one or more energy storage elements SE1, SE2, SE3. This recovered and stored energy can then be used, for example, to perform subsequent charging operations. As described, in some embodiments, the impeller 200 further includes additional components to selectively prevent current flow to various parts of the impeller. For example, in the embodiment illustrated in Figure 6, the impeller 200 includes the insulating component 212 configured to selectively permit current flow between the power supply 210 and other parts of the impeller. Similarly, the impeller 200 includes an insulating component 224 configured to selectively permit current flow between ground 220 and other parts of the impeller 200. In some instances, the insulating components 212 and 224 can be controlled by the controller 260 during various phases of impeller operation. The insulating components can include any of a variety of components suitable for selectively permitting and / or preventing current flow between various components of the impeller.For example, in various embodiments, the insulating components 212, 224 may include switches, transistors (e.g., power MOSFETs) or other components or combinations thereof. Figures 7-10 illustrate a variety of switching network configurations and transitions that can be used to apply a voltage alternately in a first polarity and an opposite polarity to a load by means of a switching network and driver configuration as shown in Figure 6. Example loading process Figures 7A-7D illustrate an example charging process for charging a load through a driver as shown in Figure 6. Figure 7A shows the first stage of the charging process. In the first stage, the third switching mechanism SW3 and the second switching mechanism SW2 are closed, while the first switching mechanism SW1 and the fourth switching mechanism SW4 are open. This creates a current path 270 from the power supply 210 and / or the first energy storage element SE1 through the third switching mechanism SW3, the second energy storage element SE2, the load 240, the third energy storage element SE3, the second switching mechanism SW2 to ground 220. In this example, the current flows in one direction through the load 240 (from the first side 235 to the second side 245).In some examples, for instance, in the case of a capacitive load, load 240 is charged in a first polarity. In some examples, during this stage, the energy stored in SE1 contributes to the charging process, and storage elements SE2 and SE3 are charged. Figure 7B shows a second stage in the charging process. In the second stage (relative to the configuration shown in the first stage), the third switching mechanism SW3 opens and the first switching mechanism SW1 closes. This creates a current path 272 that includes the load 240, the third energy storage element SE3, the second switching mechanism SW2, the first switching mechanism SW1, and the second energy storage element SE2. In some embodiments, the insulating component 224 prevents current leakage to ground 220. In some examples, during the second stage, the current temporarily continues to flow in the first direction, charging load 240, due to the behavior of load 240 and / or the discharge of stored energy from one or both of the second energy storage element SE2 and the third energy storage element SE3. For example, in one embodiment, the second energy storage element SE2 and the third energy storage element SE3 comprise matched inductors, which are energized by the current flowing through them in stage one shown in Figure 7A. The energized inductors discharge the stored energy, causing the current to continue flowing through the load via current path 272 l / ol Ln / nznz / E / Yi when the first stage shown in Figure 7B is carried out. Figure 70 shows a third stage in the charging process. In the illustrated example, the first switching mechanism SW1 opens, eliminating any current loop containing the load 240. In some of these examples, the second switching mechanism SW2 also opens; however, in alternative embodiments, the second switching mechanism SW2 may remain closed. In still other alternative embodiments, the second switching mechanism SW2 could be open, and the first switching mechanism SW1 could be either open or closed.In some embodiments, with respect to the embodiment illustrated, the first switching mechanism SW1 opens at or approximately at the time when the second energy storage element SE2 and the third energy storage element SE3 have discharged their energy and before the current path 272 described with respect to Figure 7B causes energy to dissipate from the load 240. In some examples, this time can be controlled by a system controller and can be determined based on, for example, various values ​​associated with the driver, such as the power supply voltage 210, the inductance values ​​of the energy storage elements, the capacitance values ​​of the load 240, or the like. Eliminating the current paths as illustrated in Figure 7C maintains the charge level of the load 240 at an approximately constant value. Figure 7D shows an example graph of voltage versus time at load 240 (e.g., a capacitive load) during the charging stages shown in Figures 7A–7C. As shown, the charging process 350 includes a first stage 300 corresponding to the stage shown in Figure 7A, which results in the charging of the load. The charging process 350 further includes a second stage 302 corresponding to the stage shown in Figure 7B, where the load continues to charge. The charging process 350 also includes a third stage 304, as shown in Figure 7C, where current paths are removed from the load to maintain a charged state. In the example illustrated in Figure 7D, the voltage across the load after the charging process 350 is approximately equal to the voltage Va supplied by the power supply 210. It will be appreciated that the graph in Figure 7D is illustrative and does not limit the charging process 850. For example, in various embodiments, the relative widths (durations) of each stage (300, 302, 304) may differ from what is shown in the example diagram. For instance, in some examples, the duration of stage 302 (e.g., the duration of the configuration shown in Figure 7B) is limited to prevent energy drain to ground 220 instead of contributing to the charging of the load 240, as in embodiments without an insulating component 224. Additionally or alternatively, the voltage versus time graph may not necessarily be linear during one or more stages of the charging process 350. Example download process Figures 8A-8D illustrate an example discharge process for discharging a charge through a driver as shown in Figure 6. Figure 8A shows a first stage of the discharge process, for example, to be performed after the charging process described with respect to Figures 7A-7D. For example, in some embodiments, after a charging process, a positive voltage is present across the charge 240, where the first side 235 of the charge 240 is at a higher voltage than the second side of the charge 240. The first stage of the discharge process comprises positioning the switching mechanisms so that the first switching mechanism SW1 and the second switching mechanism SW2 are closed, creating a current path 274 that includes the load 240, the second energy storage element SE2, the first switching mechanism SW1, the second switching mechanism SW2, and the third energy storage element SE3. The third switching mechanism SW3 and the fourth switching mechanism SW4 are open.Once current path 274 is created, a positive voltage on load 240 (e.g., a capacitive load) can cause current to flow from load 240 through current path 274, initiating the discharge of load 240 and, in some examples (e.g., those involving inductive energy storage elements SE2 and SE3), energizing the energy storage elements SE2 and SE3 by the flow of current through them. In some examples, isolating component 224 can prevent current leakage to ground 220. Figure 8B shows a second stage in the discharge process. As shown, the first switching mechanism SW1 opens and the third switching mechanism SW3 closes, creating a current path 276. Current can flow through current path 276 to the first energy storage element SE1, for example, due to the energy stored in the second energy storage element SE2 and the third energy storage element SE3 in the first stage of the discharge process (Figure 8A). That is, in some embodiments (for example, those including inductive SE2, SE3), the energy stored in the second and third energy storage elements SE2, SE3 during the first stage (Figure 8A) can be discharged to the first energy storage element SE1 when the switching mechanisms are set as shown in Figure 8B.This allows at least some of the electrical energy used to charge load 240 during the charging process (e.g., as shown in stages 7A-7C) to be used to energize the second and third energy storage elements SE2, SE3, and then the first energy storage element SE1. In some examples, isolating component 212 can prevent the power supply 210 from affecting the energy transfer, for example, to the first energy storage element SE1. Figure 8C shows a third stage in the discharge process. In the third stage, the third switching mechanism SW3 and the second switching mechanism SW2 are open, while the first switching mechanism SW1 and the fourth switching mechanism SW4 remain open. This eliminates the current flow paths of load 240 and the first energy storage element SE1, causing load 240 to float at a low (discharged) voltage while SE1 remains charged with recycled energy from the previously charged load 240. Figure 8D shows an example graph of voltage versus time at load 240 (e.g., a capacitive load) during the charging stages shown in Figures 7A–7C and the discharging stages shown in Figures 8A–8C. As shown, the discharge process 352 includes a first discharge stage 306 corresponding to the stage shown in Figure 8A, which results in the discharge of the load (e.g., triggering the energy storage elements SE2 and SE3). The discharge process 352 further includes a second stage 308 corresponding to the stage shown in Figure 8B, where the load continues to discharge while energy is transferred to the first energy storage element SE1. The discharge process 352 also includes a third stage 310, as shown in Figure 8C, where current paths are removed from the load to maintain a discharged state. As noted with respect to Figure 7D, the voltage-versus-time graph at the load is illustrative and not necessarily shown to scale. In several examples, the shape of the voltage-versus-time graph need not be linear during one or more stages of the discharge process 352. Additionally or alternatively, the discharge process 352 may be carried out a plurality of times to achieve complete discharge of the load. Example reverse charging process liol Ln / nznz / E / YiAi Figures 9A-9D illustrate an example reverse charging process for charging a load in the opposite polarity to the charging process in Figures 7A-7D using a driver as shown in Figure 6. Figure 9A shows the first stage of the reverse charging process. In the first stage, the first switching mechanism SW1 and the fourth switching mechanism SW4 are closed, while the third switching mechanism SW3 and the second switching mechanism SW2 are open. This creates a current path 278 from the power supply 210 and / or the first energy storage element SE1 through the fourth switching mechanism SW4, the third energy storage element SE3, the load 240, the second energy storage element SE2, the first switching mechanism SW1 to ground 220.In this example, the current flows in a second direction (from the second side 245 to the first side 235) through the charge 240, where the second direction is opposite to that of the first charge. In some examples, for instance, in the case of a capacitive charge, the charge 240 is charged in a second polarity opposite to the first polarity. As indicated, the current flowing in the current path 278 could be supplied at least partially by the first energy storage element SE1, for example, by using energy recovered from the first discharge process described with respect to Figures 8A-8D. In some examples, the insulating component 212 can be used to prevent current from being supplied from the power supply 210, instead of drawing current from the first energy storage element SE1. Figure 9B shows a second stage in the reverse charging process. In the second stage (relative to the configuration shown in the first stage), the fourth switching mechanism SW4 opens and the second switching mechanism SW2 closes. This creates a current path 280 that includes the load 240, the second energy storage element SE2, the first switching mechanism SW1, the second switching mechanism SW2, and the third energy storage element SE3. In some instances, current continues to flow in the reverse direction through the load 240 depending on the behavior of the load 240 and / or one or both of the second energy storage element SE2 and the third energy storage element SE3.For example, in one exemplary embodiment, the second energy storage element SE2 and the third energy storage element SE3 comprise matched inductors, which are energized by the current flowing through them in stage one of the reverse charging process shown in Figure 9A. The energized inductors cause the current to continue flowing through the load in the second direction via current path 280 when the first stage shown in Figure 9B is carried out. The insulating component 224 can be used to prevent current leakage from current path 280 to ground 220. Figure 9C shows a third stage in the reverse charging process. In the illustrated example, the second switching mechanism, SW2, is opened, eliminating any current loop containing load 240. In some such examples, the first switching mechanism, SW1, is also opened, in which case the second switching mechanism, SW2, may remain closed. Interrupting the current path by opening both SW1 and SW2 maintains the charging level of load 240 at approximately a constant value. Figure 9D shows an example graph of voltage versus time at load 24Q (e.g., a capacitive load) during the reverse charging stages shown in Figures 9A–9C, in addition to the preceding charging and discharging stages. As shown, the reverse charging process 354 follows the discharging process 352 and includes a first stage 312 corresponding to the stage shown in Figure 9A, which results in the charging of load 340 in the second polarity. The second polarity is opposite to the first polarity, in which the load was charged during the charging process 350. For example, as shown in Figure 9D, during the first stage 312 of the reverse charging process 354, the voltage magnitude generally increases similarly to how it does in the first stage 300 of the charging process 350, but in the opposite polarity.Therefore, the reverse charging process 354 generally increases the magnitude of the charge at the charge 240, but in the opposite polarity to that of the charging process 350. The reverse charging process 354 further includes a second stage 314 corresponding to the stage shown in Figure 9B, where the load continues to charge in the second polarity. The charging process 350 further includes a third stage 304, as shown in Figure 9C, in which the current paths are removed from the load to maintain a reverse charging state. In the example illustrated in Figure 9D, the voltage across the load 240 in stage 304 of the charging process 350 is approximately equal in magnitude but opposite in polarity to the voltage across the load 240 in stage 316 of the reverse charging process 354. In various examples, the magnitude of the voltage in one or both of these stages is approximately equal to the rail voltage (VA) applied by the power supply 210. It will be appreciated that, similarly to the graphs in Figures 7D and 8D, the graph in Figure 9D is illustrative and does not limit the charging process 854. For example, in various embodiments, the relative widths (durations) of each stage (312, 314, 316) may differ from what is shown in the example diagram. For instance, in some examples, the duration of stage 314 (e.g., the duration of the configuration shown in Figure 9B) is limited to prevent energy drain to ground 220 rather than to contribute to the reverse charging of the load 240, as in embodiments without an insulating component 224. Additionally or alternatively, the voltage versus time graph may not necessarily be linear during one or more stages of the reverse charging process 354. Example reverse download process Figures 10A-10D illustrate an example reverse discharge process for discharging a reverse-charged load through a driver as shown in Figure 6. Figure 10A shows a first stage of the reverse discharge process, to be performed after the reverse charge process described with respect to Figures 9A-9D. For example, in some embodiments, after a reverse charge process, a voltage of the second polarity is present across the load 240, where the second side 245 of the load 240 has a higher voltage than the first side 235 of the load 240 (for example, approximately -Va as shown in Figure 9D). The first stage of the discharge process involves positioning the switching mechanisms so that the first switching mechanism SW1 and the second switching mechanism SW2 are closed, creating a current path 282 that includes the load 240, the third energy storage element SE3, the second switching mechanism SW2, the first switching mechanism SW1, and the second energy storage element SE2. The third switching mechanism SW3 and the fourth switching mechanism SW4 are open. Once current path 282 is created, a voltage on the load 240 in the second polarity (where the voltage on the second side 245 of the load 240 is greater than on the first side 235) can cause current to flow from the load 240 through current path 282, initiating the discharge of the load 240.In some examples (for instance, those involving inductive energy storage elements SE2 and SE3), discharging the charge through current path 282 can energize energy storage elements SE2 and SE3, causing current to flow through them. Insulating component 224 can be used to prevent current leakage from current path 282 to ground 220. Figure 10B shows a second stage in the reverse discharge process. As shown, the second switching mechanism SW2 opens and the fourth switching mechanism SW4 closes, creating a current path 284. Current can flow through current path 284 to the first energy storage element SE1, for example, due to the energy stored in the second energy storage element SE2 and the third energy storage element SE3 in the first stage of the reverse discharge process (Figure 10A). That is, in some embodiments (for example, those including inductive SE2, SE3), the energy stored in the second and third energy storage elements SE2, SE3 during the first stage (Figure 10A) can be discharged to the first energy storage element SE1 when the switching mechanisms are configured as shown in Figure 10B.This allows at least some of the electrical energy used to recharge load 240 during the reverse charging process (e.g., as shown in stages 9A-9C) to be used to energize the second and third energy storage elements SE2 and SE3, and then the first energy storage element SE1. In some examples, isolating component 212 can prevent the power supply 210 from affecting the energy transfer, for example, to the first energy storage element SE1. Figure 10C shows a third stage in the reverse discharge process. In the third stage, the fourth switching mechanism SW4 and the first switching mechanism SW1 are open, while the second switching mechanism SW2 and the third switching mechanism SW3 remain open. This eliminates the current flow paths of charge 24Q and the first energy storage element SE1, causing charge 240 to float at a low (discharged) voltage while SE1 remains charged with recycled energy from the previously reverse-charged charge 240. Figure 10D shows an example graph of voltage versus time at load 240 (e.g., a capacitive load) during the charging stages shown in Figures 7A–7C, the discharging stages shown in Figures 8A–8C, the reverse charging stages shown in Figures 9A–9C, and the reverse discharging stages shown in Figures 10A–10C. As shown, the reverse discharge process 356 includes a first reverse discharge stage 318 corresponding to the stage shown in Figure 10A, which results in the discharge of the load (e.g., triggering the energy storage elements SE2, SE3). The reverse discharge process 356 also includes a second stage 320 corresponding to the stage shown in Figure 10B, where the charge continues to discharge while energy is transferred to the first energy storage element SE1.The reverse discharge process 356 further includes a third stage 322, as shown in Figure 10C, where current paths are removed from the load to maintain an uncharged state. The graph in Figure 10D shows an example graph of voltage across load 240 versus time during a charging process 350, a discharging process 352, a reverse charging process 354, and a reverse discharging process 356. In the illustrated example, the reverse charging process 354 appears to be approximately equal in magnitude and opposite in sign to the charging process 350. Similarly, the reverse discharging process 356 appears to be approximately equal in magnitude and opposite in sign to the discharging process 352. Therefore, the voltage across load 240 alternates between approximately Va and -Va. As described elsewhere, the voltage-versus-time graphs in Figures 7D, 8D, 9D, and 10D are not necessarily to scale. For example, in some embodiments, the duration of an approximately constant charging state in which the voltage magnitude is approximately equal to Va (stage 304 in charging process 350 and stage 316 in reverse charging process 354) is significantly longer than the combined durations of the intermediate stages (for example, the discharge process 352 and the first 312 and second 314 stages of the discharge process). In some embodiments, a driver (for example, driver 200 in Figure 6, which includes controller 260) can be configured to repeatedly apply a voltage signal to a load, as shown in Figure 10D. That is, after completing the reverse discharge process 356, the driver can repeat the signal upon initiating the charging process 350. In some examples, the driver can be configured to repeatedly carry out the charging process 350, the discharging process 352, the reverse charging process 354, and the reverse discharging process 356. Such a cycle through these processes can continuously alternate the polarities of a voltage Va applied to a load, such as an optically active material. With further reference to Figure 6, the drive 200 includes a power supply 210, a switching network 230 comprising a plurality of switching mechanisms SW1, SW2, SW3, SW4, energy storage elements SE1, SE2, SE3, and a controller 260 configured to operate the switching network. When configured to drive an optically active material, as shown in the configuration of Figure 3 (for example, including the drive 60 arranged to control the optically active material 18 through the electrode layers 20 and 22), the drive can be configured to apply a voltage VA corresponding to a desired optical state (for example, a transparent state) to the optically active material.The driver can further be configured to alternately apply the voltage Va to the optically active material at different polarities, for example, as shown in the voltage versus time curve in Figure 10D, repeated a plurality of times. Referring again to Figure 6, in one example embodiment, controller 260 can be configured to control the switching of the SW1, SW2, SW3, and SW4 switching mechanisms of the 230 switching network in a particular order of switching combinations to apply a specific voltage to the optically active material. In one example embodiment, the order of the sequential switching mechanism configurations can include the configurations shown in Figures: 7A^7B^7C^8A^8B^8C^9A-v9B^9C^10A-^10B^10C^7A^7B^... where the cycle is repeated as desired. The cycle can be executed in reverse, or similarly, the phase can be changed, for example, by half a period, where the order of the sequential switching mechanism configurations can include the configurations in the Figures: 10C^10B—d0A-v9C^9B^9A^8C->8B^8A^7C^7B^7A^10C^10B^... which can be repeated similarly if desired. Any order (for example, if the voltage on the first side 235 is greater or less than the voltage on the second side 245 in the first reverse charge / charge cycle) can ultimately generate alternating polarities of a voltage Va applied to the optically active material, for example, to approximate a square wave. With respect to the drive configurations shown in Figures 6 to 10, in various embodiments, a variety of energy storage technologies can be used as energy storage elements, such as inductive elements, capacitive elements, or the like. In some examples, the first energy storage element SE1 comprises a capacitive energy storage element. Additionally or alternatively, the second energy storage element SE2 and / or the third energy storage element SE3 may include an inductive energy storage element. In some embodiments, the load 240 comprises a capacitive load. For example, in some embodiments, an optically active material placed between electrodes (e.g., the optically active material 18 between the first layer of electrodes 20 and the second layer of electrodes 22) comprises a capacitive load. The configuration of the energy storage elements, in combination with the operation of the switching mechanisms, allows energy to be applied to and stored in the optically active material, and then extracted from it and at least partially recycled for later use. This leads to greater efficiency in controlling a load (e.g., a capacitive load) with a signal that has alternating polarities, such as a square wave. In one particular implementation, this leads to greater efficiency in controlling an optically active material with a driver that produces an approximate square wave trigger signal to reduce errors when applying a DC signal. In several examples, optically active materials can be optically controlled by an applied electrical potential, regardless of the potential's polarity. For instance, in some embodiments, a sufficiently large electrical potential applied across an optically active material can generate a first optical state, while a sufficiently small electrical potential applied across it can generate a second optical state. In some of these examples, the first optical state may correspond to a substantially transparent state, while the second optical state may correspond to a substantially opaque state. In other examples, the first optical state corresponds to a substantially opaque state, while the second optical state corresponds to a substantially transparent state.In other examples, an optically active material can assume more than two optical states depending on the magnitude of the electrical potential applied across it; for example, electrochromic materials, dye-tinted liquid crystals, or similar materials. In general, applying a variety of voltage magnitudes across an optically active material can be useful for controlling the optical states of an optical structure, such as an electrically dynamic window. Referring again to Figure 6, in some embodiments, the controller 260 can be configured to adjust the magnitude of the voltage Va supplied by the power supply 210. For example, in some instances, the controller 260 communicates with a user interface and is configured to receive input from the user interface, such as the selection of a desired optical state from an optically dynamic window driven by the impeller 200. The controller 260 can be configured to identify a desired optical state, such as one received through a user interface, and determine an appropriate voltage Va to apply to the switching network 230 to achieve the desired optical state. In several instances, the controller 260 can determine the appropriate voltage based on an equation relating an input signal to an applied voltage, using a lookup table or other techniques. Figure 11 shows an example voltage-versus-time graph of signals from a driver to effect two different optical states from an optically active material. In the illustrated example, a first signal 400 corresponds to a voltage magnitude of Va, which varies between voltage values ​​of Va and Va' (e.g., by transitioning between switching arrangements as described elsewhere herein). A second signal 410, corresponding to a voltage magnitude of VA', switches between voltage values ​​of Va' and -Va'. In some instances, the switching between signals 400 and 410 corresponds to the changing of a voltage applied by the power supply 210, while it continues to control the switching mechanisms in a cyclic pattern as described elsewhere herein. The example graph in Figure 11 includes a threshold voltage VT. In one example embodiment, VT corresponds to a voltage magnitude above which an optically active material assumes a first optical state (e.g., substantially transparent) and below which the optically active material assumes a second optical state (e.g., substantially opaque). As shown, 0 < |Va'| < |Vt| < |VA|, so when the driver applies signal 400 to the optically active material, the optically active material assumes the first optical state, and when signal 410 is applied to the optically active material, the optically active material assumes the second optical state.As described elsewhere herein, in some examples, the driver is configured to adjust the applied voltage (e.g., between Va and Va') in response to an input received from a user interface to adjust the optical state of an optically active material. In some embodiments, several stages in the transition between different switching configurations are carried out quickly enough to minimize the duration of each stage. As described elsewhere herein, in some embodiments, a voltage above or below a threshold can result in a difference between a first and a second optical state. For example, with reference to Figure 11, the magnitude of signal 410 alternates between Va' and -Va', which is below the magnitude of the threshold voltage Vt. Therefore, the optical state associated with signal 410 must remain constant in the second optical state. The magnitude of signal 400, on the other hand, alternates between Va and -Va, which is greater than Vt, to achieve the first optical state.However, during the transition between Va and -Va, there are times when the magnitude of the signal voltage 400 falls below the threshold voltage Vt, which could undesirably cause the optical state to fluctuate from the first optical state. Consequently, in some embodiments, several transitions between and through certain switching configurations of the switching mechanisms in the switching network can be performed quickly enough to minimize and / or eliminate undesirable optical effects. For example, with reference to Figure 10D, stages 306, 308, and 310 in the discharge process 352, as well as stages 312 and 314 in the reverse charge process, are carried out quickly enough to avoid the transition between optical states between stages 304 and 316. Instead, the optical state associated with the voltage in stages 304 and 316 is retained during the transition between these stages due to sufficiently rapid switching of the switching mechanisms. In some examples, the switching between the various switching mechanisms is synchronized so that the signal applied to the load approximates a square wave. As described, in various embodiments, a driver can be configured to apply different electrical signals to an optically active material corresponding to different desired optical states of the material. In some embodiments, the driver is configured to continuously apply an alternating signal (e.g., a square wave) to the optically active material regardless of the desired optical state. For example, with respect to Figure 11, when switching between optical states, the driver can be configured to apply signal 400 and signal 410 to the optically active material. However, neither of these states (e.g., corresponding to Va or Va') corresponds to the application of any alternating signal to the optically active material.However, in other examples, for instance, if a desired optical state corresponds to a potential of 0 V across an optically active material, an alternating signal can be interrupted and / or disconnected from the optically active material to achieve and maintain the optical state. Figure 12 is a process flow diagram illustrating an example control process for operating an optically active material, such as in an electrically dynamic window. The method according to Figure 12 includes the step of receiving a selection of a desired optical state for the optically active material (500) and applying a voltage to the switching arrangement based on the received selection (510). As described elsewhere herein, the applied voltage may be sufficient to achieve the desired optical state and may be determined by a lookup table stored in memory or similar. The method further comprises the step of applying a series of charge-switching configurations to the optically active material (520), for example, to apply a charge to the optically active material in a first polarity. The series of charge-switching configurations may correspond, for example, to the configurations shown in Figures 7A-7C. The method then involves applying a series of discharge switching configurations to the optically active material (530) to reduce the load on the material. As described, in some embodiments, the energy discharged from the optically active material during the discharge process can be recovered and stored for future use. The series of discharge switching configurations may correspond, for example, to the configurations shown in Figures 8A–8C. The method also includes the step of applying a series of reverse charge switching configurations to the optically active material (540), for example, to apply a charge to the optically active material in a second polarity opposite to the first. The series of reverse charge switching configurations may correspond, for example, to the configurations shown in Figures 9A-9C. The method then involves applying a series of reverse discharge switching configurations to the optically active material (550) to reduce the load on the material. As described, in some embodiments, the energy discharged from the optically active material during the reverse discharge process can be recovered and stored for future use. The series of discharge switching configurations may correspond, for example, to the configurations shown in Figures 10A-10C. The method according to Figure 12 may further include the step of determining whether or not the optical state (560) should be changed. If not, the switching process can be repeated, for example, by applying the series of load switching configurations (520) and proceeding to carry out the method again. However, if the optical state needs to be changed (in step 560), the method may include the step of adjusting the applied voltage (570) before applying the (updated) voltage to the switching arrangement (510). In various embodiments, the application steps of a series of charge switching configurations (520) and / or application of the series of reverse charge switching configurations (540) may include applying energy to the optically active material recaptured from the optically active material in a previous discharge process (e.g., energy stored in the first energy storage element SE1). As described elsewhere herein, in some embodiments, a drive for driving an optically active material may include a controller configured to adjust the operation of one or more switching mechanisms in a switching network and / or to adjust the voltage applied to the switching mechanisms. In some examples, the controller operates in response to input from a user interface, such as a user interface command to change the optical state of the optically active material. In various examples, the controller may include one or more components configured to process received information, such as input from a user interface, and perform one or more corresponding actions in response. Such components may include, for example, one or more application-specific integrated circuits (ASICs), microcontrollers, microprocessors, field-programmable gate arrays (FPGAs), or other appropriate components capable of receiving and transmitting data and / or signals according to a predefined relationship. In some examples, one or more such components may be physically integrated with other drive components, such as the switching network and the like. A user interface communicating with the controller may include a switch or other component in wired or wireless communication with the controller. For example, a physical switch (e.g., a wall switch near an optically dynamic window structure) may be coupled to the controller and can switch between two or more switching states, each corresponding to an optical state of the controller's optically active material. Additionally or alternatively, the controller may be configured to communicate with an external component, such as a smartphone or tablet via wireless communication, or with an internet-connected device (e.g., via a wired or wireless network connection).In some embodiments, the controller can receive a signal from such an external device corresponding to a desired optical state of the optically active material, and can control the optically active material accordingly. Several examples have been described. These and other examples are within the scope of the following claims.

Claims

1. An electrically dynamic window structure comprising: a first panel of transparent material; a second panel of transparent material; an electrically controllable optically active material located between the first panel of transparent material and the second panel of transparent material, the electrically controllable optically active material being further located between a first electrode layer and a second electrode layer; and a drive electrically connected to the first electrode layer and the second electrode layer, wherein the drive is electrically connected to a power source and configured to provide a drive signal to the first electrode layer and the second electrode layer to control the electrically controllable optically active material.wherein the drive includes an energy storage element and is configured to: charge the electrically controllable optically active material to a first state of charge, subsequently discharge the electrically controllable optically active material in a first discharge process, which includes storing energy in the energy storage element released from the electrically controllable optically active material during the first discharge process, and subsequently charge the electrically controllable optically active material to a second state of charge opposite to the first state of charge.

2. The structure according to claim 1, wherein the impeller is further configured to: subsequently discharge the electrically controllable optically active material in a second discharge process, which includes storing the energy released from the electrically controllable optically active material during the second discharge process in the energy storage element, and subsequently charge the electrically controllable optically active material to the first charged state, 3. The structure according to any of claims 1 or 2, wherein the impeller is configured to supply energy stored by the energy storage device during the first discharge process and / or the second discharge process to charge the electrically controllable optically active material to the first charge state and / or the second charge state.

4. The structure according to claim 3, wherein the drive is configured to supply power from the power supply in addition to the energy stored by the energy storage device to charge the electrically controllable optically active material.

5. The structure according to any of the preceding claims, wherein the energy storage device comprises a capacitor.

6. The structure according to any of the preceding claims, wherein the first charging state comprises a rail voltage applied across the electrically controllable optically active material in a first polarity and the second charging state comprises the rail voltage applied across the electrically controllable optically active material in a second polarity opposite to the first polarity.

7. The structure according to claim 6, wherein the driver is configured to change the rail voltage between at least a first rail voltage and a second rail voltage, wherein the first rail voltage is greater than the second rail voltage.

8. The structure according to claim 7, wherein the first charge state and the second charge state at the first rail voltage each correspond to a first optical state of the electrically controllable optically active material, and the first charge state and the second charge state at the second rail voltage each correspond to a second optical state of the electrically controllable optically active material.

9. The structure according to claim 8, wherein the first optical state is a transparent state and the second optical state is an obscured state.

10. The structure according to any of the preceding claims, wherein the drive further comprises: a switching network comprising a plurality of switching mechanisms; and a controller in communication with the switching network and configured to switch the plurality of switching mechanisms between switching states in order to: cause current to flow from the power supply and through the electrically controllable optically active material in a first direction during a charging cycle; stop the flow of current through the electrically controllable optically active material; and cause current to flow through the electrically controllable optically active material in a second direction opposite to the first direction during a discharging cycle.

11. The structure according to claim 10, wherein: the energy storage element comprises a first energy storage element, the drive further comprises a second energy storage element, a power supply, and a switching network comprising: a first switching mechanism coupled between a first side of a privacy structure and ground, wherein the privacy structure comprises an electrically controllable optically active material located between a first electrode carried by a first panel of transparent material and a second electrode carried by the second panel of transparent material; a second switching mechanism coupled between a second side of the privacy structure and ground; and a third switching mechanism coupled between the power supply and the first side of the privacy structure.and a fourth switching mechanism coupled between the power supply and the second side of the privacy structure; wherein the switching network is arranged in an H-bridge configuration to provide bidirectional power to the privacy structure. a first energy storage element, a second energy storage element coupled between the first side of the privacy structure and the first and third switching mechanisms; a third energy storage element coupled between the second side of the privacy structure and the second and fourth switching mechanisms;and a controller in communication with the switching network and configured to selectively switch the first, second, third, and fourth switching mechanism such that: energy is transferred from the power supply to the electrically controllable optically active material to charge the electrically controllable optically active material in a first polarity; energy is transferred from the electrically controllable optically active material to the second energy storage element and / or the third energy storage element; and energy is transferred from the second energy storage element and / or the third energy storage element to the first energy storage element.

15. The electric drive according to claim 14, wherein the first energy storage element is a capacitive energy storage element.

16. The electric drive according to any of claims 14 or 15, wherein the second and third energy storage elements are inductive elements.

17. The electric drive according to claim 16, wherein transferring energy from the electrically controllable optically active material to the second energy storage element and / or the third energy storage element comprises creating a current path in which: the current flows from the electrically controllable optically active material through the second energy storage element and / or the third energy storage element; and the energy is stored in the second inductive energy storage element and / or the third inductive energy storage element as a magnetic field.

18. The electric drive according to any of claims 14 to 17, wherein the controller is configured to place the switching network in a first load state by closing the third switching mechanism and the second switching mechanism to create a current path from the power supply through the third switching mechanism, the second energy storage element, the privacy structure, the third energy storage element, and the second switching mechanism.

19. The electric drive according to claim 18, wherein: the controller is configured to transition the switching network from the first charging state to a second charging state by opening the third switching mechanism and closing the first switching mechanism to create a current path comprising the privacy structure, the third energy storage element, the second switching mechanism, the first switching mechanism, and the second energy storage element; and current flows through the privacy structure in a first direction in the first charging state and the second charging state so that energy is stored in the electrically controllable optically active material.

20. The electric drive according to claim 19, wherein the controller is configured to make the switching network transition from the second charging state to a third charging state by opening one or both of the first switching mechanism and the second switching mechanism to eliminate the current paths connected to the privacy structure so that the electrically controllable optically active material maintains a charging state.

21. A method for providing electrical power to a privacy structure and recapturing energy to a first energy storage element from the privacy structure, wherein the privacy structure includes an electrically controllable optically active material located between a first electrode layer and a second electrode layer, wherein the method comprises: arranging a plurality of switching mechanisms in a first load configuration so that a current flows in a first current path from a power source to the first electrode layer of the privacy structure in a first direction;arranging the plurality of switching mechanisms in a second charging configuration, wherein the second charging configuration creates a second current path that includes the privacy structure and a second energy storage element such that the current flows through the privacy structure in the first direction; arranging the plurality of switching mechanisms in a third charging configuration, wherein the third charging configuration eliminates the current flow paths to and from the privacy structure and maintains the privacy structure in a first charging state; arranging the plurality of switching mechanisms in a first discharging configuration such that the current flows through the second energy storage element and the privacy structure in a second direction opposite to the first direction;and arranging the plurality of switching mechanisms in a second discharge configuration so that the current flows through the privacy structure in the second direction to the first energy storage element.