Patent Publication Number: US-2023149186-A1

Title: Titanium dioxide composite insulator artificial muscle

Description:
TECHNICAL FIELD 
     The present specification generally relates to artificial muscles and, in particular, to artificial muscles utilizing nanoparticle composite electrical insulators. 
     BACKGROUND 
     Artificial muscles attempt to mimic the versatility, performance, and reliability of biological muscles. Some artificial muscles rely on fluidic actuators, but fluidic actuators require a supply of pressurized gas or liquid and fluid transport must occur through systems of channels and tubes, limiting the speed and efficiency. Other artificial muscles use thermally activated polymer fibers, but these are difficult to control and operate at low efficiencies. Moreover, in order to exert increasing amounts of force, current attempts at artificial muscles often require bulky actuators and/or increasing their operating voltage. 
     Accordingly, there exists a need to create more force output with the same size actuator and the same operating voltage. 
     SUMMARY 
     In one embodiment, an artificial muscle includes a housing including an electrode region and an expandable liquid region. The artificial muscle also includes a dielectric liquid housed within the housing. The artificial muscle further includes an electrode pair positioned in the electrode region of the housing, the electrode pair including a first electrode and a second electrode, wherein the electrode pair is configured to actuate between a non-actuated state and an actuated state such that actuation from the non-actuated state to the actuated state directs the dielectric liquid into the expandable liquid region, expanding the expandable liquid region. The artificial muscle additionally includes a composite electrical insulating layered structure in contact with at least one of the first electrode or the second electrode. The composite electrical insulating layered structure includes an electrical insulator layer surrounded by adhesive surfaces. The composite electrical insulating layered structure also includes adhesive surfaces located between one or more flexible electrical insulators. The composite electrical insulating layered structure further includes one or more flexible electrical insulators of which at least one is directly affixed to one of the first electrode and the second electrode. 
     In another embodiment, an artificial muscle includes a housing including an electrode region and an expandable liquid region. The artificial muscle also includes a dielectric liquid housed within the housing. The artificial muscle further includes an electrode pair positioned in the electrode region of the housing, the electrode pair including a first electrode and a second electrode, wherein the electrode pair is configured to actuate between a non-actuated state and an actuated state such that actuation from the non-actuated state to the actuated state directs the dielectric liquid into the expandable liquid region, expanding the expandable liquid region. The artificial muscle additionally includes composite electrical insulating layered structure in contact with at least one of the first electrode or the second electrode. The composite electrical insulating layered structure includes a plurality of electrical insulator nanoparticles located within a subset of an adhesive surface. The composite electrical insulating layered structure also includes the adhesive surface located between one or more flexible electrical insulators. The composite electrical insulating layered structure further includes one or more flexible electrical insulators of which at least one is directly affixed to one of the first electrode and the second electrode. 
     In a further embodiment, an artificial muscle includes a housing including an electrode region and an expandable liquid region. The artificial muscle also includes a dielectric liquid housed within the housing. The artificial muscle further includes an electrode pair positioned in the electrode region of the housing, the electrode pair including a first electrode and a second electrode, wherein the electrode pair is configured to actuate between a non-actuated state and an actuated state such that actuation from the non-actuated state to the actuated state directs the dielectric liquid into the expandable liquid region, expanding the expandable liquid region. The artificial muscle additionally includes composite electrical insulating layered structure in contact with at least one of the first electrode or the second electrode. The composite electrical insulating layered structure includes an electrical insulator layer including titanium dioxide nanoparticles, wherein the electrical insulator layer has a thickness in a range of 10-15 μm and is surrounded by acrylic adhesives. The composite electrical insulating layered structure also includes the acrylic adhesives located between one or more biaxially oriented polypropylene films. The composite electrical insulating layered structure further includes one or more biaxially oriented polypropylene films of which at least one is directly affixed to one of the first electrode and the second electrode. 
     These and additional features provided by the embodiments described herein will be more fully understood in view of the following detailed description, in conjunction with the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The embodiments set forth in the drawings are illustrative and exemplary in nature and not intended to limit the subject matter defined by the claims. The following detailed description of the illustrative embodiments can be understood when read in conjunction with the following drawings, where like structure is indicated with like reference numerals and in which: 
         FIG.  1 A  schematically depicts a cross section view of an artificial muscle with titanium dioxide (TiO 2 ) nanomaterial composite electrical insulating layered tape structures affixed to aluminum film electrodes, according to one or more embodiments shown and described herein: 
         FIG.  1 B  depicts a comparison chart of artificial muscle force output improvement for the artificial muscle realized from using TiO 2  nanoparticle composite electrical insulators, according to one or more embodiments shown and described herein: 
         FIG.  2 A  schematically depicts a cross section view of an embodiment of an electrode having a TiO 2  nanomaterial composite electrical insulating layered tape structure having a discrete TiO 2  nanoparticle layer, according to one or more embodiments shown and described herein; 
         FIG.  2 B  schematically depicts a cross section view of another embodiment of an electrode having a TiO 2  nanomaterial composite electrical insulating layered tape structure having a TiO 2  nanoparticle layer partially mixed into surrounding adhesive layers, according to one or more embodiments shown and described herein: 
         FIG.  2 C  schematically depicts a cross section view of another embodiment of an electrode having a TiO 2  nanomaterial composite electrical insulating layered tape structure having TiO 2  nanoparticles mixed within a combined adhesive layer, according to one or more embodiments shown and described herein: 
         FIG.  3    schematically depicts a top view of an illustrative artificial muscle of the artificial muscle of  FIG.  1    with a pressure sensor affixed thereon, according to one or more embodiments shown and described herein; 
         FIG.  4    schematically depicts an exploded view of the artificial muscle of  FIG.  3    without the pressure sensor affixed thereon, according to one or more embodiments shown and described herein; 
         FIG.  5    schematically depicts a top view of the artificial muscle of  FIG.  4   , according to one or more embodiments shown and described herein; 
         FIG.  6    schematically depicts a cross-sectional view of the artificial muscle of  FIG.  4    taken along line  6 - 6  in  FIG.  5    in a non-actuated state, according to one or more embodiments shown and described herein; 
         FIG.  7    schematically depicts a cross-sectional view of the artificial muscle of  FIG.  4    taken along line  6 - 6  in  FIG.  5    in an actuated state, according to one or more embodiments shown and described herein; 
         FIG.  8    schematically depicts a cross-sectional view of another illustrative artificial muscle in a non-actuated state, according to one or more embodiments shown and described herein; 
         FIG.  9    schematically depicts a cross-sectional view of the artificial muscle of  FIG.  4    in an actuated state, according to one or more embodiments shown and described herein: 
         FIG.  10    schematically depicts an exploded view of another illustrative artificial muscle, according to one or more embodiments shown and described herein; 
         FIG.  11    schematically depicts a top view of the artificial muscle of  FIG.  10   , according to one or more embodiments shown and described herein: 
         FIG.  12    schematically depicts a top view of another artificial muscle, according to one or more embodiments shown and described herein; and 
         FIG.  13    schematically depicts an actuation system for operating an artificial muscle, according to one or more embodiments shown and described herein. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments described herein are directed to artificial muscles configured to exert outward pressure. The artificial muscles are more lightweight than traditional motors or actuators, making them better-suited for any potential use that could benefit from a lighter and stronger actuator. The artificial muscles described herein may include a housing having an electrode region and an expandable fluid region, a first electrode and a second electrode each disposed in the electrode region of the housing. Composite electrical insulating layered structures in contact with the electrodes includes titanium dioxide (TiO 2 ) (as a discrete layer, a region of nanoparticles, or a combination thereof) surrounded by adhesive surfaces, which may be surrounded by flexible electrical insulators, such as a biaxially oriented polypropylene (BOPP) film. A dielectric fluid (i.e., a dielectric liquid or dielectric gas) may be disposed within the housing, where the first and second electrodes may electrostatically attract, inflating the expandable fluid region with dielectric fluid and thereby applying outward pressure. The artificial muscle may then be utilized to provide a variety of beneficial types of pressure, such as massaging patterns of pressure, haptic feedback based upon a user, and/or as output from an infotainment device, in which the amount of pressure may vary depending on the thickness and/or amount of TiO 2  present within the composite electrical insulating layered structures. Various embodiments of artificial muscles and the operation of which, are described in more detail herein. Whenever possible, the same reference numerals will be used throughout the drawings to refer to the same or like parts. 
     Referring now to  FIG.  1 A , an artificial muscle  101  may reside within a vehicle (car, truck, sport utility vehicle, van, motorcycle, aircraft, boat, ship, submersible craft, spacecraft, and the like), a house, an office, wearables (clothing, hats, shoes), furniture (seat cushion, arm rest, a foot rest, any other portion which may have contact with a user), and the like. An artificial muscle  101  may actuate/de-actuate at varying rates, intervals, intensity, and the like over time. In this way, any type of pressure pattern can be applied, such as changing pressure, which may be utilized for massaging pressure such as in the form of waves of pressure over time. 
     The artificial muscle  101  is schematically depicted as having a pair of electrodes  106  each in contact with (such as via an adhesive, fastener, or the like) a flexible electrical insulator  105  such as BOPP film or any other suitable type of electrical insulator. In this embodiment, the BOPP film may be wrapped around adhesive surfaces  182  (such as an acrylic adhesive and/or any other suitable adhesive). Between the adhesive surfaces  182  resides an electrical insulator layer  107 , which in this embodiment may be a composite of nanomaterials such as TiO 2  nanoparticles doped (e.g., covered with, immersed in, and the like) with 1% manganese, although any suitable concentration of manganese and/or any other suitable substance may be utilized for the nanoparticles and/or doping of the nanoparticles. 
     The electrical insulator layer  107  (i.e., a layer of TiO 2  in this embodiment) may have a thickness in the range of 10-15 μm (micrometer), although any suitable thickness may be utilized in other embodiments. In another embodiment, the thickness of the TiO 2  layer may be in a range that exceeds 0.1 μm and is less than 100 μm. As shown with respect to  FIG.  1 B , the thickness of the TiO 2  layer may impact artificial muscle force output, with a goal of increasing permittivity (dielectric constant) between the electrodes  106 . Permittivity is the ability of a material to store electrical potential energy under the influence of an electric field, and is measured by the ratio of the capacitance of a capacitor with the material as dielectric to its capacitance with vacuum as dielectric. Rather than a constant, TiO 2  may have differing dielectric values in relation to TiO 2  particle size (which can vary) in relation to the TiO 2  surface area. In determining an amount of thickness for the electrical insulator layer  107 , it may be desirable to increase the thickness of the TiO 2  layer such that a value of the increased thickness, squared, is less than the corresponding increase in the dielectric constant. 
     Referring now to  FIG.  1 B , a graph  102  depicts artificial muscle force output improvement for an artificial muscle as realized from using TiO 2  nanoparticle composite electrical insulators. Specifically, the graph  102  depicts the output force at 0.5 mm displacement for a series of oval-shaped artificial muscles using a 7 kV actuation voltage. The vertical axis represents an increasing amount of force output by an artificial muscle as measured in millimeters (i.e., the amount of displacement provided by an artificial muscle). The horizontal axis represents an increasing amount of TiO 2  as indicated by the mass of TiO 2  nanoparticles per 10 mL of methanol slurry used in fabrication of the nanoparticle composite electrical insulator for each respective muscle. When a TiO 2  thin film is introduced between adhesive surface layers (such as insulation tape) to make a nanomaterial composite layered structure, in this embodiment the force output of the artificial muscle may be increased (by way of non-limiting example) by 72% over a control muscle does not utilize any TiO 2  layer or nanoparticles. 
     Referring now to  FIG.  2 A , an embodiment depicts an electrode  106  in contact with a composite electrical insulating layered structure  111 . A having a discrete electrical insulator layer  107 . Within the composite electrical insulating layered structure  111 A, the electrical insulator layer  107  resides between adhesive surfaces  182 . The adhesive surfaces  182  are located between the electrical insulator layer  107  and respective flexible electrical insulators  105 , one of which is in direct contact with the electrode  106 . 
     Referring to  FIG.  2 B , another embodiment depicts an electrode  106  in contact with a composite electrical insulating layered structure  111 B having a discrete electrical insulator layer  107  thinner than the electrical insulator layer  107  illustrated in  FIG.  2 A , along with electrical insulator nanoparticles  109  residing within the adhesive surfaces  182  proximate to the discrete electrical insulator layer  107 . In some embodiments, this may be due to electrical insulator nanoparticles  109  (e.g., TiO 2  nanoparticles) from the electrical insulator layer  107  becoming pushed into adjacent portions of the adhesive surfaces  182  due to time, pressure, friction, and/or the like. In this embodiment, the electrical insulator nanoparticles  109  may reside within areas of the adhesive surfaces  182  adjacent the remaining electrical insulator layer  107  that generally correspond to the electrical insulator layer  107  depicted in  FIG.  2 A . In other embodiments, the electrical insulator nanoparticles  109  may be distributed into other areas of the adhesive surfaces  182  beyond this. In some embodiments, the electrical insulator nanoparticles  109  may be in a concentration/density that increases with proximity to the electrical insulator layer. The adhesive surfaces  182  are located between the electrical insulator layer  107  and respective flexible electrical insulators  105 , one of which is in direct contact with the electrode  106 . 
     Referring to  FIG.  2 C , a further embodiment depicts an electrode  106  in contact with a composite electrical insulating layered structure  111 C having electrical insulator nanoparticles  109  disposed within an adhesive surface  182  but without a discreet electrical insulator layer. For example, the adhesives may join over time to form a single adhesive surface  182 . In another embodiment, there may be two or more adhesive surfaces  182 . In this embodiment, the electrical insulator nanoparticles  109  may reside in areas adjacent the remaining electrical insulator layer  107  that generally correspond to the electrical insulator layer  107  depicted in  FIG.  2 A . In other embodiments, the electrical insulator nanoparticles  109  may be distributed into other areas of the adhesive surfaces  182  beyond this. In some embodiments, the electrical insulator nanoparticles  109  may be in a concentration/density higher in the area corresponding to the electrical insulator layer  107  with the one or more adhesive surfaces  182 , and which may decrease in concentration/density further out. This may be due, for example, to the electrical insulator layer  107  in  FIGS.  2 A- 2 B  having been completely dissolved within the adhesive surface(s)  182 . The adhesive surface(s)  182  is/are located between the electrical insulator layer  107  and respective flexible electrical insulators  105 , one of which is in direct contact with the electrode  106 . 
     Referring now to  FIGS.  3 - 5   , an artificial muscle  100  is depicted in more detail, and may also include an electrode pair  104  disposed in a housing  110  together with a dielectric fluid  198 . The electrode pair  104  is disposed in an electrode region  194  of the housing  110 , adjacent an expandable fluid region  196 . In operation, voltage may be applied to the electrode pair  104 , drawing the electrode pair  104  together, which directs dielectric fluid into the expandable fluid region  196 , expanding the expandable fluid region  196 . Actuation of artificial muscles  10  may be made to maintain a periodic actuation pressure. In operation, actuation of the one or more artificial muscles  100  may be controlled by an actuation system  1300 , described in more detail with respect to  FIG.  13   . This may include, for example, utilizing a pressure value (Pa/pascal, PSI, etc.) to determine the actuation amount of the one or more artificial muscles  100 . 
     The artificial muscle  100  includes the housing  110 , the electrode pair  104 , including a first electrode  106  and a second electrode  108 , fixed to opposite surfaces of the housing  110 , a first composite electrical insulating layered structure  11  IC fixed to the first electrode  106 , and a second composite electrical insulating layered structure  112  fixed to the second electrode  108 . In some embodiments, the housing  110  is a one-piece monolithic layer including a pair of opposite inner surfaces, such as a first inner surface  114  and a second inner surface  116 , and a pair of opposite outer surfaces, such as a first outer surface  118  and a second outer surface  120 . In some embodiments, the first inner surface  114  and the second inner surface  116  of the housing  110  are heat-sealable. In other embodiments, the housing  110  may be a pair of individually fabricated film layers, such as a first film layer  122  and a second film layer  124 . Thus, the first film layer  122  includes the first inner surface  114  and the first outer surface  118 , and the second film layer  124  includes the second inner surface  116  and the second outer surface  120 . 
     While the embodiments described herein primarily refer to the housing  110  as comprising the first film layer  122  and the second film layer  124 , as opposed to the one-piece housing, it should be understood that either arrangement is contemplated. In some embodiments, the first film layer  122  and the second film layer  124  generally include the same structure and composition. For example, in some embodiments, the first film layer  122  and the second film layer  124  each comprises biaxially oriented polypropylene. 
     The first electrode  106  and the second electrode  108  are each positioned between the first film layer  122  and the second film layer  124 . In some embodiments, the first electrode  106  and the second electrode  108  are each aluminum-coated polyester such as, for example, Mylar®. In addition, one of the first electrode  106  and the second electrode  108  is a negatively charged electrode and the other of the first electrode  106  and the second electrode  108  is a positively charged electrode. For purposes discussed herein, either electrode  106 ,  108  may be positively charged so long as the other electrode  106 ,  108  of the artificial muscle  100  is negatively charged. 
     The first electrode  106  has a film-facing surface  126  and an opposite inner surface  128 . The first electrode  106  is positioned against the first film layer  122 , specifically, the first inner surface  114  of the first film layer  122 . In addition, the first electrode  106  includes a first terminal  130  extending from the first electrode  106  past an edge of the first film layer  122  such that the first terminal  130  can be connected to a power supply to actuate the first electrode  106 . Specifically, the terminal is coupled, either directly or in series, to a power supply and a controller of an actuation system  1300 , as shown in  FIG.  13   . Similarly, the second electrode  108  has a film-facing surface  148  and an opposite inner surface  150 . The second electrode  108  is positioned against the second film layer  124 , specifically, the second inner surface  116  of the second film layer  124 . The second electrode  108  includes a second terminal  152  extending from the second electrode  108  past an edge of the second film layer  124  such that the second terminal  152  can be connected to a power supply and a controller of the actuation system  1300  to actuate the second electrode  108 . 
     The first electrode  106  includes two or more tab portions  132  and two or more bridge portions  140 . Each bridge portion  140  is positioned between adjacent tab portions  132 , interconnecting these adjacent tab portions  132 . Each tab portion  132  has a first end  134  extending radially from a center axis C of the first electrode  106  to an opposite second end  136  of the tab portion  132 , where the second end  136  defines a portion of an outer perimeter  138  of the first electrode  106 . Each bridge portion  140  has a first end  142  extending radially from the center axis C of the first electrode  106  to an opposite second end  144  of the bridge portion  140  defining another portion of the outer perimeter  138  of the first electrode  106 . Each tab portion  132  has a tab length L 1  and each bridge portion  140  has a bridge length L 2  extending in a radial direction from the center axis C of the first electrode  106 . The tab length L 1  is a distance from the first end  134  to the second end  136  of the tab portion  132  and the bridge length L 2  is a distance from the first end  142  to the second end  144  of the bridge portion  140 . The tab length L 1  of each tab portion  132  is longer than the bridge length L 2  of each bridge portion  140 . In some embodiments, the bridge length L 2  is 20% to 50% of the tab length L 1 , such as 30% to 40% of the tab length L 1 . 
     In some embodiments, the two or more tab portions  132  are arranged in one or more pairs of tab portions  132 . Each pair of tab portions  132  includes two tab portions  132  arranged diametrically opposed to one another. In some embodiments, the first electrode  106  may include only two tab portions  132  positioned on opposite sides or ends of the first electrode  106 . In some embodiments, as shown in  FIGS.  4 - 6   , the first electrode  106  includes four tab portions  132  and four bridge portions  140  interconnecting adjacent tab portions  132 . In this embodiment, the four tab portion  132  are arranged as two pairs of tab portions  132  diametrically opposed to one another. Furthermore, as shown, the first terminal  130  extends from the second end  136  of one of the tab portions  132  and is integrally formed therewith. 
     Like the first electrode  106 , the second electrode  108  includes at least a pair of tab portions  154  and two or more bridge portions  162 . Each bridge portion  162  is positioned between adjacent tab portions  154 , interconnecting these adjacent tab portions  154 . Each tab portion  154  has a first end  156  extending radially from a center axis C of the second electrode  108  to an opposite second end  158  of the tab portion  154 , where the second end  158  defines a portion of an outer perimeter  160  of the second electrode  108 . Due to the first electrode  106  and the second electrode  108  being coaxial with one another, the center axis C of the first electrode  106  and the second electrode  108  are the same. Each bridge portion  162  has a first end  164  extending radially from the center axis C of the second electrode to an opposite second end  166  of the bridge portion  162  defining another portion of the outer perimeter  160  of the second electrode  108 . Each tab portion  154  has a tab length L 3  and each bridge portion  162  has a bridge length L 4  extending in a radial direction from the center axis C of the second electrode  108 . The tab length L 3  is a distance from the first end  156  to the second end  158  of the tab portion  154  and the bridge length L 4  is a distance from the first end  164  to the second end  166  of the bridge portion  162 . The tab length L 3  is longer than the bridge length L 4  of each bridge portion  162 . In some embodiments, the bridge length L 4  is 20% to 50% of the tab length L 3 , such as 30% to 40% of the tab length L 3 . 
     In some embodiments, the two or more tab portions  154  are arranged in one or more pairs of tab portions  154 . Each pair of tab portions  154  includes two tab portions  154  arranged diametrically opposed to one another. In some embodiments, the second electrode  108  may include only two tab portions  154  positioned on opposite sides or ends of the first electrode  106 . In some embodiments, as shown in  FIGS.  4 - 6   , the second electrode  108  includes four tab portions  154  and four bridge portions  162  interconnecting adjacent tab portions  154 . In this embodiment, the four tab portions  154  are arranged as two pairs of tab portions  154  diametrically opposed to one another. Furthermore, as shown, the second terminal  152  extends from the second end  158  of one of the tab portions  154  and is integrally formed therewith. 
     Referring now to  FIGS.  3 - 9   , at least one of the first electrode  106  and the second electrode  108  has a central opening formed therein between the first end  134  of the tab portions  132  and the first end  142  of the bridge portions  140 . In  FIGS.  6  and  7   , the first electrode  106  has a central opening  146 . However, it should be understood that the first electrode  106  does not need to include the central opening  146  when a central opening is provided within the second electrode  108 , as shown in  FIGS.  8  and  9   . Alternatively, the second electrode  108  does not need to include the central opening when the central opening  146  is provided within the first electrode  106 . Referring to  FIGS.  3 - 9   , the first composite electrical insulating layered structure  111  and the second composite electrical insulating layered structure  112  have a geometry generally corresponding to the first electrode  106  and the second electrode  108 , respectively. Thus, the first composite electrical insulating layered structure  111  and the second composite electrical insulating layered structure  112  each have tab portions  170 ,  172  and bridge portions  174 ,  176  corresponding to like portions on the first electrode  106  and the second electrode  108 . Further, the composite electrical insulating layered structure  111  and the second composite electrical insulating layered structure  112  each have an outer perimeter  178 ,  180  corresponding to the outer perimeter  138  of the first electrode  106  and the outer perimeter  160  of the second electrode  108 , respectively, when positioned thereon. 
     It should be appreciated that, in some embodiments, the first composite electrical insulating layered structure  111  and the second composite electrical insulating layered structure  112  generally include the same structure and composition. As such, in some embodiments, the first composite electrical insulating layered structure  111  and the second composite electrical insulating layered structure  112  each include an adhesive surface  182 ,  184  and an opposite non-sealable surface  186 ,  188 , respectively. Thus, in some embodiments, the first composite electrical insulating layered structure  111  and the second composite electrical insulating layered structure  112  are each a polymer tape adhered to the inner surface  128  of the first electrode  106  and the inner surface  150  of the second electrode  108 , respectively. 
     Referring again to  FIGS.  3 - 9   , the artificial muscle  100  is shown in its assembled form with the first terminal  130  of the first electrode  106  and the second terminal  152  of the second electrode  108  extending past an outer perimeter of the housing  110 , i.e., the first film layer  122  and the second film layer  124 . As shown in  FIG.  4   , the second electrode  108  is stacked on top of the first electrode  106  and, therefore, the first electrode  106 , the first film layer  122 , and the second film layer  124  are not shown. In its assembled form, the first electrode  106 , the second electrode  108 , the first composite electrical insulating layered structure  111 , and the second composite electrical insulating layered structure  112  are sandwiched between the first film layer  122  and the second film layer  124 . The first film layer  122  is partially sealed to the second film layer  124  at an area surrounding the outer perimeter  138  of the first electrode  106  and the outer perimeter  160  of the second electrode  108 . In some embodiments, the first film layer  122  is heat-sealed to the second film layer  124 . Specifically, in some embodiments, the first film layer  122  is sealed to the second film layer  124  to define a sealed portion  190  surrounding the first electrode  106  and the second electrode  108 . The first film layer  122  and the second film layer  124  may be sealed in any suitable manner, such as using an adhesive, heat sealing, or the like. 
     The first electrode  106 , the second electrode  108 , the first composite electrical insulating layered structure  111 , and the second composite electrical insulating layered structure  112  provide a barrier that prevents the first film layer  122  from sealing to the second film layer  124  forming an unsealed portion  192 . The unsealed portion  192  of the housing  110  includes the electrode region  194 , in which the electrode pair  104  is provided, and the expandable fluid region  196 , which is surrounded by the electrode region  194 . The central openings  146 ,  168  of the first electrode  106  and the second electrode  108  form the expandable fluid region  196  and are arranged to be axially stacked on one another. Although not shown, the housing  110  may be cut to conform to the geometry of the electrode pair  104  and reduce the size of the artificial muscle  100 , namely, the size of the sealed portion  190 . 
     A dielectric fluid  198  is provided within the unsealed portion  192  and flows freely between the first electrode  106  and the second electrode  108 . A “dielectric” fluid as used herein is a medium or material that transmits electrical force without conduction and as such has low electrical conductivity. Some non-limiting example dielectric fluids include perfluoroalkanes, transformer oils, and deionized water. It should be appreciated that the dielectric fluid  198  may be injected into the unsealed portion  192  of the artificial muscle  100  using a needle or other suitable injection device. 
     Referring now to  FIGS.  6  and  7   , the artificial muscle  100  is actuatable between a non-actuated state and an actuated state. In the non-actuated state, the first electrode  106  and the second electrode  108  are partially spaced apart from one another proximate the central openings  146 ,  168  thereof and the first end  134 ,  156  of the tab portions  132 ,  154 . The second end  136 ,  158  of the tab portions  132 ,  154  remain in position relative to one another due to the housing  110  being sealed at the outer perimeter  138  of the first electrode  106  and the outer perimeter  160  of the second electrode  108 . In the actuated state, as shown in  FIG.  7   , the first electrode  106  and the second electrode  108  are brought into contact with and oriented parallel to one another to force the dielectric fluid  198  into the expandable fluid region  196 . This causes the dielectric fluid  198  to flow through the central openings  146 ,  168  of the first electrode  106  and the second electrode  108  and inflate the expandable fluid region  196 . 
     Referring now to  FIG.  6   , the artificial muscle  100  is shown in the non-actuated state. The electrode pair  104  is provided within the electrode region  194  of the unsealed portion  192  of the housing  110 . The central opening  146  of the first electrode  106  and the central opening  168  of the second electrode  108  are coaxially aligned within the expandable fluid region  196 . In the non-actuated state, the first electrode  106  and the second electrode  108  are partially spaced apart from and non-parallel to one another. Due to the first film layer  122  being sealed to the second film layer  124  around the electrode pair  104 , the second end  136 ,  158  of the tab portions  132 ,  154  are brought into contact with one another. Thus, dielectric fluid  198  is provided between the first electrode  106  and the second electrode  108 , thereby separating the first end  134 ,  156  of the tab portions  132 ,  154  proximate the expandable fluid region  196 . Stated another way, a distance between the first end  134  of the tab portion  132  of the first electrode  106  and the first end  156  of the tab portion  154  of the second electrode  108  is greater than a distance between the second end  136  of the tab portion  132  of the first electrode  106  and the second end  158  of the tab portion  154  of the second electrode  108 . This results in the electrode pair  104  zippering toward the expandable fluid region  196  when actuated. In some embodiments, the first electrode  106  and the second electrode  108  may be flexible. Thus, as shown in  FIG.  5   , the first electrode  106  and the second electrode  108  are convex such that the second ends  136 ,  158  of the tab portions  132 ,  154  thereof may remain close to one another, but spaced apart from one another proximate the central openings  146 ,  168 . In the non-actuated state, the expandable fluid region  196  has a first height H 1 . 
     When actuated, as shown in  FIG.  7   , the first electrode  106  and the second electrode  108  zipper toward one another from the second ends  144 ,  158  of the tab portions  132 ,  154  thereof, thereby pushing the dielectric fluid  198  into the expandable fluid region  196 . As shown, when in the actuated state, the first electrode  106  and the second electrode  108  are parallel to one another. In the actuated state, the dielectric fluid  198  flows into the expandable fluid region  196  to inflate the expandable fluid region  196 . As such, the first film layer  122  and the second film layer  124  expand in opposite directions. In the actuated state, the expandable fluid region  196  has a second height H 2 , which is greater than the first height H 1  of the expandable fluid region  196  when in the non-actuated state. Although not shown, it should be noted that the electrode pair  104  may be partially actuated to a position between the non-actuated state and the actuated state. This would allow for partial inflation of the expandable fluid region  196  and adjustments when necessary. 
     In order to move the first electrode  106  and the second electrode  108  toward one another, a voltage is applied by a power supply (such as power supply  48  of  FIG.  13   ). In some embodiments, a voltage of up to 10 kV may be provided from the power supply to induce an electric field through the dielectric fluid  198 . The resulting attraction between the first electrode  106  and the second electrode  108  pushes the dielectric fluid  198  into the expandable fluid region  196 . Pressure from the dielectric fluid  198  within the expandable fluid region  196  causes the first film layer  122  and the first composite electrical insulating layered structure  111  to deform in a first axial direction along the center axis C of the first electrode  106  and causes the second film layer  124  and the second electrical composite electrical insulating layered structure  112  to deform in an opposite second axial direction along the center axis C of the second electrode  108 . Once the voltage being supplied to the first electrode  106  and the second electrode  108  is discontinued, the first electrode  106  and the second electrode  108  return to their initial, non-parallel position in the non-actuated state. 
     It should be appreciated that the present embodiments of the artificial muscle  100  disclosed herein, specifically, the tab portions  132 ,  154  with the interconnecting bridge portions  174 ,  176 , provide a number of improvements over actuators that do not include the tab portions  132 ,  154 , such as hydraulically amplified self-healing electrostatic (HASEL) actuators described in the paper titled “ Hydraulically amplified self - healing electrostatic actuators with muscle - like performance ” by E. Acome. S. K. Mitchell, T. G. Morrissey, M. B. Emmett, C. Benjamin, M. King, M. Radakovitz, and C. Keplinger (Science 5 Jan. 2018: Vol. 359, Issue 6371, pp. 61-65). Embodiments of the artificial muscle  100  including two pairs of tab portions  132 ,  154  on each of the first electrode  106  and the second electrode  108 , respectively, reduces the overall mass and thickness of the artificial muscle  100 , reduces the amount of voltage required during actuation, and decreases the total volume of the artificial muscle  100  without reducing the amount of resulting force after actuation as compared to known HASEL actuators including donut-shaped electrodes having a uniform, radially-extending width. More particularly, the tab portions  132 ,  154  of the artificial muscle  100  provide zipping fronts that result in increased actuation power by providing localized and uniform hydraulic actuation of the artificial muscle  100  compared to HASEL actuators including donut-shaped electrodes. Specifically, one pair of tab portions  132 ,  154  provides twice the amount of actuator power per unit volume as compared to donut-shaped HASEL actuators, while two pairs of tab portions  132 ,  154  provide four times the amount of actuator power per unit volume. The bridge portions  174 ,  176  interconnecting the tab portions  132 ,  154  also limit buckling of the tab portions  132 ,  154  by maintaining the distance between adjacent tab portions  132 ,  154  during actuation. Because the bridge portions  174 ,  176  are integrally formed with the tab portions  132 ,  154 , the bridge portions  174 ,  176  also prevent leakage between the tab portions  132 ,  154  by eliminating attachment locations that provide an increased risk of rupturing. 
     In operation, when the artificial muscle  100  is actuated by providing a voltage and applying the voltage to the electrode pair  104  of the artificial muscle  100 , expansion of the expandable fluid region  196  produces a force of 3 Newton-millimeters (N·mm) per cubic centimeter (cm 3 ) of actuator volume or greater, such as 4 N·mm per cm 3  or greater, 5 N·mm per cm 3  or greater, 6 N·mm per cm 3  or greater, 7 N·mm per cm 3  or greater, 8 N·mm per cm 3  or greater, or the like. Providing the voltage may comprise generating the voltage, for example, in an embodiment in which the power supply  48  ( FIG.  13   ) is a battery, converting the voltage, for example in embodiment in which the power supply  48  ( FIG.  13   ) is a power adaptor, or any other known or yet to be developed technique for readying a voltage for application. In one example, when the artificial muscle  100  is actuated by a voltage of 9.5 kilovolts (kV), the artificial muscle  100  provides a resulting force of 5 N. In another example, when the artificial muscle  100  is actuated by a voltage of 10 kV the artificial muscle  100  provides 440% strain under a 500 gram load. 
     Moreover, the size of the first electrode  106  and the second electrode  108  is proportional to the amount of displacement of the dielectric fluid  198 . Therefore, when greater displacement within the expandable fluid region  196  is desired, the size of the electrode pair  104  is increased relative to the size of the expandable fluid region  196 . It should be appreciated that the size of the expandable fluid region  196  is defined by the central openings  146 ,  168  in the first electrode  106  and the second electrode  108 . Thus, the degree of displacement within the expandable fluid region  196  may alternatively, or in addition, be controlled by increasing or reducing the size of the central openings  146 ,  168 . 
     As shown in  FIGS.  8  and  9   , another embodiment of an artificial muscle  201  is illustrated. The artificial muscle  201  is substantially similar to the artificial muscle  100 . As such, like structure is indicated with like reference numerals. However, as shown, the first electrode  106  does not include a central opening. Thus, only the second electrode  108  includes the central opening  168  formed therein. As shown in  FIG.  8   , the artificial muscle  201  is in the non-actuated state with the first electrode  106  being planar and the second electrode  108  being convex relative to the first electrode  106 . In the non-actuated state, the expandable fluid region  196  has a first height H 3 . In the actuated state, as shown in  FIG.  9   , the expandable fluid region  196  has a second height H 4 , which is greater than the first height H 3 . It should be appreciated that by providing the central opening  168  only in the second electrode  108  as opposed to both the first electrode  106  and the second electrode  108 , the total deformation may be formed on one side of the artificial muscle  201 . In addition, because the total deformation is formed on only one side of the artificial muscle  201 , the second height H 4  of the expandable fluid region  196  of the artificial muscle  201  extends further from a longitudinal axis perpendicular to the central axis C of the artificial muscle  201  than the second height H 2  of the expandable fluid region  196  of the artificial muscle  100  when all other dimensions, orientations, and volume of dielectric fluid are the same. 
     In some embodiments, as shown in  FIG.  3   , a pressure sensor  80  may reside on the housing  110  and be aligned with the central opening  168  or central opening  146 , which are openings in the first electrode  106  and second electrode  108 , respectively. In some embodiments, the pressure sensor  80  may be disposed on the expandable fluid region  196  of the housing  110 . In other embodiments, the pressure sensor  80  may be located on any suitable surface of the housing  110  or an artificial muscle  100 . 
     In some embodiments, different pressure sensors  80  may be located at different locations with respect to different embodiments of housings  110  and/or artificial muscles  100 . In this embodiment, the pressure sensor  80  has two sensor protrusions  82  that extend outwardly from the pressure sensor  80  and may be disposed between the inner layer  30  and outer layer  20 . Sensor protrusions may be used, for example, to wirelessly communicate with other components, such as a controller  50  (as shown in  FIG.  13   ) and/or other wireless sensors located on other artificial muscles  100 . In other embodiments, any number of sensor protrusions  82  of any shape, size, and/or configuration may be utilized. In still other embodiments, the pressure sensor  80  may have no sensor protrusions  82 . 
     In some embodiments, the pressure sensor  80  may be of any suitable type, such as, by way of non-limiting example, absolute, gauge, or differential pressure sensors. Sensing by the pressure sensor  80  may include any suitable technique such as resistive sensing, capacitive sensing, piezoelectric sensing, optical sensing, micro electro-mechanical system (MEMS), or any other suitable type of pressure sensing technique. Output from the pressure sensor  80  may be by millivolt-output transducers, volt-output transducers, transmitters, or any other suitable components. 
     As shown in  FIGS.  10 - 12   , another embodiment of an artificial muscle  300  is illustrated. The artificial muscle  101  embodiment depicted in  FIG.  1 A  may correspond to the artificial muscle embodiment  100  depicted in  FIG.  3    and/or the artificial muscle embodiment  300  depicted in  FIG.  10   . It should be appreciated that the artificial muscle  300  includes similar structure as the artificial muscle  100  ( FIGS.  3 - 9   ) and therefore operates similarly in operation to the artificial muscle  100  ( FIGS.  3 - 9   ). Notably, the artificial muscle  300  includes fan portions  332  in place of the tab portions  132  discussed in relation to the artificial muscle  100 . However, it should be understood that both the fan portions  332  of the artificial muscle  300  and the tab portions  132  are each generally a radially extending portion of an electrode of an artificial muscle, are positioned adjacent bridge portions, and provide a zipping functionality, as described above with respect to the artificial muscle  100 . Indeed, these radially extending portions (e.g., tab portions and fan portions) each provide increased actuator power per unit volume, while minimizing buckling and rupture during operation. 
     Referring now to  FIGS.  10  and  11   , the artificial muscle  300  includes a housing  302 , an electrode pair  304 , including a first electrode  306  and a second electrode  308 , fixed to opposite surfaces of the housing  302 , a first electrical insulator layer  310  fixed to the first electrode  306 , and a second electrical insulator layer  312  fixed to the second electrode  308 . In some embodiments, the housing  302  is a one-piece monolithic layer including a pair of opposite inner surfaces, such as a first inner surface  314  and a second inner surface  316 , and a pair of opposite outer surfaces, such as a first outer surface  318  and a second outer surface  320 . In some embodiments, the first inner surface  314  and the second inner surface  316  of the housing  302  are heat-sealable. In other embodiments, the housing  302  may be a pair of individually fabricated film layers, such as a first film layer  322  and a second film layer  324 . Thus, the first film layer  322  includes the first inner surface  314  and the first outer surface  318 , and the second film layer  324  includes the second inner surface  316  and the second outer surface  320 . 
     While reference may be made to the housing  302  including the first film layer  322  and the second film layer  324 , as opposed to the one-piece housing. It should be understood that either arrangement is contemplated. In some embodiments, the first film layer  322  and the second film layer  324  generally include the same structure and composition. For example, in some embodiments, the first film layer  322  and the second film layer  324  each comprises biaxially oriented polypropylene. 
     The first electrode  306  and the second electrode  308  are each positioned between the first film layer  322  and the second film layer  324 . In some embodiments, the first electrode  306  and the second electrode  308  are each aluminum-coated polyester such as, for example, Mylar®. In addition, one of the first electrode  306  and the second electrode  308  is a negatively charged electrode and the other of the first electrode  306  and the second electrode  308  is a positively charged electrode. For purposes discussed herein, either electrode  306 ,  308  may be positively charged so long as the other electrode  306 ,  308  of the artificial muscle  300  is negatively charged. 
     The first electrode  306  has a film-facing surface  326  and an opposite inner surface  328 . The first electrode  306  is positioned against the first film layer  322 , specifically, the first inner surface  314  of the first film layer  322 . In addition, the first electrode  306  includes a first terminal  330  extending from the first electrode  306  past an edge of the first film layer  322  such that the first terminal  330  can be connected to a power supply to actuate the first electrode  306 . Specifically, the terminal is coupled, either directly or in series, to a power supply and a controller of the actuation system  1300  ( FIG.  13   ). Similarly, the second electrode  308  has a film-facing surface  348  and an opposite inner surface  350 . The second electrode  308  is positioned against the second film layer  324 , specifically, the second inner surface  316  of the second film layer  324 . The second electrode  308  includes a second terminal  352  extending from the second electrode  308  past an edge of the second film layer  324  such that the second terminal  352  can be connected to a power supply and a controller of the actuation system  1300  ( FIG.  13   ) to actuate the second electrode  308 . 
     With respect now to the first electrode  306 , the first electrode  306  includes two or more fan portions  332  extending radially from a center axis C of the artificial muscle  300 . In some embodiments, the first electrode  306  includes only two fan portions  332  positioned on opposite sides or ends of the first electrode  306 . In some embodiments, the first electrode  306  includes more than two fan portions  332 , such as three, four, or five fan portions  332 . In embodiments in which the first electrode  306  includes an even number of fan portions  332 , the fan portions  332  may be arranged in two or more pairs of fan portions  332 . As shown in  FIG.  10   , the first electrode  306  includes four fan portions  332 . In this embodiment, the four fan portions  332  are arranged in two pairs of fan portions  332 , where the two individual fan portions  332  of each pair are diametrically opposed to one another. 
     Each fan portion  332  has a first side edge  332   a  and an opposite second side edge  332   b . As shown, the first terminal  330  extends from a second end  336  of one of the fan portions  332  and is integrally formed therewith. A channel  333  is at least partially defined by opposing side edges  332   a .  332   b  of adjacent fan portions  332  and, thus, extends radially toward the center axis C. The channel  333  terminates at an end  340   a  of a bridge portion  340  interconnecting adjacent fan portions  332 . 
     As shown in  FIG.  10   , dividing lines D are included to depict the boundary between the fan portions  332  and the bridge portions  340 . The dividing lines D extend from the side edges  332   a .  332   b  of the fan portions  332  to a first end  334  of the fan portions  332  collinear with the side edges  332   a ,  332   b . It should be understood that dividing lines D are shown in  FIG.  10    for clarity and that the fan portions  332  are integral with the bridge portions  340 . The first end  334  of the fan portion  332 , which extends between adjacent bridge portions  340 , defines an inner length of the fan portion  332 . Due to the geometry of the fan portion  332  tapering toward the center axis C between the first side edge  332   a  and the second side edge  332   b , the second end  336  of the fan portion  332  defines an outer length of the fan portion  332  that is greater than the inner length of the fan portion  332 . 
     Moreover, each fan portion  332  has a pair of corners  332   c  defined by an intersection of the second end  336  and each of the first side edge  332   a  and the second side edge  332   b  of the fan portion  332 . In embodiments, the corners  332   c  are formed at an angle equal to or less than 90 degrees. In other embodiments, the corners  332   c  are formed at an acute angle. 
     As shown in  FIG.  10   , each fan portion  332  has a first side length defined by a distance between the first end  334  of the fan portion  332  and the second end  336  of the fan portion  332  along the first side edge  332   a  and the dividing line D that is collinear with the first side edge  332   a . Each fan portion  332  also has a second side length defined by a distance between the first end  334  of the fan portion  332  and the second end  336  of the fan portion  332  along the second side edge  332   b  and the dividing line D that is collinear with the second side edge  332   b . In embodiments, the first side length is greater than the second side length of the fan portion  332  such that the first electrode  306  has an ellipsoid geometry. 
     The second end  336 , the first side edge  332   a  and the second side edge  332   b  of each fan portion  332 , and the bridge portions  340  interconnecting the fan portions  332  define an outer perimeter  338  of the first electrode  306 . In embodiments, a central opening  346  is formed within the first electrode  306  between the fan portions  332  and the bridge portions  340 , and is coaxial with the center axis C. Each fan portion  332  has a fan length extending from a perimeter  342  of the central opening  346  to the second end  336  of the fan portion  332 . Each bridge portion  340  has a bridge length extending from a perimeter  342  of the central opening  346  to the end  340   a  of the bridge portion  340 , i.e., the channel  333 . As shown, the bridge length of each of the bridge portions  340  is substantially equal to one another. Each channel  333  has a channel length defined by a distance between the end  340   a  of the bridge portion  340  and the second end of the fan portion  332 . Due to the bridge length of each of the bridge portions  340  being substantially equal to one another and the first side length of the fan portions  332  being greater than the second side length of the fan portions  332 , a first pair of opposite channels  333  has a channel length greater than a channel length of a second pair of opposite channels  333 . As shown, a width of the channel  333  extending between opposing side edges  332   a ,  332   b  of adjacent fan portions  332  remains substantially constant due to opposing side edges  332   a ,  332   b  being substantially parallel to one another. 
     In embodiments, the central opening  346  has a radius of 2 centimeters (cm) to 5 cm. In embodiments, the central opening  346  has a radius of 3 cm to 4 cm. In embodiments, a total fan area of each of the fan portions  332  is equal to or greater than twice an area of the central opening  346 . It should be appreciated that the ratio between the total fan area of the fan portions  332  and the area of the central opening  346  is directly related to a total amount of deflection of the first film layer  322  when the artificial muscle  300  is actuated. In embodiments, the bridge length is 20% to 50% of the fan length. In embodiments, the bridge length is 30% to 40% of the fan length. In embodiments in which the first electrode  306  does not include the central opening  346 , the fan length and the bridge length may be measured from a perimeter of an imaginary circle coaxial with the center axis C. 
     Similar to the first electrode  306 , the second electrode  308  includes two or more fan portions  354  extending radially from the center axis C of the artificial muscle  300 . The second electrode  308  includes substantially the same structure as the first electrode  306  and, thus, includes the same number of fan portions  354 . Specifically, the second electrode  308  is illustrated as including four fan portions  354 . However, it should be appreciated that the second electrode  308  may include any suitable number of fan portions  354 . 
     Each fan portion  354  of the second electrode  308  has a first side edge  354   a  and an opposite second side edge  354   b . As shown, the second terminal  352  extends from a second end  358  of one of the fan portions  354  and is integrally formed therewith. A channel  355  is at least partially defined by opposing side edges  354   a ,  354   b  of adjacent fan portions  354  and, thus, extends radially toward the center axis C. The channel  355  terminates at an end  362   a  of a bridge portion  362  interconnecting adjacent fan portions  354 . 
     As shown in  FIG.  10   , additional dividing lines D are included to depict the boundary between the fan portions  354  and the bridge portions  362 . The dividing lines D extend from the side edges  354   a .  354   b  of the fan portions  354  to the first end  356  of the fan portions  354  collinear with the side edges  354   a ,  354   b . It should be understood that dividing lines D are shown in  FIG.  10    for clarity and that the fan portions  354  are integral with the bridge portions  362 . The first end  356  of the fan portion  354 , which extends between adjacent bridge portions  362 , defines an inner length of the fan portion  354 . Due to the geometry of the fan portion  354  tapering toward the center axis C between the first side edge  354   a  and the second side edge  354   b , the second end  358  of the fan portion  354  defines an outer length of the fan portion  354  that is greater than the inner length of the fan portion  354 . 
     Moreover, each fan portion  354  has a pair of corners  354   c  defined by an intersection of the second end  358  and each of the first side edge  354   a  and the second side edge  354   b  of the fan portion  354 . In embodiments, the corners  354   c  are formed at an angle equal to or less than 90 degrees. In other embodiments, the corners  354   c  are formed at an acute angle. During actuation of the artificial muscle  300 , the corners  332   c  of the first electrode  306  and the corners  354   c  of the second electrode  308  are configured to be attracted to one another at a lower voltage as compared to the rest of the first electrode  306  and the second electrode  308 . Thus, actuation of the artificial muscle  300  initially at the corners  332   c ,  354   c  results in the outer perimeter  338  of the first electrode  306  and the outer perimeter  360  of the second electrode  308  being attracted to one another at a lower voltage and reducing the likelihood of air pockets or voids forming between the first electrode  306  and the second electrode  308  after actuation of the artificial muscle  300 . 
     As shown in  FIGS.  10  and  11   , in embodiments, the first side edge  354   a  of each fan portion  354  has a first side length defined by a distance between the first end  356  of the fan portion  354  and the second end  358  of the fan portion  354  along the first side edge  354   a  and the dividing line D that is collinear with the first side edge  354   a . Each fan portion  354  also has a second side length defined by a distance between the first end  356  of the fan portion  354  and the second end  358  of the fan portion  354  along the second side edge  354   b  and the dividing line D that is collinear with the second side edge  354   b . In embodiments, the first side length is greater than the second side length of the fan portion  354  such that the second electrode  308  has an ellipsoid geometry corresponding to the geometry of the first electrode  306 . 
     The second end  358 , the first side edge  354   a  and the second side edge  354   b  of each fan portion  354 , and the bridge portions  362  interconnecting the fan portions  354  define an outer perimeter  360  of the second electrode  308 . In embodiments, a central opening  368  is formed within the second electrode  308  between the fan portions  354  and the bridge portions  362 , and is coaxial with the center axis C. Each fan portion  354  has a fan length extending from a perimeter  364  of the central opening  368  to the second end  358  of the fan portion  354 . Each bridge portion  362  has a bridge length extending from the central opening  368  to the end  362   a  of the bridge portion  362 , i.e., the channel  355 . As shown, the bridge length of each of the bridge portions  362  is substantially equal to one another. Each channel  355  has a channel length defined by a distance between the end  362   a  of the bridge portion  362  and the second end of the fan portion  354 . Due to the bridge length of each of the bridge portions  362  being substantially equal to one another and the first side length of the fan portions  354  being greater than the second side length of the fan portions  354 , a first pair of opposite channels  355  has a channel length greater than a channel length of a second pair of opposite channels  355 . As shown, a width of the channel  355  extending between opposing side edges  354   a ,  354   b  of adjacent fan portions  354  remains substantially constant due to opposing side edges  354   a ,  354   b  being substantially parallel to one another. 
     In embodiments, the central opening  368  has a radius of 2 cm to 5 cm. In embodiments, the central opening  368  has a radius of 3 cm to 4 cm. In embodiments, a total fan area of each of the fan portions  354  is equal to or greater than twice an area of the central opening  368 . It should be appreciated that the ratio between the total fan area of the fan portions  354  and the area of the central opening  368  is directly related to a total amount of deflection of the second film layer  324  when the artificial muscle  300  is actuated. In embodiments, the bridge length is 20% to 50% of the fan length. In embodiments, the bridge length is 30% to 40% of the fan length. In embodiments in which the second electrode  308  does not include the central opening  368 , the fan length and the bridge length may be measured from a perimeter of an imaginary circle coaxial with the center axis C. 
     As described herein, the first electrode  306  and the second electrode  308  each have a central opening  346 ,  368  coaxial with the center axis C. However, it should be understood that the first electrode  306  does not need to include the central opening  346  when the central opening  368  is provided within the second electrode  308 . Alternatively, the second electrode  308  does not need to include the central opening  368  when the central opening  346  is provided within the first electrode  306 . 
     Referring again to  FIG.  10   , the first electrical insulator layer  310  and the second electrical insulator layer  312  have a substantially ellipsoid geometry generally corresponding to the geometry of the first electrode  306  and the second electrode  308 , respectively. Thus, the first electrical insulator layer  310  and the second electrical insulator layer  312  each have fan portions  370 ,  372  and bridge portions  374 ,  376  corresponding to like portions on the first electrode  306  and the second electrode  308 . Further, the first electrical insulator layer  310  and the second electrical insulator layer  312  each have an outer perimeter  378 ,  380  corresponding to the outer perimeter  338  of the first electrode  306  and the outer perimeter  360  of the second electrode  308 , respectively, when positioned thereon. 
     It should be appreciated that, in some embodiments, the first electrical insulator layer  310  and the second electrical insulator layer  312  generally include the same structure and composition. As such, in some embodiments, the first electrical insulator layer  310  and the second electrical insulator layer  312  each include an adhesive surface  382 ,  384  and an opposite non-sealable surface  386 ,  388 , respectively. Thus, in some embodiments, the first electrical insulator layer  310  and the second electrical insulator layer  312  are each a polymer tape adhered to the inner surface  328  of the first electrode  306  and the inner surface  350  of the second electrode  308 , respectively. 
     Referring now to  FIG.  11   , the artificial muscle  300  is shown in its assembled form with the first terminal  330  of the first electrode  306  and the second terminal  352  of the second electrode  308  extending past an outer perimeter of the housing  302 , i.e., the first film layer  322  ( FIG.  10   ) and the second film layer  324 . The second electrode  308  is stacked on top of the first electrode  306  and, therefore, the first film layer  322  ( FIG.  10   ) is not shown. In its assembled form, the first electrode  306 , the second electrode  308 , the first electrical insulator layer  310  ( FIG.  10   ), and the second electrical insulator layer  312  ( FIG.  10   ) are sandwiched between the first film layer  322  ( FIG.  10   ) and the second film layer  324 . The first film layer  322  ( FIG.  10   ) is partially sealed to the second film layer  324  at an area surrounding the outer perimeter  338  ( FIG.  10   ) of the first electrode  306  and the outer perimeter  360  of the second electrode  308 . In some embodiments, the first film layer  322  ( FIG.  10   ) is heat-sealed to the second film layer  324  ( FIG.  10   ). Specifically, in some embodiments, the first film layer  322  ( FIG.  13   ) is sealed to the second film layer  324  to define a sealed portion  390  surrounding the first electrode  306  and the second electrode  308 . The first film layer  322  ( FIG.  10   ) and the second film layer  324  may be sealed in any suitable manner, such as using an adhesive, heat sealing, vacuum sealing, or the like. 
     The first electrode  306 , the second electrode  308 , the first electrical insulator layer  310  ( FIG.  10   ), and the second electrical insulator layer  312  ( FIG.  10   ) provide a barrier that prevents the first film layer  322  ( FIG.  10   ) from sealing to the second film layer  324 , forming an unsealed portion  392 . The unsealed portion  392  of the housing  302  includes an electrode region  394 , in which the electrode pair  304  is provided, and an expandable fluid region  396 , which is surrounded by the electrode region  394 . The central openings  346  ( FIG.  10   ),  368  of the first electrode  306  and the second electrode  308  define the expandable fluid region  396  and are arranged to be axially stacked on one another. Although not shown, the housing  302  may be cut to conform to the geometry of the electrode pair  304  and reduce the size of the artificial muscle  300 , namely, the size of the sealed portion  390 . A dielectric fluid is provided within the unsealed portion  392  and flows freely between the first electrode  306  and the second electrode  308   
     Referring now to  FIG.  12   , an alternative embodiment of an artificial muscle  300 ′ is illustrated. It should be appreciated that the artificial muscle  300 ′ is similar to the artificial muscle  300  described herein. As such, like structure is indicated with like reference numerals. The first electrode  306  and the second electrode  308  of the artificial muscle  300 ′ have a circular geometry as opposed to the ellipsoid geometry of the first electrode  306  and the second electrode  308  of the artificial muscle  300  described herein. As shown in  FIG.  12   , with respect to the second electrode  308 , a first side edge length of the first side edge  354   a  is equal to a second side edge length of the second side edge  354   b . Accordingly, the channels  355  formed between opposing side edges  354   a .  354   b  of the fan portions  354  each have an equal length. Although the first electrode  306  is hidden from view in  FIG.  12    by the second electrode  308 , it should be appreciated that the first electrode  306  also has a circular geometry corresponding to the geometry of the second electrode  308 . 
     Referring again to  FIGS.  10  and  11   , actuation of the artificial muscle  300  will be discussed. In the non-actuated state, the first electrode  306  and the second electrode  308  are partially spaced apart from one another proximate the central openings  346 ,  368  thereof and the first end  334 ,  356  of the fan portions  332 ,  354 . The second end  336 ,  358  of the fan portions  332 ,  354  remain in position relative to one another due to the housing  302  being sealed at the outer perimeter  338  of the first electrode  306  and the outer perimeter  360  of the second electrode  308 . In the actuated state, the first electrode  306  and the second electrode  308  are brought into contact with and oriented parallel to one another to force the dielectric fluid  398  into the expandable fluid region  396 . This causes the dielectric fluid  398  to flow through the central openings  346 ,  368  of the first electrode  306  and the second electrode  308  and inflate the expandable fluid region  396 . 
     In the non-actuated state, a distance between the first end  334  of the fan portion  332  of the first electrode  306  and the first end  356  of the fan portion  354  of the second electrode  308  is greater than a distance between the second end  336  of the fan portion  332  of the first electrode  306  and the second end  358  of the fan portion  354  of the second electrode  308 . This results in the electrode pair  304  zippering toward the expandable fluid region  396  when actuated. When actuated, the first electrode  306  and the second electrode  308  zipper toward one another from the second ends  336 ,  358  of the fan portions  332 ,  354  thereof, thereby pushing the dielectric fluid  398  into the expandable fluid region 3%. When in the actuated state, the first electrode  306  and the second electrode  308  are parallel to one another. In the actuated state, the dielectric fluid  398  flows into the expandable fluid region  396  to inflate the expandable fluid region  396 . As such, the first film layer  322  and the second film layer  324  expand in opposite directions. 
     Referring now to  FIG.  13   , an actuation system  1300  may be provided for operating the artificial muscle  100 . The actuation system  1300  may comprise a controller  50 , the one or more pressure sensors  80 , an operating device  46 , a power supply  48 , a display device  42 , network interface hardware  44 , and a communication path  41  communicatively coupled these components, some or all of which may be disposed in the onboard control unit  40 . 
     The controller  50  may comprise a processor  52  and a non-transitory electronic memory  54  to which various components are communicatively coupled. In some embodiments, the processor  52  and the non-transitory electronic memory  54  and/or the other components are included within a single device. In other embodiments, the processor  52  and the non-transitory electronic memory  54  and/or the other components may be distributed among multiple devices that are communicatively coupled. The controller  50  may include non-transitory electronic memory  54  that stores a set of machine-readable instructions. The processor  52  may execute the machine-readable instructions stored in the non-transitory electronic memory  54 . The non-transitory electronic memory  54  may comprise RAM, ROM, flash memories, hard drives, or any device capable of storing machine-readable instructions such that the machine-readable instructions can be accessed by the processor  52 . Accordingly, the actuation system  1300  described herein may be implemented in any computer programming language, as pre-programmed hardware elements, or as a combination of hardware and software components. The non-transitory electronic memory  54  may be implemented as one memory module or a plurality of memory modules. In some embodiments, the non-transitory electronic memory  54  includes instructions for executing the functions of the actuation system  1300 . The instructions may include instructions for operating/actuating the artificial muscle  100 . 
     The processor  52  may be any device capable of executing machine-readable instructions. For example, the processor  52  may be an integrated circuit, a microchip, a computer, or any other computing device. The non-transitory electronic memory  54  and the processor  52  are coupled to the communication path  41  that provides signal interconnectivity between various components and/or modules of the actuation system  1300 . Accordingly, the communication path  41  may communicatively couple any number of processors with one another, and allow the modules coupled to the communication path  41  to operate in a distributed computing environment. Specifically, each of the modules may operate as a node that may send and/or receive data. As used herein, the term “communicatively coupled” means that coupled components are capable of exchanging data signals with one another such as, for example, electrical signals via conductive medium, electromagnetic signals via air, optical signals via optical waveguides, and the like. 
     As schematically depicted in  FIG.  13   , the communication path  41  communicatively couples the processor  52  and the non-transitory electronic memory  54  of the controller  50  with a plurality of other components of the actuation system  1300 . For example, the actuation system  1300  depicted in  FIG.  13    includes the processor  52  and the non-transitory electronic memory  54  communicatively coupled with the pressure sensor  80 , operating device  46 , and the power supply  48 . 
     The operating device  46  allows for a user to control operation of the artificial muscle  100 . In some embodiments, the operating device  46  may be a switch, toggle, button, or any combination of controls to provide user operation. The operating device  46  is coupled to the communication path  41  such that the communication path  41  communicatively couples the operating device  46  to other modules of the actuation system  1300 . The operating device  46  may provide a user interface for receiving user instructions as to a specific operating configuration of the artificial muscle  100 , such as an amount desired actuation. 
     The power supply  48  (e.g., battery) provides power to the artificial muscle  100 . In some embodiments, the power supply  48  is a rechargeable direct current power source. It is to be understood that the power supply  48  may be a single power supply or battery for providing power to the artificial muscle  100 . A power adapter (not shown) may be provided and electrically coupled via a wiring harness or the like for providing power to the artificial muscle  100  via the power supply  48 . Indeed, the power supply  48  is a device that can receive power at one level (e.g., one voltage, power level, or current) and output power at a second level (e.g., a second voltage, power level, or current). 
     In some embodiments, the actuation system  1300  also includes a display device  42 . The display device  42  is coupled to the communication path  41  such that the communication path  41  communicatively couples the display device  42  to other modules of the actuation system  1300 . The display device  42  may output a notification in response to an actuation state of the artificial muscle  100  or indication of a change in the actuation state of the artificial muscle  100 . The display device  42  may be a touchscreen that, in addition to providing optical information, detects the presence and location of a tactile input upon a surface of or adjacent to the display device  42 . Accordingly, the display device  42  may include the operating device  46  and receive mechanical input directly upon the optical output provided by the display device  42 . For example, a user may be able to specify a desired actuation pressure value. 
     In some embodiments, the actuation system  1300  includes network interface hardware  44  for communicatively coupling the actuation system  1300  to a portable device  70  via a network  60 . The portable device  70  may include, without limitation, a smartphone, a tablet, a personal media player, or any other electric device that includes wireless communication functionality. The portable device  70  may correspond to an infotainment device, or any other type of device capable of communicating with the network interface hardware  44 , utilizing Wi-Fi, Bluetooth, and/or any other suitable communication protocol. It is to be appreciated that, when provided, the portable device  70  may serve to provide user commands to the controller  50 , instead of the operating device  46 . As such, a user may be able to control or set a program for controlling an artificial muscle  100  utilizing the controls of the operating device  46 . Thus, the artificial muscle  100  may be controlled remotely via the portable device  70  wirelessly communicating with the controller  50  via the network  60 . For example, the user may be able to specify a desired pressure value. The portable device  70  may also receive and display pressure readings from one or more pressure sensors  80  associated with the artificial muscle  100 . 
     It should now be understood that embodiments described herein are directed to an artificial muscle having an electrode in contact with a composite electrical insulating layered structure that utilizes TiO 2  nanoparticles, which may be arranged within a layer. The TiO 2  nanoparticles may be located within one or more acrylic adhesives surrounded by a biaxially oriented polypropylene film in contact with an electrode. The TiO 2  nanoparticles significantly increase the force output of the artificial muscle, thus creating more force output with the same size actuator and the same operating voltage. 
     It is noted that the terms “substantially” and “about” may be utilized herein to represent the inherent degree of uncertainty that may be attributed to any quantitative comparison, value, measurement, or other representation. These terms are also utilized herein to represent the degree by which a quantitative representation may vary from a stated reference without resulting in a change in the basic function of the subject matter at issue. 
     While particular embodiments have been illustrated and described herein, it should be understood that various other changes and modifications may be made without departing from the scope of the claimed subject matter. Moreover, although various aspects of the claimed subject matter have been described herein, such aspects need not be utilized in combination. It is therefore intended that the appended claims cover all such changes and modifications that are within the scope of the claimed subject matter.