Patent Publication Number: US-2021186139-A1

Title: Protective helmets with non-linearly deforming elements

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a Continuation of co-pending U.S. patent application Ser. No. 15/034,006, filed May 3, 2016, which is a U.S. national phase of International Patent Application No. PCT/US2014/064173, filed Nov. 5, 2014, now expired, which claims the benefit of the following pending applications: 
     (a) U.S. Provisional Patent Application No. 61/900,212, filed Nov. 5, 2013, now expired; 
     (b) U.S. Provisional Patent Application No. 61/923,495, filed Jan. 3, 2014, now expired; 
     (c) U.S. Provisional Patent Application No. 62/049,049, filed Sep. 11, 2014, now expired; 
     (d) U.S. Provisional Patent Application No. 62/049,161, filed Sep. 11, 2014, now expired; 
     (e) U.S. Provisional Patent Application No. 62/049,190, filed Sep. 11, 2014, now expired; and 
     (f) U.S. Provisional Patent Application No. 62/049,207, filed Sep. 11, 2014, now expired. 
     All of the foregoing applications are incorporated herein by reference in their entireties. Further, components and features of embodiments disclosed in the applications incorporated by reference may be combined with various components and features disclosed and claimed in the present application. 
    
    
     TECHNICAL FIELD 
     The present technology is generally related to protective helmets. In particular, several embodiments are directed to protective helmets with non-linearly deforming elements therein. 
     BACKGROUND 
     Sports-related traumatic brain injury, and specifically concussion, have become major concerns for the NFL, the NCAA, football teams and participants at all levels. Such injuries are also significant concerns for participants in other activities such as cycling and skiing. Current helmet technology is inadequate, as it primarily protects against superficial head injury and not concussions that can be caused by direct or oblique forces. Additionally, currently available helmets absorb incident forces linearly, which transmits the bulk of the incident force to the head of the wearer. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a perspective view of a protective helmet configured in accordance with embodiments of the present technology; 
         FIG. 1B  is a perspective cross-sectional view of the protective helmet shown in  FIG. 1A ; 
         FIG. 2A-C  illustrate various embodiments of filaments configured for an interface layer of a protective helmet configured in accordance with the present technology; 
         FIG. 3A-D  illustrate deformation of portion of an interface layer configured in accordance with embodiments of the present technology; 
         FIGS. 4A and 4B  illustrate an interface layer including a plurality of segmented tiles in accordance with embodiments of the present technology; 
         FIGS. 5A-I  illustrate various filament configurations and shapes in accordance with embodiments of the present technology; 
         FIG. 6  is a graph of the stress-strain behavior of an interface layer configured in accordance with embodiments of the present technology; 
         FIG. 7  illustrates a variety of filament densities for the interface layer in accordance with embodiments of the present technology; 
         FIG. 8  is a cross-sectional view of a protective helmet having an interface layer with a plurality of filaments extending from an outer surface of the helmet in accordance with embodiments of the present technology; 
         FIG. 9A  is a cross-sectional view of a protective helmet having an interface layer with two different types of filaments configured in accordance with embodiments of the present technology; 
         FIG. 9B  is an enlarged detail view of the protective helmet shown in  FIG. 9A ; 
         FIG. 9C  is a cross-sectional view of the protective helmet shown in  9 A under local deformation; 
         FIG. 9D  is an enlarged detail view of the protective helmet shown under local deformation in  FIG. 9C ; 
         FIG. 10  is a flow diagram of a method of manufacturing an interface layer in accordance with embodiments of the present technology; 
         FIG. 11  is a flow diagram of another method of manufacturing an interface layer in accordance with embodiments of the present technology; 
         FIG. 12  is a perspective cross-sectional view of a protective helmet with filaments incorporating force sensors configured in accordance with embodiments of the present technology; 
         FIG. 13  is an enlarged view of one embodiment of filaments in different orientations; and 
         FIG. 14  are cross-section views of a protective helmet with filaments positioned relative to the inner layer. 
     
    
    
     DETAILED DESCRIPTION 
     The present technology is generally related to protective helmets with non-linearly deforming elements therein Embodiments of the disclosed helmets, for example, comprise an inner layer, an outer layer, and an interface layer disposed in a space between the inner and outer layers. The interface layer can include a plurality of filaments configured to deform non-linearly in response to an incident force. 
     Specific details of several embodiments of the present technology are described below with reference to  FIGS. 1A-12 . Although many of the embodiments are described below with respect to devices, systems, and methods for protective helmets, other embodiments are within the scope of the present technology. Additionally, other embodiments of the present technology can have different configurations, components, and/or procedures than those described herein. For example, other embodiments can include additional elements and features beyond those described herein, or other embodiments may not include several of the elements and features shown and described herein. 
     For ease of reference, throughout this disclosure identical reference numbers are used to identify similar or analogous components or features, but the use of the same reference number does not imply that the parts should be construed to be identical. Indeed, in many examples described herein, the identically numbered parts are distinct in structure and/or function. 
     Selected Embodiments of Protective Helmets 
       FIG. 1A  is a perspective view of a protective helmet  101  configured in accordance with embodiments of the present technology.  FIG. 1B  is a perspective cross-sectional view of the helmet shown in  FIG. 1A . Referring to  FIGS. 1A and 1B  together, the helmet  101  comprises an outer layer  103 , an inner layer  105 , and space or gap  107  between the outer layer  103  and the inner layer  105 . An interface layer  109  comprising a plurality of filaments  111  is disposed in the space  107  between the outer layer  103  and the inner layer  105 . In the illustrated embodiment, the filaments  111  extend between an outer surface  113  adjacent to the outer layer  103  and an inner surface  115  adjacent to the inner layer  105 , and span or substantially span the space  107 . Padding  117  is disposed adjacent to the inner layer  105 . The padding  117  can be configured to comfortably conform to a head of the wearer (not shown). 
     In some embodiments, the outer layer  103  of the helmet  101  may be composed of a single, continuous shell. In other embodiments, however, the outer layer  103  may have a different configuration. The outer layer  103  and the inner layer  105  can also both be relatively rigid (e.g., composed of a hard plastic material). The outer layer  103 , however, can be pliable enough to locally deform when subject to an incident force. In certain embodiments, the inner layer  105  can be relatively stiff, thereby preventing projectiles or intense impacts from fracturing the skull or creating hematomas. In some embodiments, the inner layer  105  can be at least five times more rigid than the outer layer  103 . In some embodiments, the outer layer  103  may also comprise a plurality of deformable beams that are flexibly connected and arranged so that the longitudinal axes of the beams are substantially parallel to the surface of the outer layer. Further, in some embodiments each of the deformable beams can be flexibly connected to at least one other deformable beam and at least one filament. 
     The filaments  111  can comprise thin, columnar or elongated structures configured to deform non-linearly in response to an incident force on the helmet  101 . Such structures can have a high aspect ratio, e.g., from 3:1 to 1000:1, from 4:1 to 1000:1, from 5:1 to 1000:1, from 100:1 to 1000:1, etc. The non-linear deformation of the filaments  111  is expected to provide improved protection against high-impact direct forces, as well as oblique forces. More specifically, the filaments  111  can be configured to buckle in response to an incident force, where buckling may be characterized by a sudden failure of filament(s)  111  subjected to high compressive stress, where the actual compressive stress at the point of failure is less than the ultimate compressive stresses that the material is capable of withstanding. The filaments  111  can be configured to deform elastically, so that they substantially return to their initial configuration once the external force is removed. 
     At least a portion of the filaments  111  can be configured to have a tensile strength so as to resist separation of the outer layer  103  from the inner layer  105 . For example, during lateral movement of the outer layer  103  relative to the inner layer  105 , those filaments  111  having tensile strength may exert a force to counteract the lateral movement of the outer layer  103  relative to the inner layer  105 . In some embodiments, there may be wires, rubber bands, or other elements embedded in or otherwise coupled to the filaments  111  in order to impart additional tensile strength. 
     As shown in the embodiment illustrated in  FIG. 1B , for example, the filaments  111  may be directly attached to the outer layer  103  and/or directly attached to the inner layer  105 . In some embodiments, at least some of the filaments  111  can be free at one end, with an opposite end coupled to an adjacent surface. Due to the flexibility of the filaments  111 , the outer layer  103  can move laterally relative to the inner layer  105 . In some embodiments, the filaments  111  can optionally include a rotating member at one or both ends that is configured to rotatably fit within a corresponding socket in the inner or outer layers. In some embodiments, at least some of the filaments  111  can be substantially perpendicular to the inner surface  115 , the outer surface  113 , or both. 
     The filaments  111  may be composed of a variety of suitable materials, such as a foam, elastomeric material, polymeric material, or any combination thereof. In some embodiments, the filaments can be made of a shape memory material and/or a self-healing material. Furthermore, in some embodiments, the filaments may exhibit different shear characteristics in different directions. 
     In some embodiments, the helmet  101  can be configured to deform locally and elastically in response to an incident force. In particular embodiments, for example, the helmet  101  can be configured such that upon application of between about 100 and 500 static pounds of force, the outer layer  103  and interface layer  109  deform between about 0.75 to 2.25 inches. The deformability can be tuned by varying the composition, number, and configuration of the filaments  111 , and by varying the composition and configuration of the outer layer  103  and inner layer  105 . 
       FIG. 2A-C  illustrate various embodiments of filaments configured for an interface layer (e.g., interface layer  109 ) of a protective helmet (e.g., helmet  101 ) in accordance with embodiments of the present technology. Referring to  FIG. 2A , for example, a plurality of filaments  211   a  have a cross-sectional shape of regular polygons. Individual filaments  211   a  have a height  201 , a width  203 , and a spacing  205  between adjacent filaments  211   a . Referring to  FIG. 2B , filaments  211   b  can be connected to an inner surface  215  at one end, and can be free at the opposite end. In  FIG. 2C , filaments  211   c  can be coupled to a spine  207  at a middle point of the filaments  211   c , such that the filaments  211   c  extend outwardly in opposite directions from the spine  207 . Referring to  FIGS. 2A-2C  together, the filaments  211   a - c  can assume any suitable shape, including cylinders, hexagons (inverse honeycomb), square, irregular polygons, random, etc. The point of connection between the filaments  211   a - c  and the inner surface  215  or the spine  207 , the dimensions  201 ,  203 , and  205 , the filament material, the material in the space between the filaments  211   a - c , can all be modified to tune the orthotropic properties of the filaments. This tunability is expected to provide desired deformation properties and can be varied between different regions of the interface layer. The filaments  211   a - c  can be made from any material that allows for large elastic deformations including, for example, foams, elastic foams, plastics, etc. The spacing between filaments  211   a - c  can be filled with gas, liquid, or complex fluids, to further tune overall structure material properties. In some embodiments, for example, the space can be filled with a gas, a liquid (e.g., a shear thinning or shear thickening liquid), a gel (e.g., a shear thinning or shear thickening gel), a foam, a polymeric material, or any combination thereof. 
       FIG. 3A-D  illustrate deformation of an interface layer  309  having an outer surface  313 , an inner surface  315 , and a plurality of filaments  311  extending between the outer surface  313  and the inner surface  315 .  FIG. 3A , for example, illustrates the interface layer  309  without an external force applied. In  FIG. 3B , a downward force F 1  is applied to the outer surface  313 , resulting in deformation of a portion of the filaments  311 .  FIG. 3C  illustrates translation of the outer surface  313  with respect to the inner surface  315  in response to a tangential force F 2 . In  FIG. 3D , a vertical and tangential force F 3  results in deformation of the filaments  311 . Oblique and/or tangential forces that are distributed over a larger area of the outer surface  313  can result in shear of the filaments  311  or local buckling of some of the filaments  311 . 
       FIGS. 4A and 4B  illustrate an interface layer  409  including a plurality of segmented tiles configured in accordance with embodiments of the present technology. A plurality of filaments  411  are affixed to and extend away from an inner surface  415 . An outer surface  413  of the interface layer  409  is divided into a plurality of segmented tiles  414  (three are shown as tiles  414   a - c ). As best seen in  FIG. 4B , the filaments  411  throughout the interface layer  409  share the common inner surface  415 , but only a subset of the filaments  411  are coupled together to define individual segmented tiles  414   a - c . In  FIGS. 4A and 4B , the tiles  414   a - c  are shown as packed hexagons, but in other embodiments the tiles  414   a - c  could take other shapes including regular and irregular polygons, cylinders, etc. The tiles  414  are arranged to allow for a set of filaments  411  to respond to local impact forces and buckle, shear, or otherwise move relative to the other neighboring tiles  414 . In some embodiments, some tiles  414  can be configured to move on top of or below neighboring tiles  414  in response to impact forces. In certain embodiments, the tiles  414  may be flexibly connected to one another. The tiles  414   a - c  can be configured to tessellate with each other. The space between the tiles  414   a - c  can be air, or the space may be filled with a different material (e.g. foam, liquid, gel, etc.). 
       FIGS. 5A-5I  illustrate various filament configurations and shapes in accordance with embodiments of the present technology. The filaments of  FIGS. 5A-5I  may be used with any of the interface layers disclosed herein. Referring first to  FIG. 5A , for example, an interface layer  509  comprises a plurality of filaments  511   a  extending from an inner surface  515   a , with an outer surface  513   a  divided into separate discrete portions.  FIG. 5B  illustrates the interface layer  509  being flexibly curved. For example, the interface layer  509  may be curved to correspond to the curvature of a helmet. The material of the filaments  511   a , the outer surface  113   a , and/or the inner surface  115   a  can be flexible to permit such bending. 
       FIGS. 5C-F  illustrate plan views of an arrangement of filaments  511   c - i  in the interface layer  509 . The filaments  511   c  can have a uniform size and shape, and be distributed isotropically (as in  FIG. 5C ). With respect to  FIG. 5D , some filaments  511   d  are larger than others, and they can be distributed non-uniformly. In  FIGS. 5E and 5F , the filaments  511   e  assume irregular shapes and patterns.  FIGS. 5G-5I  illustrate side views of single filaments  511   g - i  having various configurations. In  FIG. 5G , for example, the filament  511   g  is connected to the inner surface  515   g , but is separated from the outer surface  513   g . In  FIG. 5H , the filament  511   h  has a varying thickness along its length. In Figure SI, the filament  511   h  is hollow, for example a hollow cylinder. In certain embodiments, one or more of the filaments can be hollow, such that the filament includes a lumen that extends a portion of the distance along the height of the filament. The arrangement, size, and shape of the filaments can be varied to achieve the desired mechanical properties of the corresponding interface layer, for example deformation properties, stiffness, etc. 
     In some embodiments, the filaments can be disposed between the outer surface and the inner surface such that a longitudinal axis of the filament is not perpendicular to either the outer surface  1301  or the inner surface  1303  as shown in  FIG. 13 . In some embodiments, the angle of the longitudinal axis of a first subset of filaments  1304  relative to at least one of the outer surface  1301  and/or inner surface  1303  can be supplementary to the angle of the longitudinal axis of a second subset of filaments  1305  relative to the outer surface  1301  and/or the inner surface  1303 . For example, a first filament can have a longitudinal axis disposed at a 30 degree angle with respect to the inner surface, and a second filament can have a longitudinal axis disposed at a 150 degree angle with respect to the inner surface. In some embodiments, the first and second filaments can be connected to one another at an intersection point  1306 . 
       FIG. 6  is a graph of stress-strain behavior of the interface layer in accordance with embodiments of the present technology. As illustrated, as the strain (D) increases, the stress (σ) initially increases rapidly in region I. Next, in region II, the stress is relatively flat, followed by a further increase of the stress in region III. This nonlinear relationship exhibits behavior similar to those observed in buckling in which there is an initial stiff region (region I), followed by a rapid transition to a flat, decreasing, or increasing slope (region II), followed by a third region with a different slope (region III). As depicted in  FIG. 6 , the dashed lines illustrate possible alternative stress-strain profiles for an interface layer. As the materials, arrangement and configuration of filaments within the interface layer are varied, the stress-strain relationship can be adjusted to achieve a desired profile. In some embodiments, the interface layer can be orthotropic (i.e., exhibiting different nonlinear stress-strain behaviors for different components of stress). 
       FIG. 7  illustrates a variety of filament densities for a protective helmet in accordance with embodiments of the present technology. As noted above, a protective helmet can include an interface layer comprising a plurality of filaments therein. The deformation characteristics of the interface layer can be adjusted/tuned based on a composition and arrangement of the filaments. As illustrated in  FIG. 7 , the arrangement and density of filaments can vary at different locations of the helmet. For example, the density of filaments may be greatest in the front and back portions, with a lower density of filaments on left and right, and an even lower density of filaments over the left and right ears. Because a wearer of the help may be at greater risk of receiving a high-impact force from the front or back, those portions of the helmet can have a greater density of filaments that the portion of the helmet than over the wearer&#39;s ear. The density and configuration of filaments can accordingly be varied across the helmet to account for the types and frequencies of impact expected. 
       FIG. 8  is a cross-sectional view of a protective helmet  801  having a plurality of filaments  811  extending from the outer layer  803 . As illustrated, the filaments  811  are not attached to an inner layer. Padding  817  is disposed inward from the filaments  811 . This configuration can allow for tunable shear characteristics, as well as tunable non-linear deformation of the filaments  811 . Alternatively,  FIG. 14  is a cross-sectional view of a protective helmet  1401  having an outer layer  1402 , and inner layer  1404 , and an interface layer  1403  disposed between the outer layer  1402  and the inner layer  1404 . The interface layer  1403  comprises a plurality of filaments  1405  extending from the inner layer  1404 . 
       FIG. 9A  is a cross-sectional view of a protective helmet  901  having an interface layer  909  with two different types of filaments  911  and  912  configured in accordance with embodiments of the present technology.  FIG. 9B  is an enlarged detail view of a portion of the helmet  901 . Referring to  FIGS. 9A and 9B  together, the helmet  901  comprises an outer layer  903 , an inner layer  905 , and an interface layer  909  disposed between the outer layer  903  and the inner layer  905 . The interface layer  909  comprises a first plurality of filaments  911  that span or substantially span the space between the inner layer  905  and the outer layer  903 . The interface layer  909  also comprises a second plurality of filaments  912  that do not substantially span the space. Padding  917  is disposed adjacent to inner layer  905 . The inclusion of two different types of filaments, each having different shapes, lengths, and/or stiffnesses, is expected to provide increased control of the overall material characteristics of the interface layer  909 . For example, in some embodiments the second filaments  912  can be shorter and stiffer than the first filaments  911 . Upon initial deformation of the outer layer  103 , the first filaments  911  can provide some resistance. Once the outer layer  903  has compressed enough that the second plurality of filaments  912  come into contact with the more rigid inner layer  905 , the second plurality of filaments  912  can contribute to a greater resistance of the interface layer  909  to the impact force.  FIGS. 9C and 9D , for example, illustrate the protective helmet  901  under local deformation. The first and second filaments  911  and  912  both deform non-linearly in response to the impact force incident on the outer layer  903  of the helmet  901 . The deformation can be elastic, such that after impact the interface layer  909  and outer layer  903  return to their original configurations. In some embodiments, the helmet  901  can be configured such that upon application of between about 100 and 500 static pounds of force, the outer layer  903  and interface layer  909  deform between about 0.75 to 2.25 inches. The deformability can be tuned by varying the composition, number, and configuration of the filaments  911 , and by varying the composition and configuration of the outer layer  903  and inner layer  905 . 
     Selected Embodiments of Methods for Manufacturing Interface Layers for Protective Helmets 
       FIG. 10  is a flow diagram of a method of manufacturing an interface layer in accordance with embodiments of the present technology. The process  1000  begins in block  1001  by providing a first surface. The first surface can be, for example, a sheet of a polymer, plastic, foam, elastomer, or other material suitable for forming filaments. Process  1000  continues in block  1003  by providing a second surface. In some embodiments, the second surface can have similar characteristics to the first surface. In block  1005 , an interstitial member is provided between the first surface and the second surface. The interstitial member can be, for example a plate having a plurality of apertures therein. The apertures can define the cross-sectional shapes and the distribution of the ultimate filaments to be formed between the first and second surfaces. For example, in some embodiments one or more of the apertures can assume the shape of a square, a rectangle, a triangle, an ellipse, a regular polygon, or other shape. In block  1007 , the first and second surfaces are compressed against the interstitial member so that a portion of the first and/or second surface protrudes into an aperture of the interstitial member. In block  1009 , the first and second surfaces are heated above their glass transition temperatures, resulting in a merging of the first and second surfaces and the portions of the first and/or second surface which extend through the apertures of the interstitial member to the other surface. These portions extending through the apertures become the filaments of the interface layer. The process concludes in block  1011  with removing the interstitial member. In some embodiments, removing the interstitial member can comprise burning the interstitial member, dissolving the interstitial member, or otherwise removing it. In some embodiments, after removing the interstitial member the space between the first surface and the second surface can be filled with a gas, a liquid, or a gel. 
       FIG. 11  is a flow diagram of another method of manufacturing an interface layer in accordance with embodiments of the present technology. The process  1100  begins in block  1101  by providing a first surface having a plurality of first protruding members. For example, the first surface can be a sheet having a plurality of raised portions, such as columns or bumps. Process  1100  continues in block  1103  by providing a second surface having a plurality of second protruding members that face the first protruding members of the first surface. In block  1105 , at least one of the first protruding members is aligned with at least one of the second protruding members. In block  1107 , the first and second surfaces are heated above their glass transition temperatures. The process  1100  continues in block  1109  by bringing the at least one first protruding member into contact with the at least one second protruding members. As the materials have been heated above their glass transition temperatures, the first protruding member and the second protruding member are joined by this contact. In block  1111 , the first surface is withdrawn from the second surface. This can extend the length of the joined first and second protruding members, resulting in a filament extending between the first surface and the second surface. In some embodiments, the first and second protruding members can comprise a foam, a polymer, an elastomer, or other suitable material. In some embodiments, the cross-sectional shape of the protruding members can be square, rectangular, triangular, elliptical, a regular polygon, or other shape. In some embodiments, the space between the first surface and the second surface can be filled with a gas, a liquid, or a gel. 
     Selected Embodiments of Protective Helmets Incorporating Force Sensors 
     In some embodiments, the filaments in the interface layer of the helmet can also serve as force sensors or substrates for mounting force sensors.  FIG. 12  is a perspective cross-sectional view of a protective helmet with filaments incorporating force sensors. The helmet  1201  comprises an outer layer  1203 , an inner layer  1205 , and an interface layer  1209  disposed between the outer layer  1203  and the inner layer  1205 . The interface layer  1209  comprises a plurality of filaments  1211  that span or substantially span the space between the inner layer  1205  and the outer layer  1203 . Force sensors  1212  (shown schematically) are coupled to the filaments  1211 . In some embodiments, a wire or film could be embedded in, or on, each filament  1211 . In some embodiments, the sensors  1212  can be sized and configured to produce a signal indicative of strain or deformation along the longitudinal axes of the filaments. These sensors  1212  can be configured to detect strain and or deformation of individual filaments  1211 . The strain or deformation of the filament  1211  and sensor may then be related back to force using the known mechanical properties of the filaments  1211  and helmet  1201  structure. In some embodiments, the filament may be used directly as the sensor by providing the filament with electrical properties. For example, the filaments  1211  may have doped particles embedded to provide conductivity or piezoresistive properties. Deformation will then result in a change in electrical properties (e.g., resistance), allowing for electrical measurement of force. In some embodiments, the filaments  1211  can be made piezoelectric, allowing the filaments to generate electrical potential or current when deformed. In some embodiments, a sensor can comprise an optical waveguide with a first end and a second end, a light source incident upon one end of the optical waveguide, and a photodetector adjacent to the opposite end of the optical waveguide configured to receive light transmitted through the optical waveguide. In some embodiments, the waveguide can be a Bragg diffraction grating. In some embodiments, the Bragg diffraction gratings in each of the plurality of sensors can have unique periodicities. 
     The plurality of sensors can be logically coupled to a computing device and/or a data storage device capable of storing strain and deformation signals received from the plurality of sensors. In some embodiments, a wireless communication device can be coupled to the data storage device and configured to wirelessly transmit data stored on the data storage device to a second computing device. For example, in some embodiments the data storage device and wireless communication device can be embedded within the helmet, and can transmit the stored data to an external computing device. In some embodiments, the data storage device can include stored therein computer-readable program instructions that, upon execution by the computing device, cause the computing device to determine the magnitude and direction of a force incident upon the helmet based on the strain or deformation signals generated from the plurality of sensors. In some embodiments, the computing device can be configured to determine the acceleration of the wearer&#39;s head caused by the incident force. In some embodiments, the computing device can provide a signal indicating when the helmet has received incident forces over a defined threshold. 
     By embedding sensors in individual filaments, a plurality of sensors can be integrated into the helmet structure and provide single filament resolution of force transmission. Data from the sensors can be used to quantify hit number, magnitude, and location, to correlate hit magnitude with location and acceleration, to determine the likelihood of traumatic brain injury. The data may also be used to evaluate the current condition of the helmet and possible need for refurbishment or replacement. The data from individual players can be used to tune the material characteristics of the helmet for an individual&#39;s style of play and or position. For example in football, centers may tend to receive hits top center while wide receivers may tend to receive hits tangentially on the rear corner. This impact fitting process is unique from the helmet functionality and comfort fitting. 
     Examples 
     1. A helmet, comprising:
         an inner layer;   an outer layer spaced apart from the inner layer to define a space;   an interface layer disposed in the space between the inner layer and the outer layer, wherein the interface layer comprises a plurality of filaments, the individual filaments comprising a first end proximal to the inner layer and a second end proximal to the outer layer,   wherein the filaments are configured to deform non-linearly in response to an external incident force on the helmet.       

     2. The helmet of example 1 wherein the outer layer moves laterally relative to the inner layer in response to an external oblique force on the helmet. 
     3. The helmet of any one example 1 or example 2 wherein the filaments are configured to buckle in response to axial compression. 
     4. The helmet of any one of examples 1-3 wherein the individual filaments have an aspect ratio of between 3:1 and 1,000:1. 
     5. The helmet of any one of examples 1-4 wherein the filaments comprise a material selected from the group consisting of: a foam, an elastomer, a polymer, and any combination thereof. 
     6. The helmet of any one of examples 1-4 wherein the filaments are composed of a shape memory material. 
     7. The helmet of any one of examples 1-6 wherein the filaments comprise a self-healing material. 
     8. The helmet of any one of examples 1-7 wherein the filaments exhibit different shear characteristics in different directions. 
     9. The helmet of any one of examples 1-8 wherein at least a portion of the filaments have a non-circular cross-sectional shape. 
     10. The helmet of any one of examples 1-8 wherein the filaments have a cross-sectional shape selected from one of the following: circular, hexagonal, triangular, square, and rectangular. 
     11. The helmet of any one of examples 1-10 wherein a density of the filaments is higher in some portions of the interface layer than in other portions of the interface layer. 
     12. The helmet of any one of examples 1-11 wherein a thickness of each filaments varies along a length of the filament. 
     13. The helmet of any one of examples 1-12 wherein the inner layer and/or outer layer further comprise a plurality of sockets, and wherein:
         the filaments further comprise a rotating member attached to at least one of the first end and the second end, the rotating member being configured to rotatably fit within one of the plurality of sockets.       

     14. The helmet of any one of examples 1-13 wherein at least a portion of the filaments are attached to the inner layer. 
     15. The helmet of any one of examples 1-14 wherein at least a portion of the filaments are attached to the outer layer. 
     16. The helmet of any one of examples 1-15 wherein each filament extends along a longitudinal axis, and wherein the longitudinal axes of the filaments are substantially perpendicular to a surface of at least one of the inner layer and the outer layer. 
     17. The helmet of any one of examples 1-16 wherein the outer layer comprises a plurality of segments, wherein at least one of the segments is configured to move relative to the other segments upon receiving an external incident force. 
     18. The helmet of example 17 wherein the second ends of the filaments are attached to one of the plurality of segments. 
     19. The helmet of example 17, further comprising resilient spacing members which flexibly couples the plurality of segments to one another. 
     20. The helmet of any one of examples 1-19 wherein the outer layer comprises an elastically deformable material. 
     21. The helmet of any one of examples 1-20 wherein the outer layer comprises a plurality of deformable beams, each having two ends and a longitudinal axis, wherein the ends of each of the plurality of deformable beams are flexibly connected to at least one other deformable beam, and wherein the longitudinal axis is parallel to the surface of the outer layer. 
     22. The helmet of example 21 wherein the ends of each of the deformable beams are flexibly connected to at least one other deformable beam and at least one of the filaments. 
     23. The helmet of any one of examples 1-22 wherein the inner layer comprises a shell configured to substantially surround the head of a wearer. 
     24. The helmet of any one of examples 1-23 wherein the inner layer comprises a material having a rigidity at least five times more rigid than the outer layer. 
     25. The helmet of any one of examples 1-24 wherein the inner layer comprises padding configured to substantially conform to the contours of a head. 
     26. The helmet of any one of examples 1-25 wherein at least one of the filaments is hollow. 
     27. The helmet of any one of examples 1-26 wherein at least one of the filaments is conical. 
     28. The helmet of any one of examples 1-27 wherein a longitudinal axis of a first filament of the plurality of filaments is not perpendicular to either the inner layer or the outer layer. 
     29. The helmet of example 28 wherein a longitudinal axis of a second filament of the plurality of filaments is not parallel to the longitudinal axis of the first filament. 
     30. The helmet of example 29 wherein an angle of the longitudinal axis of the first filament relative to at least one of the inner layer and the outer layer is supplementary to an angle of the longitudinal axis of the second filament relative to at least one of the inner layer and the outer layer. 
     31. The helmet of example 30 wherein the first filament is connected to the second filament at an intersection point. 
     32. A helmet comprising:
         an inner layer;   an outer layer spaced apart from the inner layer to define a space; and an interface layer disposed in the space between the inner layer and the outer layer, wherein the interface layer comprises:
           a first plurality of filaments, the individual first filaments comprising a first end proximal to the inner layer and a second end proximal to the outer layer; and   a second plurality of filaments, the second individual filaments comprising a first end proximal to the inner layer and a second end proximal to the outer layer;   
           wherein the first and second filaments are configured to deform non-linearly in response to an incident force,   wherein a height of the first filaments substantially spans the space between the inner layer and the outer layer, and   wherein a height of the second filaments does not substantially span the space between the inner layer and the outer layer.       

     33. The helmet of example 32 wherein the first ends of the second filaments are attached to the inner layer. 
     34. The helmet of example 32 or example 33 wherein the second ends of the second filaments are attached to the outer layer. 
     35. The helmet of any one of examples 32-34 wherein the second filaments have a lower aspect ratio than the first filaments. 
     36. The helmet of any one of examples 32-35 wherein the second filaments are more rigid than the first filaments. 
     37. A helmet comprising:
         an inner layer;   an outer layer spaced apart from the inner layer to define a space, wherein the space comprises a material selected from the group consisting of a gas, a liquid, a gel, a foam, a polymeric material, and any combination thereof; and   an interface layer disposed in the space between the inner layer and the outer layer, the interface layer comprising a plurality of filaments, each individual filament comprising a first end proximal to the inner layer and a second end proximal to the outer layer,   wherein the filaments are configured to deform non-linearly in response to an incident external force.       

     38. The helmet of example 37 wherein the liquid comprises a shear thinning liquid. 
     39. The helmet of example 37 wherein the liquid comprises a shear thickening liquid. 
     40. The helmet of example 37 wherein the liquid comprises a shear thinning gel. 
     41. The helmet of example 37 wherein the liquid comprises a shear thickening gel. 
     42. A method of making an interface layer comprising at least one filament disposed between a first surface and a second surface, the method comprising:
         providing a first surface comprising a plurality of first protruding elements protruding from the first surface;   providing a second surface comprising a plurality of second protruding elements protruding from the second surface, the second surface disposed opposite the first surface such at least one of the first protruding elements is aligned with at least one of the second protruding elements;   heating the first surface and second surface above their glass transition temperatures;   bringing the at least one first protruding element in contact with the at least one second protruding element; and   withdrawing the first surface from the second surface, thereby providing at least one filament disposed between the first surface and the second surface.       

     43. The method of example 42 wherein the first protruding elements and second protruding elements comprise a foam. 
     44. The method of example 42 wherein the plurality of first protruding elements and the plurality of second protruding elements comprise a polymer. 
     45. The method of any one of examples 42-44 wherein the first protruding elements and the second protruding elements comprise a cross-sectional shape selected from the group consisting of: a square, a rectangle, a triangle, and an ellipse. 
     46. The method of any one of examples 42-45 wherein the first protruding elements and the second protruding elements comprise a cross-sectional shape of a regular polygon. 
     47. The method of any one of examples 42-46, further comprising filling a space between the first surface and the second surface with a gas, a liquid, or a gel. 
     48. A method of making an interface layer comprising at least one filament disposed between a first surface and a second surface, the method comprising:
         providing a first surface;   providing a second opposite the first surface;   providing an interstitial member, disposed between the first surface and the second surface, comprising a plurality of apertures;   compressing the first surface and the second surface against the interstitial member so that a portion of the first surface and/or a portion of the second surface protrudes into the plurality of apertures;   heating the first surface and the second surface above their glass transition temperatures; and   removing the interstitial member, thereby providing at least one filament disposed between the first surface and the second surface.       

     49. The method of example 48 further comprising withdrawing the first surface from the second surface. 
     50. The method of example 48 or example 49 wherein removing the interstitial member comprises burning the interface layer. 
     51. The method of example 48 or example 49 wherein removing the interstitial member comprises dissolving the interface layer. 
     52. The method of any one of examples 48-51 wherein the filament comprises a foam. 
     53. The method of any one of examples 48-52 wherein the filament comprises a polymer. 
     54. The method of any one of examples 48-53 wherein the apertures in the interstitial member are configured in a shape selected from the group consisting of: a square, a rectangle, a triangle, and an ellipse. 
     55. The method of any one of examples 48-54 wherein the apertures in the interstitial member are configured in the shape of a regular polygon 
     56. The method of any one of examples 48-55, further comprising filling the space between the first surface and the second surface with a gas, a liquid, or a gel. 
     57. A helmet comprising:
         an inner layer;   an outer layer configured to provide a space between the inner layer and the outer layer;   an interface layer disposed in the space between the inner layer and the outer layer, the interface layer comprising a plurality of filaments, each individual filament comprising a first end proximal to the inner layer and a second end proximal to the outer layer; and   a plurality of sensors coupled to at least a subset of the filaments,   wherein the filaments are configured to deform non-linearly in response to an external incident force.       

     58. The helmet of example 57 wherein the sensors are sized and configured to produce a signal indicative of strain or deformation of the filaments. 
     59. The helmet of any one of examples 57-58 wherein the sensors comprise a wire or film. 
     60. The helmet of any one of examples 57-58 wherein the sensors comprise conductive polymer filaments. 
     61. The helmet of any one of examples 57-58 wherein the sensors comprise a plurality of doped particles. 
     62. The helmet of any one of examples 57-58 wherein the sensors comprise piezoelectric sensors. 
     63. The helmet of any one of examples 57-58 wherein the sensors comprise an optical waveguide with a first end and a second end, a light source incident upon one end of the optical waveguide, and a photodetector adjacent to the opposite end of the optical waveguide configured to receive light transmitted through the optical waveguide. 
     64. The helmet of example 63 wherein the optical waveguide comprises a Bragg diffraction grating. 
     65. The helmet of example 64 wherein the Bragg diffraction gratings in each of the sensors has a unique periodicity. 
     66. The helmet of any one of examples 57-65, further comprising:
         a computing device logically coupled to the sensors; and   a data storage device, capable of storing strain and deformation signals from the plurality of sensors.       

     67. The helmet of example 66, further comprising a wireless communication device configured to wirelessly transmit data stored on the data storage device to a second computing device. 
     68. The helmet of example 66, the data storage device having stored therein computer-readable program instructions that, upon execution by the computing device, cause the computing device to perform functions comprising:
         determining a magnitude and a direction of a force incident upon the helmet based upon the strain or deformation signals generated from the sensors.       

     69. The helmet of example 68 wherein the functions further comprise determining an acceleration of a head of a wearer caused by the incident force. 
     70. The helmet of example 66, further comprising an indicator that provides a signal indicating when the helmet has received incident forces over a defined threshold. 
     CONCLUSION 
     The above detailed descriptions of embodiments of the technology are not intended to be exhaustive or to limit the technology to the precise form disclosed above. Although specific embodiments of, and examples for, the technology are described above for illustrative purposes, various equivalent modifications are possible within the scope of the technology, as those skilled in the relevant art will recognize. For example, while steps are presented in a given order, alternative embodiments may perform steps in a different order. The various embodiments described herein may also be combined to provide further embodiments. Various modifications can be made without deviating from the spirit and scope of the disclosure. For example, the interface layer can include filaments having any combination of the features described above. Additionally, the features of any particular embodiment described above can be combined with the features of any of the other embodiments disclosed herein. 
     From the foregoing, it will be appreciated that specific embodiments of the invention have been described herein for purposes of illustration, but well-known structures and functions have not been shown or described in detail to avoid unnecessarily obscuring the description of the embodiments of the technology. Where the context permits, singular or plural terms may also include the plural or singular term, respectively. 
     Moreover, unless the word “or” is expressly limited to mean only a single item exclusive from the other items in reference to a list of two or more items, then the use of “or” in such a list is to be interpreted as including (a) any single item in the list, (b) all of the items in the list, or (c) any combination of the items in the list. Additionally, the term “comprising” is used throughout to mean including at least the recited feature(s) such that any greater number of the same feature and/or additional types of other features are not precluded. It will also be appreciated that specific embodiments have been described herein for purposes of illustration, but that various modifications may be made without deviating from the technology. Further, while advantages associated with certain embodiments of the technology have been described in the context of those embodiments, other embodiments may also exhibit such advantages, and not all embodiments need necessarily exhibit such advantages to fall within the scope of the technology. Accordingly, the disclosure and associated technology can encompass other embodiments not expressly shown or described herein.