the following detailed description is of the best currently contemplated modes of carrying out exemplary embodiments of the invention . the description is not to be taken in a limiting sense , but is made merely for the purpose of illustrating the general principles of the invention , since the scope of the invention is best defined by the appended claims . broadly , an embodiment of the present invention provides a method and apparatus that adaptively protects the wearer from impact forces that range from repetitive low level events up to severe one time ( or repetitive ) events that originate at any point on the periphery of a helmet . further , subsequent to the impact event ( s ) said apparatus will automatically re - set all elements of the system to its pre - impact status . the present design accomplishes the foregoing by employing two concentric durable shells separated by one , or a plurality of elastomer form fitting bladder ( s ) called diffusion cell ( s ). the diffusion cells are sealed and contain an energy absorbing diffusing agent that is either a liquid or a gas . in no case does the diffusion cell ( s ) exchange or vent its contents with ( or into ) the surrounding mechanism or atmosphere . a flexible ( low elastic modulus ) outer shell , preferably manufactured from a low coefficient of friction material , is designed to deflect temporarily in proportion to the magnitude and shape of an impact force . the inner shell is more rigid ( higher elastic modulus ) than the outer shell . under impact load a deflection disparity develops between the outer shell and inner shell . this deflection disparity forms the intervening diffusion cell ( s ) into a configuration that adaptively forces the diffusing agent omni - directionally away from the geographic center of the impact force . this forced motion of the diffusing agent ; a form of wave propagation , follows the curved plane described by the two shells . as expected , this motion of the diffusing agent encounters drag due to friction and conversion of kinetic energy to thermal energy occurs . any residual kinetic energy that reaches the periphery of the diffusion cell ( s ) ( those surfaces not restrained by the two shells ) stretches ( or deforms ) the diffusion cell elastometric wall ( s ). this stored energy will be utilized by the apparatus to assist the re - setting of the attenuation mechanism for the next event . automatic re - set commences immediately once the initiating impact force dissipates . outer shell inward deflection ( called a dimple ) disappears due to the elastic modulus of the shell and the pressure exerted by the returning diffusing agent in the adjacent diffusion cell ( s ). a helmet system 2 , according to an exemplary embodiment of the present invention includes two major subassemblies : an inner shell assembly 10 and an outer shell 20 . the inner shell assembly 10 is made up of a shell 11 , comfort and / or “ fit ” pads 12 , and diffusion cell ( s ) 14 . the inner shell assembly 10 fits securely within the outer shell 20 and is held in place by various connecting devices . fig1 illustrates the separate parts of the helmet system 2 ( also referred to as system 2 ) in a partial exploded view . optional “ comfort ” and / or “ fit ” pads are shown attached to the inside of inner shell 11 . some of these pads may require inflation so appropriate inflation ports 16 are shown on outer shell 20 and duplicated on inner shell assembly 10 . optional cooling may be required so appropriate cooling vents ( typical ) 18 are shown on both major sub - assemblies 10 and 20 . the diffusion cell ( s ) 14 are shown positioned on the outer surface of shell 11 . after final assembly the diffusion cell ( s ) 14 will be firmly in contact with the two shells facing surfaces ( see fig2 ). adhesion of the diffusion cell ( s ) to one ( or both ) of the facing surfaces may be employed to ease the assembly process . for simplicity various attachment devices or other possible accessories are not shown . in some embodiments , the dual shell concept of the present invention can isolate the primary energy absorbing mechanism ( diffusion cell ( s ) 14 ) between a flexible outer shell 20 and a more rigid inner shell 10 . the diffusion cell ( s ) 14 include a sealed elastomer bladder which contains a diffusing agent 19 . the flexible outer shell 20 is designed to deflect inward ( toward the diffusion cell ( s )) in proportion to an impact force . due to the natural convex curve of a helmet , virtually all shapes of impacting surfaces ( including a flat surface ) will initially intersect the curved plane of the outer shell 20 as a point contact . a depression ( called a “ dimple ”) will form in the outer shell 20 and the adjacent diffusion cell ( s ) ( see fig3 ). this “ dimple ” will widen and deepen in proportion to the energy level of the impacting force . due to the more rigid nature of the inner shell 11 , a shaping of the diffusion cell ( s ) 14 occurs adjacent to the “ dimple ” that forces diffusing agent 19 ( either gas or liquid ) radially away from the geographical center of the impact force . the amount of diffusing agent 19 displaced and its velocity is proportional to the kinetic energy transferred to the helmet by the impacting object . depending on the location on the helmet of the impact force this radial outflow of diffusing agent 19 may be present in more than one diffusion cell 14 ( see fig6 ). the diffusing agent outflow takes the form of a wave ( see fig3 ) that propagates through the diffusion cell ( s ) 14 generating turbulence which in turn causes kinetic energy to convert to heat due to friction . residual kinetic energy not converted to heat causes the periphery walls 13 of the diffusing cell ( s ) 14 to expand ( or deform ) outward ( see dimension “ x ” and “ y ” of fig3 ) away from the geographical center of the impact force and become stored energy . this stored energy will be utilized to re - set the helmets primary force attenuation mechanism immediately following the impact event . fig4 illustrates the reversal of agent flow following removal of the impact force . the diffusion cell ( s ) 14 peripheral walls 13 contract to their pre - impact positions ( see fig4 ). outward diffusion cell ( s ) 14 pressure at the “ dimple ”, plus the elastic modulus of the outer shell 20 , act to return the outer shell 20 to its pre - impact shape . the present invention discloses two general types of diffusing agents but the theory of operation disclosed herein is identical for both liquid or gas . either diffusing agent may be utilized singularly or in combination with the other . embodiments of the present invention can be adaptable to many possible applications where concussion avoidance is a design objective . many of these applications dictate that care should be taken to ensure that inter - shell assembly hardware and / or attachment of ancillary equipment do not , inadvertently , negate the advantages of the concept described herein . features such as cooling vents ( 18 ); “ fit ” and / or comfort pads ( 12 ); radio and communications equipment ; eye shields ( 62 ); face masks ( 62 ); and artistic shaping of helmet shell should all be designed with an objective of minimizing their effect on the flexibility of the outer shell ( 20 ) or provide a mechanism for impact force to by - pass the diffusion cell 14 network . fig5 and fig6 show an example of type of telescoping cooling vent that would not inhibit deflection of the outer shell ( 20 ) or provide a bypass route for impact force . fig8 a , 8 b , 8 c , and 8 d show typical examples of inter - shell assembly mechanisms 51 , 41 , and 31 , that provide structural stability while minimizing inter - shell impact force transfer . fig9 a , 9 b , 9 c , and 9 d illustrate a type of minimum impact force transmitting device 61 that could be utilized for helmet assembly or attachment of a face mask / eye shield 62 . the spring shown would have weak compression resistance . the end cap 63 would have a low elastic modulus and would deflect under load as shown in fig9 d . fig1 a and 10b show another form of end cap that would defect as shown under load . a recitation on the present invention would not be complete without a discussion about the effects of the features described herein on the overall envelope and weight of the present invention as compared to conventional designs . the reader should not automatically conclude the addition of two new elements ( a second shell and diffusion cell ( s )) will materially increase the weight and outside envelope of the assembly . by allowing a relatively thin outer shell 20 to facilitate deflection and considering the reduced load requirement of the inner shell 11 , due to diffusion cell 14 energy absorption , the aggregate thickness and weight of the two shells may be less than a single conventional shell . another trade - off is obvious due to the energy absorbing efficiency of the diffusion cell ( s ) 14 . “ fit ” and / or comfort pads 12 are no longer required to absorb high impact loads and therefore can be reduced in thickness ( and weight ) freeing up envelope for the diffusion cell ( s ) 14 . having now fully set forth the preferred embodiments and certain modifications of the concept underlying the present invention , various other embodiments , as well as certain variations and modifications of the embodiments herein shown and described will obviously occur to those skilled in the art upon becoming familiar with said underlying concept . in is to be understood , therefore , that the invention may be practiced otherwise than as specifically set forth in the appended claims .
a method and apparatus for construction of a protective head covering to be worn by individuals engaged in activity that may , without the apparatus , cause concussive brain injury . the helmet , which is comparable in weight and envelope to conventional helmets , can be constructed from commercially available materials . the design features a dual shell concept where outer shell deflection under load triggers the primary attenuation mechanism . a second more rigid inner shell defines a space where one or more compartmentalized sealed elastomer energy absorbing cells are located . these cells contain either a gas or liquid agent designed to adaptively convert potentially injurious normal impact force energy to energy that is channeled between the shells and therefore harmless to the wearer . a portion of this converted energy will be stored and then utilized to automatically re - set the apparatus for the next impact event .