the principles and operation of the minefield shoe according to the present invention may be better understood with reference to the drawings and the accompanying description . before explaining at least one embodiment of the invention in detail , it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of the components set forth in the following description or illustrated in the drawing . the invention is capable of other embodiments or of being practiced or carried out in various ways . also , it is to be understood that the phraseology and terminology employed herein is for the purpose of description and should not be regarded as limiting . referring now to the drawings , fig1 is a side view of a minefield shoe , attached to the boot of a wearer , disclosed by u . s . pat . no . 4 , 611 , 411 to ringler , et al ., which is incorporated by reference for all purposes as if fully set forth herein . the prior - art minefield shoe includes an inflatable air cushion 2 composed of a plurality of chambers or compartments 4 . when inflated , the compartments form an air cushion having upper and ground contacting surfaces that are substantially flat . the air cushion 2 may be made of an inner , inflatable , rubber , neoprene or the like , balloon 6 and of an outer abrasion and cut resistant fabric 8 . the air cushion may otherwise be composed of an integral single layer of material that is impermeable to gas and having an outer surface which is abrasion and cut resistant . such a layer should be capable of limiting the extent to which the compartments are inflated and of keeping their volume substantially constant below a certain maximum . the interiors of the compartments communicate with each other by means of tubing 10 extending along the sides of the compartments 4 . one end of tubing 10 may be fixedly closed for example , by folding the tubing edge and clamping the same in its folded configuration as seen at 16 , while the other end of tubing 10 is provided with a valve ( not shown ), for inflation and deflation of the air cushion . the minefield shoe taught by u . s . pat . no . 4 , 611 , 411 to ringler , et al ., further includes a rigid tread surface 20 for evenly distributing the wearer &# 39 ; s weight along the air cushion on top of each of the compartments 4 . while the illustrated tread surface 20 is designed to facilitate compacting the mine - field shoe for carrying and transporting purposes , it is disclosed that the tread surface could also be embodied by a single , rigid plate having an overall surface area substantially the same as that of the upper surface of the air cushion . the tread surface 20 is fitted with straps 26 arranged for easy attachment to a wearer &# 39 ; s boot 28 . although the multiple - compartment air cushion 2 , the tubing 10 interconnecting the compartments , and the tread surface 20 essentially form the mine - field shoe of the instant invention , it has been found advantageous to attach to the upper major flat surface of each compartment , a support plate 30 , thus effecting an even more uniform weight distribution along the entire surface area of the air cushion . the shoe is of the foldable type , including an inflatable gas cushion composed of a plurality of chambers or compartments . when inflated , the compartments form a gas cushion having upper and ground contacting surfaces that are substantially flat . fig2 shows an air cell 86 of u . s . pat . no . 4 , 611 , 411 along with t - connectors 116 in the first four cells , an l - connector 118 in the last cell , and four intermediate rubber tubing sections 120 . a first tubing section 122 is provided with a schematically indicated pinch cock 124 . as mentioned hereinabove , the minefield shoe taught by u . s . pat . no . 4 , 611 , 411 is highly prone to failures associated with deflation , and more specifically , deflation associated with the external placement of the tubes and the large plurality of accompanying fittings , each having two or three joints . each joint presents a sealing problem that detracts from the reliability of the device . moreover , deflation can also occur when the tubing is caught by a foreign object , such that the tube is separated from a fitting , punctured by a nail or other sharp object , or torn ( e . g ., due to excessive wear ). although it is disclosed by u . s . pat . no . 4 , 611 , 411 that the air cushion can be inflated by means of a pump or by means of a pressurized gas bottle , it has been the experience of the present inventors that such means are inappropriate , unless the inflation is performed in a very slow , gradual , controlled manner . when the inflation is performed in a less gradual fashion , the device is highly susceptible to a sealing failure , such as a tubing section 120 becoming detached from a t - connector 116 , because the external tubing has a relatively small diameter , and further in view of the numerous fittings , all of which represent weak points , particularly under high - pressure conditions . by sharp contrast , the minefield shoe of the present invention has compartments that fluidly communicate by means of passages that are internal to the cushion structure . these internal passages are shown in cross - sectional views of the long side ( fig3 ) and short side ( fig4 a - 4 b ) of the air cushion of the inventive device . as in the prior art device , the inventive minefield shoe includes an inflatable air cushion 202 composed of a plurality of chambers or compartments 204 . when inflated , the compartments form an air cushion having upper and ground contacting surfaces that are substantially flat . unlike the prior - art minefield shoe , however , the interiors of the compartments 204 communicate with each other by a series of internal passages 210 . internal passages 210 are inherently protected by compartments 204 , and are thus not vulnerable to damage and / or failure due to external sharp objects , rough use under battlefield conditions , and blowouts or leakage due to overinflation , excessive pressures , etc . there is no external tubing for linking compartments 204 , such that the serious problems associated with external tubes and fittings are eliminated . in simplest form , internal passages 210 are one or more sealing gaps disposed in each of internal walls 220 . it has been found to be advantageous , however , to place a fitting in internal passage 210 , as shown in fig4 a and 4 b . in fig4 a , the fitting is a tubular orifice 222 . fig4 b is a schematic representation of a multiple - orificed fitting 224 . preferably , multiple - orificed fitting 224 , and tubular orifice 222 have a rectangular profile . an additional inventive aspect of the minefield shoe of the present invention is illustrated in a schematic side view in fig5 . minefield shoe 300 has a top level 310 of gas - containing compartments 312 and a bottom level 320 of gas - containing compartments 322 . gas - containing compartments 312 in top level 310 fluidly communicate with each other , preferably by means of internal passages , such as multiple - orificed fitting 224 shown in fig4 b . similarly , gas - containing compartments 322 in bottom level 320 fluidly communicate with each other . however , top level 310 is fluidly sealed from bottom level 320 . in the event that one or more of gas - containing compartments 322 in bottom level 320 is punctured , top level 310 remains pressurized and intact , thereby maintaining the main safety function of the minefield shoe . hence , the reliability of minefield shoe 300 is substantially improved relative to the shoe disclosed by u . s . pat . no . 4 , 611 , 411 . preferably , top level 310 and bottom level 320 each have a dedicated valve ( 316 , 326 , respectively ) for inflation and deflation . however , it will be appreciated by one skilled in the art that various configurations are possible . in a preferred embodiment , top level 310 and bottom level 320 are fluidly isolated by at least one self - adjusting partition 315 . self - adjusting partition 315 is typically a flexible , loosely disposed layer that serves both as a bottom wall of top level 310 and as a top wall for bottom level 320 . it has been found to be advantageous to fill top level 310 with at least 60 % of the total amount of gas used to inflate minefield shoe 300 , and more preferably , between ⅔ and ¾ of the total amount of gas . consequently , in the event of a puncture in bottom level 320 , the bulk of the gas remains contained in top level 310 . moreover , when self - adjusting partition 315 is a flexible , loosely disposed layer , attached approximately near the vertical middle ( at a height of h / 2 ) of levels 310 , 320 , self - adjusting partition 315 is distended below the vertical middle , upon inflation , as top level 310 and bottom level 320 reach an identical pressure . in the event that bottom level 320 is punctured , top level 310 continues to provide a thick cushion of pressurized air , such that the weight distribution functionality of the shoe is substantially maintained . yet another inventive aspect of the minefield shoe of the present invention will be made apparent in comparison to the prior art and in conjunction with the schematic illustration of a minefield shoe contacting a mine detonator plate ( fig6 a - 6 b ). perhaps the most significant feature of the minefield shoe taught by u . s . pat . no . 4 , 611 , 411 to ringler , et al ., is the improved ground - conforming property relative to the rigid snowshoe - type minefield shoe described hereinabove . fig6 a shows a somewhat flexible bottom surface 350 of a minefield shoe that insufficiently conforms to a mine detonator plate ( or mine trigger ) 352 protruding from the ground . although the weight distribution is improved with respect to a rigid bottom surface , the surface area 354 that is unsupported by ground surface 356 is relatively large , such that the force exerted down on the detonator plate surface is high . consequently , the risk of detonation is correspondingly high . in fig6 b , the bottom surface 360 is more flexible , conforming more snugly to detonator plate 352 . the result is improved performance ( weight distribution ): the surface area 364 that is unsupported by ground surface 356 is decreased , such that less weight is placed on detonator plate 352 . it is thus a cardinal design principle to make the bottom surface of the minefield shoe as flexible as possible . the bottom surfaces of the minefield shoe taught by u . s . pat . no . 4 , 611 , 411 are designed not only for flexibility , but for cut and abrasion resistance as well . alternatively , the air cushion is composed of a single integral layer of material that is impermeable to gas and having an outer ( bottom ) surface that is abrasion and cut resistant . in both cases , the additional design constraints result in a bottom surface that is far from optimal in terms of flexibility and weight distribution on uneven terrain . the flexibility compromise is particularly severe because a puncture or tear in the bottom surface completely destroys the efficacy of the minefield shoe . by sharp contrast , and as developed hereinabove , the minefield shoe of the present invention has a two - level design in which the levels are fluidly incommunicable , such that the shoe remains completely functional in the event of a tear or puncture . the ramification , from a design standpoint , is manifest : the requisite double design constraint of flexibility and toughness in the shoe taught by u . s . pat . no . 4 , 611 , 411 is now substantially decoupled . in the minefield shoe of the present invention , the toughness constraint on the bottom surface is greatly relaxed , such that the bottom surface can be designed to have increased flexibility , thereby improving the ground - conforming property and hence , performance . fig7 is a schematic , exploded cross - sectional view of the various layers that make up the top and bottom levels of the gas cushion according to one embodiment of the present invention . a cushion 410 contains a top gas compartment 417 and a bottom gas compartment 420 . sheet 412 defines the top of compartment 417 , sheet 422 defines the bottom of compartment 420 , and sheet 418 defines the bottom of compartment 417 and the top of compartment 420 . sheets 418 and 422 are made of any impermeable , and preferably flexible synthetic material such as pvc , polyurethane , or nylon fabric . sheet 412 is composed of a fabric 414 having an impermeable coating 416 on the underside thereof . bottom sheet 426 is composed of a porous and flexible fabric that is loosely attached ( e . g ., sewn ) to the bottom surface of sheet 422 . bottom sheet 426 is sufficiently loose and pliable so as to conform freely to protruding objects that the shoe wearer might step on , such as a mine detonator pin , thereby improving the performance of the inventive minefield shoe . fig8 a is a schematic illustration of a top sheet 448 and a bottom sheet 452 of an inventive gas cushion , and a bridge - like device 454 for attaching therebetween . fig8 b is a schematic cross - sectional view of the components of fig8 a , after bonding , in which bridge - like device 454 forms internal passageways 462 for fluid communication between adjacent cushions . fig9 is a graph illustrating the improved weight distribution of the inventive minefield shoe as compared with the minefield shoe disclosed by u . s . pat . no . 4 , 611 , 411 . the x - axis represents the force acting on the mine trigger , for a soldier weighing 100 kg . the y - axis represents the area of the mine trigger , in cm 2 . multiple plots are presented , as a function of the length ( in cm ) of mine trigger protruding from the soil . it is evident that the force acting on the mine trigger increases with increasing area of the mine trigger , and with increasing of the length of mine trigger protruding from the soil , for both the inventive device and the prior - art device . significantly , with the inventive device , lower forces are exerted on the mine trigger , relative to the shoe disclosed by u . s . pat . no . 4 , 611 , 411 , at virtually every measured point on the graph . without wishing to be bound by theory , this superior performance is attributed , at least in part , to the superior flexibility of the bottom surface of the inventive device . yet another aspect of the present invention is a manufacturing method for producing a minefield shoe having the basic design taught herein . whereas u . s . pat . no . 4 , 611 , 411 to ringler , et al ., teaches a device having individual balloons or compartments , fabric housing for the compartments , and a large plurality of tubes and fittings for fluid communication between the compartments , the design of the present invention allows for production using a simple , inexpensive , and highly - efficient bonding process . two sheets of polyester or nylon fabric , coated with polyurethane , are held together , with the coated sides facing and contacting one another . it will be appreciated by one skilled in the art that other suitable fabrics and coatings may be utilized . the sheets are then bonded at a pre - determined interval along the length of the sheets to form a series of pockets in a single unit - operation . the bonding is preferably effected by high - frequency welding using a single top electrode , or by various , conventional heat - sealing techniques . the passages for fluid communication between the pockets , described hereinabove , may be effected in several ways , including : ( 1 ) prior to the heat sealing operation , a strip of proper dimensions ( e . g ., 7 mm by 30 mm ) is temporarily inserted between the sheets during the heat - sealing process , in order to provide a suitable internal gap or passageway between pockets . typically the strip is left in place only during the welding operation . ( 2 ) prior to the heat sealing operation , fittings such as tubular orifice 222 or multiple - orificed fitting 224 ( see fig4 a - 4 b ) are inserted between the sheets and are preferably bonded to the sheets at intervals corresponding to a designed , pre - determined length of each pocket . it is presently preferred to use a multiple - orificed fitting 224 having a rectangular profile . the fittings provide the pockets with a mechanically strong passageway that assures full fluid communication between pockets , even under extenuating circumstances ( e . g ., significant overinflation of the pockets ). although the invention has been described in conjunction with specific embodiments thereof , it is evident that many alternatives , modifications and variations will be apparent to those skilled in the art . accordingly , it is intended to embrace all such alternatives , modifications and variations that fall within the spirit and broad scope of the appended claims . all publications , patents and patent applications mentioned in this specification are herein incorporated in their entirety by reference into the specification , to the same extent as if each individual publication , patent or patent application was specifically and individually indicated to be incorporated herein by reference . in addition , no citation or identification of any reference in this application shall be construed as an admission that such reference is available as prior art to the present invention .
a minefield shoe for reducing the danger of accidental detonation of a land mine by a wearer of the shoe , the shoe including : a cushion including a plurality of inflatable compartments , the cushion having , when inflated , at least one flexible , substantially flat , ground - contacting surface extending across the compartments ; passages , disposed within the cushion , for providing fluid communication between the compartments , and means for attaching the shoe to a boot of the wearer , wherein each of the compartments is in fluid communication with at least one other compartment , via the passages , so as to prevent any significant increase in internal pressure of any one of the compartments resulting from a decrease in internal volume of another compartment , thereby to allow deformation of the ground - contacting surface to form a matching counterpart of terrain engaged by the shoe , while maintaining a substantially even distribution of the load on the shoe along all of the ground - contacting surface .