referring to the drawings , fig1 and 2 illustrate a headset or helmet 10 into which a plurality of improved electrode assemblies of the present invention are mounted . the headset includes a helmet liner 12 with a plurality of electrode assemblies 20 placed or mounted at predetermined positions about the liner . the liner 12 may be fabricated from a rigid thermoplastic material and may be in the form so as to reassemble a modified version of a hockey , football or other type helmet . nineteen electrode assemblies are provided at fixed location about the headset and are positioned in accordance with standard electroenciphalographic procedures , i . e . international 10 - 20 system , for performing conventional eeg testing . in order to accommodate each of the electrode assemblies 20 , a like number of apertures or mounting holes 22 are provided in the liner 12 at positions where the electrode assemblies are to be inserted or mounted . each electrode assembly 20 is retained within its respective aperture and each electrode 50 is retained in its respective electrode assembly . the assembly 2 is retained by a resilient mesh 24 which encircles and supports the assembly , the mesh being adhesively bonded to the liner . by securing the electrode assembly 20 within the aperture 22 by use of the resilient mesh 24 , or open elastic grid or web line support the positioning of each electrode assembly and its contained electrode 50 is automatically adjusted to accommodate subjects having skulls of different sizes and shapes . because of the resilience of the mesh , and therefore the mounting of the electrode assembly , all that is required of the technician is to oscillate the electrode assembly so as to displace hair from the tip of the electrode 50 , according better placement of the electrode 50 on the scalp . using an electrolyte gel , good electrical contact ma be achieved between the electrode and the scalp with minimal pressure of the electrode tip against the scalp . an additional advantage of using a mesh 24 is that the open material permits ventilation , permitting passage of air through the liner making the headset more comfortable to wear for prolonged periods of time thereby according and / or reducing scalp perspiration and attendant problems thereof . the resilient mesh may be replaced by other resilient material , if desired . it is however preferred that the electrode assemblies be mounted so that the electrode 50 in the electrode assembly 20 travels substantially perpendicular relative to the supporting shell at place of attachment of the assemblies to the shell with conformity of electrode tip contact being made in accordance with the international 10 - 20 system , but with sufficient pivotal movement of the electrode assembly in the mounting to ensure proper placement of the electrode tip on the scalp of the subject regardless of the variations in cranial size and / or contour . the preferred embodiment of the electrode assembly 20 is represented in more detail in fig3 where the electrode assembly 20 includes an outer cylinder 30 , preferably fabricated from a thermoplastic material such as , lucite , for example or polystyrene . the cylinder 30 is adapted to be located in the aperture 22 of the liner 12 and is captured therein by the resilient mesh 24 which is secured about the periphery of the cylinder , preferably adhesively bonded thereto , such that the lip 38 is above and protects the security between the shell of the cylinder and the resilient mesh . the cylinder is sealed at its upper end 31 by an end cap 32 , with a top cap 33 provided in the end cap permitting access to the interior of the cylinder when the top cap 33 is removed . a post 40 is secured to the top cap 33 and extends downwardly into the interior of the cylinder 30 . it should be noted that in the preferred embodiment , practical elements of the electrode assembly may be constructed out of a plastic material . where two plastic elements of the assembly are secured together , this security or securing may be accomplished by adhesively bonding the elements together or by welding the elements together , such as by thermal or sonic welding . in the case of the top cap 33 , this cap is secured to the end cap 32 and , since access to the interior of the assembly is desirable , the end cap 32 may be bonded to the cylinder wall 30 and the top cap 33 may be threadedly coupled or secured to the end cap 32 for easy removal for removing the post 40 , when desired . with the end cap 32 bonded to the wall of cylinder 30 , the bottom cap 35 may be threadedly coupled or secured to the wall of cylinder 30 for permitting access to the internal structure and elements of the electrode assembly . assembly of the electrode assembly so that coupled elements holding the assembly together are non - destructively disassembled provides an electrode assembly that is easily repairable in the event of breakdown . the rod 40 coupled to the top cap 33 extends into the interior of the hollow piston rod 42 and aids in keeping the piston rod 42 in alignment , giving the upper ends of the hollow piston rod support . the hollow piston rod 42 has an upper end 43a which receives the rod 40 and reciprocates on the same , and a lower end 43b adapted to receive the electrode element 50 . the electrode element 50 is mounted in the cylinder of rod 42 so as to have limited movement going into the cylinder 42 when the tip 50a of the electrode element 50 makes contact with the subject being tested . travel of the electrode element is limited but sufficient to compress the spring 72 so that the battery 75 may come in contact with the top end of the electrode element and the lsi chip 80 mounted in the hollow cylinder of rod 42 , below the plug 44 . it will be appreciated that the elements within the hollow cylinder of rod 42 are represented in the exploded view for purposes of clarity . the spring 72 is very small and sufficiently strong to separate the battery 75 from the electrode element 50 so as to maintain an open circuit when the electrode element is out of contact with the subject being tested . the lsi chip 80 is mounted on a substrate 81 which is held in place by the plug 44 . a lead 82 is connected to the output of the amplifier lsi chip and conducts the amplified signals to the input interface of the computer ( not shown ). the hollow rod 42 passes through the bottom cap 35 through an aperture 35a . the rod 42 floats in the aperture 35a but is held and prevented from full escape by the top shoulder 62 which is adhesively bonded to the rod 42 and to the upper end of the bellows 60 at 60b the bottom end of the bellows 60 is bonded to a bottom shoulder 46 through which the hollow rod 42 passes . the bottom cap 35 includes a gas ; for example an inlet 35b and a gas outlet 35c . the gas pressure build up around the bellows 60 acts to drive the hollow rod 42 toward the bottom of the electrode assembly , thereby effectively extending or driving the electrode element 50 toward the center of the liner 12 . the gas pressure system is connected in series connection among the electrode assemblies mounted in the headset so that gas pressure build up is uniform in each electrode assembly and , if there is a gas pressure failure in any one electrode assembly the gas pressure in all the connected electrode assemblies is adversely effected . this type of connection of the gas pressure system is preferred as such system is fail safe , that is , a drop in gas pressure in one electrode assembly causes a drop in gas pressure in all electrode assemblies in the same headset . the bellows 60 is a flexible , compressible bellows , which returns to its original shape when the air pressure on both sides of the bellows is equalized . the bellows may be fabricated from synthetic or natural rubber or neoprene or other flexible material with memory characteristics . the interior of the bellows is open to atmospheric pressure through the aperture 35a which extends through the bottom cap 35 and shoulder 46 . a positive pressure applied through the gas pressure lads 70 causes a collapsing of the bellows driving the rod 42 and its contents , toward the interior of the liner 12 . as the hollow rod or cylinder 42 is driven toward the interior of the liner 12 , which is toward the scalp of the person on whose head the headset is mounted , the rod carries with it the electrode 50 , the spring 72 , the battery 75 , and the substrate 81 on which the lsi chip 80 is mounted . when the tip of the electrode 50 contacts the scalp back pressure from such contact with the scalp causes the electrode to stop its forward drive and ride back into the hollow rod 42 and overcome the bias of the spring 72 . when the spring is compressed the electrical circuit normally held open by the spring 72 is completed thus turning on the amplifier on the lsi chip 80 . release of the gas pressure or equalization of the air pressure on both sides of the bellows causes the bellows to relax , causing the bellows to recover to its normal condition thereby withdrawing the hollow rod 42 , and its contents back into the cavity of the electrode assembly . as the rod 42 recedes back into the cavity back pressure on the electrode 50 is removed and the spring 72 separates the battery from the electrode element breaking electrical connection thereby turning off the amplifier . the amplifier is turned on when electric connection is made between the one terminal of the battery and the electrode element and the other terminal of the battery and the amplifier input terminal on the substrate carrying the lsi chip . the electrode element 50 is preferably fabricated from a good electrical conductor material , for example , copper or silver . the electrode element preferably includes a center aperture defining a channel or cavity 52 . the channel is extended and opened along the body of the element and adapted to receive a tube 53 . the tube 53 is connected to a source of electrolytic material 100 via the conduct 110 . when the tip of the electrode element 50 is in contact with the scalp of the subject or patient being tested , a predetermined amount of an electrolytic material may be metered on to the surface of the scalp to aid in electrical contact between the electrode and the surface of the skin . several electrolytic gels are commercially available but one preferred electrolytic material is electrode gel marketed by parker laboratories , which is a buffered , non - corrosive electrolytic material it will be apparent that the battery 75 and spring 72 may be replaced by a biased switch and the battery may be mounted on the substrate 81 supporting the lsi chip 80 . the biased switch would serve the purpose of opening and closing the circuit to turn the amplifier off and on respectively and as an electrical conductor , when closed , to conduct the electrical impulses or brain waves detected to the amplifier for amplification . the lsi chip may also include an analog to digital signal converter for converting the electrical impulse from analog form in to digital form . the preferred embodiment of the invention having heretofore been described it will be apparent that changes and modification may be made , as will be apparent to one skilled in the art , without departing from the invention as defined in the appended claims .
an electrode assembly is mounted in a helmet like headset for use in making multiple electrode contact with the scalp . each electrode assembly includes an electrode that floats in a cylinder mounted in a pressure responsive drive , which , when under pressure carries the electrode toward the scalp of a patient wearing the headset . mounted in the cylinder above the electrode and biased away from the electrode is an lsi chip carrying an operation amplifier and a power supply for the amplifier . when the electrode makes contact with the scalp the cylinder continues to drive forward . back pressure from contact with the scalp overcomes the bias and completes a circuit to turn on the amplifier . the amplifier is connected via wire or a wireless signal transmit system to a computer into which amplified signals are fed .