A process for producing a carbon material comprising a step of polymerizing a compound represented by the formula wherein R is independently in each occurrence a hydrogen atom etc. An ultrasonic emitter system is included that is constructed to emit an inaudible signal having properties to reduce perception of the system noise about at least a portion of the imaging area. The interior liner is adapted for receipt over and conform to an exterior surface of the helmet. The bio-active reagent entrapped within the hydrophilic polyurethane film can retains its high activity for an extended period of time and the intrinsic potentiometric response of the underlying ion-selective polymeric membrane is not affected by the bio-active reagent immobilized polyurethane film coated on its sensing surface.