The die has a bore that is generally sized to fit onto a like-sized stud. A first back-face electrode layer and a second back-face electrode layer are stacked in order on the other face of the insulating substrate. Thus, an engine operable condition is ensured under abnormal conditions, such as bird strikes, in which the coaxial relationship between the inner and outer rotating shafts are affected by unbalancing forces caused by the bird strike, thereby causing a failure of the radial seal.