Abstract: A golf club head having a face portion for striking a ball, the face portion being formed by a complex block comprising a plurality of ceramic plates and layers of glass fibers or carbon fibers laminated alternately. By such a complex construction, the sweet spot and the center of gravity distribution as well as the hardness and roughness of a ball striking surface can be changed as desired.

Abstract: A flat thermionic cathode is provided with a substrate having at least one main heating element thereon to produce at least one substantially localized area of heat and a sub-heating element to substantially define a heating area, the localized area being produced within the heating area. A cathode element including electron emissive material is disposed at the localized area. While the localized area tends to produce a temperature gradient directed from the localized area toward the perimeter of the substrate so as to create thermal stress in the substrate along the perimeter thereof, the sub-heating element reduces this temperature gradient and, consequently, the thermal stress.

Abstract: A thermionic cathode structure includes a ceramic base plate, a heater layer of tungsten coated on the ceramic base plate, a cathode lead layer of tungsten formed on a ceramic insulating layer covering the heater layer, a base metal layer coated on the cathode lead layer, and a cathode material coated on the base metal layer.