Abstract: An improved dielectric resonator for high frequency operation having improved unloaded Q is provided which is prepared by forming a first copper coating on the ceramic body to a thickness of 0.2 to 1 .mu.m by electroless plating or vacuum deposition, electrolytic plating a second copper coating on the first coating to a thickness of at least two-fold of the skin depth, and heat treating the thus coated body at 120.degree.-300.degree. C. in a reducing atmosphere or at 700.degree.-1080.degree. C. in a weakly acidic atmosphere.

Abstract: A current restriction device for alternate circuit with small size, low producing cost and low power loss has been found by using a ferro-electric body with rectangular hysterisis characteristics. Said device is used for instance as a ballast for restricting current in a fluorescent lamp. Said ferro-electric body has main component of B.sub.a T.sub.i O.sub.3, additive of S.sub.r or P.sub.b for substitution of part of B.sub.a and Z.sub.n or S.sub.n for substitution of part of T.sub.i, and a mineralizer of M.sub.n o or C.sub.r2 O.sub.3. The voltage-current characteristics of said ferro-electric body show non-linearity that the impedance ratio (Z.sub.2 /Z.sub.1) of the impedance Z.sub.2 measured with alternate field of 500 volts/mm to the impedance Z.sub.1 measured with alternate field of 5 volts/mm is less than 1/10.