Ceramic-metal composite resonators

The results of investigations into the design and performance of composite resonators, for use in electric wave filters in the frequency range 15¿30 kc/s, are reported. Each resonator comprises a ferro-electric ceramic element bonded between two metal rods so as to form a half-wavelength resonator. By using metal having a low temperature coefficient of elastic modulus, the frequency/temperature stability of the resonators can be restricted to a few parts per million per degree Celsius over the range 10¿50° C. Ageing of the electrical parameters at present imposes limitations on the use of such resonators which, by comparison with low-frequency quartz crystals, offer advantages of cheapness, simplicity of manufacture and low capacitance ratios.