Piezoelectrics for superceding ferrites in telecommunications

Low temperature heat treatment was studied for preparing low loss and high stability MnZn ferrites. A prototype channel filter available for high packing density (e.g., 600 channels/bay) was made using MnZn ferrite cores. Difficulties in continuing the miniaturization of the L-C channel filter are discussed. Advantages of mechanical filters are explained in view of miniaturization. Piezoelectric materials were developed as transducer materials for mechanical filters and will be gradually used to supersede ferrites.