A Piezoelectric-Piezomagnetic Gyrator

A linear passive unilateral element, which has a high forward/backward transmission ratio at all frequencies, is realized by combining two resistances and an electromechanical gyrator according to Gamo´s theory. The gyrator consists of three mechanically coupled ceramic elements, two of which may be piezomagnetic and the third piezoelectric, or two of which may be piezoelectric and the third piezomagnetic. In either arrangement, a unilateral coupling between mechanical and electrical systems is provided by using one piezoelectric and one piezomagnetic element. The third element is merely for driving the mechanical system. Such a design makes manufacturing considerably easier. Characteristics of the gyrator have been discussed based on an equivalent circuit. A constant input resistance can be obtained at a terminal pair of the isolator by purely electrical means even after the fabrication of the gyrator. This simplifies the matching at this terminal. The theoretical minimum insertion loss is 3 db under the matched termination conditions. A few models have been made at 150 kc using both the sandwiched and the cascaded structures. A highly achromatic suppression of backward transmission (45 db) has been obtained in agreement with theoretical predictions. Minimum forward insertion loss consists of the theoretical minimum of 3 db and an excess loss of a few db due principally to mechanical losses.