Tohoku Metal Industries

Hiroshi Watanabe

Hiroshi Shimizu

Yuji Iseki

A multimode piezoelectric mechanical filter using edge-mode piezoelectric transducers, each comprising a semi-infinite or long piezoelectric plate polarized in the thickness direction, and a pair of exciting electrodes formed on the plate at an end portion thereof. Input and output edge-mode transducers are supported at their other ends together with optional resonator elements. The transducer and/or resonator elements are mechanically coupled with one another by a coupling rod at their end portions opposite the support to transmit the edge-mode vibration from one to the other. All of the transducers and resonator elements may be disposed in a common plane and may be integrally formed by punching a single piezoelectric plate to form a monolithic type mechanical filter. In such monolithic type filter, coupling rods are also integrally formed with the transducers and resonators. Alternatively, the transducer regions and/or resonator regions are separated and defined by a slit or slits formed in a large square piezoelectric plate, the bottom portion of each slit being usable as the mechanical coupling.

Multiple resonant electromechanical filters using edge-mode vibration of

A piezoelectric resonator of a width-extensional mode vibratory-energy trapping type having a rectangular piezoelectric plate of a width corresponding to a desired resonance frequency. Peripheral electrodes are deposited apart from one another in its lengthwise direction to cover over the width of opposite end portions of the piezoelectric plate in order to lower the cut-off frequency of the opposite end portions of the piezoelectric plate in comparison with the intervening central portion of the plate, so that the width-extensional mode vibratory energy may be trapped or confined within the central portion of the piezoelectric plate. The resonator can be supported and are connected to lead wires at peripheral electrodes. In the piezoelectric plate polarized in its width direction, two excitation electrodes are provided on a surface of the central portion of the piezoelectric plate in parallel with one another, one connected with one of the peripheral electrodes and the other connected to the other peripheral electrode. A set of two excitation electrodes and two spaced peripheral electrodes may be formed on the reverse surface of the piezoelectric plate in registry with those electrodes on its opposite surface. A stray strip-like electrode may be formed between the two excitation electrodes of one surface of the piezoelectric plate. In the case, the stray electrode and two excitation electrodes are disposed so that centers of respective distances between respective adjacent electrode is corresponding to zero point of stress distribution due to the third-harmonic-mode vibration to suppress the third harmonic mode. In the piezoelectric plate polarized in its thickness direction, four peripheral electrodes are formed on the opposite surfaces of the piezoelectric plate, and peripheral electrodes at each end portion are short-circuited with one another. Excitation electrodes are formed on the central exposed regions of the plate intervening between peripheral electrodes. Two excitation electrodes may be formed on each surface of the plate, and are disposed at positions corresponding to zero points of stress distribution due to the third-harmonic mode vibration to suppress the third-harmonic mode.

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Izumi, Japan

Hiroshi Watanabe