日本音響学会誌

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This paper deals with some experimental results of the tuning fork (Fig. 1 )with double resonance and its applications to electromechanical filters. Two resonance modes of the tuning fork are the horizontal flexural vibration mode f_&ltBH&gt and the vertical vibration mode f_&ltBV&gt (Fig. 2) , and each resonance frequency is determined as a function of the thickness and the length of the arms and the base part of the tuning fork (Fig. 3, 6, 7). As the two modes f_&ltBH&gt and f_&ltBV&gt approach each other, they change into the diagonal modes f_&ltBL&gt and f_&ltBR&gt owing to the small internal coupling in the base part (Fig. 2, 3, 4). In these diagonal modes, it is possible to easily adjust the resonance frequencies by chamfering the arms of the tuning fork (Fig. 9). The polarities of piezo-electric ceramics in constructing the filters are as shown in Fig. 11 in the case of the tuning fork with double resonance of f_&ltBH&gt and f_&ltBV&gt modes, and are as shown in Fig. 13 in the case of f_&ltBL&gt and f_&ltBR&gt modes, respectively. The equivalent electrical network of the filters is also shown in Fig. 12. Attenuation characteristics of the filters composed of a tuning fork with double resonance of f_&ltbH&gt and f_&ltBV&gt modes or f_&ltBL&gt and f_&ltBR&gt modes are shown in Figs. 14, 16, where the inductance coils are connected in parallel at both electrical end-terminals of the filters. By reason of using the double resonance of only one vibrator without the need of ideal transformer, the filters described in this paper are suitable for miniaturing an electro-mechanical filter and are favorable for practical use in low frequencies.

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