A piezoelectric double-mode filter using the complex-branch-type energy trapping

A piezoelectric double-mode filter using the complex-branch-type energy trapping, that is caused by contributions from the complex branches of dispersion curves is proposed, and its theoretical and experimental results are presented for the width-extensional modes in a thin piezoelectric ceramic strip. Characteristics of the symmetric and antisymmetric trapped-energy modes in this filter have some interesting features different from those of the usual trapped-energy modes, such as noticeable undulations in the resonant frequency spectrum and sinusoidally oscillating decay of displacement in the unelectroded region. Based on these results, double-mode filters with a center frequency of about 1 MHz and a 3-dB fractional bandwidth of 3% are constructed. The filters of this type are useful in the medium frequency range below several megahertz because of the miniature size and the ease of supporting.<
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