| 摘要 |
A wideband ultrasonic transducer comprises at least two stretched piezoelectric polymer films rolled together in a lengthwise direction so as to form a scroll having an axis parallel to a stretch direction of the polymer films. Each of the polymer films has a different width W in a longitudinal direction of the scroll, where the widths W are related to respective acoustic wavelengths lambda of the polymer films. A resonant frequency of each polymer film is selected by varying the widths W of each polymer film and the resonant frequencies of the polymer films are preferably selected so as to occupy a desired contiguous frequency band. An electric field is applied to each of the polymer films in parallel so as to induce expansion or shrinkage of the polymer films in their stretched directions, thereby causing resonance at their respective resonant frequencies. In one embodiment, a radiator disk is attached to one end of the scroll, while in another embodiment a second disk is attached to the other end of the scroll. In still another embodiment, the axis of the scroll is positioned parallel to the surface of a medium and a right angle acoustic reflector is connected to one end of the scroll to reflect acoustic waves radiated axially by the scroll into the medium. In yet another embodiment, the wideband transducer comprises at least two piezoelectric bimorphs spaced in proximal relation and coupled to the medium.
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