音響ヘリカルアンテナの指向性の帯域特性

抄録

In many piezoelectric transducer applications, we call for directional rather than omnidirectional transducers. One way to obtain the desired directional radiation pattern is to deploy multiple transducer elements in a long linear array or large planar array. Another interesting method is to use an acoustic helical antenna which consists of an inactive cylindrical helix made of a brass rod and exciter of the Langevin piezoelectric transducer.
In this paper, the effect of the variation of phase velocity in a metal wire helix of the acoustic helical antenna on the directional pattern is studied, and it is clarified that the directional pattern of endfire radiation occurs for the helix over a wide band of frequencies. In addition, it is suggested that a conical logarithmic-spiral antenna is suitable to reduce greatly side lobes without paying the expense of a wider main lobe.