| 摘要 |
PURPOSE:To perform a simple and high degree of spatial modulation by providing a transmission wave space filled with a pressure wave medium and having distributive leak passages and piezoelectric energy transducers arranged in at least two spaced positions in the transmission wave space. CONSTITUTION:Piezoelectric energy transducers 10 and 12 are mounted on both ends of a metallic pipe 14 constituting a transmission space. When the same AC energizing signals are applied to the two transducers 10 and 12, a standing wave which is an acoustic pressure wave is formed in a medium in the metallic pipe 14. Since, when the frequency of one of the transducers 10 and 12 is made slightly different from the other, the standing wave moves in accordance with a frequency deviation thus produced, an acoustic signal temporally and spatially modulated with respect to an ambient sound field can be emitted when a frequency difference between the transducers 10 and 12 is modulated. Therefore, a reflected wave from a given position or direction can be selectively measured by producing a local signal whose modulation mode is assumed in advance and measuring a correlation with a received signal.
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