| 摘要 |
PURPOSE:To reduce harmonic spurious noise by adopting the shape of a delay medium so that a wavefront of a sound wave propagated in the delay medium is inputted obliquely in an output transducer and a waveform component cancelling mutually the generation of an output voltage corresponding to the sound wave of the 3rd harmonic component is inputted. CONSTITUTION:The reflecting face 2a of the delay medium 2 is formed with a slope to an imaginary reflecting face 2a' so that the wavefront of the sound wave 3' reflected on the mirror surface of the reflecting face 2a is inputted obliquely to an output transducer 4. Assuming an angle between the reflecting face 2a and the imaginary reflecting face 2a' as theta, the sound wave 3' reflected in the reflecting face 2a is inputted to the output transducer 4 by an angle 2theta with respect to the imaginary reflecting wave 3''. Then the relation of alpha=2theta is established. Assuming the width of the output transducer 4 by W and the wavelength of the 3rd harmonic of the sound wave 3' as lambda, then the waveform component of opposite phase cancelling generation of an output voltage corresponding to the 3rd harmonic component is inputted to the transducer 4 in case the relation of lambda=Wsin 2theta exists. Thus, the main signal is not almost attenuated but only the spurious components of the 3rd harmonic or over are attenuated remarkably.
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