| 摘要 |
<p>PROBLEM TO BE SOLVED: To detect even a closest object accurately by providing a filter for passing a difference frequency between a resonance frequency and an oscillation frequency and extracting a reflection wave in reverberation vibration. SOLUTION: When the resonance frequency of a transducer is set to fr, an oscillation circuit performs a pulse oscillation output with a frequency f1 that is different from the resonance frequency fr. A filter for passing a frequency of|fr-f1|is used. Reverberation vibration after a transducer sends the ultrasonic signal with a frequency of f1 is generated by a resonance frequency of fr. Therefore, when a reflection wave R from an object overlaps with the reverberation vibration, a beat with a frequency of|fr-f1|is generated by the reverberation vibration of the reflection wave R with a frequency of f1 and a resonance frequency of fr. The filter can pass the frequency|fr-f1|. Therefore, when there is the reflection wave R that overlaps with the reverberation vibration, an output with a frequency of|fr-f1|appears in the filter, thus calculating a distance to the object by a processing circuit.</p> |
