| 摘要 |
<p>An ultrasonic signal is radiated, a reflection signal of the ultrasonic signal is received, an amplitude of the reflection signal is measured for comparison with a threshold level, a majority processing is performed on a plurality of comparison results obtained at a signal processing unit (15) and any one of the comparison results is selected, thereby specifying the position of a crew member in the passenger seat next to the driver based on the selected comparison result. A change in an amplitude of a reflection signal is monitored to judge as to whether a human being or an object is present in the passenger seat.</p> |
