| 摘要 |
<p>A plurality of ultrasonic transmitters (12) at distinct locations and with distinct transmitting frequencies, direct beams of ultrasonic sound waves at one or more detection regions (16) of space. The amplitude of the ultrasonic sound waves is sufficient to generate from each detection region (16) a sound wave (17) having a frequency corresponding to the difference of the frequencies of the respective ultrasonic sound waves. A receiver (18) disposed proximate to the ultrasonic transmitters detects the generated sound wave. An object occupying the detection region blocks one or more of the beams, and is detected therein when the magitude of the generated sound wave (17) is below a threshold. In another aspect of the instant invention, the ultrasonic transmitters (12) are adapted to transmit pulses forming relatively broad spherical wavefronts (38) which intersect to form a circular detection region which propagate with time, thereby enabling the detection of a profile of an object.</p> |
