| 摘要 |
A presence detection system includes a reader device (10) attached to a first body, and a tag device (22) attached to a second body. The reader device (10) has an ultrasonic transducer (14) for generating and transmitting ultrasonic pulses at a first rate of occurrence; an RF receiver (18) for receiving a RF signal; and a microcontroller (12) coupled to the ultrasonic transducer (14) and the RF receiver (18) for receiving signals from the ultrasonic transducer (14) and the RF receiver (18) and for controlling the operation of ultrasonic transducer (14) and the RF receiver (18). The tag device (22) has an ultrasonic receiver (28) for receiving ultrasonic pulses from the ultrasonic transducer (14) of the reader device (10); and an RF pulse generator (32) for generating and transmitting an RF pulse. The distance between the reader device (10) and the tag device (22) is determined based on the amount of time between the transmission of the ultrasound pulse by the reader device (10) and the reception of the response RF pulse by the reader device (10). |
