Patent ID: 6057760
Filing Date: 2000-05-02
Classification: G01S

Abstract:
A method for detecting intrusion into a vehicle in which ultrasound waves are emitted and reflected inside the vehicle comprising:obtaining a pair of quadrature demodulated signal by mixing a signal comprising a combination of the waves emitted and reflected with two reference signals having a relative phase difference of .pi./2 and having the same frequency as a carrier of the emitted ultrasound waves;comparing the absolute value of each of the demodulated signals of each pair of signals obtained to a respective threshold value to determine pairs of valid signals if the absolute value of at least one of the two demodulated signals is higher than the respective threshold value, and invalid pairs otherwise;counting the number of successive rotations of a vector whose coordinates correspond to the values of the successive valid pairs of the demodulated signals;reducing progressively for each invalid pair, the value of the count of the number of rotations if the demodulated signals are lower than the respective threshold value; andcommanding the tripping of an alarm if the value of the count of the number of rotations reaches a given threshold.