Ultrasonic breathing sensor and sensing method for vehicle occupant monitoring
Breathing sensors, sensing methods, and vehicle occupant monitoring systems may employ ultrasonic transducers. One illustrative sensing method includes: sensing an acoustic transducer's responses to a series of acoustic bursts emitted in a vehicle's cabin; differencing pairs of said responses to obtain difference signals; converting the difference signals into magnitude signals; performing peak detection on each of the magnitude signals to obtain at least one peak amplitude; and providing a breathing signal based on the at least one peak amplitude. The breathing signal may be an occupancy detection flag, an occupant position, a breathing frequency, and/or any combination thereof.
1. A method that comprises:
sensing an acoustic transducer's responses to a series of acoustic bursts;
differencing pairs of said responses to obtain difference signals;
converting the difference signals into magnitude signals each representing a time-dependent magnitude of a difference between responses in one of the pairs of said responses;
performing peak detection on each of the magnitude signals to obtain at least one peak amplitude; and
providing a breathing signal based on the at least one peak amplitude.
2. The method of claim 1 , wherein said performing peak detection includes determining a peak amplitude for each of multiple peaks in each of the magnitude signals, and wherein a breathing signal is determined for each of the multiple peaks.
3. The method of claim 2 , further comprising associating each of the breathing signals with a respective position in a vehicle's cabin.
4. The method of claim 1 , wherein said providing a breathing signal includes comparing the at least one peak amplitude to a predetermined threshold.
5. The method of claim 4 , wherein said providing a breathing signal further includes asserting the breathing signal only if a moving window contains at least a minimum number of times that the peak amplitude exceeds the predetermined threshold.
6. The method of claim 1 , wherein said providing a breathing signal includes determining a breathing frequency of a human occupant of a vehicle.
7. The method of claim 6 , wherein said providing a breathing signal includes performing a Fast Fourier Transform of the at least one peak amplitude as a function of time to determine the breathing frequency.
8. The method of claim 6 , further comprising: setting an alert if the breathing frequency indicates an impaired driver.
9. The method of claim 1 , further comprising: setting an alert if the breathing signal indicates a rear seat occupant of a vehicle when a front door of the vehicle is opened.
10. A controller for an acoustic transducer, the controller comprising:
a receiver configured to sense the acoustic transducer's response to each of a series of acoustic bursts; and
a processing circuit configured to derive a breathing signal from said responses in part by:
obtaining difference signals from pairs of said responses;
converting each difference signal into a magnitude signal representing a time-dependent magnitude of that difference signal; and
performing peak detection on each said magnitude signal to obtain at least one peak amplitude.
11. The controller for an acoustic transducer of claim 10 , wherein said performing peak detection includes determining a peak amplitude for each of multiple peaks in each of the magnitude signals, and wherein a breathing signal is determined for each of the multiple peaks.
12. The controller for an acoustic transducer of claim 10 , wherein said processing circuit is configured to derive the breathing signal in part by: comparing the at least one peak amplitude to a predetermined threshold; and asserting the breathing signal only if a moving window contains at least a minimum number of times that the peak amplitude exceeds the predetermined threshold.
13. The controller for an acoustic transducer of claim 10 , wherein said processing circuit is configured to derive the breathing signal in part by determining a breathing frequency of a human occupant of a vehicle.
14. The controller for an acoustic transducer of claim 10 , wherein said processing circuit is configured to derive the breathing signal in part by performing a Fast Fourier Transform of the at least one peak amplitude as a function of time to determine a breathing frequency of a human occupant of a vehicle.
15. The controller for an acoustic transducer of claim 14 , further comprising: a status register having a flag signifying whether the breathing frequency indicates an impaired driver.
16. A vehicle that comprises:
at least one seat configured to accommodate an occupant;
at least one acoustic transducer configured to receive a series of acoustic burst echoes from the occupant when the occupant is present in the vehicle; and
a controller configured to derive a breathing signal from the series of acoustic burst echoes by:
obtaining difference signals from pairs of said acoustic burst echoes;
converting each difference signal into a magnitude signal representing a time-dependent magnitude of that difference signal; and
performing peak detection on each said magnitude signal to obtain at least one peak amplitude.
17. The vehicle of claim 16 , wherein as part of said performing peak detection, the controller is configured to determine a peak amplitude for each of multiple peaks in each of the magnitude signals, the peaks corresponding to occupants of different seats in the vehicle, and wherein the controller is configured to derive a breathing signal for each occupant.
18. The vehicle of claim 16 , wherein the controller is configured to derive the breathing signal in part by determining a breathing frequency of the occupant.
19. The vehicle of claim 18 , wherein the controller includes a status register having a flag signifying whether the breathing frequency indicates an impaired driver.
20. The vehicle of claim 16 , wherein the at least one acoustic transducer is integrated with a component of an audio system for the vehicle, the component including a microphone or speaker.