Complex Signal Demodulation and Angular Demodulation for Non-contact Vital Sign Detection

• US 20100241010A1
• Filed: 12/08/2008
• Published: 09/23/2010
• Est. Priority Date: 12/07/2007
• Status: Active Grant

• Current Assignee: University of Florida Research Foundation, Incorporated (State University System of Florida)
• Original Assignee: University of Florida Research Foundation, Incorporated (State University System of Florida)
• Inventors: Lin, Jenshan, Li, Changzhi
• Granted Patent: US 8,814,805 B2
• Time in Patent Office: Days
• US Class Current: 600/484
• CPC Class Codes: A61B 5/024 Detecting, measuring or recording pulse rate or heart rate A61B5/0205, A61B5/021 take precedence
• CPC Class Codes: A61B 5/05 Detecting, measuring or recording for diagnosis by means of electric currents or magnetic fields; Measuring using microwaves or radio waves impedance plethysmography A61B5/0295; measuring movement of the entire body or parts thereof A61B5/11; detecting, measuring or recording bioelectric or biomagnetic signals of the body or parts thereof A61B5/24
• CPC Class Codes: A61B 5/1114 Tracking parts of the body
• CPC Class Codes: A61B 5/113 occurring during breathing
• CPC Class Codes: A61B 5/7214 using signal cancellation, e.g. based on input of two identical physiological sensors spaced apart, or based on two signals derived from the same sensor, for different optical wavelengths
• CPC Class Codes: A61B 5/7253 characterised by using transforms
• CPC Class Codes: A61B 5/7257 using Fourier transforms
• CPC Class Codes: G01S 13/56 for presence detection presence detection using near field arrangements G01V3/00, e.g. G01V3/08, G01V3/12; burglar, theft or intruder alarms with electrical actuation G08B13/22 - G08B13/26
• CPC Class Codes: G01S 7/2886 using I/Q processing

Abstract

Methods for recovering a detected signal in non-contact vital sign detection are provided. According to one embodiment, a detected reflected signal from a non-contact vital sign detection system can be received and provided along I channel and Q channel signal lines. A complex signal S(t) can then be reconstructed from the I channel and Q channel signal lines through complex signal demodulation. A Fourier transform can be used to obtain the detected signal'"'"'s spectrum for spectrum analysis. Angular demodulation can be used to recover the information corresponding to original body movement. The complex signal demodulation and angular demodulation techniques used to provide information to determine original body movement are capable of avoiding the null detection point without limitations on frequency tuning or channel selection.

Claims

1. A method for recovering a detected signal in non-contact vibration detection, comprising:

reconstructing a complex signal from an I channel and a Q channel for a received reflected signal;

applying a Fourier transform to the reconstructed signal to obtain the detected spectrum;

extracting angular information of the reconstructed complex signal; and

obtaining original vibration information by analyzing the angular information.

2. The method according to claim 1, wherein obtaining original vibration information comprises obtaining original body movement information.

3. The method according to claim 2, wherein further comprising obtaining vital sign information from the original body movement function.

4. The method according to claim 1, further comprising:

calibrating out a DC offset of the detected spectrum.

5. The method according to claim 1, wherein reconstructing the complex signal from the I channel and the Q channel is performed using the following relation:

6. The method according to claim 5, wherein reconstructing the complex signal from the I channel and the Q channel is performed via hardware.

7. The method according to claim 5, wherein reconstructing the complex signal from the I channel and the Q channel is performed via software.

8. The method according to claim 5, wherein the first periodic vibration is due to heartbeat and the second periodic vibration is due to respiration.

9. The method according to claim 1, wherein calibrating out the DC offset of the detected spectrum comprises subtracting a complex average from every time domain sliding window.

10. The method according to claim 1, wherein extracting the angular information of the reconstructed complex signal comprises applying the following relation:

11. The method according to claim 1, further comprising:

transmitting a signal at a target receiving the received reflected signal from the target.

12. The method according to claim 11, wherein the signal has a frequency in a range of 9 kHz-1 terahertz.

13. The method according to claim 11, wherein the signal has a frequency in a range of 1 GHz-30 GHz.

14. The method according to claim 11, wherein the I channel is a real component I of the received reflected signal, wherein the I channel is in-phase with the transmitted signal, wherein the Q channel is an imaginary quadrature component Q of the received reflected signal, wherein the Q channel is 90 degrees out of phase with the transmitted signal.

15. The method according to claim 1, wherein analyzing the angular information comprises determining how fast an angle changes.

16. The method according to claim 15, wherein a vibration rate of the target is how fast the angle changes.

19. The method according to claim 12, wherein reconstructing the first complex signal and reconstructing the second complex signal are performed via hardware.

20. The method according to claim 12, wherein reconstructing the first complex signal and reconstructing the second complex signal are performed via software.

17. A method for cancelling random body movement effects in non-contact vibration detection, comprising:

providing a first transceiver in a first position with respect to a body and a second transceiver in a second position with respect to the body, wherein the first transceiver comprises a least one first antenna having a first polarization and the second transceiver comprises at least one second antennas having a second polarization;

reconstructing a first complex signal from a first I channel and a first Q channel for a received reflected first signal from the first transceiver and reconstructing a second complex signal from a second I channel and a second Q channel for a received reflected second signal from the second transceiver; and

combining the first complex signal and the second complex signal to produce a combined signal.

18. The method according to claim 17, wherein reconstructing the first complex signal from the I channel and the first Q channel for a received reflected first signal from the first transceiver and reconstructing a second complex signal from a second I channel and a second Q channel for a received reflected second signal from the second transceiver is performed using the following relations:

21. The method according to claim 18, wherein λ

_{1 and} λ

₂ are within 0.0001% of each other.

22. The method according to claim 18, wherein the first periodic vibration is due to the heartbeat and the second periodic vibration is due to respiration.

23. The method according to claim 17, wherein combining the first complex signal and the second complex signal comprises performing a convolution and frequency shift in the frequency domain.

24. The method according to claim 23, wherein combining the first complex signal and the second complex signal comprises applying the following relation:

25. The method according to claim 24, wherein the first periodic vibration is due to the heartbeat and the second periodic vibration is due to respiration.

26. The method according to claim 24, wherein the combined signal is approximated to:

27. The method according to claim 17, further comprising:

applying a Fourier transform to the combined signal to obtain the detected spectrum;

extracting angular information of the combined signal; and

obtaining original body movement information by analyzing the angular information.

28. The method according to claim 27, further comprising:

calibrating out a DC offset of the detected spectrum.

29. The method according to claim 18, wherein λ

₁ and λ

₂ are within 0.0001% of each other.