Random body movement cancellation for non-contact vital sign detection
View Patent ↗A method and system for cancelling body movement effect for non-contact vital sign detection is described. The method begins with sending on a first electromagnetic wave transceiver a first electromagnetic signal with a first frequency to a first side of a body, such as a person or animal. Simultaneously using a second electromagnetic wave transceiver a second electromagnetic signal is sent with a second frequency to a second side of a body, wherein the first frequency and the second frequency are different frequencies. A first reflected electromagnetic signal reflected back in response to the first electromagnetic wave on the first transceiver is received and a first baseband complex signal is extracted. Likewise a second reflected electromagnetic signal reflected back in response to the second electromagnetic wave on the second transceiver is received and a second baseband complex signal is extracted. The first baseband complex signal is mathematically combined with the second baseband complex signal to cancel out a Doppler frequency drift therebetween to yield a periodic Doppler phase effect.
1. A method for cancelling body movement effect for non-contact vital sign detection, comprising:
sending a first electromagnetic signal with a first frequency to a first side of a body from a first electromagnetic wave transceiver and a second electromagnetic signal with a second frequency to a second side of the body from a second electromagnetic wave transceiver, where the first frequency of wavelength λ 1 and the second frequency of wavelength λ 2 are close to each other so that (λ 1 ≈λ 2 ≈λ);
receiving at least a first reflected electromagnetic signal reflected back in response to the first electromagnetic signal via the first electromagnetic wave transceiver and receiving at least a second reflected electromagnetic signal reflected back in response to the second electromagnetic signal via the second electromagnetic wave transceiver;
generating a baseband output by combining a first baseband complex signal extracted from the first reflected electromagnetic signal with a second baseband complex signal extracted from the second reflected electromagnetic signal to cancel out a Doppler frequency drift therebetween to yield a periodic Doppler phase effect, where the first baseband complex signal and the second baseband complex signal are combined by complex signal demodulation as expressed by:
S
f
(
t
)
=
exp
{
j
[
4
π
x
h
1
(
t
)
λ
+
4
π
x
r
1
(
t
)
λ
+
4
π
y
(
t
)
λ
+
ϕ
1
]
}
and
S
b
(
t
)
=
exp
{
j
[
4
π
x
h
2
(
t
)
λ
+
4
π
x
r
2
(
t
)
λ
-
4
π
y
(
t
)
λ
+
ϕ
2
]
}
,
where x h1 (t) and x r1 (t) are heartbeat-induced and respiration-induced physiological movements on the first side of the body, x h2 (t) and x r2 (t) are heartbeat-induced and respiration-induced physiological movements on the second side of the body, φ 1 , φ 2 are residual phases of the first electromagnetic wave transceiver and the second electromagnetic wave transceiver, and y(t) is a body movement, where the y(t) term in the baseband output S fb (t)=S f (t)·S b (t) is cancelled out by multiplying S f (t) and S b (t), while terms of physiological movement x h1 (t), x h2 (t), x r1 (t) and x r2 (t) are enhanced as expressed by:
S
fb
(
t
)
=
exp
{
j
[
4
π
[
x
h
1
(
t
)
+
x
h
2
(
t
)
]
λ
+
4
π
[
x
r
1
(
t
)
+
x
r
2
(
t
)
]
λ
+
ϕ
1
+
ϕ
2
]
}
;
and
displaying a vital sign of the body extracted from the baseband output.
2. The method of claim 1 , further comprising:
extracting at least one of respiration rate and heart rate from the periodic Doppler phase effect.
3. The method of claim 2 , further comprising:
sending the at least one of the respiration rate and the heart rate extracted from the periodic Doppler phase effect to a display.
4. The method of claim 1 , wherein a DC offset in at least one of the first baseband complex signal and the second baseband complex signal is not calibrated out.
5. The method of claim 1 , wherein the first electromagnetic wave transceiver and the second electromagnetic wave transceiver are anyone of:
5.8 GHz quadrature radar transceivers; and
24 GHz quadrature radar transceivers.
6. A method for cancelling body movement effect for non-contact vital sign detection, comprising:
sending a first electromagnetic signal with a first frequency to a first side of a body from a first electromagnetic wave transceiver and a second electromagnetic signal with a second frequency to a second side of the body from a second electromagnetic wave transceiver, where the first frequency of wavelength λ 1 and the second frequency of wavelength λ 2 are close to each other so that (λ 1 ≈λ 2 ≈λ);
receiving at least a first reflected electromagnetic signal reflected back in response to the first electromagnetic signal via the first electromagnetic wave transceiver and receiving at least a second reflected electromagnetic signal reflected back in response to the second electromagnetic signal via the second electromagnetic wave transceiver; and
generating a baseband output by combining a first baseband complex signal extracted from the first reflected electromagnetic signal with a second baseband complex signal extracted from the second reflected electromagnetic signal to cancel out a Doppler frequency drift therebetween to yield a periodic Doppler phase effect, where the first baseband complex signal and the second baseband complex signal are combined by arctangent demodulation as expressed by:
S
f
(
t
)
=
exp
{
j
[
4
π
x
h
1
(
t
)
λ
+
4
π
x
r
1
(
t
)
λ
+
4
π
y
(
t
)
λ
+
ϕ
1
]
}
and
S
b
(
t
)
=
exp
{
j
[
4
π
x
h
2
(
t
)
λ
+
4
π
x
r
2
(
t
)
λ
-
4
π
y
(
t
)
λ
+
ϕ
2
]
}
,
where x h1 (t) and x r1 (t) are heartbeat-induced and respiration-induced physiological movements on the first side of the body, x h2 (t) and x r2 (t) are heartbeat-induced and respiration-induced physiological movements on the second side of the body, φ 1 , φ 2 are residual phases of the first electromagnetic wave transceiver and the second electromagnetic wave transceiver, and y(t) is a body movement, where the y(t) term in the baseband output S fb (t)=S f (t) is cancelled out by multiplying S f (t) and S b (t), while terms of physiological movement x h1 (t), x h2 (t), x r1 (t) and x r2 (t) are enhanced and expressed by:
S
fb
(
t
)
=
exp
{
j
[
4
π
[
x
h
1
(
t
)
+
x
h
2
(
t
)
]
λ
+
4
π
[
x
r
1
(
t
)
+
x
r
2
(
t
)
]
λ
+
ϕ
1
+
ϕ
2
]
}
;
and
displaying a vital sign of the body extracted from the baseband output.
7. The method of claim 6 , wherein a DC offset in the first baseband complex signal and the second baseband complex signal is calibrated out.
8. The method of claim 6 , wherein the first electromagnetic wave transceiver and the second electromagnetic wave transceiver are anyone of:
5.8 GHz quadrature radar transceivers; and
24 GHz quadrature radar transceivers.
9. The method of claim 6 , further comprising:
extracting at least one of respiration rate and heart rate from the periodic Doppler phase effect.
10. The method of claim 9 , further comprising:
sending the at least one of the respiration rate and the heart rate extracted from the periodic Doppler phase effect to a display.
11. A system for cancelling body movement effect for non-contact vital sign detection, comprising:
a first electromagnetic wave transceiver configured to send a first electromagnetic signal with a first frequency to a first side of a body and receive a first reflected electromagnetic signal reflected back in response to the first electromagnetic signal;
a second electromagnetic wave transceiver configured to send a second electromagnetic signal with a second frequency to a second side of the body, where the first frequency and the second frequency are different frequencies, and receive a second reflected electromagnetic signal reflected back in response to the second electromagnetic signal, where the first frequency of wavelength λ 1 , and the second frequency of wavelength λ 2 are close to each other so that (λ 1 ≈λ 2 ≈λ);
a processing system configured to generate a baseband output by combining a first baseband complex signal extracted from the first reflected electromagnetic signal with a second baseband complex signal extracted from the second reflected electromagnetic signal to cancel out a Doppler frequency drift therebetween to yield a periodic Doppler phase effect, where the first baseband complex signal and the second baseband complex signal are combined by complex signal demodulation as expressed by:
S
f
(
t
)
=
exp
{
j
[
4
π
x
h
1
(
t
)
λ
+
4
π
x
r
1
(
t
)
λ
+
4
π
y
(
t
)
λ
+
ϕ
1
]
}
and
S
b
(
t
)
=
exp
{
j
[
4
π
x
h
2
(
t
)
λ
+
4
π
x
r
2
(
t
)
λ
-
4
π
y
(
t
)
λ
+
ϕ
2
]
}
,
where x h1 (t) and x r1 (t) are heartbeat-induced and respiration-induced physiological movements on the first side of the body, x h2 (t) and x r2 (t) are heartbeat-induced and respiration-induced physiological movements on the second side of the body, φ 1 , φ 2 are residual phases of the first electromagnetic wave transceiver and the second electromagnetic wave transceiver, and y(t) is a body movement, where the y(t) term in the baseband output S fb (t)=S f (t)·S b (t) is cancelled out by multiplying S f (t) and S b (t), while terms of physiological movement x h1 (t), x h2 (t), x r1 (t) and x r2 (t) are enhanced as expressed by:
S
fb
(
t
)
=
exp
{
j
[
4
π
[
x
h
1
(
t
)
+
x
h
2
(
t
)
]
λ
+
4
π
[
x
r
1
(
t
)
+
x
r
2
(
t
)
]
λ
+
ϕ
1
+
ϕ
2
]
}
,
and display a vital sign of the body extracted from the baseband output.
12. The system of claim 11 , wherein the processing system is further configured to extract at least one of respiration rate and heart rate from the periodic Doppler phase effect.
13. The system of claim 12 , further comprising:
a display that displays the at least one of the respiration rate and the heart rate extracted from the periodic Doppler phase effect.
14. The system of claim 11 , wherein a DC offset in at least one of the first baseband complex signal and the second baseband complex signal is not calibrated out.
15. The system of claim 11 , wherein the first electromagnetic wave transceiver and the second electromagnetic wave transceiver are anyone of:
5.8 GHz quadrature radar transceivers; and
24 GHz quadrature radar transceivers.
16. A system for cancelling body movement effect for non-contact vital sign detection, comprising:
a first electromagnetic wave transceiver configured to send a first electromagnetic signal with a first frequency to a first side of a body and receive a first reflected electromagnetic signal reflected back in response to the first electromagnetic wave signal;
a second electromagnetic wave transceiver configured to send a second electromagnetic signal with a second frequency to a second side of the body, where the first frequency and the second frequency are different frequencies, and receive a second reflected electromagnetic signal reflected back in response to the second electromagnetic signal, where the first frequency of wavelength λ 1 , and the second frequency of wavelength λ 2 are close to each other so that (λ 1 ≈λ 2 ≈λ);
a processing system configured to generate a baseband output by combining a first baseband complex signal extracted from the first reflected electromagnetic signal with a second baseband complex signal extracted from the second reflected electromagnetic signal to cancel out a Doppler frequency drift therebetween to yield a periodic Doppler phase effect, where the first baseband complex signal and the second baseband complex signal are combined by arctangent demodulation as expressed by:
S
f
(
t
)
=
exp
{
j
[
4
π
x
h
1
(
t
)
λ
+
4
π
x
r
1
(
t
)
λ
+
4
π
y
(
t
)
λ
+
ϕ
1
]
}
and
S
b
(
t
)
=
exp
{
j
[
4
π
x
h
2
(
t
)
λ
+
4
π
x
r
2
(
t
)
λ
-
4
π
y
(
t
)
λ
+
ϕ
2
]
}
,
where x h1 (t) and x r1 (t) are heartbeat-induced and respiration-induced physiological movements on the first side of the body, x h2 (t) and x r2 (t) are heartbeat-induced and respiration-induced physiological movements on the second side of the body, φ 1 , φ 2 are residual phases of the first electromagnetic wave transceiver and the second electromagnetic wave transceiver, and y(t) is a body movement, where the y(t) term in the baseband output S fb (t)=S f (t)·S b (t) is cancelled out by multiplying S f (t) and S b (t), while terms of physiological movement x h1 (t), x h2 (t), x r1 (t) and x r2 (t) are enhanced as expressed by:
S
fb
(
t
)
=
exp
{
j
[
4
π
[
x
h
1
(
t
)
+
x
h
2
(
t
)
]
λ
+
4
π
[
x
r
1
(
t
)
+
x
r
2
(
t
)
]
λ
+
ϕ
1
+
ϕ
2
]
}
,
and display a vital sign of the body extracted from the baseband output.
17. The system of claim 16 , wherein a DC offset in the first baseband complex signal and the second baseband complex signal is calibrated out.
18. The system of claim 16 , wherein the first electromagnetic wave transceiver and the second electromagnetic wave transceiver are anyone of:
5.8 GHz quadrature radar transceivers; and
24 GHz quadrature radar transceivers.
19. The system of claim 16 , wherein the processing system is further configured to extract at least one of respiration rate and heart rate from the periodic Doppler phase effect.
20. The system of claim 19 , further comprising:
a display that displays the at least one of the respiration rate and the heart rate extracted from the periodic Doppler phase effect.