Microwave Doppler Radar Sensor for
Detection of Human Vital Signs and
Mechanical Vibrations
Prof. Jenshan Lin
University of Florida
Gainesville, FL
http://www.lin.ece.ufl.edu/
Video
2
A Simple Theory
How does it work? Doppler Effect.
x(t)  sin(t)
x(t)  v0t
T (t )
R(t )
d0
x(t )
Constant Velocity
 Frequency Shift
Periodic Chest Wall Movement
 Phase Shift
T (t)  cos 2 ft  (t)
4 d0 4 x(t)
2d0 

R(t)  cos 2 ft 

 (t 
)


c 

3
A Simple Theory
•
Use transmitted signal as reference to mix with received signal by
using a mixer or multiplier (similar to direct down-conversion), the
output baseband signal contains the vital sign signal in its phase.
T (t)  cos 2 ft  (t)
4 d0 4 x(t)
2d0 

R(t)  cos 2 ft 

 (t 
)


c 

T(t) x R(t)  Baseband Signal B(t):
 4 d0 4 x(t)

B(t)  cos 

 0   

 

4 d0
 Antenna-to-target round-trip delay 4 x(t)  Phase modulation due to
chest-wall movement


0  Phase delay in receiver circuit
  (t)  (t 
2d0
)
c
4
Small Angle Approximation (Linear)
 4x(t ) 4d 0

B (t )  cos 

  0   

 

90, 270 , …
When
small
negligible
If x(t) <<  and [(4d0)/+0] = 90°, 270°, …
 4x(t )  4x(t )
B (t )  sin 






This is what we want!
It is similar to measuring very small phase noise using FM discriminator
technique.
5
Range Correlation Effect
• If the distance between radar sensor and target is small
enough, close-in phase noise of R(t) and T(t) are
correlated.
Close-in phase noise correlated
T (t)  cos 2 ft  (t)
4 d0 4 x(t)
2d 

R(t)  cos 2 ft 

 (t  0 )


c 

 4 d0 4 x(t)

B(t)  cos 

 0   

 

~ 0 @ short-range
A. D. Droitcour, O. Boric-Lubecke, V. Lubecke, J. Lin, G. Kovacs, “Range Correlation and I/Q
performance benefits in single chip silicon Doppler radars for non-contact cardiopulmonary signs
sensing,” IEEE Trans. Microwave Theory Tech., Vol. 52, No. 3, pp. 838-848, March 2004
6
Early Research Effort
Rabbit
Human
•
J. C. Lin, "Noninvasive Microwave Measurement of Respiration,"
Proceedings of the IEEE, vol. 63, no. 10, p. 1530, Oct. 1975.
7
Early Research Effort
10 GHz
•
•
K.-M. Chen and H.-R. Chuang, “Measurement of Heart and
Breathing Signals of Human Subjects Through Barriers with
Microwave Life-Detection Systems,” IEEE EMBC 1988.
– 10GHz: 1.5 ft of dry bricks
– 2GHz: 3 ft of dry bricks
H.-R. Chuang, Y.-F. Chen, and K.-M. Chen, “Automatic ClutterCanceler for Microwave Life-Detection System,” IEEE Trans.
Instrumentation and Measurement, Vol. 40, No. 4, August 1991.
8
First Non-Contact Vital Sign Sensor Chip
•
•
•
•
0.25 µm BiCMOS
1.6 GHz transmission
frequency
3.75mmx3.75mm
Output power = 6.5dBm
Baseband out
Balun
RF in
(from Rx antenna)
RF out
(to Tx antenna)
Balun
RF Out to
Tx Antenna
Buffer
Free-running VCO. No PLL.
VCO
Mixer
Balun
LO
Buffer
VCO
Mixer
Test Structures
Baseband +
Buffer
Baseband -
Mixer
RF In from
Rx Antenna
VCO
RF
Buffer
LO Buffer
RF Buffer
A. D. Droitcour, O. Boric-Lubecke, V. Lubecke, J. Lin, “0.25m CMOS and BiCMOS Single Chip
Direct Conversion Doppler Radars for Remote Sensing of Vital Signs,” IEEE International Solid
State Circuits Conference Digest of Technical Papers, pp. 348-349, 2002.
9
Ka-band Bench-Top System
Baseband
LabVIEW
DAQ
Ka radar
Antenna
Subject
under test
10
User Interface
Labview – data acquisition and signal processing
11
Typical Test Result
Time-Domain Signal
Detected Signal (V)
3
2
1
0
-1
-2
-3
0
5
10
15
Time (Sec)
20
25
Calculated Heart Rate
Beats/Min
95
90
2 % Higher than
Reference
85
80
0
Detected heart beat
Reference heart beat
2 % Lower than
Reference
5
10
15
Time (Sec)
20
25
12
Overnight Measurement
Beats/Min
Measured from Back
80
Reference (Fingertip sensor)
60
100
Results of Ka - band radar
60
40
40
20
20
Breaths/Min
Beats/Min
80
Carrier freq: 27.1 GHz
Duration:
6 hours
Accuracy: 92.96%
(Accuracy defined as within 2% of reference)
0
0
1
2
3
4
Time (Hour)
5
0
6
C. Li, J. Lin, Y. Xiao, "Robust Overnight Monitoring of Human Vital Signs by a Non-contact
Respiration and Heartbeat Detector," Proceedings of the 28th IEEE Engineering in Medicine
and Biology Society Annual International Conference, pp. 2235-2238, September 2006
13
Nonlinear Doppler Phase Modulation
Small angle approximation
B(t )  cos(

4 xh (t )

4 xh (t )



4 xr (t )

4 xr (t )

 )
when  = 90 and
xh(t), xr(t) << 
However, at mm-wave, the respiration movement is
no longer very small.
xr(t) << 
14
Nonlinear Doppler Phase Modulation
Periodic body movements due to heartbeat and respiration
xh(t) = mh·sinωht, xr(t) = mr·sinωrt
B(t )  cos(



4 xh (t )


 Jl (
k  l 
k=0
l=0

4 xr (t )

4 mh

)J k (
k=1
l=0
 )
4 mr

)cos(kr t  lht   )
k=2
k=0
l=0 k=-1
k=3 l=1
l=1 l=0
k=1
l=1
f
0
R1
R2 C1a R3
H1
C1b
C. Li, Y. Xiao, J. Lin, "Experiment and Spectral Analysis of a Low-Power Ka-Band Heartbeat Detector
Measuring from Four Sides of a Human Body," IEEE Transactions on Microwave Theory and
Techniques, IMS2006 Special Issue, Vol. 54, No. 12, pp. 4464-4471, December 2006.
15
Accurate Measurement of Periodic Motion
• Determining factors for harmonics due to phase
modulation
– Wavelength, or carrier frequency
– Residual phase
– Amplitude of periodic movement
H1 : H 2 : H 3 : H 4 | J1 (
4 m
) cos  |:| J 2 (
4 m
)sin  |:


4 m
4 m
| J3 (
) cos  |:| J 4 (
)sin  | .


H1 H2 H3 H4
The amplitude of movement can be accurately determined
from the ratio of harmonics!
C. Li, J. Lin, "Non-Contact Measurement of Periodic Movements by a 22-40GHz Radar Sensor Using
Nonlinear Phase Modulation," IEEE MTT-S International Microwave Symposium Digest, pp. 579-582,
June 2007
16
Measurement Example
1
5
0.5
4
0
-0.5
0
5
10
Time (Second)
15
1
Harmonic Ratio
Normalized Spectrum
Baseband Signal (V)
• Movement period T = 3 sec
amplitude = 2 mm
• fRF: 40 GHz,
• Transmission power: 50 µW
• Distance: 1.65m
H3/H1 ratio
H4/H2 ratio
2.056 mm
3
Meaured H3/H1
2
2.045 mm
1
0.5
Meaured H4/H2
0
0
0
1
1/3
2/3
1
4/3
Frequency (Hz)
5/3
2
(a) Baseband signal, spectrum
1.5
2
2.5
Displacement (mm)
3
(b) Displacement extraction,
self-verification
17
Random Body Movement Cancellation – Concept
Heart
90
0
0
Body
I f Qf
90
Qb I b
DAQ
Demodulation
DAQ
• Physiological movements on both sides of the body
move in the same direction relative to their
respective detecting radar
• Random body drift move in the opposite direction
relative to their respective detecting radar
18
Random Body Movement Cancellation – Theory
  4 xh1 (t ) 4 xr1 (t ) 4 y (t )

S
(
t
)

exp
j




 
Front: f
1 




 
  4 xh 2 (t ) 4 xr 2 (t ) 4 y(t )



 2  
Back: Sb (t )  exp  j 



  
xh1, xh2, xr1, xr2: physiological movements
xh1
xh 2
xr1
xr 2
y
y(t): random body movement
Combine signals from both sides:
  4  xh1 (t )  xh 2 (t ) 4  xr1 (t )  xr 2 (t ) 

S fb (t )  S f (t )  Sb (t )  exp  j 

 1  2  



 
y(t) (random body movement) disappeared!
19
Random Body Movement Cancellation – Experiment
Heart
Res
90
0
Res
0
Body
I f Qf
Qb
DAQ
Demodulation
90
Ib
DAQ
Isolation between two radars: antenna polarizations & slight frequency
offset between TX and RX
20
Random Body Movement Cancellation – Result
1
0
-0.5
0.5
I Channel
Q Channel
2
4
6
8
Time (Second)
Back
(b)
10
-0.5
-1
0
2
4
6
8
Time (Second)
10
12
(a)
Front
Back
0.5
0
0
12
I Channel
Q Channel
0
Spectrum
Front
0.5
-1
0
Amplitude
(a)
Combined Spectrum
Amplitude
1
1
20
40
60
Beats/Min
80
100
120
(b)
Recovered heartbeat
0.5
0
0
20
40
60
Beats/Min
80
100
C. Li, J. Lin, “Random Body Movement Cancellation in Doppler Radar Vital Sign
Detection,” IEEE Transactions on Microwave Theory and Techniques, vol. 56,
issue 12, pp. 3143-3152, December 2008.
120
21
Portable Module
Can be attached to laptop and powered through USB cable or
powered by battery.
22
Search and Rescue Robot
23
Software Configurable Radar Sensor Chip
LO I + LO I 
5.8 GHz Radar Receiver
LNA
Mixer
VGA
I
MixerI
PreAmp
LNA
RFin
Q
VGA
Pre-Amp
RFin
Gm Boosted Bias
DAQ
Bandgap
3 Wire Control Unit
Clock Data
Constant Gm
CPLD
Iout +
I
Iout -
VGA
Q
Qout +
MixerQ
Gm-boosted
Bandgap Const-Gm
bias
3-wire control
Qout -
Load
Load Clk Data
LOQ + LOQ 
UMC 0.13 µm CMOS
1.2×1.2 mm2
C. Li, X. Yu, D. Li, L. Ran, J. Lin, "Software Configurable 5.8 GHz Radar Sensor Receiver
Chip in 0.13 μm CMOS for Non-contact Vital Sign Detection," IEEE RFIC Symposium
Digest of Papers, June 2009
24
Test Result
0
-20
0
CSD Spectrum
I/Q Signal [mV]
20
5
1
10
15
Time (Second)
Respiration
20
25
CSD Spectrum
I/Q Signal [mV]
Power: 1.5 V battery
3-wire program: Xilinx XC9536 CPLD
Antenna: 2-by-2 patch array, 9 dB gain
DAQ: NI USB-6008, 12 bit, 0-5V input
Heartbeat
0.5
0
0
20
40
60
Beats/Min
80
100
120
Detect from the back @ 0.5m away
20
0
-20
-40
0
5
1
10
15
Time (Second)
20
25
Respiration
0.5
0
0
Heartbeat
20
40
60
Beats/Min
80
100
120
Detect from the front @ 1.5m away
25
Applications
Security
Rescue
Baby Monitor
See-thru-wall
Radar
Battlefield
Triage
Telemedicine
Sleep Apnea
Veterinary
Medicine
26
Applications
•
•
•
•
•
•
Lie Detector – covert detection
Emotion Detector – vital sensor in a phone
Personal Radar  Tricorder
Sports – fitness center/gym
RF Vibrometer
Gaming/Entertainment
– quiz contests, video games
– virtual reality
27
Summary
• Prototypes have been demonstrated at different
integration levels – bench-top, modules, and IC
chips.
• Basically, the technology can be used to detect
any motion of an object reflecting radio waves
• With proper signal processing, useful and
interesting information can be extracted for
various applications.
– Biometric Radar possible
28