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/

2

Video

A Simple Theory

Constant Velocity

Frequency Shift

Periodic Chest Wall Movement

Phase Shift

How does it work? Doppler Effect.

( )R t

( )T t

0d( )x t

0( )x t v t ( ) sin( )x t t

T t ft t ( ) cos 2 ( )

d dx tR t ft t

c

0 04 24 ( )

( ) cos 2 ( )3

• 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.

A Simple Theory

T t ft t ( ) cos 2 ( )

d dx tR t ft t

c

0 04 24 ( )

( ) cos 2 ( )

T(t) x R(t) Baseband Signal B(t):

d x tB t

00

4 4 ( )( ) cos

0 d

t tc

02

( ) ( )Phase delay in receiver circuit

d

0

4 x t

4 ( )Antenna-to-target round-trip delay Phase modulation due to

chest-wall movement

4

Small Angle Approximation (Linear)

If x(t) << and [(4d0)/+0] = 90°, 270°, …

)(4)(4sin)(

txtxtB

This is what we want!

It is similar to measuring very small phase noise using FM discriminator

technique.

5

0

04)(4cos)(

dtxtB

90, 270 , … When

small negligible

• If the distance between radar sensor and target is small

enough, close-in phase noise of R(t) and T(t) are

correlated.

Range Correlation Effect

T t ft t ( ) cos 2 ( )

d dx tR t ft t

c

0 04 24 ( )

( ) cos 2 ( )

d x tB t

00

4 4 ( )( ) cos

Close-in phase noise correlated

~ 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

7

• J. C. Lin, "Noninvasive Microwave Measurement of Respiration," Proceedings of the IEEE, vol. 63, no. 10, p. 1530, Oct. 1975.

Rabbit

Human

Early Research Effort

8

• 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 Clutter-Canceler for Microwave Life-Detection System,” IEEE Trans. Instrumentation and Measurement, Vol. 40, No. 4, August 1991.

10 GHz

RF Out to

Tx Antenna

Baseband +

Baseband -

RF In from

Rx Antenna

Buffer LO

Buffer

VCORF

Buffer

Mixer

RF Out to

Tx Antenna

Baseband +

Baseband -

RF In from

Rx Antenna

Buffer LO

Buffer

VCORF

Buffer

Mixer

• 0.25 µm BiCMOS

• 1.6 GHz transmission frequency

• 3.75mmx3.75mm

• Output power = 6.5dBm

First Non-Contact Vital Sign Sensor Chip

9

Balun

Balun

Balun

VCO

Mixer

RF out

(to Tx antenna)

RF in

(from Rx antenna)

Baseband out

Test Structures

VCO

LO Buffer

Buffer

RF Buffer

Mixer

Test Structures

VCO

LO Buffer

Buffer

RF Buffer

Mixer

A. D. Droitcour, O. Boric-Lubecke, V. Lubecke, J. Lin, “0.25m 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.

Free-running VCO. No PLL.

Ka-band Bench-Top System

LabVIEW

Ka radar

Antenna

Subject

under test

Baseband

DAQ

10

User Interface Labview – data acquisition and signal processing

11

Typical Test Result

0 5 10 15 20 25-3

-2

-1

0

1

2

3

Time (Sec)D

ete

cte

d S

ign

al (V

)

0 5 10 15 20 2580

85

90

95

Time (Sec)

Be

ats

/Min

Detected heart beatReference heart beat2 % Higher than

Reference

2 % Lower thanReference

Time-Domain Signal

Calculated Heart Rate

12

Overnight Measurement

60

80

Be

ats

/Min

0 1 2 3 4 5 60

20

40

60

80

100

Time (Hour)

Be

ats

/Min

0 1 2 3 4 5 60

20

40

Bre

ath

s/M

in

Reference (Fingertip sensor)

Results of Ka - band radar

Duration: 6 hours

Accuracy: 92.96%

(Accuracy defined as within 2% of reference)

Carrier freq: 27.1 GHz

Measured from Back

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

when = 90 and

xh(t), xr(t) <<

xr(t) <<

However, at mm-wave, the respiration movement is

no longer very small.

4 ( ) 4 ( )( ) cos( )

4 ( ) 4 ( )

h r

h r

x t x tB t

x t x t

14

Small angle approximation

Nonlinear Doppler Phase Modulation

4 ( ) 4 ( )( ) cos( )

4 4( ) ( )cos( )

h r

h rl k r h

k l

x t x tB t

m mJ J k t l t

Periodic body movements due to heartbeat and respiration

xh(t) = mh·sinωht, xr(t) = mr·sinωrt

f

k=1

l=0k=2

l=0k=3

l=0

k=0

l=1

0

k=0

l=0

k=-1

l=1

k=1

l=1

R1 R3 H1 R2 C1a 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

1 2 3 4 1 2

3 4

4 4: : : | ( ) cos |:| ( )sin |:

4 4| ( )cos |:| ( )sin | .

m mH H H H J J

m mJ J

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

H1 H2 H3 H4

Measurement Example

0 5 10 15-0.5

0

0.5

1

Time (Second)

Ba

se

ba

nd

Sig

na

l (V

)

0 1/3 2/3 1 4/3 5/3 20

0.5

1

Frequency (Hz)

No

rma

lize

d S

pe

ctr

um

1 1.5 2 2.5 30

1

2

3

4

5

Displacement (mm)

Ha

rmo

nic

Ra

tio

H3/H1 ratioH4/H2 ratio

Meaured H3/H1

Meaured H4/H2

• Movement period T = 3 sec amplitude = 2 mm

• fRF: 40 GHz,

• Transmission power: 50 µW

• Distance: 1.65m

(a) Baseband signal, spectrum (b) Displacement extraction,

self-verification 17

2.056 mm

2.045 mm

Random Body Movement Cancellation – Concept

• 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

Heart

fI fQ

090

bIbQ

DAQ DAQDemodulation

090Body

18

Random Body Movement Cancellation – Theory

1 11

4 ( ) 4 ( ) 4 ( )( ) exp h r

f

x t x t y tS t j

2 22

4 ( ) 4 ( ) 4 ( )( ) exp h r

b

x t x t y tS t j

1 2 1 2

1 2

4 ( ) ( ) 4 ( ) ( )( ) ( ) ( ) exp h h r r

fb f b

x t x t x t x tS t S t S t j

Front:

Back:

Combine signals from both sides:

xh1, xh2, xr1, xr2: physiological movements

y(t): random body movement

1hx 2hx

1rx2rx

y

19

y(t) (random body movement) disappeared!

Random Body Movement Cancellation – Experiment

Body

ResHeart

fI fQ

090

bIbQ

DAQ DAQDemodulation

Res0

90

20 Isolation between two radars: antenna polarizations & slight frequency

offset between TX and RX

Random Body Movement Cancellation – Result

0 20 40 60 80 100 1200

0.5

1

Beats/Min

Co

mb

ine

d S

pe

ctr

um

Recovered heartbeat

(b)

0 20 40 60 80 100 1200

0.5

1

Beats/Min

Sp

ectr

um

FrontBack

(a)

0 2 4 6 8 10 12-1

-0.5

0

0.5

1

Time (Second)

Am

plit

ud

e

I ChannelQ Channel

(a)

0 2 4 6 8 10 12-1

-0.5

0

0.5

Time (Second)

Am

plit

ud

e

I ChannelQ Channel

(b)

Front

Back

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. 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

inRF

outI +

outI -

outQ +

outQ -

Load Clk DataQ

LO +Q

LO

ILO +

ILO

LNAPre-Amp

MixerI

MixerQ

VGA

I

VGA

Q

Gm-boosted

biasBandgap Const-Gm

3-wire control

Gm Boosted Bias

Bandgap Constant Gm

LNA PreAmp

Mixer VGA

3 Wire Control Unit

RFin

Clock Data Load

Q

I

DAQ CPLD

5.8 GHz Radar Receiver

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

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

0 5 10 15 20 25

-20

0

20

Time (Second)

I/Q

Sig

na

l [m

V]

0 20 40 60 80 100 1200

0.5

1

Beats/Min

CS

D S

pe

ctr

um

Respiration Heartbeat

0 5 10 15 20 25-40

-20

0

20

Time (Second)

I/Q

Sig

na

l [m

V]

0 20 40 60 80 100 1200

0.5

1

Beats/Min

CS

D S

pe

ctr

um

Respiration

Heartbeat

Detect from the back @ 0.5m away Detect from the front @ 1.5m away 25

Applications

Telemedicine

Rescue Security Sleep Apnea Baby Monitor

Veterinary

Medicine Battlefield

Triage

See-thru-wall

Radar

26

• 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

Applications

27

• 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

Summary

28