bio-radar performance evaluation for different antenna design

Bio-Radar Performance

Evaluation for Different

Antenna Design11th Congress of the Portuguese Committee of URSI "New technologies

for mobility", November 24, 2017

Authors: Carolina Gouveia

Daniel Malafaia

José Vieira

Pedro Pinho

Motivation

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Bio-Radar Performance Evaluation for Different Antenna Design

Bio-radar system can measure vital signals accurately byusing the Doppler effect principle that relates the receivedsignal properties with the distance change between the radarantennas and the person’s chest-wall.

Applications Bedridden patients monitoring;

Sleeping monitoring;

Rescuing people from collapsed buildings.

In this work we show the importance of the antenna directivity pattern on the radar performance.

Bio-radar mathematical model

3

d(t)

d0

RF Front End

IQ Modulation

s(t)x(t)

DSP Module

Recovered Signal

RF Front End

IQ Demodulation

fo=10kHz

c(t)fc=5.8GHz

d1

r1(t)

r0(t)

x(t) is the transmitted signal

r0(t) is the desired signal with breathing rate information

r1(t) undesired reflections from the environment


Bio-radar mathematical model

The phase variation due to thetarget’s motion, is representedin the polar plot by an arc;

In real scenarios: IQ imbalance;

DC offsets (due to r1(t)).

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Influence of the carrier’s wavelength for the same motion amplitude

ro(t)

r1(t)


fc=5,8GHz fc=2,5GHz fc=10GHz

Breathing Signal’s Extraction Algorithm

5

D

LPFr(t) RF Front End

s*(t)

g(t)

gI(t)

gQ(t)

fo=10kHz

ArctangentDemodulation

Gram-Schmidt Method

y(t)Circle Fitting

ϕ(t)

Mean(ϕ(t))

gI,O(t)

gQ,O(t)

gI(t)gQ(t)

DSP Module

Recovered Signal

y(t)IQ

Demodulation


ImplementationSet-up characterization

6

Bio-Radar

Tx

Rx

d0ar

Bio-Radar Set-up Chest-Wall Simulator


7

ImplementationAntennas characterizationand conducted experiment

Antenna 1

Antenna 2

Simulated

Radiation Pattern Antenna 2

Measured

Radiation Pattern Antenna 1

Simulated


As this antenna has a radiation pattern with more directivity, the

contribution to r1(t) is reduced.

Results Discussion

do = 50 cm do = 70 cm

Antenna 1 – 5,8 GHz 0,0115 0,0044

Antenna 2 – 2,5 GHz 0,2330 0,2521

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DC values for each experimental test

Target’s motion extraction at a distance of d0 = 50 cm for: (a) Antenna 1, (b) Antenna 2

(a) (b)


Higher SNR

ro(t)

r1(t)

Conclusion

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Mathematical model of the bio-radar system was introduced;

A DSP algorithm implemented to extract the respiratory signalwas proposed;

The impact of the antennas design and its carrier frequency arestudied;

Experimental test using a chest-wall simulator have demonstratedthat directive antennas acquire better signals with small DC;

Although, narrow beam imply better alignment between the antennaand the patient.

As future work beamforming techniques can be applied with atracking algorithm to maintain the alignment.


Thank you!


bio-radar performance evaluation for different antenna design

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