bio-radar performance evaluation for different antenna design
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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
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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.
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Bio-radar mathematical model
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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 Performance Evaluation for Different Antenna Design
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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)
Bio-Radar Performance Evaluation for Different Antenna Design
fc=5,8GHz fc=2,5GHz fc=10GHz
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Breathing Signal’s Extraction Algorithm
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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
Bio-Radar Performance Evaluation for Different Antenna Design
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ImplementationSet-up characterization
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Bio-Radar
Tx
Rx
d0ar
Bio-Radar Set-up Chest-Wall Simulator
Bio-Radar Performance Evaluation for Different Antenna Design
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ImplementationAntennas characterizationand conducted experiment
Antenna 1
Antenna 2
Simulated
Radiation Pattern Antenna 2
Measured
Radiation Pattern Antenna 1
Simulated
Bio-Radar Performance Evaluation for Different Antenna Design
As this antenna has a radiation pattern with more directivity, the
contribution to r1(t) is reduced.
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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)
Bio-Radar Performance Evaluation for Different Antenna Design
Higher SNR
ro(t)
r1(t)
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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.
Bio-Radar Performance Evaluation for Different Antenna Design
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Thank you!
Bio-Radar Performance Evaluation for Different Antenna Design