AWR6843AOPEVM: The reflection electromagnetic wave against materials: Plastic, Paper, Cloth, Metal, and Human body.

Wayne Tsao

Part Number: AWR6843AOPEVM

Tool/software:

Hello TI experts,

While testing the vital sign lab, we found vibrating nonhuman object, such as plastic bag, paper, or a cloth glove, make Vital Sign.

Following videos are experiment making plastic/paper/cloth vibrating by a handheld fan, we can see vital sign is detected in TI mmWave industrial Visualizer

Video 1: plastic bag

Video 2: cloth glove

I tried to explain the phenomenon, according to TI Radome Design document page 4: Electromagnetic wave reflection of an object is related to its dielectric constant(ε_r) . The more dielectric constant(ε_r) close to 1, the less reflection.

Base on the reflection coefficient formula below:

PE(ε_r=2), Γ=-0.17. means 17% electric filed is reflected
Cotton (ε_r=1.6), Γ=-0.117, means 11.7% electric filed is reflected.
Paper (ε_r=1.4), Γ=-0.083, means 8.3% electric filed is reflected.
Metal (ε_r=∞), Γ=-1, means 100% electric filed is reflected.

So for paper, the 8.3% reflection electric field reflection is sufficient for mmWave Radar to detect, then it makes the vital Sign in TI mmWave industrial Visualizer.

Is my above understanding correct?

over 1 year ago

0 Kristien Everett over 1 year ago

TI__Genius 13156 points

Hey Wayne,

Thank you for reaching out to us regarding your question. As far as I'm aware, we have not looked into this phenomenon before, but I can check with other engineers to confirm whether this is something we've observed or researched.

Regards,

Kristien

0 Abhishek Karkisaval over 1 year ago in reply to Kristien Everett

TI__Genius 11750 points

Vital signs demo works on the principle that, it first tracks the person and then locates the centroid of the tracked person and computes the chest displacement

In this case, as you have different objects with motion, that object is tracked and the the heart beat(0.8 to 2Hz) and breathing rate(0.1-0.5Hz) frequency are extracted from the tracked object. So, it is possible that any moving object will have some of the frequency in this range. Demo does not have the intelligence to distinguish between a Human and non living object

Regards

0 Wayne Tsao over 1 year ago in reply to Abhishek Karkisaval

Prodigy 50 points

Hello Abhishek and Kristien,

Many thanks for your guidance.

I have a further question: why only 8.3% reflection of electric filed caused by paper will make the same Vital Sign as metal while it is 100% reflection?

Regards

Wayne

+1 Abhishek Karkisaval over 1 year ago in reply to Wayne Tsao

TI__Genius 11750 points

Hi Wayne

Reflection will determine the received signal strength. It does not have any dependency on the frequency of vibration of that object in the HR and BR frequency range

Regards

0 Wayne Tsao over 1 year ago in reply to Abhishek Karkisaval

Prodigy 50 points

Many thanks for your guidance.

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AWR6843AOPEVM: The reflection electromagnetic wave against materials: Plastic, Paper, Cloth, Metal, and Human body.