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IWR1443BOOST: Penetration of mmWave?

Wonjin Eom
Prodigy 140 points
Part Number: IWR1443BOOST

Hi all! 

I'm Wonjineom.

I want to use mmWave Radar for our machine vision system and I have a question.

I know that the FMCW signal can penetrate all materials except metal, then how can the sensor recognize some material?

I guess that some of the wave is reflected and other penetrate the material. Is it right? 

I already saw the post below

https://e2e.ti.com/support/sensor/mmwave_sensors/f/1023/t/624607?tisearch=e2e-sitesearch                

But I can not be sure about this issue.

Thank you.

  • 0
    TI__Mastermind 28247 points

    Hi Wonjineom,

    Millimeter waves do not penetrate metal nor polar molecules like water. The reflectivity of a medium is a function of its relative permittivity Er. When the wave goes through an interface between 2 media of different relative permittivity Er1 and Er2, the reflectivity you get is the following:

    R = ((sqrt(Er1) - sqrt(Er2)) / (sqrt(Er1) + sqrt(Er2)))^2

    The higher the Er difference, the higher R is. For example, considering an oil-to-water interface with Er1 = 3 and Er2 = 80, you get R = 0.45, so 45% of the energy that had penetrated the oil will be reflected by water. Or an air-to-gasoline interface with Er1 = 1 and Er2 = 2 translates to R = 0.03. That is, 3% of the energy coming from the antenna through the air will be reflected by the gasoline.

    If your application is dealing with a limited set of materials that have very different relative permittivity, like air, oil and water, you could perform some limited material recognition.


    Thanks,
    François.