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AFE4300: The issue of using AFE4300 to measure impedance of human body

Lin Zhou
Prodigy 40 points
Part Number: AFE4300

Dear sir,

We design 20kHz and 100kHz excitation frequency of current to measure human body's trunk impedance. And found that  impedance in 20kHz is small than impedance in 100kHz. It is not match the theory.

Have you ever found this phenomenon? The following is the current injecting enterclose and voltage measuring enterclose

The current inject from left hand to left leg

The voltage measure from right hand to right leg

Is it possible that the input imppedance of AFE4300 is not big enough? The following picture show that input impedance is 50k. 

Is there any solution to fix this issue or increase the chip's input impedance.

Thank you!

Lin 

lin.zhou@lifesense.com

  • 0
    TI__Genius 12555 points
    Hi Lin,

    Are you calibration after you change the excitation frequency?
    Also what kind for body model you are looking at? Will it be possible for you to model the body with discrete components (R and C) and do the test?

    Regards,
    Prabin
  • 0 in reply to Prabin Yadav
    Prodigy 40 points

    Hi  Prabin,

    Yes I do calibration every time. The body model of we using are five segments impedance. As the following picture, left hand inpedance, trunk impedance, right leg impedance, left leg impedance. Each segment is paralleling by R and C.  Is there any problem with this model?

  • 0 in reply to Lin Zhou
    TI__Genius 12555 points
    Hi Lin,

    Can you replace the body with parallel R and C and do the same test for 20KHz and 100KHz excitation frequency?
    So now the expected result will be : 100KHz's value < 20KHz's value.
    If you get the expected result as mentioned above, then there is nothing wrong in the AFE side (i.e Register setting, setup, ...) and the model for the body is different from simple R||C.
    But if you do not get the expected result, then we may have debug the AFE side.

    Regards,
    PRabin