Frequency of Impedance Measurement using Cyton Board

abummu1abummu1 Malaysia
edited March 20 in Cyton

@wjcroft and @retiutut
Hi, Thank you so much for previous response. I was to use the board excellently. The attached screenshot was the ECG I collected using dry capacitive bioelectrodes (in non-contact mode). The dielectric material I used was polymer about 0.14mm thick. Please may I know at what frequency does the board measure skin impedance? I mean the pre-set frequency. Also, where can I find addition details about the board?
This will help in analysis while I write my thesis.
Thank you

Comments

  • wjcroftwjcroft Mount Shasta, CA

    Abummu, hi.

    There are many previous threads discussing Cyton ADS1299 impedance measurement. Such as this list using the "Google Advanced Search" button in the upper right column:

    https://www.google.com/search?as_q=impedance+ADS1299&as_sitesearch=openbci.com

    The injected frequency is at 31 Hz. Further details of the ADS1299 are in the TI data sheet:

    https://www.ti.com/product/ADS1299


    It's interesting you mention "the ECG I collected using dry capacitive bioelectrodes (in non-contact mode)." Do you have any further references? It sounds like these are your own construction. I do note a couple things about your ECG signal: the amplitude seems quite low 118 uV RMS. I guess this is explained by the non-contact coupling. And the signal also appears completely 'centered' as far as polarity. Also explained by the AC coupling from the non-contact.

    Regards, William

  • abummu1abummu1 Malaysia

    Hi @wjcroft
    Thanks for the response. My goal is to test the polymer dielectric I fabricated and observe its performance in capacitive ECG recording. Though, I also collected ECG using the AgCl (Ambu White Sensors), Silver Coin, and Flexible PCB. I tested the last 2 under different skin conditions (dry skin and sweating). In capacitive biopotential technique, the dielectric material strongly influences the quality of ECG wave. Like I said earlier, I am only performing a test to prove that capacitive ECG sensing is possible with the polymer dielectric I fabricated. The amplitude of the ECG will be affected due to limitation of the Cyton board and dielectric polymer. ..Meanwhile, I fabricated the bioelectrodes in various sizes. ..the performance was not the same in all.

  • wjcroftwjcroft Mount Shasta, CA

    Abummu, thanks.

    Do note that the ADS1299 impedance testing circuitry will likely give results that are difficult to interpret, when using your capacitive electrodes. Normally the impedance test is done with electrodes that have direct skin contact. Your measured values are likely to be larger (possibly much larger) than what is normally measured with Ag-AgCl gel ECG electrodes.

    Regards, William

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