Negative voltage for fwd.solve_eit

[ccfbeltran]

Hi I have a question. when doing this function when transforming from mesh to voltage f1 = fwd.solve_eit(ex_mat, step=step, perm=mesh_obj["perm"]) I received some negative voltage on the 208 array(f1.v).

I don't understand why I am receiving negative data. Using conventional data acquisition on a human, I don't receive any negative voltage. So I'm trying to have the same results from the algorithm.

Thanks for the help :)

[liubenyuan]

The boundary measurement are complex-valued voltage differences on adjacent electrodes, So there might be negative measurements if you are using opposition excitation configurations. In real life applications, adjacent stimulation is often used. And also, the boundary measurements are usually taking an abs value for matching the physical meaning of impedance.

[ccfbeltran]

when you are saying opposition excitation configurations, are you talking about this kind of measurement?

if so, what I'm looking for is to do adjacent excitation so this way:

is there a way to simulate that for the fwd.solve_eit?

thanks for your help is really appreciated!

[liubenyuan]

sure, newer version of pyeit use a PyEIT.Protocol dataclass to specify the stimulation pattern. You can use protocol_obj = protocol.create(16, dist_exc=1, step_meas=1, parser_meas="fmmu") for the below illustration figure.

[ccfbeltran]

thanks!