For reference, the wavelength of an 8 KiHz electromagnetic wave (the Nyquist frequency at their sampling rate) is over 36 km. (Edit: at the speed of light in vacuum, that is.)

Perhaps I'm misunderstanding something, but this would seem to limit the spatial resolution that could be achieved by sampling a single stream of passive voltages at that rate, and I would expect differences between materials to mostly be on the microscale. But they don't say what other constraints might be in effect or what the materials or environment are, either, so…