  A new pressure sensor array, positioned on the bottom plate of a standard
torsional rheometer is presented. It is built from a unique piezo-capacitive
polymeric foam, and consists of twenty-five capacitive pressure sensors (of
surface 4.5$\times$4.5 mm$^2$ each) built together in a 5$\times$5 regular
array. The sensor array is used to obtain a local mapping of the normal
stresses in complex fluids, which dramatically extends the capability of the
rheometer. We demonstrate this with three examples. First, the pressure profile
is reconstructed in a polymer solution, which enable the simultaneous
measurement of the first and the second normal stress differences $N_1$ and
$N_2$, with a precision of 2 Pa. In a second part, we show that negative normal
stresses can also be detected. Finally, we focus on the normal stress
fluctuations that extend both spatially and temporally ina shear-thickening
suspension of cornstarch particles. We evidence the presence of local a unique
heterogeneity rotating very regularly. In addition to their low-cost and high
versatility, the sensors show here their potential to finely characterize the
normal stresses in viscosimetric flows.
