The very low cost and compliant touch sensor is made out of a polyurethane sponge dip-coated in a suspension of graphene nano-flakes, then sandwiched between thin film electrodes deposited on a protective PEN film.
As the conductive graphene sponge is squeezed, the piezo-resistive sensor yields a progressive change in conductance (the graphene flakes getting closer). The 15x15x15mm sensor was able to reliably distinguish vertical pressures as low as a few Pa (from placing a 0.11g mass on top) to 20kPa (similar to human pressure perception from 100 to 100 000 Pa). The flexible sensor was also tested in frequency, exhibiting over 20 dB of signal to noise ratio up to a frequency of 50 Hz. Although the signals gradually decreased with increasing frequency, due to the time lag resulting from elastic deformation and restoration of the sponge, SNR did not drop below 10 dB at up to 500Hz, again corresponding roughly to human sensitivity to vibrations (up to about 400Hz) for texture information.