The present work describes new results using a contact free impedance device, which permits to reach a best understanding of the free contact transduction. Measurements were carried out through a polyethylene terephthalate (PET) microchannel photoablated. Impedance measurement of empty microchannel at different PET thickness separating the two electrodes demonstrate that the recorded impedance is not changed whatever the PET thickness. The result shows that the polyethylene (PE) film lamination has an effect on the impedance measurement in empty microchannel. Then impedances diagrams in the filled microchannel were plotted by subtracting impedance contribution in empty microchannel from the global microdevice response. The Nyquist diagram of filled microchannel exhibits a loop diameter from high to medium frequencies, and a capacitive behavior at low frequencies. The loop diameter obtained is inversely proportional to the microchannel conductivity. Modeling impedance of microsystem highlighted the effect of microchannel rough surface phenomena.