Implementation of wide range soil moisture profile probe by coplanar plate capacitor on film substrate

In this paper, we present a suitable electrode design for capacitive sensor for low-cost soil moisture profile probes. The probe can be implemented in quite low cost because it only requires single-side conductive patterns on PET film. Although inter-digital capacitor (IDC) is commonly used for coplanar capacitive sensor since it can sense wider area with sufficient accuracy, particularly for profile probe, narrower sensing area is preferred in order to observe capacitance on each depth. Coplanar plate capacitor (CPC) can focus on soil moisture on each profile level thanks to its single gap design so we conclude the CPC should be suitable for profile probes. We confirmed that CPC has almost identical or even better performance compared to IDC. In addition to that, CPC has an advantage that it has less sensitivity degradation with thick protective coating than IDC.