High-Sensitivity and Compact Time Domain Soil Moisture Sensor Using Dispersive Phase Shifter for Complex Permittivity Measurement

This article presents a time domain transmissometry soil moisture sensor (TDT-SMS) using dispersive phase shifter (DPS), consisting of an interdigital capacitor that is loaded with stacked four-turn complementary spiral resonator (S4-CSR). Soil measurement technique the proposed based on complex permittivity sensing property DPS in domain. relative which varies its content measured by burying under mass and changing difference while excited 114-MHz sine wave (single tone). output magnitude are compared reference signal phase/loss detector. The exhibits accuracy better than ±1.2% at highest volumetric water (VWC = 30%) for sandy-type soil. Precise design guide developed simulations performed to achieve highly sensitive sensor. results validate theoretical analysis procedure. Owning advantages low profile, power consumption, high sensitivity makes TDT-SMS good candidate precision farming internet things (IoT) systems.