Highly Sensitive Differential Microwave Sensor for Soil Moisture Measurement

TL;DR

This paper introduces a highly sensitive differential microwave soil moisture sensor utilizing dual resonators, demonstrating significant frequency shifts correlating with soil moisture levels, suitable for precision agriculture applications.

Contribution

The paper presents a novel differential microwave sensor with dual resonators for precise soil moisture measurement, validated through prototype experiments and circuit analysis.

Findings

Frequency shift of 110 MHz for 1% soil moisture change

Resonance frequency varies from 4 to 2.38 GHz with moisture levels

Sensor effectively detects soil moisture for precision agriculture

Abstract

This paper presents a highly sensitive differential soil moisture sensor (DSMS) using a microstrip line loaded with triangular two turn resonator(T2 SR) and complementary of the rectangular two turn spiral resonator(CR2 SR),simultaneously.Volumetric Water Content (VWC) or permittivity sensing is conducted by loading the T2 SR side with dielectric samples.Two transmission notches are observed for identical loads relating to T2 SR and CR2 SR.The CR2 SR notch at 4.39 GHz is used as a reference for differential permittivity measurement method.Further, the resonance frequency of T2 SR is measured relative to the reference value. Based on this frequency difference,the permittivity of soil is calculated which is related to the soil VWC.Triangular two turn resonator (T2 SR) resonance frequency changes from 4 to 2.38 GHz when VWC varies 0 percent to 30 percent.The sensor's operation principle is described through circuit model analysis and simulations.To validate the differential sensing concept, prototype of the designed 3 cell DSMS is fabricated and measured.The proposed sensor exhibits frequency shift of 110 MHz for 1 percent change at the highest soil moisture content (30 percent) for sandy type soil.This work proves the differential microwave sensing concept for precision agriculture.