Application of a Monopole Antenna Probe with an Optimized Flange Diameter for Tdr Soil Moisture Measurement.

Jacek Majcher,Wojciech Skierucha,Andrzej Wilczek,Justyna Szerement,Marcin Kafarski,Arkadiusz Lewandowski,Aleksandra Woszczyk,Agnieszka Szypłowska

doi:10.3390/s20082374

Abstract

Soil volumetric water content (θ) is a parameter describing one of the most important factors conditioning proper plant growth. Monitoring soil moisture is of particular importance in the rational use of water resources for irrigation, especially during periods of water scarcity. This paper presents a method of measuring soil moisture in the vicinity of the plant root system by means of a probe designed to be mounted on a mobile device used for precise plant irrigation. Due to the specific field conditions of the measurement, the design of the probe was proposed as a monopole antenna. Electromagnetic simulations of the probe were carried out with Ansys HFSS software to optimise its dimensions. Then a prototype of the probe was manufactured to conduct laboratory measurements with the use of a vector network analyser (VNA) working in the 20 kHz to 8 GHz frequency range. The VNA analyser was configured to work in the time-domain reflectometry (TDR) mode. From measurements of the time distance between reflections from the probe’s elements it is possible to calculate the bulk dielectric permittivity of the soil surrounding the probe. Next, based on commonly used soil moisture dielectric calibrations one can determine θ of the soil sample. The paper presents simulation results and laboratory tests of an antenna probe. Due to its tough and durable design, this type of probe gives the possibility of easy application in field conditions, which makes it especially suitable for mechanically demanding measurement systems. As the sensitivity zone is comparatively large, this probe is well-suited to measuring soil moisture in the vicinity of the plant root system.

Highlights

Water content in soil determines the biological and mechanical properties of soil [1] and has a decisive influence on plant development [2,3]
When a thetruncated probe has with no flange, significant part the60, electromagnetic is close to 160 the probe simulated for the probe flangeashape diameters of d =of
This may result in a significant reduction in the amplitude of the impulse reflected from the end of the rod and hinder the correct interpretation of the reflectogram

Summary

Introduction

Water content in soil determines the biological and mechanical properties of soil [1] and has a decisive influence on plant development [2,3]. For plants to develop properly, constant access to water should be provided. Water demand strictly depends on the phase of plant development [4]. In order to correlate the above parameters, it is necessary to monitor plantations for water content in soil. The obtained results are necessary to decide on the moment of plant watering and the amount of water needed in this procedure.

Objectives

Methods

Results

Conclusion