Frequency Domain Probe Design for High Frequency Sensing of Soil Moisture

Pelletier, Mathew G.; Schwartz, Robert C.; Holt, Greg A.; Wanjura, John D.; Green, Timothy R.

doi:10.3390/agriculture6040060

Cited by 13 publications

(8 citation statements)

References 14 publications

(18 reference statements)

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“…However, when making use of a time-domain reflectometry (TDR) probe instead of a waveguide, the measurements in the transmission mode are necessarily given up. Incidentally, a modified TDR device has been proposed, which works in both reflection and transmission modes (Pelletier et al 2016), but its use requires the transport of the material to be investigated. The approach proposed hereafter has something in common with the Nicolson-Ross-Weir algorithm as it is based on a single-mode guided propagation of the waves, which introduces a strong constraint on the behaviour of the field and on its direction of propagation (Ghodgaonkar, Varadan and Varadan 1990).…”

Section: Measurement Of Dielectric and Magnetic Properties Of Materiamentioning

confidence: 99%

“…Yet, we will keep on using the term TDR because it is widespread in literature and it identifies more immediately the kind of device we are thinking about. In particular, the term TDR has been used in previous works (Mattei et al 2005;Cataldo et al 2007;Pelletier et al 2016) even though such works focus on analyses in the frequency domain or in both time and frequency domains.…”

Section: Measurement Of Dielectric and Magnetic Properties Of Materiamentioning

confidence: 99%

“…; Pelletier et al . ) even though such works focus on analyses in the frequency domain or in both time and frequency domains.…”

Section: Introductionmentioning

confidence: 99%

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Measurement of dielectric and magnetic properties of materials by means of a TDR probe: a preliminary theoretical investigation in the frequency domain

Persico

Pieraccini

2017

Near Surface Geophysics

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This paper is focused on the measurement of both dielectric and magnetic characteristics of a penetrable material at radio frequency through a time‐domain reflectometry probe. The goal is to prove that a time‐domain reflectometry probe can offer the possibility to discriminate the dielectric permittivity from the magnetic permeability of the material. This is due to the fact that the time‐domain reflectometry datum depends both on the propagation velocity of the electromagnetic waves in the probed medium and on the intrinsic impedance of the probe. However, the possibility to attain such a clear discrimination is bound by the condition that the reflection coefficient is measured (or calculated) along the probe at the air–soil interface in the frequency domain. Generally, time‐domain reflectometry probes measure the total (incident plus reflected) field in the time domain, and subsequently, the datum is needed to meet the condition that such claimed purpose is not just the Fourier transform of a datum collected by means of a common time‐domain reflectometry probe. Rather, either a devoted hardware should be implemented or a very accurate knowledge of the incident field should be guaranteed in order to separate the reflected wave from the incident one. In this preliminary work, our study has been restricted to a theoretical investigation in the frequency domain. In particular, our focus is set on the lossless case, and the attention is devoted to the issue of possible multiple solutions to demonstrate that this obstacle can be overcome by making the frequency step narrower or, alternatively, by narrowing the length step of the probe. Simulation results based on a bifilar transmission line model are shown.

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Section: Measurement Of Dielectric and Magnetic Properties Of Materiamentioning

confidence: 99%

Section: Measurement Of Dielectric and Magnetic Properties Of Materiamentioning

confidence: 99%

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Measurement of dielectric and magnetic properties of materials by means of a TDR probe: a preliminary theoretical investigation in the frequency domain

Persico

Pieraccini

2017

Near Surface Geophysics

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“…Due to space variability [1], precision agriculture and advanced irrigation management systems require the use of a large number of reliable and accurate soil water content sensors [2]. Although many types of soil water content sensors have been developed (time-domain reflectometry [3], tensiometers, electrical resistance blocks, electromagnetic conductivity meters [4]), one of the most used low-cost soil water content sensors are the heat pulse probe sensors. The various types of heat pulse probes (button heat pulse probes (BHPP) [5,6], dual heat pulse probes (DHPP) [7], and single heat pulse probes (SHPP) [8]) operate based on heat capacity measurements.…”

Section: Introductionmentioning

confidence: 99%

Autonomous Soil Water Content Sensors Based on Bipolar Transistors Encapsulated in Porous Ceramic Blocks

et al. 2019

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We present an autonomous sensor to measure soil water content that uses a single heat pulse probe based on a transistor encapsulated in a porous block. The sensor uses a bipolar junction transistor, which performs as both a heating and temperature-sensing element. Since the sensor depends on a porous block to measure the matric potential of the soil, it does not suffer from accuracy problems if the contact between the probe and the soil is not perfect. A prototype of the sensor showed a temperature variation of Δ T = 2.9 ∘ C when the porous ceramic was saturated with water. The sensor presented an almost linear behavior for small changes in the matric potential of a red latosol when tested in the 1-kPa and 35-kPa pressure range, showing a sensitivity of S = 0.015 ∘ C/kPa. The ultra-low power signal conditioning circuit can read the sensor’s temperature with a resolution of approximately 0.02 ∘ C, so the matric potential can be read in increments of at least 1.33 kPa. When powered only by a 2-F supercapacitor from the energy-harvesting system, the interrogation circuit is able to take one soil water content measurement per day, for eleven days.

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“…In examining this issue in soil research, [19] compared time-domain reflectometry, TDR, and microwave response using a network analyzer and a high-quality through-transmission line where it was determined that salt concentration did not affect microwave measurements above 500 MHz. Given these results, coupled with the target frequency range being well above 500 MHz, this study will not examine the influence of any potential variation due to any salt contamination that might occur from settling of various types of soils through dust accumulation on the cotton bolls.…”

Section: Introductionmentioning

confidence: 99%

Microwave Moisture Sensing of Seedcotton: Part 1: Seedcotton Microwave Material Properties

Pelletier

Wanjura

Holt

2016

Sensors

Self Cite

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Moisture content at harvest is a key parameter that impacts quality and how well the cotton crop can be stored without degrading before processing. It is also a key parameter of interest for harvest time field trials as it can directly influence the quality of the harvested crop as well as skew the results of in-field yield and quality assessments. Microwave sensing of moisture has several unique advantages over lower frequency sensing approaches. The first is that microwaves are insensitive to variations in conductivity, due to presence of salts or minerals. The second advantage is that microwaves can peer deep inside large bulk packaging to assess the internal moisture content without performing a destructive tear down of the package. To help facilitate the development of a microwave moisture sensor for seedcotton; research was performed to determine the basic microwave properties of seedcotton. The research was performed on 110 kg micro-modules, which are of direct interest to research teams for use in ongoing field-based research projects. It should also prove useful for the enhancement of existing and future yield monitor designs. Experimental data was gathered on the basic relations between microwave material properties and seedcotton over the range from 1.0 GHz to 2.5 GHz and is reported on herein. This research is part one of a two-part series that reports on the fundamental microwave properties of seedcotton as moisture and density vary naturally during the course of typical harvesting operations; part two will utilize this data to formulate a prediction algorithm to form the basis for a prototype microwave moisture sensor.

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Frequency Domain Probe Design for High Frequency Sensing of Soil Moisture

Cited by 13 publications

References 14 publications

Measurement of dielectric and magnetic properties of materials by means of a TDR probe: a preliminary theoretical investigation in the frequency domain

Measurement of dielectric and magnetic properties of materials by means of a TDR probe: a preliminary theoretical investigation in the frequency domain

Autonomous Soil Water Content Sensors Based on Bipolar Transistors Encapsulated in Porous Ceramic Blocks

Microwave Moisture Sensing of Seedcotton: Part 1: Seedcotton Microwave Material Properties

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