A novel sensor design for the determination of dielectric profiles using time domain reflectometry

Will, B.; Gerding, M.

doi:10.23919/eumc.2009.5296291

Cited by 5 publications

(6 citation statements)

References 7 publications

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“…A main task concerning the sensor design is given by the requirement that all necessary connectors must be placed on one side of the sensor. In order to deal with this challenge, concentric reversion couplers, which are introduced in [6], are used. The concentric reversion coupler consists of two concentrically arranged coaxial lines as shown in Fig.…”

Section: Sensor Designmentioning

confidence: 99%

“…Compared with the sensor described in [6], this setup offers the advantage that the external feeding lines do not carry high-frequency measuring signals. Thus, a movement of the sensor inside the material under test has no influence on the measurement accuracy, due to the fact that only digital data signals are carried on the connecting cables.…”

Section: Sensor Designmentioning

confidence: 99%

“…Nevertheless, the accuracy of TDR measurements is limited due to multiple reflections caused by inhomogenities of the material under test. In contrast to this, time domain transmission (TDT) measurements [5] yield accurate measurement results independent of the constitution of the surrounding material due to the fact that the first measured impulse is unique and presents the useful signal, which is only slightly influenced by multiple reflections [6]. To validate this assumption, an electromagnetic simulation inside layered materials is performed for TDR and TDT measurements.…”

Section: Introductionmentioning

confidence: 99%

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A time domain transmission measurement system for dielectric characterizations

Will

Gerding

Schulz

et al. 2012

Int. J. Microw. Wireless Technol.

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Delay time measurements are a commonly used technique for the characterization of dielectric materials. Especially with regard to the characterization of water-solid mixtures like soil or grain delay time measurements, e.g., time domain reflectometry offers a powerful method. However, the accuracy of reflection measurements is limited due to multiple reflections caused by inhomogenities of the environmental material of the sensor. This contribution deals with an improved sensor design based on time domain transmission (TDT) measurements. Thus, the first received impulse includes the necessary information. Multiple reflections are received at later time steps and their influence on the measurement accuracy is nearly negligible. To improve the performance and the applicability of the designed sensor, a cost-efficient TDT system is designed, which is integrated in the sensor. Additionally, a so-called "concentric reversion coupler" is used, which offers the possibility to perform TDT measurements without the necessity of external measuring ports.There are several well-established techniques available for the determination of the permittivity in homogeneous and inhomogeneous materials [1]. In particular, time domain reflectometry (TDR) measurements are an often applied method for the determination of the dielectric properties of various materials like soil, grain, or coal [2, 3]. The popularity of these reflection measurements is based on the advantage that microwave measurements like TDR are non-destructive and are available in real time. Additionally, baseband signals used for TDR measurements are highly sensitive against the water content due to the extraordinary dielectric properties of water at lower frequencies [4]. Nevertheless, the accuracy of TDR measurements is limited due to multiple reflections caused by inhomogenities of the material under test. In contrast to this, time domain transmission (TDT) measurements [5] yield accurate measurement results independent of the constitution of the surrounding material due to the fact that the first measured impulse is unique and presents the useful signal, which is only slightly influenced by multiple reflections [6]. To validate this assumption, an electromagnetic simulation inside layered materials is performed for TDR and TDT measurements. For this purpose, a two-wire line is inserted in a layered material with varying permittivities of the different layers as shown in Fig. 1. For the investigation of the influence of multiple reflections on the measurement accuracy, layer III, with a permittivity of 1 r = 20, is displaced within layer II with a permittivity of 1 r = 3. Based on the delay time, the mean value of the permittivity of the layers I-IV is determined for every position of layer III as shown in Fig. 1. Ideally, this mean value should be constant independent of the position of layer III. These results show that the accuracy of the TDR system is decreased due to multiple reflections caused by the layered surrounding material. In contrast to this, the TDT ...

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Section: Sensor Designmentioning

confidence: 99%

Section: Sensor Designmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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A time domain transmission measurement system for dielectric characterizations

Will

Gerding

Schulz

et al. 2012

Int. J. Microw. Wireless Technol.

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“…Creation of the dielectric profile for the soil using TDR has been discussed in literature. 9 For the measurement of spatially resolved dielectric profiles by using delay time measurements, a transmission line is used. The delay time of an electromagnetic pulse along the transmission line is measured with the help of an industrial TDR system operating in the baseband up to 3 GHz with a pulse width of 300 ps.…”

Section: Introductionmentioning

confidence: 99%

A multi-frequency, self-calibrating, in-situ soil sensor with energy efficient wireless interface

Pandey¹,

Kumar²,

Weber³

2013

SPIE Proceedings

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Real time and accurate measurement of sub-surface soil moisture and nutrients is critical for agricultural and environmental studies. This paper presents a novel on-board solution for a robust, accurate and self-calibrating soil moisture and nutrient sensor with inbuilt wireless transmission and reception capability that makes it ideally suited to act as a node in a network spread over a large area. The sensor works on the principle of soil impedance measurement by comparing the amplitude and phase of signals incident on and reflected from the soil in proximity of the sensor. Accuracy of measurements is enhanced by considering a distributed transmission line model for the on-board connections. Presence of an inbuilt self-calibrating mechanism which operates on the standard short-open-load (SOL) technique makes the sensor independent of inaccuracies that may occur due to variations in temperature and surroundings. Moreover, to minimize errors, the parasitic impedances of the board are taken into account in the measurements. Measurements of both real and imaginary parts of soil impedance at multiple frequencies gives the sensor an ability to detect variations in ionic concentrations other than soil moisture content. A switch-controlled multiple power mode transmission and reception is provided to support highly energy efficient medium access control. 1

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“…The reflection coefficient along with the characteristic impedance of the line gives the impedance of the surface at which reflection takes place. Creation of the dielectric profile for the soil using TDR has been discussed in literature Will and Gerding (2009). For the measurement of spatially resolved dielectric profiles by using delay time measurements, a transmission line is used.…”

Section: Soil Moisture and Impedance Sensorsmentioning

confidence: 99%

Development of impedance spectroscopy based in-situ, self-calibrating, on-board wireless sensor with inbuilt metamaterial inspired small antenna for constituent detection in multi-phase mixtures like soil

Pandey

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A novel sensor design for the determination of dielectric profiles using time domain reflectometry

Cited by 5 publications

References 7 publications

A time domain transmission measurement system for dielectric characterizations

A time domain transmission measurement system for dielectric characterizations

A multi-frequency, self-calibrating, in-situ soil sensor with energy efficient wireless interface

Development of impedance spectroscopy based in-situ, self-calibrating, on-board wireless sensor with inbuilt metamaterial inspired small antenna for constituent detection in multi-phase mixtures like soil

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