A New Method to Determine the Spatial Sensitivity of Time Domain Reflectometry Probes Based on Three-Dimensional Weighting Theory

The time domain reflectometry (TDR) method has been widely used to measure soil water content for agriculture and engineering applications. Quick design and optimization of the probe is crucial to achieving practical utilization. Generally, the two-dimensional weighting theory, calculation of the spatial sensitivity of TDR probes in the plane transverse to the direction of electromagnetic wave propagation, and relevant numerical simulation techniques can be used to solve any issues. However, it is difficult to tackle specific problems such as complex probe shape, end effect, and so forth. In order to solve these issues, a method including a three-dimensional weighting theory and the relevant numerical simulation technique was proposed and verified to confirm the feasibility of this method by means of comparing the existing experimental results and the computational values. First, a shaft probe was used to determine the impact of the shaft on the effective dielectric constant of the probe. Then, three-rod probes were calibrated by a sample with a special shape and water-level variations around the probe using the proposed method to determine the values of the apparent dielectric constant. Besides, model boundary size and end effect were also considered in the computation of dielectric constants. Results showed that compared with the experimental and computational data, the newly proposed method calculated the measurement sensitivity of the shaft probes well. In addition, it was observed that experiment dielectric constant values were slightly different from computational ones, not only using a vertical probe but also horizonal probe. Moreover, it was also found that there was a slight influence of sample shape and end effect on the apparent dielectric constant, but model boundary size has a certain impact on the values. Overall, the new method can provide benefits in the design and optimization of the probe.

Dielectric Spectroscopy Using Dual Reflection Analysis of TDR Signals

Time-domain reflectometry (TDR) has been a powerful tool for measuring soil dielectric properties. Initiating from apparent dielectric constant ( K a ) measurement up until apparent and complex dielectric spectroscopies, the embedded information in the TDR signal can be extracted to inspire our understanding of the underlying dielectric behaviors. Multiple full waveform inversion techniques have been developed to extract complex dielectric permittivity (CDP) spectrum, but most of them involved prior knowledge of input function and tedious calibration. This rendered the field dielectric spectroscopy challenging and expensive to conduct. Dual reflection analysis (DRA) is proposed in this study to measure CDP spectrum from 10 MHz to 1 GHz. DRA is a simple, robust, model-free, and source-function free algorithm which requires minimal calibration effort. The theoretical framework of DRA is established and the necessary signal processing procedures are elaborated in this study. Eight materials with different dielectric characteristics are selected to evaluate DRA’s performance, by using both simulated and experimental signals. DRA is capable of measuring non-dispersive materials very well, whereas dispersive materials require the assistance of a long-time-window (LTW) extraction method to further extend the effective bandwidth. The DRA approach is suitable for field applications that can only record a limited amount of data points and in-situ dielectric spectroscopy.

Physical origin of colossal dielectric constant in CaCu3Ti4O12 thin film by Pulsed Laser Deposition

ABSTRACTThe (001) preferentially oriented CCTO thin film was grown on Pt/Ti/TiO2/Si (100) substrate by pulsed laser. I-V and C-V relationships of the CCTO thin film showed characteristics typical of a tunnel metal-insulator-semiconductor (MIS) structure and its capacitance response is the origin of the high apparent dielectric constant observed in CCTO thin films. The very thin insulating layer on top of the film can be reduced in thickness by treatment in HCl acid, as shown by smaller threshold voltages in the I-V curves. The overall behavior is compatible with a conduction activation energy of ∼80 to 100 meV in the bulk of the film, and a diffusion potential at the interface of 500 to 800 meV. The acceptor concentration is of the order of 1019cm−3.

Time domain reflectometry for water content and density of soils: study of soil-dependent calibration constants

The paper studies the soil-dependent calibration constants used for determining water content and density of soil using time domain reflectometry (TDR), specifically, to establish the typical soil calibration values and study the extent of the uncertainty in calibration factors on measurement accuracy. The TDR method described here makes use of a calibration equation normalized by soil dry density, which involves two soil-dependent constants, a and b. Both a and b have physical significance, with the value of a related to the apparent dielectric constant of the dry density – normalized dry soil solids and the value of b related to the apparent dielectric constant of the pore fluid. From theoretical predictions, typical values of a are around 1.0, and typical values of b are around 9. Practically, the constants a and b are obtained through calibration tests performed in conjunction with standard compaction tests. Experimental study shows that calibration constants fall within the ranges from theoretical predictions. Tests on five soil mixtures provided average values of a = 0.945 and b = 8.76, while 11 clean sands resulted in average values of a = 1.0 and b = 8.5. The study also shows that there are no significant effects of compaction energy on the measured values of a and b. Sensitivity analyses indicate that variations in a and b both cause variations in TDR-determined water content and density, but the variations are typically within acceptable limits for engineering application purpose. Results from TDR tests on simulated field experiments are consistent with the sensitivity analyses.Key words: time domain reflectometry, TDR, calibration constants, water content, dry density, sensitivity.

CALIBRAÇÃO DE UM EQUIPAMENTO TDR EM CONDIÇÕES DE CAMPO

CALIBRAÇÃO DE UM EQUIPAMENTO TDR EM CONDIÇÕES DE CAMPO Rosangela Villwock; Maria Hermínia Ferreira Tavares; Márcio Antônio Vilas BoasCentro de Ciências Exatas e Tecnológicas, Universidade Estadual do Oeste do Paraná, Cascavel , PR, [email protected] 1 RESUMO A utilização da Reflectometria no Domínio do Tempo (TDR) tornou-se um método muito bem aceito nas avaliações de teores de água no solo. Todavia, para utilização do equipamento há a necessidade de calibrá-lo para que se obtenha valores acurados de umidade volumétrica, devendo-se sempre respeitar as peculiaridades de cada solo para que o processo de calibração ocorra de forma correta. O objetivo deste trabalho foi calibrar o equipamento TDR em condições de campo, especificamente para um Latossolo Vermelho distroférrico, localizado no Núcleo Experimental de Engenharia Agrícola, Universidade Estadual do Oeste do Paraná, Campus de Cascavel. O modelo polinomial cúbico foi o que melhor se ajustou aos dados para a calibração do equipamento. UNITERMOS: constante dielétrica aparente, modelo polinomial cúbico, umidade do solo. VILLWOCK, R.; TAVARES, M. H. F.; VILLAS BOAS, M. A.TDR EQUIPMENT CALIBRATION IN FIELD CONDITIONS 2 ABSTRACT The use of Time Domain Reflectometry (TDR) has become a very well accepted method to evaluate soil water content. However, for the equipment utilization there is the need to calibrate it to obtain accurate values of volumetric soil water content, always respecting the soil characteristics. The objective of this research was to calibrate the TDR equipment in field conditions, specifically for a Rhodic Hapludox, at the UNIOESTE Experimental Station of Agricultural Engineering, in the campus of Cascavel, State of Parana. The cubic polynomial model was the model that best adjusted the data for the calibration of the equipment. KEYWORDS: apparent dielectric constant, cubic polynomial model, soil moisture.