土壤剖面水分传感器的边缘电磁场分析.

A soil moisture sensor has been widely used to measure the volumetric water content in soil at present. However, the detection of soil profile moisture sensors is often affected by the air and wiring in the pipeline, due to the inconsistent production and measurement direction of the probes. In this study, a small directional measuring probe was designed for the soil profile moisture non-contact sensor using the principle of Standing Wave Rate (SWR), electromagnetic simulation, and printed circuit board technology. Then, the impedance conversion circuit of the probe was designed to meet the requirements of SWR measurement. A vector network analyzer was utilized to determine the relationship among the probe measurement, medium, and conductivity. In detail, firstly, the impedance characteristics of the probe structure were verified to simulate the High-Frequency Structure Simulator (HFSS) electromagnetic field. The optimal probe size was then determined as the radius 15 mm and height 20 mm, according to the impedance and standing wave ratio of the probe at different heights and radii. The impedance of the probe was transformed in the impedance circuit, further to determine the relationship between the probe impedance and the object to be measured under different conductivity, as well as the dielectric constant. Secondly, the appropriate impedance conversion circuit of the probe was designed to verify in the range suitable for SWR to detect soil moisture using a vector network analyzer. Thirdly, a series of tests were performed on the different dielectric constants to evaluate the measurement accuracy of the probe. The measuring range of the probe was an approximate cylinder with a height of 15 mm and a radius of 37 mm, according to the impedance characteristics of the soil moisture sensor in the profile. Finally, the soil samples with multiple moisture and conductivity gradients were configured to evaluate the probe impedance. The results showed that, when the soil conductivity was less than 6 300 μS/cm in the range of soil moisture content 3%-56%, that was, in non saline alali soil, the relative error of the maximum soil volume moisture content of the sensor was 6.33% affected by soil conductivity. Consequently, the maximum error of the sensor was reduced by 0.17-5.27 percentage points in the non saline soil, where the electrical conductivity was in the range of 0-6 300 μS/cm, compared with the commonly-used ET-5 and 5TE sensors in the foreign market. As such, this new sensor can fully meet the needs of actual detection in the field. Therefore, the finding can provide new theoretical and technical support for the localization of profile soil moisture sensors. [ABSTRACT FROM AUTHOR]