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Proceedings Paper

Microstrip transmission line for soil moisture measurement
Author(s): Xuemin Chen; Jing Li; Renyue Liang; Yijie Sun; C. Richard Liu; Richard Rogers; German Claros
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Paper Abstract

Pavement life span is often affected by the amount of voids in the base and subgrade soils, especially moisture content in pavement. Most available moisture sensors are based on the capacitive sensing using planar blades. Since the planar sensor blades are fabricated on the same surface to reduce the overall size of the sensor, such structure cannot provide very high accuracy for moisture content measurement. As a consequence, a typical capacitive moisture sensor has an error in the range of 30%. A more accurate measurement is based on the time domain refelctometer (TDR) measurement. However, typical TDR system is fairly expensive equipment, very large in size, and difficult to operate, the moisture content measurement is limited. In this paper, a novel microstrip transmission line based moisture sensor is presented. This sensor uses the phase shift measurement of RF signal going through a transmission line buried in the soil to be measured. Since the amplitude of the transmission measurement is a strong function of the conductivity (loss of the media) and the imaginary part of dielectric constant, and the phase is mainly a strong function of the real part of the dielectric constant, measuring phase shift in transmission mode can directly obtain the soil moisture information. This sensor was designed and implemented. Sensor networking was devised. Both lab and field data show that this sensor is sensitive and accurate.

Paper Details

Date Published: 8 December 2004
PDF: 8 pages
Proc. SPIE 5590, Sensors for Harsh Environments, (8 December 2004); doi: 10.1117/12.571448
Show Author Affiliations
Xuemin Chen, Univ. of Houston (United States)
Jing Li, Univ. of Houston (United States)
Renyue Liang, Univ. of Houston (United States)
Yijie Sun, Univ. of Houston (United States)
C. Richard Liu, Univ. of Houston (United States)
Richard Rogers, Texas Dept. of Transportation (United States)
German Claros, Texas Dept. of Transportation (United States)

Published in SPIE Proceedings Vol. 5590:
Sensors for Harsh Environments
Anbo Wang, Editor(s)

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