Frequency Domain Probe Design for High Frequency Sensing of Soil Moisture

• Main Authors: Mathew G. Pelletier, Robert C. Schwartz, Greg A. Holt, John D. Wanjura, Timothy R. Green
• Format: Article
• Language: English
• Published: MDPI AG 2016-11-01
• Series: Agriculture
• Subjects: TDR; soil moisture sensing; soil moisture; frequency domain sensing; permittivity; dielectric constant
• Online Access: http://www.mdpi.com/2077-0472/6/4/60

Accurate moisture sensing is an important need for many research programs as well as in control of industrial processes. This paper describes the development of a high accuracy frequency domain sensing probe for use in obtaining dielectric measurements of materials suitable for work ranging from 300 MHz to 1 GHz. The probe was developed to accommodate a wide range of permittivity’s ranging from εr = 2.5 to elevated permittivity’s as high as εr = 40. The design provides a well-matched interface between the soil and the interconnecting cables. A key advantage of the frequency domain approach is that a change of salt concentration has a significantly reduced effect on ε′, versus the traditional time-domain reflectometry, TDR, measured apparent permittivity, Ka.