Measurement of the broadband complex permittivity of soils in the frequency domain with a low-cost vector network analyzer and an open-ended coaxial probe

González-Teruel, Juan D.; Jones, Scott B.; Robinson, David A. ORCID: https://orcid.org/0000-0001-7290-4867; Giménez-Gallego, Jaime; Zornoza, Raúl; Torres-Sánchez, Roque. 2022 Measurement of the broadband complex permittivity of soils in the frequency domain with a low-cost vector network analyzer and an open-ended coaxial probe. Computers and Electronics in Agriculture, 195, 106847. 11, pp. 10.1016/j.compag.2022.106847

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Official URL: http://dx.doi.org/10.1016/j.compag.2022.106847

Abstract/Summary

The performance of a handheld Vector Network Analyzer (VNA), the nanoVNA, a low-cost, open-source instrument, was evaluated. The instrument measures the complex permittivity of dielectric media from 1-port reflection parameters in the 1 – 900 MHz bandwidth. We manufactured an open-ended coaxial probe using a SMA-N coaxial adapter to perform dielectric measurements. The accuracy of the nanoVNA was comparable to that of a commercial VNA between 1 and 500 MHz according to tests in reference organic liquids, while a lack of stability was found beyond 700 MHz. The self-manufactured open-ended coaxial probe was subjected to a Finite Element Method (FEM) analysis and its electromagnetic (EM) field penetration depth was determined to be 1.5 mm at 100 MHz, being reduced to 1.3 at 900 MHz and thus demonstrating a frequency-dependent support volume. The broadband complex permittivity of three mineral soils of varied textures was obtained for a range of bulk densities and water contents from dry to water-saturated conditions. The dielectric response of the soils approximated the well-known Topp et al. (1980) equation at high frequencies. At lower frequency however, higher permittivities were exhibited due to dielectric dispersion, which emphasizes the importance of EM-based soil moisture sensor operating frequency when considering sensor calibration or comparing the response of different sensors.

Item Type:	Publication - Article
Digital Object Identifier (DOI):	10.1016/j.compag.2022.106847
UKCEH and CEH Sections/Science Areas:	Soils and Land Use (Science Area 2017-)
ISSN:	0168-1699
Additional Information. Not used in RCUK Gateway to Research.:	Open Access paper - full text available via Official URL link.
Additional Keywords:	complex permittivity, soil spectroscopy, frequency domain reflectometry, soil moisture, open-ended coaxial probe, nanoVNA, low-cost instrument, vector network analyzer, dielectric dispersion
NORA Subject Terms:	Electronics, Engineering and Technology Agriculture and Soil Science
Date made live:	06 Apr 2022 12:48 +0 (UTC)
URI:	https://nora.nerc.ac.uk/id/eprint/532422

Item Type:

Publication - Article

Digital Object Identifier (DOI):

10.1016/j.compag.2022.106847

UKCEH and CEH Sections/Science Areas:

Soils and Land Use (Science Area 2017-)

ISSN:

0168-1699

Additional Information. Not used in RCUK Gateway to Research.:

Open Access paper - full text available via Official URL link.

Additional Keywords:

complex permittivity, soil spectroscopy, frequency domain reflectometry, soil moisture, open-ended coaxial probe, nanoVNA, low-cost instrument, vector network analyzer, dielectric dispersion

NORA Subject Terms:

Electronics, Engineering and Technology
Agriculture and Soil Science

Date made live:

06 Apr 2022 12:48 +0 (UTC)

URI:

https://nora.nerc.ac.uk/id/eprint/532422