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Open AccessArticle

Evaluation of Apple Maturity with Two Types of Dielectric Probes

1
Institute of Agrophysics, Polish Academy of Sciences, Doświadczalna 4, 20-290 Lublin, Poland
2
Institute of Electronic Systems, Warsaw University of Technology, Nowowiejska 15/19, 00-665 Warsaw, Poland
3
Institute of Enviromental Protection and Development, Wroclaw University of Environmental and Life Sciences, Pl. Grunwaldzki 24, 50-363 Wrocław, Poland
*
Author to whom correspondence should be addressed.
Sensors 2018, 18(1), 121; https://doi.org/10.3390/s18010121
Received: 26 September 2017 / Revised: 21 December 2017 / Accepted: 29 December 2017 / Published: 4 January 2018
(This article belongs to the Special Issue Sensors in Agriculture)
The observed dielectric spectrum of ripe apples in the last period of shelf-life was analyzed using a multipole dielectric relaxation model, which assumes three active relaxation processes: primary α-process (water relaxation) and two secondary processes caused by solid-water-ion interactions α’ (bound water relaxations), as well as β’ (Maxwell-Wagner effect). The performance of two designs of the dielectric probe was compared: a classical coaxial open-ended probe (OE probe) and an open-ended probe with a prolonged central conductor in a form of an antenna (OE-A-probe). The OE-A probe increases the measurement volume and consequently extends the range of applications to other materials, like granulated agricultural products, soils, or liquid suspensions. However, its measurement frequency range is limited as compared to the OE probe because, above 1.5 GHz, the probe with the antenna generates higher propagation modes and the applied calibrations and calculations are not sufficient. It was shown that data from measurements using the OE-A probe gave slightly stronger correlations with apples’ quality parameters than using the typical OE probe. Additionally, we have compared twelve multipole fitting models with different combinations of poles (eight three-pole and four two-pole models). It was shown that the best fit is obtained using a two-pole model for data collected for the OE-A probe and a three-pole model for the OE probe, using only Cole-Cole poles in both cases. View Full-Text
Keywords: dielectric probe; apple shelf-life; dielectric dispersion dielectric probe; apple shelf-life; dielectric dispersion
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Kafarski, M.; Wilczek, A.; Szypłowska, A.; Lewandowski, A.; Pieczywek, P.; Janik, G.; Skierucha, W. Evaluation of Apple Maturity with Two Types of Dielectric Probes. Sensors 2018, 18, 121.

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