Influence of rapeseed ripening stage on dielectric permittivity spectrum in the frequency range 20-500 MHz

MINIATURA 7

Funding Organization: National Science Centre

Project title: Influence of rapeseed ripening stage on dielectric permittivity spectrum in the frequency range 20-500 MHz

Agreement number: DEC-2023/07/X/ST2/00735

Project implementation period: 05.10.2023 - 04.04.2025

Principal Investigator: dr inż. Jacek Majcher

Project value: 15 763,00 PLN

Funds granted for Lublin University of Technology: 15 763,00 PLN

Abstract: Nowadays, non-destructive measurement methods play a key role in the evaluation of plant products. These methods make it possible to quickly assess the individual parameters of a given material. Among these methods, methods that measure the electrical parameters of a given material are developing rapidly. Based on the electrical parameters, other parameters such as the moisture content of the material are calculated. An example of a simple, fast and non-destructive measurement technique is dielectric spectroscopy, which provides a range of information about the dielectric response of materials to electromagnetic fields [1,2]. The problem that remains to be solved is to propose a fast method to evaluate the germination rate of rapeseed. So far, germination rate is determined by sowing seeds and observing their growth phase, which can take several days depending on the plant species. Unfortunately, due to the different weather patterns and the difficulties associated with the optimal harvesting date, it is necessary to propose a measurement method that will allow the harvesting of rapeseed at an earlier date without losing its technological properties (adequate germination rate).  Seeds collected earlier will be able to be re-dried in dryers so that they can be useful for a longer period of time. As the seeds mature, many physicochemical processes take place in them, affecting various physical parameters. The electrical properties of rapeseed, such as dielectric permittivity and electrical conductivity, will be used as a measurement method. Electrical permittivity is determined using dielectric spectroscopy methods to obtain a frequency dependence (permittivity spectrum). It is most desirable to obtain a spectrum over the widest possible frequency range, but the bandwidth largely depends on the chosen measurement method. Simple, reflective measurement methods usually achieve narrow bandwidths in the range of 20 MHz to 200 MHz while elaborate transmission systems are capable of achieving bandwidths from tens of MHz to even tens of GHz. Usually the bandwidth is determined by the proper selection of measurement apparatus and especially measurement probes. The literature presents similar measurement systems, in which the authors use the electric  spectrum to estimate the moisture content of rapeseed [3].
The purpose of the proposed scientific activity is to study the spectra of the combined electrical permeability of rapeseed samples at different stages of their growth (germination). It is planned to test rapeseed at each seed development stage (every day 30 days before the scheduled harvest) and to relate the obtained electric permittivity spectra to the germination capacity of individual seeds.
General research plan: 30 days before the rapeseed harvest, seed samples will be taken from the designated field, after which the moisture content of the collected material will be determined. The samples will then be placed in a cylindrical dish of a certain capacity so that its volume can be accurately determined, and knowing the mass, its density as well. Different types of measurement probes will be introduced from above, which will be connected to a single-port vector network analyzer (VNA). The selection of the probe, as well as the special measuring station, will be prepared as part of the proposed research task. At the same time, the emphasis during the construction of the measurement system will be placed on the ease of application of the method under field conditions. In the first part of the experiment, the electric permittivity spectrum will be measured using several measurement probes in the 20 - 500 MHz band. Subsequently, the germination rate of seeds will be determined in accordance with PN-R-65950. It is supposed that the corresponding developmental stage of plants will cause differences in the shape of the electric permittivity spectrum. If the expected differences are found to occur then the observed differences will be correlated with seed germination rate. The final results will also take into account the effect of the moisture content of a given sample on the shape of the electrical permittivity spectrum.